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Elasmobranch fisheries: status, assessment and management 1996

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Elasmobranch Fisheries: Status, Assessment and Management by Ramon Bonfil-Sanders B.Sc. (Hons), Universidad Autonoma de Baja California (Mexico), 1983 M.Sc, University College of North Wales (UK), 1991 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Resource Management and Environmental Studies) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February 1996 © Ramon Bonfil-Sanders 1996 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of 2&t/£&M^MMr/hW£m£0MtV7?rl S7l»/£S The University of British Columbia Vancouver, Canada Date ^B3-X9- DE-6 (2/88) II A b s t r a c t . A n o v e r v i e w of the s i tuat ion of e l a s m o b r a n c h f i sher ies a r o u n d the w o r l d a n d p r o b l e m s for thei r a s s e s s m e n t a n d m a n a g e m e n t a re p r e s e n t e d . F o u r different s tud ie s a r e ca r r i ed out, e a c h a t t ack ing a par t icu lar p r o b l e m u n d e r this g e n e r a l top ic . T h e first, is a n in-depth r ev i ew of recent t r ends in e l a s m o b r a n c h explo i ta t ion a n d m a n a g e m e n t o n a w o r l d w i d e b a s i s a i m e d at c l o s i n g the g a p in b a s e l i n e informat ion abou t t h e s e f i she r i es o n a g l o b a l s c a l e . In the s e c o n d s tudy, a de te rmin i s t i c age - s t ruc tu red s imula t ion m o d e l is d e v e l o p e d to a n a l y s e d e n s i t y - d e p e n d e n t c h a n g e s in fecundi ty a s a r e s p o n s e to i n c r e a s e d f i sh ing mortal i ty in a hypo the t i ca l s h a r k popu l a t i on . T h e u s e of the m o d e l a s a n a i d in m a n a g e m e n t d e c i s i o n - m a k i n g is e x e m p l i f i e d with a c a s e from a t rop ica l s h a r k f i shery . M o n t e C a r l o a n a l y s i s is u s e d in the third s tudy, to eva lua t e the S c h a e f e r a n d F o x s u r p l u s p r o d u c t i o n m o d e l s a n d the de lay-d i f fe rence m o d e l o f D e r i s o - S c h n u t e for the e s t ima t ion o f a s s e s s m e n t a n d m a n a g e m e n t p a r a m e t e r s o f e l a s m o b r a n c h f i sher ies . T h e f i shery m o d e l s a re e v a l u a t e d by c o m p a r i n g their e s t ima te s o f s tock a s s e s s m e n t a n d m a n a g e m e n t p a r a m e t e r s aga ins t the k n o w n v a l u e s o f a full age - s t ruc tu red s tochas t i c s imu la t ion m o d e l o f a s h a r k popu la t i on . Different s c e n a r i o s o f s tock recrui tment re la t ionsh ip , f i shab le s tock s i z e , spa t i a l b e h a v i o u r o f the s h a r k s , a n d da t a qual i ty a re u s e d for tes t ing r o b u s t n e s s . N o n e o f the f i shery m o d e l s per forms sat isfactor i ly u n d e r s i tua t ions o f d e n s i t y - d e p e n d e n t ca tchab i l i ty . W h e n ca tchabi l i ty r e m a i n s cons tan t , the D e r i s o - S c h n u t e m o d e l ou tper forms the S c h a e f e r o r F o x m o d e l s , both for b i o m a s s a n d m a n a g e m e n t p a r a m e t e r e s t ima t ion . In the f inal s tudy , the m u l t i s p e c i e s s h a r k f i shery o f Y u c a t a n , M e x i c o , is u s e d a s a n e x a m p l e o f the p r o b l e m s for e l a s m o b r a n c h s tock a s s e s s m e n t in the rea l w o r l d . T h e f i shery is a n a l y s e d by fitting the S c h a e f e r m o d e l to c a t c h a n d c p u e da ta . T h e resul ts highl ight s e v e r e d e f i c i e n c i e s in the da t a a v a i l a b l e for a s s e s s m e n t w h i c h a re c h a r a c t e r i s e d by a l ack o f cont ras t in the c p u e da ta . S o m e al ternat ive m a n a g e m e n t r e c o m m e n d a t i o n s a i m e d at i m p r o v i n g the da t a for a s s e s s m e n t are g i v e n . iii Table of Contents Abstract ii Table of Contents iii List of tables viii List of figures xi Acknowledgements xx Preface ., xxiii Chapter 1. Elasmobranchs: a Specific Problem of Fisheries Assessment and Management 1 1.1 Introduction 1 1.2 A note on taxonomy 2 1.3 Problems for the Assessment and Management of Elasmobranch Fisheries 3 1.3.1 Biology and Ecology 3 1.3.2 Fisheries theory 4 1.3.3 Informational constraints 5 1.3.4 Economics 6 1.4 Thesis outline 7 Chapter 2 Trends and Patterns in Elasmobranch Exploitation: An Overview of World Fisheries for Sharks, Rays and Relatives 10 2.1 Introduction. . 10 2.1.1 Organisation of this work 11 2.2 Characterisation of elasmobranch fisheries 12 2.2.1 The Official Statistics 12 2.2.1.1 Trends and outlooks by FAO Major Fishing Areas. . . . 12 iv 2.2.1.2 Catches by countries 16 2.2.2 Major Fisheries for Elasmobranchs 21 2.2.2.1 America 21 2.2.2.2 Europe 45 2.2.2.3 Africa and Indian subcontinent 62 2.2.2.4 Asia 72 2.2.2.5 Australian subcontinent 89 2.2.3 Bycatches and Discards of Elasmobranchs at Sea 96 2.2.3.1 Drift gillnet fisheries 97 2.2.3.2 Longline fisheries 123 2.2.3.3 Purse Seine Fisheries 151 2.2.3.4 Other miscellaneous fisheries 156 2.2.3.5 Overview. 157 2.3 Discussion 160 2.3.1 Current Situation of Elasmobranch Fisheries 160 2.3.2 Conservation of elasmobranchs 162 2.4 Summary and conclusions 164 Chapter 3 . Density-Dependent Fecundity in Elasmobranchs and Its Implications in Fisheries Management: A Deterministic Age-structured Simulation Model 167 3.1 Introduction 167 3.1.1 Biological characteristics of the group in relation to exploitation 167 3.1.2 Definition of the problem 168 3.2 Construction of the model 169 3.2.1 Model-building considerations 169 3.2.2 Biological considerations 170 3.2.2.1 Early life natural mortality 170 3.2.2.2 Life history functional relationships 170 3.2.3 General characteristics of the model 171 3.2.4 Formulation 172 3.2.5 Initial parameters 174 V 3.2.6 Sensitivity analysis 175 3.3 Results 176 3.3.1 Baseline run 176 3.3.2 Sensitivity analysis 179 3.3.3 The value of fecundity increases 181 3.3.3 A tropical paradigm with management applications 187 3.4 Discussion 191 3.4.1 Simulation results and documented changes in fecundity 191 3.4.2 Trade-off between fecundity and early life natural mortality. . . . 193 3.4.3 Compensatory mechanisms in elasmobranch populations 194 3.4.4 Considerations for fisheries management and research 194 3.4.5 From model to reality 195 Chapter 4. A Monte Carlo Analysis of Fishery Models for Sharks 197 4.1 Introduction 197 4.1.1 Problems for shark fisheries assessment and management. .. 197 4.1.2 Holden's view and modern methods in fisheries science 198 4.2 Methods 199 4.2.1 General approach 199 4.2.2 A set of simulation models of a shark population under exploitation 200 4.2.3 Spatial behaviour and its representation in the operating models 207 4.2.4 Fishery models examined 211 4.2.4.1 Surplus production models 212 4.2.4.2 Delay difference model 214 4.2.5 Benchmarks for model performance 220 4.2.6 Fitting fishery models to data 221 4.2.7 The types of trials performed 224 4.2.7.1 Nomenclature 224 4.2.7.2 Sequence of trials 224 4.3 Results 225 4.3.1 Simulated populations and fishery data time series 225 vi 4.3.2 Tests with the 'proportionality' operating populations 228 4.3.2.1 Tests of observation error assumptions and different versions of the Deriso-Schnute model 228 4.3.2.2 Tests between the Schaefer, Fox, and Deriso- Schnute model 230 4.3.2.3 The B0=K assumption 233 4.3.3 Changes in the spatial behaviour of the stock: hyperstability and hyperdepletion 233 4.3.4 Unproductive stocks 236 4.3.5 Trials with uninformative data 240 4.4 Discussion 244 4.4.1 Unsuccessful estimation assumptions and model misspecifications 244 4.4.2 Changes in the CPUE-biomass relationship 244 4.4.3 Performance of the estimation procedures, and choice of the best model 246 4.4.4 Significance for the assessment and management of real shark fisheries 249 4.4.5 The B0=K strategy 250 4.4.6 Summary and conclusions 250 Chapter 5 Elasmobranch Stock Assessment and Management in the Real World: The Multispecies Shark Fishery of Yucatan, Mexico 252 5.1 Introduction 252 5.2 The shark fishery of Yucatan: a typical case study 253 5.3 Methods 254 5.4 Results 256 5.5 Discussion 264 5.5.1 Shortcomings of the data 264 5.5.2 Harnessing uncertainty 267 5.5.3 How can we improve future assessments of the Yucatan shark fishery? 271 5.6 Summary and conclusions 273 R e f e r e n c e s 2 7 4 A P P E N D I X 1. Lis t o f c o m m o n a n d latin n a m e s o f the e l a s m o b r a n c h s m e n t i o n e d in the text 2 9 7 A P P E N D I X 2 . C a l c u l a t i o n o f true v a l u e s o f fopt a n d Copt for the o p e r a t i n g p o p u l a t i o n s 2 9 9 VIII List of tables. Table 2.1 Elasmobranch catches by FAO Statistical Area 1967-1991. Mean catch, variation and Index of Relative Production (IRP) are given for the last 25 yr, and catch trends for the last 10 yr. 13 Table 2.2 Reported world catches in commercial elasmobranch fisheries (thousand tonnes). (Data from Compagno, 1990 and FAO, unless otherwise indicated). (T.W.F. = total world fisheries, T.W.CLUP = total world clupeoid fisheries, T.ELAS = total world elasmobranch fisheries. EL/FISH = T.ELAS as % of T.W.F., CLUP/FISH = T.W.CLUP as % of T.W.F.). 18 Table 2.3 Sharks species considered in each of the USA east coast management unit (from NOAA 1991). 28 Table 2.4 Shark landings, in dressed weight (kg), west coast USA (adapted from Cailliet et al. 1993). 30 Table 2.5 Shark species found in the commercial fisheries of Mexico. 37 Table 2.6 Shark species reported in Spanish commercial fisheries (adapted from Munoz- Chapuli 1985 a,b). 61 Table 2.7 Percentage catches of sharks and rays according to fishing gear and zones in Taiwan (Prov. of China) and Malaysia (data from SEAFDEC 1988). 82 Table 2.8 Percentage catches of sharks and rays according to fishing gear and zones in Philippines and Thailand (data from SEAFDEC 1988). 87 Table 2.9 Estimation of shark bycatches in the Japanese salmon fisheries, based on information from research cruises. 102 Table 2.10 Alternative estimates of shark bycatches in Japanese salmon fisheries, based on Canadian research cruise (LeBrasseur et al. 1987). 102 Table 2.11 Effort statistics for the flying squid driftnet fishery in the North Pacific for the period 1988-1990 (from Yatsu et al. 1993, Gong et al. 1993 and Yeh & Tung 1993). 108 Table 2.12 Estimation of bycatches of elasmobranchs in 1990 Squid driftnet fishery based on reports of observer programme on board commercial vessel (INPFC 1991). ix 108 Table 2.13 Estimated bycatches of elasmobranchs in the 1990 North Pacific large-mesh driftnet based on reports of the observer programme 1990 (INPFC 1992). 113 Table 2.14 Reported bycatches of elasmobranchs in South Pacific driftnet fisheries. 116 Table 2.15 Elasmobranchs caught in Mediterranean driftnets (adapted from Northridge 1991). 120 Table 2.16 Summary of estimated bycatch of elasmobranchs in high seas driftnet fisheries. 122 Table 2.17 Catch rates and estimated total catch of sharks in the Spanish swordfish fishery. 135 Table 2.18 Shark species commonly caught by tuna longlining in the Indian Ocean (adapted from Sivasubramaniam, 1964). 139 Table 2.19 Estimated bycatch of sharks in tuna longline fisheries of the Central and South Pacific (SPC zone), based on the results of Strasburg (1958). 146 Table 2.20 Estimated bycatch of sharks in the North Pacific by the longline fleets of Japan and Korea, based on the results of Strasburg (1958). 150 Table 2.21 Selected estimates of shark bycatches in high seas longline fisheries. 150 Table 3.1 Results of sensitivity analysis of the model. B%- proportion of virgin biomass remaining after 100yr of fishing; N%= proportion of virgin population remaining after 100yr of fishing. Numbers in parentheses are percentage change from values of the baseline run. 180 Table 4.1 Types of trials performed with informative effort pattern and productive stock (age or recruitment = 7yr). A= additive observation error; M= multiplicative observation error; S= Schaefer; F=Fox; D=Deriso-Schnute; Dn=non-delay Deriso-Schnute; D**= misspecified Deriso-Schnute. 226 Table 4.2 Types of trials performed with clue proportional to biomass and an unproductive stock (age of recruitment = y). Key as in table 4.1. 220 Table 5.1. Results of first set of trials: Total Least Squares (TLS) fits of the Schaefer Model to CPUE and catch data for the entire data set of the Yucatan shark fishery. x 258 Table 5.2. Results of second set of trials: TLS fits of the Schaefer Model to CPUE and catch data for the downward portion of the time series (years 85-89) from the shark fishery of Yucatan. 261 Table A.1. Median and quartiles of true fopl and C o p ( values for the different operating populations as characterised by cpue-biomass relationship, stock-recruitment function, and age of entry to the fishery ("productivity"). 291 XI List of figures. Figure 2.1 World reported catch of elasmobranch fishes 1947-1991. (Data from FAO, SEAFDEC, Fishery Yearbooks for Taiwan Area, and Secretaria de Pesca). 13 Figure 2.2 Historical catches of elasmobranchs for the 25 major elasmobranch-fishing countries, arranged by geographical area. 20 Figure 2.3 Elasmobranch catches of the USA by major groups and regions as reported by FAO, during 1977-1991. 23 Figure 2.4 Elasmobranch catches from the east coast of the USA during 1980-1989. Bars represent shark fisheries. (Data from FAO and Hoff 1990). 23 Figure 2.5 Elasmobranch catches in the Pacific and Gulf of Mexico/Caribbean coasts of Mexico during 1977-1991 (sh = sharks). (Data from Secretaria de Pesca, Mexico). 35 Figure 2.6 Elasmobranch catches of Peru, by species groups, during 1977-1991 (Data from FAO). 41 Figure 2.7 Elasmobranch catches of Brazil, by species groups, during 1977-1991. (Data from FAO). 41 Figure 2.8 Elasmobranch catches of Argentina, by species groups, during 1977-1991. (Data from FAO). 47 Figure 2.9 Elasmobranch catches of Norway, by species groups, during 1978-1991. (Data from FAO). 47 Figure 2.10 Elasmobranch catches of former USSR, by species groups, during 1978-1991. (Data from FAO). 52 Figure 2.11 Elasmobranch catches of U.K., by country and species groups, during 1978-1991. (Data from FAO). 52 Figure 2.12 Elasmobranch catches of Ireland, by species groups, during 1978-1991. (Data from FAO). 57 Figure 2.13 Elasmobranch catches of France, by species groups, during 1978-1991. (Data from FAO). 57 Figure 2.14 Elasmobranch catches of Spain, by species groups, during 1978-1991. (Data from FAO). 61 Figure 2.15 Elasmobranch catches of Italy, by species groups, during 1978-1991 (Data from FAO). 63 Figure 2.16 Elasmobranch catches of Nigeria, by species groups, during 1977-1991. (Data from FAO). 65 Figure 2.17 Elasmobranch catches of Pakistan, by species groups, during 1977-1991. (Data from FAO). 65 Figure 2.18 Elasmobranch catches of India, by region, during 1977-1991. (Data from FAO). 70 Figure 2.19 Elasmobranch catches of Sri Lanka, by species groups, during 1977-1991 (Data from FAO). 70 Figure 2.20 Elasmobranch catches in different fisheries of Japan during 1976-1984 (S=sharks, B=batoids, IMongline). (Data from Taniuchi (1990) and Ishihara (1990)). 74 Figure 2.21 Elasmobranch catches of Japan, by species groups and region, during 1977- 1991. (Data from FAO). 74 Figure 2.22 Elasmobranch catches of South Korea, by species groups and region, during 1977-1991. (Data from FAO). 77 Figure 2.23 Estimated shark catches for the People's Republic of China from fin exports, using 3% and 5% conversion factor. (Fin export data from P. Wongsawang, pers. comm.). 77 Figure 2.24 Elasmobranch catches of Taiwan, by species groups, during 1978-1990. (Data from FAO). 82 XIII Figure 2.25 Elasmobranch catches of Malaysia, by species groups and region, during 1976- 1990 (E.P.M.=eastern peninsular Malaysia, W.P.M.=western peninsular Malaysia). (Data from SEAFDEC). 85 Figure 2.26 Elasmobranch catches of Philippines, by species groups and region, during 1976- 1990. (Data from SEAFDEC). 85 Figure 2.27 Elasmobranch catches of Thailand, by species groups and region, during 1976- 1991. (Data from SEAFDEC). 87 Figure 2.28 Elasmobranch catches of Indonesia, by species groups and region, during 1976- 1990 (B=batoids, S=sharks). (Data from SEAFDEC). 90 Figure 2.29 Elasmobranch catches of Australia, by FAO statistical areas, during 1977-1991. (Data from FAO). 95 Figure 2.30 Elasmobranch catches of New Zealand, by species groups, during 1977-1991. (Data from FAO). 95 Figure 2.31 Generalized area of operation of the Japanese landbased and non-traditional (ex- mothership) fisheries in 1990. (Based on INPFC 1993). 99 Figure 2.32 Legal boundaries of the Japanese, Korean and Taiwanese flying squid driftnet fisheries. (Redrawn from Pella et al. 1993). 105 Figure 2.33 Area of operation of Japanese large-mesh drift net fishery. (Redrawn from Nakano etal. 1993). 111 Figure 2.34 South Pacific Commission statistical area. (Taken from Lawson 1991). 115 Figure 2.35 Effort distribution of Japanese longline fishery in the Atlantic Ocean in the 1980's. Keys indicate accumulated nominal hook numbers in thousands. (Redrawn from Nakano 1993). 125 Figure 2.36 Distribution of Korean long-line catches, no units given. (Redrawn from NFRDA 1988). 130 xiv Figure 2.37 Distribution of nominal CPUE of bigeye tuna (a) and albacore (b) in the deep and regular longline fisheries of Taiwan in the Atlantic Ocean, 1990. (Redrawn from Hsu and Liu 1992). 131 Figure 2.38 Distribution of effort (in thousands of hooks) by the Spanish swordfish longline fishery in the Atlantic Ocean during 1988-1991. (Redrawn from Mejuto et al. 1993). 135 Figure 2.39 Distribution of Taiwanese catch per unit effort of albacore by (a) regular and (b) deep longline fisheries during 1988 in the Indian Ocean. (Redrawn from Hsu and Liu 1990). 137 Figure 2.40 Distribution of longline effort in the SPC area during 1990, units not given. (Taken from Lawson 1991). 143 Figure 2.41 Major areas of Tuna purse seine fisheries in the world. 153 Figure 3.1 Values of the natural mortality coefficient used by the density dependent function of the model. 177 Figure 3.2 Growth of the simulated elasmobranch population according to parameters defined in the text. 177 Figure 3.3 Stationary (stable) structure of the simulated population at the asymptotic size (virgin population), defined by the mortality and natality schedules. 178 Figure 3.4 Decay of the simulated population under the baseline fishing mortality pattern. 178 Figure 3.5 Total numbers ( ) and recruitment (—) trends of the simulated shark population. The top histograms show the structure of the population every 10 years, a) F=0.05 times baseline, fecundity=5 times baseline; b) F=0.9 times baseline, fecundity=1.6 times baseline; c) F=3 times baseline, fecundity=1.6 times baseline. 182 Figure 3.6 Response surfaces of population numbers (left) and biomass (right) to different fishing regimes during 100 years, when fecundity is increased 100% from baseline values. Values of F are multipliers of the baseline fishing mortality. Note the steepness of both surfaces as F decreases, indicating the sensitivity of the model to changes in F. The axes in the figures have been switched to offer the best view of the surfaces. 184 XV Figure 3.7 Response surface of population numbers to changes in fecundity during a 100 years' period when F is 1.8 times the baseline value. Compare the flatness of the surface with that of figure 6. The axes in the figure have been switched to offer the best view of the surface. 184 Figure 3.8 Proportion of the virgin population after 100 yr of fishing (A/%) against fishing intensity (expressed as multipliers), for different fecundity increase multipliers (numerals on each line). ( — baseline fishing mortality; .... virgin population size in numbers). 185 Figure 3.9 Response surfaces of A/% (upper) and B% (lower) as a function of fecundity increases and F values (both plotted as multipliers). Y axis reversed in order to facilitate view. 186 Figure 3.10 Growth in weight of Carcharhinus falciformis from Yucatan, used for the calculation of population biomass. 189 Figure 3.11 Age-specific density-dependent mortality coefficients used for the simulation of the silky shark (Carcharhinus falciformis). 189 Figure 3.12. Forecasted evolution of the silky shark fishery of Yucatan under 4 different management scenarios: a) no change in estimated fishing mortality; b) a total ban of the bycatch of juveniles in the red grouper hook & line fishery; c) a reduction of 50% in the fishing mortality from the gillnet fishery for adults; d) a total ban of the gillnet fishery for adults. ( tot. numbers; — recruits; .... tot. biomass). 190 Figure 3.13 Proportion of the biomass (B%) and numbers (N%) from the virgin stock left after 100 yr of fishing under 4 management alternatives (numbered 1-4 in the Y axis), under initial and doubled fishing mortalities, for 3 different fecundities: Top- baseline fecundity; Centre- increase of 40% in fecundity; Bottom- increase of 100% in fecundity. (For explanation of the management alternatives see text). 192 Figure 4.1 Schematic representation of the approach taken in this study for testing the performance of three fisheries models for the estimation of assessment and management parameters for shark fisheries. The process is repeated 100 times (Monte Carlo simulations). 201 xvi Figure 4.2 Characteristics of the simulated age structured shark population. The two vulnerability schedules differ only in the age of entry to the fishery. 203 Figure 4.3 Effort patterns used to simulate the harvesting process in the operating models, a) High contrast effort, b) Uninformative effort. 206 Figure 4.4 Theoretical relationships between cpue and abundance. 208 Figure 4.5 Hyperstability (top), proportionality (centre) and hyperdepletion (bottom) as simulated with equation 4.9. (top, Q=5; centre, Q=1; bottom, Q=0.5). 210 Figure 4.6 Total biomass trajectory of the simulated shark populations simulated stock-recruitment data. Top figures, Beverton-Holt OP; Bottom figures, Ricker OP. Fishing starts at year 80. 227 Figure 4.7 Examples of one realization of biomass and cpue trends for different types of operating populations. 229 Figure 4.8 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the multiplicative observation error assumption. Monte Carlo simulations performed with the proportionality OP, high contrast effort, and productive stock. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 231 Figure 4.9 Examples of model fits to biomass time series. A) Beverton-Holt OP; B) Ricker OP; C) Beverton-Holt OP with the Bo=K assumption. Legend key: OP is true biomass, S is Schaefer model, F is Fox model,D is Deriso-Schnute model; and D** is Deriso-Schnute model with mis-specified stock-recruitment function. 232 Figure 4.10 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using multiplicative observation error and the B„=K assumptions. Monte Carlo simulations performed with the proportionality OP and the high contrast effort pattern. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 234 xvii Figure 4.11 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the multiplicative observation error assumption. Monte Carlo simulations performed with the Hyperstability and Hyperdepletion OPs and high contrast effort pattern. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1.. ()= number of failed trials. 235 Figure 4.12 Examples of model fits to biomass time series for the Beverton-Holt OP. A) Hyperstability Case; B) Hyperdepletion Case. Legend key as in fig. 4.9. By chance, fig B shows a relatively good fit of the Fox model, however, note large uncertainty of TD values for this model in fig. 4.11. 237 Figure 4.13 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the multiplicative observation error assumption. Monte Carlo simulations performed with the unproductive stock (age of recruitment =4yr) and proportionality OP. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 238 Figure 4.14 Examples of model fits to biomass time series. A) Ricker OP with low productivity; B) Same as above, with uninformative effort pattern; C) As above, with Bo=K assumption. Legends as in Figure 4.9. 239 Figure 4.15 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the B„=K and the multiplicative observation error assumptions. Monte Carlo simulations performed with the high contrast effort pattern, unproductive stock (age of recruitment =4yr) and the proportionality OP. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 241 Figure 4.16 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the multiplicative observation error assumption. Monte Carlo simulations performed with the uninformative effort pattern, the unproductive stock (age of recruitment =4yr) and the proportionality OP. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 242 xviii Figure 4.17 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the multiplicative observation error and the B„=K assumptions. Monte Carlo simulations performed with the uninformative effort pattern, the unproductive stock (age of recruitment =4yr) and the proportionality OP. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. 243 Figure 4.18 Distribution of errors around a q value of 0.3, according to the two observation error assumptions considered in the study: additive and multiplicative. All data are simulated with the multiplicative model. 245 Figure 5.1. Historical catches of the Yucatan shark fishery. R = Reconstructed from shark by-products; O = Official data, Ministry of Fisheries (25 species of which 7 are common). 255 Figure 5.2. CPUE time series for shark fisheries in two neighbouring localities of Yucatan. 255 Figure 5.3 Approximate range of action of the artisanal shark fisheries of Rio Lagartos and El Cuyo. Additional constrains are imposed by depth. Deployment of nets is not possible beyond 75 m. 257 Figure 5.4. Standardized CPUE time series for shark fisheries in two neighbouring localities of Yucatan. 257 Figure 5.5. Examples of fits to the entire CPUE series: a) 'good' visual fit, but high TLS score. b) Low TLS score, but poor visual fit at the beginning of the time series. 260 Figure 5.6. Examples of fits to the downward portion of the CPUE series (years 85-92) : a) unconstrained fit (trial 2.7); b) using the Bo-K constraint (trial 2.38). 263 Figure 5.7. Plot of CPUE and effort for the shark fishery of Yucatan, (effort estimated from the total catch and the available CPUE series). 266 Figure 5.8. The uncertainty around the MSY value is roughly bounded by MSY isolines of less than 2 (thousand tonnes). Pairs of estimated r and K values for the Schaefer model are plotted for runs using the Bo=K assumption (crosses) and for runs not using this assumption (circles). Inset shows the complete range of estimated parameter values. 268 XIX Figure 5.9 Scatter plot of r and q values obtained from fits with (crosses) and without (circles) the Bo=K assumption. The straight lines are lines of equal fopt values. 269 Figure 5.10 Uncertainty in the CPUE-Biomass relationship. Isolines of MSY = 1.5 thousand tonnes, for different values of the parameter beta representing proportionality (1), hyperdepletion (1.5) and hyperstability (0.5). Key to symbols as in figure 5.8. 270 Figure A.1 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model using the two observation error assumptions. Monte Carlo simulations performed with the proportionality Beverton-Holt OP and high contrast effort. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1.. For each estimation model, A means additive, M means multiplicative observation error assumption. ()= number of failed trials. 300 Figure A.2 Modified box plots showing distribution of estimates of management and biomass assessment benchmarks for each estimation model and the two observation error assumptions, using the B0=K assumption. Monte Carlo simulations performed with the proportionality Ricker OP and high contrast effort. Codes in the x axis correspond to letters used to name estimation procedures in table 4.1. For each estimation model, A means additive, M means multiplicative observation error assumption. ()= number of failed trials. 301 A c k n o w l e d g e m e n t s . x x F i n a n c i a l suppor t for a la rge part o f m y s tud ie s is gratefully a c k n o w l e d g e d to C O N A C y T , a n d the Instituto N a c i o n a l de la P e s c a , M e x i c o . M y t h a n k s a l s o to the F i s h e r i e s C e n t r e , U B C , a n d the B . C . Min i s t ry o f E n v i r o n m e n t ' s F i s h e r i e s R e s e a r c h B r a n c h , for s o m e add i t i ona l shor t - term suppor t in the form of a R e s e a r c h A s s i s t a n t s h i p . F o r the p repa ra t ion o f C h a p t e r 2, the fo l lowing p e r s o n s p r o v i d e d v a l u a b l e informat ion abou t the f i sher ies of the i r coun t r i e s o r f i sher ies u n d e r their expe r t i s e : M r . L e o n a r d o C a s t i l l o , Instituto N a c i o n a l de la P e s c a , M e x i c o C i ty , M e x i c o ; Dr . C h e - T s u n g C h e n , N a t i o n a l T a i w a n O c e a n Univers i ty ; Dr . P a u l i n e D a y a r a t n e , N a t i o n a l A q u a t i c R e s o u r c e s A g e n c y , C o l o m b o , S r i L a n k a ; M r . S h i g e t o H a s e , Nor th P a c i f i c A n a d r o m o u s F i s h C o m m i s s i o n , V a n c o u v e r , C a n a d a ; Dr . D a v i d Ho l t s , N a t i o n a l M a r i n e F i s h e r i e s S e r v i c e , L a J o l l a , U S A ; Dr . R o s a n g e l a L e s s a , U n i v e r s i d a d e F e d e r a l R u r a l do P e r n a m b u c o , R e c i f e , B r a z i l ; M r . J u l i o M o r o n , Indo- P a c i f i c T u n a D e v e l o p m e n t a n d M a n a g e m e n t P r o g r a m m e , C o l o m b o , S r i L a n k a ; Dr . R a m o n M u n o z - C h a p u l i , Un ive r s i t y o f M a l a g a , S p a i n ; Dr . S i g m u n d M y k l e v o l l , Institute of M a r i n e R e s e a r c h , B e r g e n , N o r w a y ; M r . La r ry J . P a u l , M A F F i s h e r i e s , W e l l i n g t o n , N . Z . ; M s . C h e e P h a i k E a n , F i s h e r i e s R e s e a r c h Institute at P e n a n g , M a l a y s i a ; Dr . A n d r e w R i c h a r d s , M r . P a u l T a u r i k i a n d M r . P a u l V . N i c h o l s , F o r u m F i s h e r i e s A g e n c y , H o n i a r a , S o l o m o n Is lands; M r . Pa i ro j S a i k l i a n g , D e p a r t m e n t of F i s h e r i e s , B a n g k o k , T h a i l a n d ; Dr . C a r o l u s M . V o o r e n , F u n d a c a o U n i v e r s i d a d e d o R i o G r a n d e , B r a z i l ; M s . P o u c h a m a r n W o n g s a w a n g , S o u t h e a s t A s i a n F i s h e r i e s D e v e l o p m e n t C e n t e r , S a m u t p r a k a r n , T h a i l a n d . Dr . T i m o t h y A . L a w s o n , S o u t h P a c i f i c C o m m i s s i o n , N o u m e a , N e w C a l e d o n i a , k ind ly con t r ibu ted m a p s for s o m e f igures . I w i s h to t hank m y s u p e r v i s o r Prof . T o n y J . P i t c h e r for h is suppor t a n d s u p e r v i s i o n . M y t h a n k s to Prof . C a r l J . W a l t e r s for h is helpful a d v i c e a n d a s s i s t a n c e wi th m a n y t e c h n i c a l matters , a n d for s o m e ha rd to get but v e r y fruitful d i s c u s s i o n s a b o u t m a n y a s p e c t s of f i sher ies a s s e s s m e n t a n d m a n a g e m e n t that h a d a b e a r i n g in c h a p t e r s 4 a n d 5. Prof . E m e r i t u s D o n L u d w i g a l s o p r o v i d e d helpful a d v i c e a n d useful d i s c u s s i o n s a b o u t M o n t e C a r l o a n a l y s i s a n d f i shery s y s t e m s . M y s i n c e r e a p p r e c i a t i o n to the r e m a i n i n g m e m b e r s of m y s u p e r v i s o r y c o m m i t t e e not yet m e n t i o n e d , Prof . L e s M . L a v k u l i c h , Prof . P a u l H . L e B l o n d , xxi Prof. J. Donald McPhajl, and Prof. Tony R.E. Sinclair, for their support and helpful advice to keep my work in focus. Mr. Cesareo Cabrera and his staff at Rio Lagartos, Yucatan, along with the personnel of Compania Pesquera Atlantida in El Cuyo, Yuc. allowed me access to their shark landing data. Their cooperation to obtain the fishery data for Chapter 5 is greatly acknowledged. Ms. Alida Bundy kindly gave useful comments to a large part of the text. Special mention of appreciation goes to my wife Ying Chuenpagdee for her continuous assistance in the collection of data, preparation of figures and tables, and final editing and typing of the thesis, as well as for her financial support during the last year of my studies that made it possible to finish this thesis. xxii To my wife, Ying, for her unconditional support and love, which made this work possible. XXIII P r e f a c e . T h i s d i sse r ta t ion c o m p r i s e s four m a i n chap t e r s w h i c h a r e e s s e n t i a l l y s e p a r a t e s tud ies . A l t h o u g h t h e s e s tud ie s a re l i nked by the c o m m o n subject o f f i she r i e s for s h a r k s a n d rays , they might be r e g a r d e d a s a d d r e s s i n g a different a s p e c t o f that subject . In part icular , C h a p t e r 2 is a c o m p r e h e n s i v e r ev i ew of wor ld ' s f i sher ies for e l a s m o b r a n c h s , w h i c h s h o u l d be c o n s i d e r e d a s a re fe rence s o u r c e for the rest o f the d i s se r t a t ion . C h a p t e r 2 w a s p u b l i s h e d by the F o o d a n d Agr i cu l t u r e O r g a n i z a t i o n o f the U n i t e d N a t i o n s du r ing 1 9 9 4 . P e r m i s s i o n h a s b e e n o b t a i n e d from F A O to i n c l u d e this w o r k in the present d i s se r t a t ion . T h e full c i ta t ion o f the d o c u m e n t is: Bonf i l , R . 1 9 9 4 . O v e r v i e w of W o r l d E l a s m o b r a n c h F i s h e r i e s . F A O F i s h e r i e s T e c h n i c a l P a p e r 3 4 1 . 1 1 9 p . F A O , R o m e . T h e r e m a i n i n g c h a p t e r s a d d r e s s m o r e quant i ta t ive a s p e c t s o f p o p u l a t i o n d y n a m i c s a n d f i sher ies a s s e s s m e n t . R e a d e r s in te res ted in popu la t ion d y n a m i c s s h o u l d refer to c h a p t e r 3 . T h o s e in te res ted in the theore t i ca l a s p e c t s o f a s s e s s m e n t m e t h o d s a r e a d v i s e d to go straight to C h a p t e r 4 . F ina l ly , r e ade r s l o o k i n g for a p rac t i ca l e x a m p l e o f a s s e s s m e n t of a rea l f i shery for s h a r k s s h o u l d g o direct ly to C h a p t e r 5. A list o f the sc ient i f ic a n d c o m m o n n a m e s of the s h a r k s a n d r ays m e n t i o n e d th roughou t this t hes i s is i n c l u d e d in a p p e n d i x 1. 1 C H A P T E R 1 E L A S M O B R A N C H S : A SPEC IF IC P R O B L E M O F F ISHERIES A S S E S S M E N T A N D M A N A G E M E N T . The most chivalrous fish of the ocean, To ladies forbearing and mild, Though his record be dark Is the man-eating shark Who will eat neither woman nor child... Wallace Irwin 1.1 Introduct ion. E l a s m o b r a n c h f i sher ies a re c o m i n g of a g e , a n d with t h e m , a n e e d for the r e s p o n s i b l e m a n a g e m e n t of t h e s e r e s o u r c e s . W h i l e s h a r k s a n d rays h a v e u s u a l l y b e e n s h u n n e d by mos t w e s t e r n cu l tu res a s unpa l a t ab l e o r u n d e s i r a b l e , they h a v e b e e n the f o c u s of important f i sher ies in o ther par ts of the w o r l d for a l ong t ime . A c c o r d i n g to c a t c h stat is t ics , e l a s m o b r a n c h s p l ay o n l y a s e c o n d a r y role in the w o r l d f i sher ies a r e n a . T h e g l o b a l r e c o r d e d c h o n d r i c h t h y a n c o m m e r c i a l c a t c h to ta l led 7 0 4 , 0 0 0 t in 1 9 9 1 , a n equ iva l en t to 0 . 7 % of the w o r l d f i sher ies du r ing that y e a r ( see s ec t ion 2 .2 .1 .1) ; e v e n c o n s i d e r i n g a n under - repor t ing l eve l of 5 0 % of the r e c o r d e d c a t c h , s h a r k s a n d rays c o m p r i s e o n l y a b o u t 1% of the w o r l d f i sher ies p roduc t ion . D e s p i t e this m o d e s t role, e l a s m o b r a n c h s c a n be o f p r ime impor t ance in s o m e r e g i o n s o f the w o r l d w h e r e they p resen t ly sus t a in s igni f icant f i she r ies . In coun t r i e s l ike S r i - L a n k a , P a k i s t a n , a n d A u s t r a l i a , e l a s m o b r a n c h s r ep resen t b e t w e e n 5 % a n d 9 % of the total f i sher ies p roduc t ion . In t hese coun t r i e s , a n d in o ther c a s e s o f loca l ly important e l a s m o b r a n c h f i she r i es (i.e. U S A At l an t i c s h a r k f ishery) , the a d e q u a t e a s s e s s m e n t a n d m a n a g e m e n t of the r e s o u r c e s s h o u l d be a major c o n c e r n . O v e r the last f ew d e c a d e s the a c c e p t a n c e of e l a s m o b r a n c h s a s f o o d a n d their impor t ance a s f i shery r e s o u r c e s h a v e g r o w n w o r l d w i d e , a l t hough for r e a s o n s d i s c u s s e d b e l o w , th is is not a l w a y s p roper ly ref lected in the f i shery stat is t ics . T w o m a i n fac tors h a v e c o n v e r g e d in the c rea t ion o f n e w marke t s for e l a s m o b r a n c h s a s f o o d a r o u n d the g l o b e . No tab ly , e n h a n c e d l eve l s o f i n c o m e in m a n y coun t r i e s a re appa ren t l y r e s p o n s i b l e for a n e n o r m o u s e x p a n s i o n o f m a r k e t s for shark-f in s o u p . T h i s c o m m o d i t y h a s s u p e r s e d e d its role a s a pure ly traditional Chinese dish to become a trendy gastronomic icon of wealth and power. Parallel to this, there are pressing needs to increase the catches of non-traditional species in order to replace many established fisheries that are currently overexploited (Garcia and Newton 1995). As a net result, elasmobranch fisheries continue to develop in many parts of the globe and the total catches of sharks and rays keep growing without any apparent levelling off. The problem with unchecked fishery exploitation or inadequate fisheries assessment and management is that they almost inevitably lead to stock collapse and ensuing socio- economic hardship. The NW Atlantic cod fishery is a recent bitter example of this reality. In the case of elasmobranchs, there are more causes for concern about their overexploitation than is usual with most fishery resources. Elasmobranchs and their fisheries possess particular characteristics that warrant their treatment as a specific problem of fisheries science deserving a careful and close attention. This thesis is conceived precisely with this in mind. 1.2 A note on taxonomy. The elasmobranchs are part of the Chondrichthyes. The Class Chondrichthyes comprises a diverse group of fishes whose most obvious common feature is the possession of a cartilaginous skeleton, as opposed to the bony skeleton of the Osteichthyes or bony fishes. The cartilaginous fishes form an ancient successful group dating back to the Devonian, in which basic models remain largely unchanged since their last large flourish during the Cretaceous. Despite their ancient origin, they possess some of the most acute and remarkable senses found in the animal kingdom, allowing them to coexist successfully with the more modern teleost designs. The chondrichthyans are grouped into two main subclasses: Holocephalii (Chimaeras or ratfishes and elephant fishes) with 3 families and approximately 37 species inhabiting cool and deep waters; and the Elasmobranchii which is a large and diverse group (including sharks and rays) with representatives in all types of environments, from fresh waters to the depths of marine trenches and from polar regions to warm tropical waters. The great majority of the commercially important species of chondrichthyans are elasmobranchs. The 3 latter r e c e i v e the i r n a m e from their p la ted gi l ls , w h i c h c o m m u n i c a t e to the ex te r io r by m e a n s of 5-7 o p e n i n g s . T h e c l a s s i f i ca t ion o f e l a s m o b r a n c h s is a subject of c o n t i n u o u s d e b a t e but t hey a re gene ra l l y d i v i d e d into 3 g r o u p s o f s h a r k s (i.e. s q u a l o m o r p h s , g a l e o m o r p h s a n d s q u a t i n o m o r p h s ) w h i c h i nc lude 3 0 f ami l i e s a n d a p p r o x i m a t e l y 3 6 8 s p e c i e s , a n d a g r o u p k n o w n a s the ba to ids , c o m p r i s i n g the rays , ska te s , t o r p e d o e s a n d s a w f i s h e s , a n d e m b r a c i n g a total o f 14-21 fami l i e s a n d a b o u t 4 7 0 s p e c i e s ( C o m p a g n o 1977 , 1984 ; S p r i n g e r a n d G o l d 1989) . F o r the p rac t i ca l p u r p o s e s of this thes i s , a l l the C h o n d r i c h t h y e s ( sha rks , ska t e s , r ays a n d c h i m a e r a s ) wi l l often be t rea ted toge ther u n d e r the n a m e " e l a s m o b r a n c h s " o r " sha rks a n d rays". A l t h o u g h this is a n inaccura t e te rm if t a k e n strictly, it s impl i f ies wr i t ing a n d r e a d i n g by a v o i d i n g u n c o m m o n or l eng thy t e rmino logy s u c h a s " c h o n d r i c h t h y a n s " o r " sharks , ska te s , r ays a n d c h i m a e r a s " e v e r y t ime I n e e d to m a k e re fe rence to the g r o u p . 1.3 P r o b l e m s for the A s s e s s m e n t a n d M a n a g e m e n t o f E l a s m o b r a n c h F i s h e r i e s . T h e e l a s m o b r a n c h s p resen t a n a r ray o f p r o b l e m s for f i sher ies a s s e s s m e n t a n d c o n s e r v a t i o n . T h e s e p r o b l e m s c a n be l o o s e l y c l a s s i f i ed a s t h o s e a s s o c i a t e d with the par t icular b i o l o g y a n d e c o l o g y o f t he se f i shes , p e r c e i v e d p r o b l e m s wi th f i sher ies theory, p r o b l e m s c a u s e d by informat iona l cons t ra in t s , a n d f inal ly p r o b l e m s that d e p e n d o n e c o n o m i c factors . 1.3.1 B i o l o g y a n d E c o l o g y . O n e o f the c h i e f p r o b l e m s f a c e d w h e n d e a l i n g with e l a s m o b r a n c h f i she r i es is that thei r b io log i ca l a n d e c o l o g i c a l profi les m a k e s t h e m h igh ly p rone to ove rexp lo i t a t i on . M o s t sha rk a n d m a n y ray s p e c i e s c a n be c l a s s i f i ed a s s t rong K s t ra tegis ts ( H o e n i g a n d G r u b e r 1990) : they are l o n g - l i v e d a n d this , toge ther with their t yp ica l s l o w growth , resul ts in a late a g e of first s e x u a l matura t ion , w h i c h c o m m o n l y r a n g e s b e t w e e n 3 a n d 2 5 y e a r s d e p e n d i n g o n the s p e c i e s . M o s t e l a s m o b r a n c h s h a v e ve ry l ow fecundi ty w h e n c o m p a r e d wi th b o n y f i shes o r m a r i n e inver tebra tes , the r ange of y o u n g p r o d u c e d by e a c h f e m a l e is b e t w e e n 2 a n d 125 per litter ( see Prat t a n d C a s e y 1 9 9 0 for a s u m m a r y of k e y l i fe-history cha rac t e r i s t i c s o f 4 sha rks ) . T h e c o m b i n a t i o n o f the a b o v e factors t r ans la tes into a l o w rep roduc t ive potent ia l a n d m e a n s that the product ivi ty a n d r e s i l i ence of e l a s m o b r a n c h s t o c k s is c o m p a r a t i v e l y low. A t the c o m m u n i t y l eve l , the top p reda tor n i che o c c u p i e d by m a n y s h a r k s r a i s e s the ques t ion of thei r i m p o r t a n c e a s regula tors o f o ther s p e c i e s ' dens i t i e s . W h a t a r e the impl i ca t ions of thei r r e m o v a l / d e p l e t i o n from the e c o s y s t e m ? A l t h o u g h it c o u l d be d e s i r a b l e to cont ro l sha rk p o p u l a t i o n s in v e r y spec i f i c s i tua t ions (i.e. b e c a u s e they c a n affect the e c o n o m y of important b e a c h resort a r e a s l ike N a t a l o r H a w a i i ) , it is l ikely that the i r r e m o v a l c o u l d br ing u n d e s i r a b l e e c o l o g i c a l a n d e c o n o m i c a l c o n s e q u e n c e s , a s d o c u m e n t e d in the c o a s t o f N a t a l by v a n d e r E ls t (1979) . It is v e r y difficult h o w e v e r , to a s s e s s the effects o f s h a r k dep le t ion in the e c o s y s t e m o r to k n o w w h i c h s t o c k s o f e l a s m o b r a n c h s a re ac tua l ly e n d a n g e r e d , w h e n there is insufficient informat ion abou t thei r b a s i c b i o l o g y a n d e c o l o g y , the s i z e a n d state of thei r s t ocks , a n d the rea l m a g n i t u d e of thei r exp lo i ta t ion . 1.3.2 F i s h e r i e s theory . It is c o m m o n be l i e f that a n o t h e r cons t ra in t for the a s s e s s m e n t a n d m a n a g e m e n t of s h a r k s a n d rays is p o o r d e v e l o p m e n t o f theory ( A n d e r s o n 1 9 9 0 , A n d e r s o n a n d T e s h i m a 1990) . F i s h e r i e s r e s e a r c h o n e l a s m o b r a n c h s h a s b e e n s c a n t y if not i n a d e q u a t e a n d to date there is no spec i f i c m e t h o d o l o g i c a l f r amework for a s s e s s i n g their f i she r i e s . F o r a start, su rp lus p roduc t ion m o d e l s h a v e b e e n t radi t ional ly d i s r e g a r d e d for the a s s e s s m e n t of s h a r k a n d ray f i sher ies for s e v e r a l r e a s o n s , wi thout au tho r s ac tua l ly e x a m i n i n g the sui tabi l i ty of the r ange of t he se m o d e l s to spec i f i c e l a s m o b r a n c h f i sher ies . S o m e au tho r s ( A n d e r s o n 1990 , A n d e r s o n & T e s h i m a 1990 , S i l v a 1993) be l i eve that p roduc t ion m o d e l s a re o f l imited use ma in ly b e c a u s e o f thei r l ack of b i o l o g i c a l reali ty (no a g e s t ructure , no expl ic i t a c c o u n t of growth a n d rep roduc t ive m o d e s , on ly a ve ry c r u d e incorpora t ion o f c o m p e n s a t o r y m e c h a n i s m s , etc.) . O the r s , l ike H o l d e n (1977) a n d W o o d et a l . (1979) , d i s m i s s su rp lus p roduc t ion m o d e l s a r g u i n g that e l a s m o b r a n c h b io logy v io l a t e s s o m e o f the a s s u m p t i o n s o f t he se m o d e l s ( see C h a p t e r 4) . T h e mul t i spec i f i c a n d mul t igea r nature of mos t sha rk a n d ray f i she r i es further c o m p l i c a t e s thei r a s s e s s m e n t . T a k e the f i sher ies for s h a r k s a n d rays in the t rop ics a s a n e x a m p l e (which inc iden ta l ly a c c o u n t for m o r e than 5 0 % of the repor ted w o r l d e l a s m o b r a n c h c a t c h e s ) . T h e s e 5 fisheries include a mixed catch of several species of sharks and rays; furthermore, these catches are often obtained with a great variety of gears and from several types of vessels. Multispecies fisheries present serious methodological problems because of their complex biological and technological interactions. As a consequence, the theoretical development of multispecies assessment and management is still lagging behind the rest of fisheries science (Hilborn and Walters 1992). In addition to this, the usage of multiple gears and fleets for the exploitation of any fish resource introduces another level of complexity for their assessment and management (e.g. standardisation of effort, the complications of allocating quotas to the various types of gears and vessels). 1.3.3 Informational constraints. There are several kinds of information deficiencies that make the assessment of elasmobranch fisheries very difficult. Probably the most widespread and pressing of them is the lack of adequate fishery statistics. The latter are not well maintained for elasmobranchs around the world, partly because of problems in species identification (specially for tropical species), partly for economic reasons. Most statistical records aggregate all skates and rays in a single group without further species identification, while shark catches are commonly split into two categories, large and small sharks (Chapter 2). In the worst cases, all elasmobranchs are reported together as a single item: "various elasmobranchs". Without statistics by species or species groups it is very difficult to implement most fishery models or to get any insight into the dynamics of the stocks. This sets obvious constraints on our ability to do assessment and management. The lack of statistics by species or species groups has a large economic component: it is not cost effective to sort catches by species when they all attain the same price. Nonetheless, it has been shown that whenever a specific market is developed for an elasmobranch species, catch information becomes readily available. Lack of information on some relevant areas of elasmobranch population dynamics is also a constraining factor for their assessment and management. First, stock-recruitment relationships have never been documented with hard data for any elasmobranch, although an almost proportional relationship is suspected due to the reproductive strategies of the group (Holden 1973, Hoff 1990). Secondly, there is a general shortage of hard evidence 6 abou t d e n s i t y - d e p e n d e n t m e c h a n i s m s regula t ing e l a s m o b r a n c h p o p u l a t i o n s i z e . Thi rd ly , the spa t ia l s t ructure a n d d y n a m i c s o f mos t s t o c k s a re a l m o s t total ly u n k n o w n . T h i s often o v e r l o o k e d i s s u e is o f par t icular impor t ance to f i sher ies m a n a g e m e n t both at the l oca l a n d in terna t ional l e v e l . Inadequa te k n o w l e d g e o f migra t ion routes , s t o c k de l imi ta t ion a n d m o v e m e n t ra tes a m o n g s t t he se s t o c k s / s u b s t o c k s , c a n s e r i o u s l y u n d e r m i n e o the rwi se " so l id" a s s e s s m e n t a n d m a n a g e m e n t r e g i m e s . F ina l ly , the difficulties in f ind ing a d e q u a t e m o d e l s for e l a s m o b r a n c h s a re e x a c e r b a t e d by c o n s i d e r a b l e g a p s in o u r u n d e r s t a n d i n g o f their b io logy . T h e life c y c l e s o f mos t s p e c i e s , e v e n in t e rms o f the b a s i c p a r a m e t e r s o f age , growth a n d r ep roduc t ion , h a v e just s tar ted to be u n v e i l e d du r ing the last fifteen y e a r s o r so , a n d o n l y for a handfu l o f e l a s m o b r a n c h s tocks , ma in ly t h o s e of c o m m e r c i a l i m p o r t a n c e in d e v e l o p e d coun t r i e s . T h i s s i tuat ion h a s h i n d e r e d the u s e of the m o r e "b io log ica l ly correct" age - s t ruc tu red m o d e l s . 1.3.4 E c o n o m i c s . S h a r k s a n d r ays a re not a h igh ly p r i c e d f i shery p roduc t (e .g . in the T a i w a n e s e gil lnet f i sher ies o f the C e n t r a l W e s t e r n Pac i f i c , p r i ces for sha rk in t runk at ta in o n l y 2 0 % a n d 6 0 % of the pr ice of w h o l e t unas a n d m a c k e r e l s r e spec t ive ly (Mi l l ing ton 1981)) . S o m e e x c e p t i o n s are sport f i sher ies , w h i c h c a n be o f c o n s i d e r a b l e e c o n o m i c v a l u e , ce r t a in s p e c i e s for w h o m a t rendy g a s t r o n o m i c d e m a n d h a s recent ly d e v e l o p e d in s o m e parts o f the w o r l d (i.e. m a k o a n d th r e she r s h a r k s in U S A ) , o r t hose s p e c i e s w h i c h unfor tunately a r e h igh ly - sough t o n l y for thei r teeth a n d j a w s , like the great whi te shark . S h a r k ' s fins for o r ien ta l s o u p s t and a s the o n l y h i g h l y - p r i c e d e l a s m o b r a n c h product ; a ki lo of top-qual i ty dry f ins c a n fetch m o r e than $ 1 0 0 U S . A n u m b e r o f the p r o b l e m s a s s o c i a t e d with e l a s m o b r a n c h exp lo i ta t ion c a n be t r a c e d b a c k to e c o n o m i c factors . In par t icular , two e c o n o m i c cons t ra in t s s u r r o u n d i n g e l a s m o b r a n c h f i sher ies c a u s e w h a t I c a l l the " t ragedy of sha rks" . First , r e s e a r c h a n d m a n a g e m e n t for s h a r k s a n d rays a re h a m p e r e d by the low e c o n o m i c v a l u e o f this g r o u p : in a t ime w h e n budge t s a l l o c a t e d for sc ient i f ic r e s e a r c h a n d for r e s o u r c e m a n a g e m e n t con t inue to d e c r e a s e , priori t ies a re g i v e n to r e s o u r c e s e c o n o m i c a l l y m o r e important than e l a s m o b r a n c h s , i.e. s a l m o n s , p r a w n s , tunas , etc. T h e s e c o n d , is the h igh pr ice a t ta ined by sha rk fins in the in terna t ional market . T h i s h igh pr ice s t imula tes i n c r e a s i n g explo i ta t ion a n d is a l s o the force b e h i n d "f inning" p rac t i ces in m a n y f i sher ies . W i t h i n th is context , "f inning" ( cons i s t ing in cutt ing-off the fins from the s h a r k a n d d u m p i n g the c a r c a s s to the s ea ) is a n e x c e s s i v e l y was te fu l habit w h i c h is unfortunately ve ry c o m m o n a m o n g f i s h e r m e n th roughout the w o r l d : w h e n s h a r k s a re c a u g h t a s a b y c a t c h , the ex t ra high-profi ts o b t a i n e d from cutt ing the fins off the s h a r k a re difficult to fo rgone in the n a m e o f c o n s e r v a t i o n . A p a r t from the e th ica l i s s u e s o f this p rac t ice ( m a n y t imes the s h a r k is d u m p e d still a l ive ) , f inning is r e s p o n s i b l e for h igh dea th rates o f s h a r k s at s e a . H e n c e , the d y n a m i c s o f the g e n e r a l l ow pr ice o f e l a s m o b r a n c h s a n d the h igh pr ice of s h a r k fins k e e p s h a r k s c a u g h t h o p e l e s s l y i n - b e t w e e n . A t present , this d i l e m m a s e e m s to h a v e no v i a b l e so lu t ion that is cons i s t en t wi th both e c o n o m i c a n d c o n s e r v a t i o n interests . In add i t ion , the e c o n o m i c incen t ive b e h i n d f inning p rac t i ces is indi rec t ly r e s p o n s i b l e for the fact that a subs tan t i a l part of the s h a r k c a t c h n e v e r m a k e s it to the official s tat is t ics; a s no sha rk c a r c a s s e s a re brought to port, in mos t c a s e s sha rk fin l a n d i n g s a re not c o n v e r t e d to l ive we igh t a n d a c c o u n t e d for. T h i s is p robab ly o n e of the major r e a s o n s w h y official s tat is t ics do not truly reflect the recent i n c r e a s e in e l a s m o b r a n c h explo i ta t ion w o r l d w i d e . 1.4 T h e s i s ou t l ine . C o n s i d e r i n g the r ange of p r o b l e m s a s s o c i a t e d with e l a s m o b r a n c h f i sher ies , it is not su rp r i s ing that there is a his tory o f fa i led sus ta inab i l i ty in thei r exp lo i t a t ion ( A n d e r s o n 1990 , a n d H o l d e n 1977) p rov ide a list o f fa i l ed e l a s m o b r a n c h f i sher ies ) . In recen t y e a r s h o w e v e r , there h a s b e e n g r o w i n g in ternat ional c o n c e r n o v e r the c o n s e r v a t i o n o f s o m e e l a s m o b r a n c h s tocks a n d it s e e m s that now, m o r e than ever , there is a n e e d for a m o r e de t a i l ed a p p r o a c h to the p r o b l e m of e l a s m o b r a n c h a s s e s s m e n t a n d m a n a g e m e n t . T h i s t he s i s is c o n c e i v e d wi thin the contex t o f e l a s m o b r a n c h s a s a s p e c i a l c a s e of f i sher ies m a n a g e m e n t requ i r ing spec i f i c a t tent ion. A l t h o u g h e a c h of t h e s e c h a p t e r s cons t i tu tes a s epa ra t e a n d i n d e p e n d e n t s tudy, they a re a l l l iked by the c o m m o n p u r p o s e o f cont r ibu t ing t o w a r d s the e s t a b l i s h m e n t o f g e n e r a l ru les for the ra t ional exp lo i ta t ion o f e l a s m o b r a n c h s . In this s e n s e , the c o n c e p t o f t a ck l i ng f i shery r e s o u r c e s in a t a x o n o m i c / s p e c i f i c b a s i s is not a novel ty . A s the w i d e s p r e a d app l i ca t i on o f t radi t ional f i shery m o d e l s to a l l t ypes o f r e s o u r c e s h a s f requent ly p r o v e n to be a n u n s u c c e s s f u l s t rategy, m o r e a n d m o r e f i shery sc ien t i s t s a re tu rn ing t o w a r d s d e v e l o p i n g m e t h o d s t a i lo red to the spec i f i c n e e d s o f the r e s o u r c e o f the i r c o n c e r n ( see I W C 1987 , Pun t 1988) . 8 T h e first s tudy, C h a p t e r 2 , s e r v e s two p u r p o s e s , it is a b a c k g r o u n d a n d f r a m e w o r k for the thes i s , a n d cons t i tu tes a major re fe rence s o u r c e for e l a s m o b r a n c h f i she r i e s w o r l d w i d e . T h i s o v e r v i e w in tegra tes in a s ing le v o l u m e the mos t important informat ion a v a i l a b l e abou t f i sher ies for e l a s m o b r a n c h s a r o u n d the w o r l d , a n d p r o v i d e s a p re l imina ry a n a l y s i s o f the g l o b a l s i tua t ion . It c o n t a i n s de ta i l ed a n a l y s e s o f e l a s m o b r a n c h f i she r i es in coun t r i e s that h a v e s ignif icant s h a r k a n d ray c a t c h e s , a n d g i v e s the first e v e r e s t ima te o f g l o b a l b y c a t c h e s in h i g h - s e a s f i she r i es o f the w o r l d . C h a p t e r 2 w a s p u b l i s h e d du r ing 1 9 9 4 by the F o o d a n d Agr i cu l t u r e O r g a n i z a t i o n o f the U n i t e d N a t i o n s , a s F A O F i s h e r i e s T e c h n i c a l P a p e r 3 4 1 , a n d h a s b e e n r e c e i v e d wi th great interest by the scient i f ic c o m m u n i t y . In C h a p t e r 3,1 cont r ibute t o w a r d s the u n d e r s t a n d i n g o f the popu l a t i on d y n a m i c s o f s h a r k s , a n d its re la t ion with exp lo i t a t ion . In this s tudy, a s i m p l e de te rmin i s t i c s imu la t i on m o d e l with expl ic i t a g e s t ructure is u s e d to a n a l y s e the effects of d e n s i t y - d e p e n d e n t fecundi ty u p o n the abil i ty o f a s h a r k popu la t i on to sus t a in f i sh ing mortal i ty. T h i s is d o n e by s imu la t i ng the na tura l g rowth of a popu la t ion a n d its l ong te rm trajectory u n d e r different s c e n a r i o s of explo i ta t ion a n d fecundi ty i n c r e a s e s . In add i t ion , the u s e o f the m o d e l a s a n a i d in m a n a g e m e n t d e c i s i o n m a k i n g is exempl i f i ed with a c a s e from a t rop ica l s h a r k f ishery. Ul t imate ly , this c h a p t e r i l lustrates the b io log i ca l l imita t ions that c o n s t r a i n m o s t e l a s m o b r a n c h f i sher ies . T h e s e a r c h for a d e q u a t e f i shery m o d e l s for the a s s e s s m e n t o f e l a s m o b r a n c h popu la t ions is t rea ted in C h a p t e r 4 . T h i s is a la rge M o n t e C a r l o a n a l y s i s o f the p e r f o r m a n c e o f three f i sher ies m o d e l s for the es t imat ion o f a s s e s s m e n t a n d m a n a g e m e n t p a r a m e t e r s of e l a s m o b r a n c h f i she r ies . T h i s m o d e l l i n g e x e r c i s e a i m s at d e t e r m i n i n g if s i m p l e f i shery m o d e l s c a n be u s e d for s h a r k a s s e s s m e n t a n d m a n a g e m e n t p a r a m e t e r e s t ima t ion , w h i c h m o d e l is best, a n d h o w robus t s u c h m o d e l s a re . A full age - s t ruc tu red s t o c h a s t i c s imu la t i on m o d e l of a sha rk popu la t i on is u s e d to gene ra t e c a t c h a n d c p u e da t a v i a a s t o c h a s t i c ha rves t ing s u b m o d e l . A total o f 10 different s c e n a r i o s i nc lud ing va r i a t i ons in s t o c k recrui tment re la t ionsh ips , f i shab le s tock s i z e , spa t ia l b e h a v i o u r o f the s h a r k s , a n d da t a qual i ty , a re a n a l y s e d to test the r o b u s t n e s s of the f i shery m o d e l s . T h e s e a re the s u r p l u s p roduc t ion m o d e l s o f S c h a e f e r (1957) a n d F o x (1971) , a n d the de lay-d i f fe rence m o d e l o f D e r i s o (1980) 9 a n d S c h n u t e (1985) . T h e M o n t e C a r l o a n a l y s i s i n c l u d e s s e v e r a l a l t e rna t ives for i m p l e m e n t i n g the es t ima t ions ; pe r fo rmance is e x a m i n e d by c o m p a r i n g the e s t i m a t e s of s tock a s s e s s m e n t a n d m a n a g e m e n t pa r ame te r s from e a c h f i shery m o d e l a g a i n s t the k n o w n v a l u e s of the s i m u l a t e d popu la t i ons . F ina l ly , C h a p t e r 5 is a n e x a m p l e o f the p rac t i ca l difficulties f a c e d du r ing rea l e l a s m o b r a n c h f i sher ies a s s e s s m e n t work . In this c h a p t e r I a n a l y s e the m u l t i s p e c i e s s h a r k f ishery of Y u c a t a n t h rough the app l i ca t i on of o n e of the f i shery m o d e l s s t u d i e d in c h a p t e r 4, a n d s u g g e s t s o m e p o s s i b l e so lu t ions to o v e r c o m e the s h o r t c o m i n g s o f the a v a i l a b l e da ta . 10 C H A P T E R 2 T R E N D S A N D P A T T E R N S IN E L A S M O B R A N C H EXPLOITATION: A N O V E R V I E W O F W O R L D F ISHERIES FOR S HARKS , R A Y S A N D RELATIVES. 2.1 Introduct ion. T h e a p p a r e n t fragility of e l a s m o b r a n c h s a n d the pas t h is tory o f c o l l a p s e s in their f i sher ies ( see A n d e r s o n (1990) for a rev iew) a re c a u s e s for c o n c e r n . T h i s is s p e c i a l l y true n o w that the c o n t i n u i n g i n c r e a s e in their c a t c h e s ( see 2.2) a n d the e v e r d e m a n d i n g marke t for sha rk fins m a y be e n d a n g e r i n g the sus ta inabi l i ty o f t h e s e f i sher ies . In recen t y e a r s , there h a s b e e n g r o w i n g in te rna t iona l c o n c e r n o v e r the state o f e l a s m o b r a n c h s tocks , a n d s o m e conse rva t i on i s t m o v e m e n t s a re start ing to r ing the a l a r m o v e r the plight o f s h a r k s a n d rays a r o u n d the w o r l d . Unfor tunate ly , whi l s t the e v e n t u a l a d o p t i o n o f a n y h a r s h uni la tera l c o n s e r v a t i o n m e a s u r e (i.e. e m b a r g o e s l ike t h o s e o f the t u n a - d o l p h i n c o n t r o v e r s y ) c o u l d h a v e nega t ive effects in the f i sher ies o f m a n y coun t r i e s for w h i c h e l a s m o b r a n c h s a re of c o n s i d e r a b l e impor t ance , the reali ty is that the p resen t i m p a c t s o f f i she r i es o n s h a r k a n d ray s tocks o n a g l o b a l s c a l e a re difficult to a s s e s s . T h i s h a p p e n s b e c a u s e there is not o n l y a l ack o f informat ion o n the s i z e of mos t e l a s m o b r a n c h s tocks , but b e c a u s e there is no readi ly a v a i l a b l e b a s i c informat ion abou t thei r f i sher ies w o r l d w i d e . M u c h of the ex i s t i ng information abou t s h a r k a n d ray f i sher ies is not on ly d i s p e r s e , but is u s u a l l y u n p u b l i s h e d a n d kept by t hose c o n c e r n e d with their s tudy o r m a n a g e m e n t in m a n y l abora to r i e s a r o u n d the w o r l d . E v e n the rea l m a g n i t u d e of the total w o r l d c a t c h e s o f s h a r k s a n d r ays is uncer ta in , ma in ly b e c a u s e o f p o o r k n o w l e d g e o f the total l eve l s of b y c a t c h e s a n d d i s c a r d s . T h i s c h a p t e r is o r i en t ed t o w a r d s a l l ev ia t ing the l ack o f b a s e l i n e informat ion a b o u t s h a r k a n d ray f i sher ies w o r l d w i d e . T h e p resen t o v e r v i e w of e l a s m o b r a n c h f i she r i es puts toge ther for the first t ime m o s t o f the ex i s t ing informat ion abou t the cha rac t e r i s t i c s a n d d ivers i ty o f thei r f i sher ies , the s p e c i e s u n d e r explo i ta t ion , the extent o f the c a t c h e s , the l e v e l o f b y c a t c h e s a n d d i s c a r d s in the h igh s e a s , a n d abou t m a n a g e m e n t m e a s u r e s cur ren t ly in use for e l a s m o b r a n c h f i sher ies . 11 2.1.1 O r g a n i s a t i o n of this work . S e c t i o n 2.2.1 part ia l ly d e s c r i b e s the s c a l e of g l o b a l e l a s m o b r a n c h f i sh ing by e x a m i n i n g the official s ta t is t ics w o r l d w i d e . T h i s s ec t ion c o n s i s t s o f a n o v e r v i e w of the c a t c h stat is t ics by F A O major f i sh ing a r e a s i nc lud ing short- term pro jec ted c a t c h e s , a n d a n o v e r v i e w of the t r ends in the mos t important f i sher ies for e l a s m o b r a n c h s in the w o r l d o n a coun t ry b a s i s . F o r this r ev iew, coun t r i e s wi th official e l a s m o b r a n c h c a t c h e s o f 1 0 , 0 0 0 t/yr o r m o r e are c a l l e d "major" e l a s m o b r a n c h - f i s h i n g coun t r i e s . S e c t i o n s 2 .2 .2 a n d 2 .2 .3 d e a l wi th the major f i sher ies for e l a s m o b r a n c h s , a n d the b y c a t c h e s a n d d i s c a r d s at s e a , r e spec t ive ly . A l t h o u g h it is difficult to d i s t i ngu i sh b e t w e e n d i rec ted a n d inc iden ta l f i sher ies , e s p e c i a l l y w h e n d e a l i n g with f i shes that a re s e l d o m ta rge ted and /o r c a u g h t a l o n e a s is the c a s e o f s h a r k s a n d rays , I wi l l u s e the fo l lowing t w o m a i n d i v i s i o n s for the t rea tment of e l a s m o b r a n c h c o m m e r c i a l f i sher ies : I wi l l treat u n d e r the n a m e "direct", a l l f i sher ies that target e l a s m o b r a n c h s , toge ther with a l l c o a s t a l f i she r i es a n d s m a l l s c a l e m u l t i s p e c i e s f i sher ies w h i c h c a t c h e l a s m o b r a n c h s inc iden ta l ly . T y p i c a l l y , the c a t c h e s from the se t w o s o u r c e s a re m i x e d toge ther in the official s ta t is t ics o f m o s t coun t r i e s a n d it b e c o m e s n e c e s s a r y to treat t h e m together . O n the o ther h a n d , there is a g r o u p of l a rge- s c a l e l ong - r ange f i sher ies that ma in ly target h igh v a l u e s p e c i e s o n the h igh s e a s . T h e s e f i sher ies v e r y f requent ly c a t c h e l a s m o b r a n c h s inc iden ta l ly but u s u a l l y d i s c a r d t he se b y c a t c h e s for v a r i o u s r e a s o n s . T h e y c o m p r i s e e s sen t i a l l y a different c a t e g o r y of f i sher ies in w h i c h the e l a s m o b r a n c h s are not on ly b e i n g w a s t e d , but the a c t u a l n u m b e r s of e l a s m o b r a n c h s c a u g h t a re a l s o poor ly k n o w n a n d usua l ly d o not m a k e it to the ca t ch s tat is t ics . M o s t c a s e s in this c a t e g o r y a re h i g h - s e a s la rge s c a l e f i she r i es wi th driftnets a n d long l ines c a r r i e d out by a few coun t r i e s a n d target ing h igh profile r e s o u r c e s s u c h a s tunids , bi l l f ishes , s a l m o n i d s a n d s q u i d . T h e s e f i sher ies a re s u s p e c t e d of c a u s i n g subs tan t i a l kills of e l a s m o b r a n c h s , m a i n l y s h a r k s . T h i s h a s r a i s e d c o n c e r n o v e r the c o n s e r v a t i o n of t he se f i shes , a l t hough o n a v e r y different s c a l e than the c o n c e r n o v e r m a r i n e m a m m a l s , w h i c h a re a l s o f requent ly t a k e n a s b y c a t c h e s in t he se f i sher ies . D e p e n d i n g o n the a m o u n t of informat ion a v a i l a b l e , the s p e c i e s , c a t c h e s , gea r s , f i sh ing units , loca l i t i es , l eve l s of explo i ta t ion a n d ex i s t ing m a n a g e m e n t o r c o n s e r v a t i o n m e a s u r e s , a re s u m m a r i s e d for e a c h c a s e . 2.2 C h a r a c t e r i s a t i o n o f e l a s m o b r a n c h f i sher ies . 12 2.2.1 T h e Official S ta t i s t ics . T h e da t a u s e d in this a n a l y s i s is t a k e n from official f i shery s ta t is t ics o f e a c h count ry . T h e first s o u r c e is the c o m p i l a t i o n o f C o m p a g n o (1990) w h o a n a l y s e d F A O da t a for the pe r iod 1 9 4 7 - 1 9 8 5 . F A O f igures s i n c e 1 9 7 0 h a v e b e e n u p d a t e d u s i n g F i s h e r i e s Y e a r b o o k s for 1 9 8 8 - 1991 ( F A O 1 9 9 0 - 1 9 9 3 ) a n d da t a p r o v i d e d direct ly from the F A O sta t is t ica l d a t a b a s e ( D a v i d D i e , F A O , pe r s . c o m m . A u g u s t 2 , 1 9 9 3 ) . A d d i t i o n a l s o u r c e s a re : F i s h e r y S ta t i s t i ca l Bu l l e t ins for the S o u t h C h i n a S e a A r e a y e a r s 1 9 7 6 - 1 9 9 0 ( S E A F D E C 1 9 7 7 - 1 9 9 3 ) , the F i s h e r i e s Y e a r b o o k o f T a i w a n A r e a for 1 9 7 0 a n d 1 9 8 8 - 1 9 9 0 a n d the M e x i c a n F i s h e r y Sta t i s t ica l Y e a r b o o k s 1 9 7 6 - 1 9 9 0 (Sec re t a r i a de P e s c a 1 9 7 9 - 1 9 9 2 ) . Af te r the t h o r o u g h r e v i e w of F A O da ta d o n e by C o m p a g n o (1990) , the informat ion is he re u p d a t e d a n d e x p a n d e d , i nc lud ing expl ic i t ly the c a t c h e s of T a i w a n a n d e s t ima tes o f the c a t c h e s o f the P e o p l e ' s R e p u b l i c of C h i n a . 2.2.1.1 T r e n d s a n d o u t l o o k s by F A O M a j o r F i s h i n g A r e a s . To ta l w o r l d e l a s m o b r a n c h c a t c h e s repor ted for the pe r iod 1 9 4 7 - 1 9 9 1 (fig. 2 .1) a m o u n t e d to a r eco rd o f 7 0 4 , 0 0 0 t in 1 9 9 1 . R o u g h l y , four p e r i o d s wi th different t r ends c a n be identif ied. P o o r g rowth in c a t c h e s b e t w e e n 1947 a n d 1954 , a s u s t a i n e d i n c r e a s e o f p roduc t ion dur ing 1 9 5 5 - 1 9 7 3 f o l l o w e d by a p e r i o d of s l u g g i s h p roduc t ion for mos t o f the 70 ' s a n d finally r e n e w e d growth in c a t c h e s dur ing the last y e a r s 1 9 8 4 - 1 9 9 1 . C a t c h e s by F A O M a j o r F i s h i n g A r e a s from 1967 to 1991 a re s u m m a r i s e d in tab le 2 . 1 . A n at tempt is m a d e to rank t he se A r e a s a c c o r d i n g to thei r e l a s m o b r a n c h c a t c h e s . B e c a u s e the s i z e s , c o a s t l i n e l eng ths a n d h u m a n popu la t i ons o f e a c h A r e a v a r y no tab ly , a rough i n d e x of relat ive p roduc t ion w a s d e v i s e d for c o m p a r i s o n p u r p o s e s . T h i s i n d e x is de f ined a s the a v e r a g e total e l a s m o b r a n c h ca t ch o f e a c h A r e a d i v i d e d by the s q u a r e root o f the sur face of that A r e a in k m 2 . A better i n d e x might h a v e b e e n to u s e the e x t e n s i o n o f con t inen ta l she l f for e a c h A r e a , but it w a s not p o s s i b l e to ob ta in t he se da ta . Arbi t ra r i ly , v a l u e s o f the i n d e x b e l o w 5 w e r e c o n s i d e r e d indica t ive o f l ow relat ive p roduc t ion , t h o s e b e t w e e n 5 a n d 10 in te rmedia te a n d t h o s e of m o r e than 10 a s h igh . A d d i t i o n a l l y , the t r end in c a t c h e s dur ing the 13 Table 2.1 Elasmobranch catches by FAO Statistical Area 1967-1991. Mean catch, variation and Index of Relative Production (IRP) are given for the last 25 yr, and catch trends for the last 10 yr. (All weights in tonnes, live weight.) F . A . O . M a j o r F i sh ing A r e a s A r e a M e a n C a t c h C o e f f i c i e n t I.R.P. T r e n d 8 2 - 9 1 Million Km2 ' 0 0 0 t of V a r i a t i o n Avg Catch/SqrtAre ' 0 0 0 t/y 2 7 N E A t l a n t i c O c e a n 1 6 . 9 . 9 4 . 8 1 2 % 2 3 . 0 7 0 . 2 6 61 N W P a c i f i c O c e a n 2 0 . 5 1 0 2 . 3 1 0 % 2 2 . 6 0 - 0 . 2 9 51 W Indian O c e a n 3 0 . 2 9 7 . 6 1 9 % 1 7 . 7 5 1.16 21 N W A t l a n t i c O c e a n 5.2 2 6 . 5 5 7 % 1 1 . 6 1 5 .48 3 7 M e d i t e r r a n e a n & B l ack S e a s 3 .0 1 8 . 2 2 9 % 1 0 . 5 0 - 0 . 7 6 71 W C e n t r a l P a c i f i c O c e a n 3 3 . 2 59.1 3 8 % 1 0 . 2 6 5 . 0 0 41 S W A t l a n t i c O c e a n 1 7 . 6 3 4 . 2 3 0 % 8 . 1 5 0 . 6 0 5 7 E Indian O c e a n 2 9 . 8 4 2 . 9 3 2 % 7 . 8 7 1.34 3 4 E C e n t r a l A t l a n t i c O c e a n 1 4 . 0 2 8 . 6 2 9 % 7 . 6 3 - 0 . 6 5 8 7 S E P a c i f i c O c e a n 1 6 . 6 2 1 . 4 3 2 % 5 . 2 4 - 0 . 3 9 31 W C e n t r a l A t l a n t i c O c e a n 1 4 . 7 1 7 . 4 4 7 % 4 . 5 4 0 . 7 7 7 7 E C e n t r a l P a c i f i c O c e a n 5 7 . 5 21.1 3 4 % 2 . 7 9 0 . 0 8 81 S W Pac i f i c O c e a n 3 3 . 2 1 0 . 4 4 7 % 1.81 0 . 5 5 6 7 N E Pac i f i c O c e a n 7.5 4 . 8 6 0 % 1 .74 0 . 2 0 4 7 S E A t l a n t i c O c e a n 1 8 . 6 6.6 4 2 % 1.53 0 . 0 7 e u u - r r 700-H 600-H 400-H 300-H 200-H' 100- IllllllllllllllllllllllllllllIllllPllll 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 Years Figure 2.1 World reported catch of elasmobranch fishes 1947-1991. (Data from FAO, SEAFDEC, Fishery Yearbooks for Taiwan Area, and Secretaria de Pesca). 14 las ts 10 y e a r s r e c o r d e d for e a c h A r e a , is e x p r e s s e d a s the s l o p e o f a l i nea r r e g r e s s i o n fitted to the da t a by leas t s q u a r e s . In the W e s t e r n A t l a n t i c O c e a n , a l l the A r e a s h a v e fairly h igh i n c r e a s i n g t rends , e s p e c i a l l y A r e a 21 (Nor th W e s t At lan t ic ) w h i c h h a s the h ighes t i n c r e a s i n g t r end o v e r a l l . T h e s e three A r e a s s h o w s t rong va r i a t ions in thei r c a t c h e s . A r e a 21 h a d the h ighes t var iabi l i ty , wi th recent y e a r s a p p a r e n t l y r e c o v e r i n g p roduc t ion from a d r a m a t i c d r o p suf fered in the late 70 ' s fo l lowing h igh y i e l d s in the ea r ly 70 ' s . A r e a 21 h a d a m a r g i n a l l y h igh i n d e x of relat ive p roduc t ion ( IRP) , but c o n s i d e r i n g that a g o o d part o f this a r e a i n c l u d e s a rc t ic wa t e r s prac t ica l ly v o i d for f i sh ing , w e s h o u l d not e x p e c t a m u c h h i g h e r future I R P from this A r e a . In the W e s t e r n C e n t r a l A t l an t i c ( A r e a 31) , there w a s a t r end o f m o d e r a t e i n c r e a s e in c a t c h e s , w h i l e the I R P ind ica t ed a l ow e l a s m o b r a n c h y i e l d . T h i s a g r e e s with S t e v e n s o n (1982) w h o s u g g e s t s that e l a s m o b r a n c h r e s o u r c e s in this A r e a c o u l d h a v e b e e n under - u t i l i sed . P e r h a p s there is still a potent ia l for e x p a n s i o n o f c a t c h e s in th is A r e a , ma in ly for coun t r i e s o f the C a r i b b e a n r eg ion . F o r A r e a 41 (Sou th W e s t e r n At lan t i c ) , e l a s m o b r a n c h c a t c h e s a l s o s h o w a m o d e r a t e i n c r e a s i n g t rend after v a r i a b l e c a t c h e s in the 60 ' s . A v e r a g e c a t c h o f e l a s m o b r a n c h s in A r e a 41 is the h ighes t in the W e s t e r n A t l a n t i c but this is a l s o the larges t a r e a . H e n c e , it h a s o n l y a n in te rmedia te I R P . S m a l l i n c r e a s e s in c a t c h e s might still be p o s s i b l e he re in the future. In c o m p a r i s o n , c a t c h e s in A r e a 31 h a v e b e e n the lowes t in the W e s t e r n At l an t i c , w h i l e in the first hal f of the p e r i o d a n d du r ing the last t w o y e a r s , A r e a 21 h a d the h ighes t y i e l d s . F o r the E a s t e r n A t l an t i c O c e a n , A r e a 2 7 ( Nor th E a s t e r n At lan t ic ) h a d by far the larges t c a t c h e s in the A t l a n t i c a s w e l l a s the third larges t a n d the s e c o n d leas t v a r i a b l e c a t c h e s in the w o r l d . A c c o r d i n g to the I R P , this A r e a h a s the h ighes t p roduc t ion o f e l a s m o b r a n c h s w o r l d w i d e but further e x p a n s i o n s in the c a t c h e s s h o u l d p r o b a b l y not be e x p e c t e d . In fact, the c a t c h t r end hard ly i n c r e a s e d a s p roduc t ion h a s fa l len s i n c e 1 9 8 8 , p e r h a p s s h o w i n g that the h igh l eve l s o f explo i ta t ion in this A r e a a re not s u s t a i n a b l e . T h e C e n t r a l E a s t e r n A t l an t i c ( A r e a 34) s h o w s a m e d i u m leve l o f var ia t ion in e l a s m o b r a n c h p r o d u c t i o n . C a t c h e s in this A r e a i n c r e a s e d du r ing the ear ly 70 ' s but the recent t rend s h o w s a s l o w d e c l i n e . T h i s is a n A r e a with a n in te rmedia te I R P , thus a g o o d r e c o v e r y in c a t c h e s c o u l d be p o s s i b l e . F o r the M e d i t e r r a n e a n S e a ( A r e a 37) , p roduc t ion w a s re la t ively v a r i a b l e du r ing the p e r i o d e x a m i n e d , but its recen t t r end of d e c l i n i n g c a t c h e s is the s teepes t . B e c a u s e o f the s m a l l s i z e a n d the 15 h igh dens i ty of h u m a n se t t l ements of this A r e a , f i sh ing is in t ense a n d the I R P for e l a s m o b r a n c h s is the third h ighes t in the A t l an t i c O c e a n . V e r y l ikely , s h a r k a n d ray s t o c k s here a re c l o s e to full exp lo i t a t ion . In A r e a 4 7 (Sou th E a s t e r n At lan t i c ) c a t c h e s h a v e b e e n fairly v a r i a b l e . It h a s the s e c o n d s m a l l e s t m e a n c a t c h o f e l a s m o b r a n c h s a n d the lowes t I R P in the w o r l d , s h o w i n g the mos t poss ib i l i t i e s for i n c r e a s e d exp lo i ta t ion o f e l a s m o b r a n c h s in the future. F r o m the four A r e a s o f the E a s t e r n At lan t i c , A r e a 2 7 d o m i n a t e d the c a t c h e s with a n e l a s m o b r a n c h p roduc t ion s u p e r i o r to t hose o f the o ther three A r e a s together . T h e r e a re o n l y two F A O A r e a s in the Indian O c e a n . T h e W e s t e r n Indian O c e a n ( A r e a 51) h a s the s e c o n d h ighes t a v e r a g e y i e l d in the w o r l d . T h i s A r e a h a s s h o w n r e a s o n a b l y l ow var iabi l i ty in c a t c h e s . C a t c h e s i n c r e a s e d s tead i ly up to the ea r ly 70 ' s but fell d r ama t i ca l ly dur ing 1 9 8 3 . J u d g i n g from the recent i n c r e a s i n g t rend in p roduc t ion , the s i tua t ion s e e m s to be r e c o v e r i n g but c a t c h e s h a v e not yet r e a c h e d p r ev ious l eve l s . T h e I R P o f A r e a 51 is the third h ighes t in the w o r l d . M o s t o f the c a t c h e s in this A r e a a re t a k e n in the nor thern reg ion by P a k i s t a n , India a n d S r i - L a n k a . S t o c k s in the nor thern r eg ion might be c l o s e to ove r - exp lo i ta t ion , but g i v e n the large e x t e n s i o n o f this A r e a a n d the l o w c a t c h e s from its sou the rn por t ion, it might p resen t s o m e poss ib i l i t i e s for i n c r e a s i n g e l a s m o b r a n c h explo i ta t ion e s p e c i a l l y f rom o c e a n i c s p e c i e s . A r e a 57 (Eas t e rn Indian O c e a n ) s h o w s m o r e va r i ab l e c a t c h e s wi th a g r o w i n g t rend . It h a s a n in te rmedia te I R P a n d h i g h e r y i e l d s a re e x p e c t e d here . In the Indian O c e a n , A r e a 51 p r o d u c e s o n a v e r a g e m o r e than d o u b l e the c a t c h e s of A r e a 5 7 . In the W e s t e r n P a c i f i c O c e a n , c a t c h e s in A r e a 61 (North E a s t e r n Pac i f i c ) h a d a d e c r e a s i n g t rend a n d the lowes t var iabi l i ty of e l a s m o b r a n c h c a t c h e s in the w o r l d . T h i s A r e a h a d the h ighes t a v e r a g e y i e l d s in the w o r l d a n d the I R P w a s a c c o r d i n g l y v e r y h igh , marg ina l ly s e c o n d to that o f the Nor th E a s t e r n At l an t i c . There fo re , c a t c h e s in th is a r e a might not i n c r e a s e subs tan t i a l ly in the future a n d s t o c k s m a y e v e n be p resen t ly o v e r e x p l o i t e d . A r e a 71 (Cen t ra l W e s t e r n Pac i f ic ) s h o w e d the s e c o n d h ighes t i n c r e a s i n g t r end in c a t c h e s , r e a c h i n g in the last f ew y e a r s c a t c h e s five t imes t hose o f the mid -60 ' s . T h e I R P in this a r e a is re la t ively h igh a n d might indica te that y i e l d s c o u l d p r o b a b l y not be e x p a n d e d m u c h more . In the S o u t h E a s t e r n P a c i f i c ( A r e a 81) , c a t c h e s h a v e v a r i e d subs tan t ia l ly , wi th a l ow pos i t ive t rend in recen t c a t c h e s . A v e r a g e c a t c h e s a n d the I R P a r e v e r y low. O n e o f the p o s s i b l e r e a s o n s for this is the re la t ively s m a l l e x t e n s i o n o f coas t l i ne i n s ide th is A r e a , t oge the r with 16 c o r r e s p o n d i n g l y few h u m a n se t t l ements . T h e potent ia l o f this a r e a to s igni f icant ly i n c r e a s e c a t c h e s wi l l d e p e n d ma in ly o n the capab i l i t i e s of the s t o c k s o f o c e a n i c a n d d e e p wa te r e l a s m o b r a n c h s p e c i e s to sus t a in f i sher ies . O f the three A r e a s o f the W e s t e r n Pac i f i c , A r e a 61 is the m o s t important in e l a s m o b r a n c h explo i ta t ion h a v i n g p r o d u c e d o n a v e r a g e a lmos t twice the c a t c h e s o f A r e a 71 a n d abou t ten t i m e s t h o s e of A r e a 8 1 . F ina l ly , for the three a r e a s of the E a s t e r n Pac i f i c , A r e a 6 7 (North E a s t e r Pac i f i c ) h a s the s m a l l e s t a v e r a g e c a t c h e s a n d the h ighes t va r ia t ion in the w o r l d . T h e I R P is the s e c o n d s m a l l e s t of a l l A r e a s a n d the t rend o f recent c a t c h e s is m o d e r a t e l y pos i t ive . L a r g e r c a t c h e s c o u l d be o b t a i n e d here in the future. A r e a 77 (Cen t r a l E a s t e r n Pac i f i c ) h a s s o m e w h a t va r i ab l e c a t c h e s wi th a v e r y l ow i n c r e a s i n g t rend a n d a v e r y l ow I R P . A r e a 7 7 is the larges t in the w o r l d but the a s s o c i a t e d l ow h u m a n popu la t ion dens i ty might a c c o u n t fo r the l ow I R P . T h e potent ia l for i n c r e a s i n g c a t c h e s here is p r o b a b l y g o o d e s p e c i a l l y in C e n t r a l A m e r i c a n coun t r i e s a n d in the vas t o c e a n i c wa te r s . T h e S o u t h E a s t e r n P a c i f i c ( A r e a 87) is the o n l y A r e a o f the E a s t P a c i f i c wi th a nega t ive t rend in c a t c h e s a n d h a s a n in te rmedia te I R P . Fur ther i n c r e a s e s in the c a t c h e s s h o u l d be p o s s i b l e he re . O f the w h o l e E a s t e r n Pac i f i c , A r e a s 7 7 a n d 87 h a v e a l m o s t the s a m e a v e r a g e c a t c h e s du r ing this p e r i o d , a m o u n t i n g to abou t four t i m e s t h o s e o f A r e a 6 7 . A s s u m i n g that recen t c a t c h t r ends wi l l r e m a i n wi thout major c h a n g e s in e a c h o f F A O ' s M a j o r F i s h i n g A r e a s , r epor ted c a t c h e s o f e l a s m o b r a n c h s in the w o r l d c a n be e x p e c t e d to r e a c h b e t w e e n 7 5 5 , 0 0 0 t a n d 8 2 7 , 0 0 0 t by the y e a r 2 0 0 0 . T h e s e fo recas t s a re b a s e d o n 5 y e a r s tep " jackknife" l inea r r e g r e s s i o n a n a l y s e s o f e l a s m o b r a n c h c a t c h e s s i n c e 1967 in e a c h F A O M a j o r F i s h i n g A r e a . 2 .2 .1 .2 C a t c h e s by coun t r i e s . D a t a fo r the p e r i o d 1947 -1991 ind ica te that 2 6 coun t r i e s p resen t ly ha rves t o r h a v e h a r v e s t e d recent ly m o r e than 1 0 , 0 0 0 t/yr o f e l a s m o b r a n c h f i shes , i.e. the re a re 2 6 "major e l a s m o b r a n c h - f i s h i n g count r ies" . A l t h o u g h there a re no official s ta t is t ics for the e l a s m o b r a n c h c a t c h e s of the P e o p l e ' s R e p u b l i c o f C h i n a , they a l s o s u r p a s s 1 0 , 0 0 0 t/yr ( see s ec t ion 2 .2 .2 .4 . ) , a n d therefore qualify the P R C a s o n e o f the major e l a s m o b r a n c h - f i s h i n g na t ions . 17 Hi s to r i ca l c a t c h s tat is t ics f o r t h e 2 5 major e l a s m o b r a n c h - f i s h i n g c o u n t r i e s for w h i c h da t a are a v a i l a b l e , a re s h o w n in tab le 2 .2 . J a p a n h a s t radi t ional ly b e e n the o v e r a l l major f i sher of e l a s m o b r a n c h s in the w o r l d with a v e r a g e c a t c h e s of 6 5 , 0 0 0 t/yr. I n d o n e s i a , India, T a i w a n a n d P a k i s t a n fo l low with c a t c h e s b e t w e e n 3 3 , 0 0 0 t/yr a n d 4 3 , 0 0 0 t/yr. F r a n c e , the U K , the former U S S R a n d N o r w a y , report ha rves t s of b e t w e e n 2 1 , 0 0 0 t/yr a n d 2 7 , 0 0 0 t/yr. M e x i c o , B r a z i l , S o u t h K o r e a , N i g e r i a , P h i l i p p i n e s , S r i - L a n k a a n d P e r u c a u g h t b e t w e e n 11 ,000 t/yr a n d 1 8 , 0 0 0 t/y. A large g roup o f coun t r i e s f o r m e d by S p a i n , U S A , M a l a y s i a , A r g e n t i n a , T h a i l a n d , A u s t r a l i a , Italy, N e w Z e a l a n d a n d Ireland f o l l o w e d wi th a v e r a g e c a t c h e s b e t w e e n 4 , 0 0 0 a n d 1 0 , 0 0 0 t/y. E v e n t h o u g h there is great var iabi l i ty in the d e v e l o p m e n t o f i nd iv idua l e l a s m o b r a n c h f i sher ies , s o m e pat terns c a n be identif ied from t h e s e da ta . A b o u t o n e th i rd o f the major e l a s m o b r a n c h s - f i s h i n g coun t r i e s s h o w recent level l ing-off t r ends in the i r c a t c h e s , p robab ly s i g n a l l i n g full exp lo i ta t ion of s h a r k a n d ray r e s o u r c e s . S e v e n c o u n t r i e s s h o w fal l ing t r ends w h i l e n ine o the r s h a v e a definite r ise in c a t c h e s (fig. 2 .2) . E l a s m o b r a n c h p roduc t ion is s p e c i a l l y h igh in Indones i a , w h e r e c a t c h e s h a v e r o c k e t e d s i n c e the ea r ly 70 ' s wi th no s i gn for a s l o w - d o w n at a l l . T a i w a n , the U S A , S p a i n a n d India are o ther e x a m p l e s o f coun t r i e s with i n c r e a s i n g f i sher ies for s h a r k s a n d rays . J a p a n , h is tor ica l ly the l e a d e r in e l a s m o b r a n c h p roduc t ion , h a s a c l e a r t r end o f d e c r e a s i n g c a t c h e s . N o r w e g i a n c a t c h e s s h o w a c l e a r t r end o f i n c r e a s e until the ea r ly 60 ' s , but th is h a s s i n c e s w i t c h e d to a s h a r p d e c r e a s e . T h e s a m e is true for the fo rmer U S S R c a t c h e s , w h i c h h a d a g r o w i n g pe r iod from the ea r ly 60 ' s to the mid -70 ' s but h a v e subs tan t i a l ly d e c r e a s e d s i n c e , without r e c o v e r i n g to fo rmer l eve l s . C a t c h e s in the U K h a v e a v e r y sl ight a l m o s t impercep t ib l e d e c r e a s i n g t r end . P a k i s t a n h a d a powerfu l t rend of i n c r e a s i n g c a t c h e s until the late 70 ' s , but d rama t i ca l ly d r o p p e d in the ea r ly 80 ' s to m a k e a s l o w but s u s t a i n e d c o m e b a c k . T h e r ange of c a u s e s for the d e c r e a s i n g t r ends is not e a s y to find in a l l c a s e s , but p o s s i b l e e x p l a n a t i o n s for s o m e c a s e s a re g i v e n b e l o w in the ind iv idua l coun t ry a c c o u n t s (2.2.2) . T h e repor ted s tat is t ics ind ica te that dur ing the last 15 y e a r s s h a r k s h a v e b e e n s l ight ly m o r e important in the c a t c h e s t han o ther e l a s m o b r a n c h s . T h e a v e r a g e r epor t ed c a t c h o f s h a r k s a n d ba to ids is 2 8 5 , 4 3 3 t/yr a n d 1 8 0 , 1 9 6 t/yr r e spec t ive ly , wi th 1 9 0 , 1 5 9 t/yr repor ted a s "var ious e l a s m o b r a n c h s " . Af ter r ea l loca t ing the repor ted c a t c h e s in this last c a t e g o r y to 18 Table 2.2 Reported world catches in commercial elasmobranch fisheries (thousand tonnes, live weight). (Data from Compagno, 1990 and FAO, unless otherwise indicated). (T.W.F. = total world fisheries, T.W.CUPL = total world cupleoid fisheries, T.ELAS = total world elasmobranch fisheries. EL/FISH = T.ELAS as % of T.W.F., CUPL/FISH = T.W.CUPL as % of T.W.F.). YEAR T.W.F. T.W.CUP T.ELAS. EL/FISH CUPL/FISH USA MEX BRA PERU ARG USSR UK EIRE NORW SPAIN % % (pi 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 20000 19600 20100 21100 23600 25200 25900 27600 28900 30500 31500 32800 36400 39500 43000 46400 47600 52000 52400 57300 60400 63900 62700 70388 70747 66121 62824 66597 66487 69930 69226 70596 71331 72141 74884 76810 77591 83989 86454 92822 94379 99016 100208 97434 96926 3481 3486 3724 4081 4392 5440 5500 5760 6410 7020 7230 7450 9060 10290 1 2620 14730 14930 18730 17442 19426 20308 21117 18786 22209 20241 14288 12073 14631 14373 15371 13043 14493 15790 16070 16920 17867 17455 19607 21101 23955 22375 24388 24800 22183 21407 201 211 245 204 197 203 204 194 270 280 310 300 300 320 370 380 400 400 405 433 444 476 502 508 482 519 583 549 586 544 556 600 603 609 612 617 568 598 623 630 666 694 . 679 695 704 1.0 1.1 1.2 1.0 0.8 0.8 0.8 0.7 0.9 0.9 1.0 0.9 0.8 0.8 0.9 0.8 0.8 0.8 0.8 0.8 0.7 0.7 0.8 0.7 0.7 0.8 0.9 0.8 0.9 0.8 0.8 0.9 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 17.4 17.8 18.5 19.3 18.6 21.6 21.2 20.9 22.2 23.0 23.0 22.7 24.9 26.1 29.3 31.7 31.4 36.0 33.3 33.9 33.6 33.0 30.0 31.6 28.6 21.6 19.2 22.0 21.6 22.0 18.8 20.5 22.1 22.3 22.6 23.3 22.5 23.3 24.4 25.8 23.7 24.6 24.7 22.8 22.1 13.1 12.8 11.2 6.1 12.8 3.1 2 2.8 2.8 3.3 14.3 16.6 16.6 16.6 5.7 9 9 8.6 8.6 6.3 7.3 7.3 7.3 1.7 1.5 1 1.8 2.2 1.7 4.1 4.7 5.9 11.1 11.2 11.0 11.7 12.4 9.3 11.9 12.1 15.2 17.2 20.4 34.6 35.5 4.1 4.5 5.6 4.6 3.6 3.4 3.5 4.4 5.1 5.3 6.5 6.3 8.9 9.1 9 8.4 14.1 16.6 14.3 16.1 15.6 21.5 24.6 26.6 35.7 34.6 31.4 34.1 33.3 29.4 27.9 34.6 33.1 38.1 34.0 4.6 5 5.9 7.6 8.9 10.6 13 12.5 12.6 12.6 3.2 15.6 9.5 9.9 6.1 7.3 9.3 21.9 23.3 25.8 31.3 29.1 25.2 29.6 25.7 27.8 24.3 24.9 24.7 25.2 1 1.4 1.2 1.3 1.1 2.5 3 4.5 3.3 3.5 3.4 4.2 7.2 3.8 5.4 5.1 6T 7.6 9.9 19.6 24.7 14.7 19 11.3 10.5 21.5 16.8 14.6 10.5 13.8 15.6 13.8 13.3 19.1 18.8 14.9 34.4 16.8 23.3 23.1 26.6 25.0 12.6 5.7 6.9 5.1 2.4 1 1.2 1.7 2.9 2.4 2.2 3.8 4.1 4.6 4 2.4 2.9 3.9 6.2 6.9 7.2 7.7 10.1 13.7 10.8 8.7 10 9.6 13.4 14.3 13.8 10.6 9.6 12.5 10.0 11.3 8.3 12.8 9.5 10.2 15.3 16.1 15.3 21.1 16.5 16.7 17.6 0.1 3.7 20.8 20.1 31.9 40.1 26.3 48.3 55.3 47.1 55.3 58.5 29.4 13.7 25.7 16.2 12.6 12.5 9.2 11.2 9.5 10.2 17.5 18.1 20.9 12.0 6.0 3.1 27.1 29.8 30.7 29.2 32.6 30.8 28.8 27.8 28.6 27.1 29.1 29.2 27.2 25.7 27.8 23.6 23.5 35.7 24.7 24.5 25.6 25.9 23.8 22.3 26.3 26.6 26 24.1 26.5 26.6 28.1 27.2 24.2 21.6 20.3 18.9 18.8 21.2 23.0 21.5 25.9 24.6 21.2 21.7 20.4 1.7 1.7 1.5 1.5 1.7 1.8 1.9 1.8 1.5 1.7 1.8 2.5 3.2 6.8 9.4 11.8 7.3 11.4 8.9 6.2 5.0 4.0 10.8 10.7 10 12 14 15.3 15.5 18.8 19.1 22.8 20.9 24.4 22 29 45.6 38.7 51.6 45.7 32.2 27.6 27.7 25.3 21.5 44.1 29.8 31.1 30.5 30.6 35.9 24.8 21.9 21.5 20.0 15.6 8.9 9.6 9.8 10.1 7.8 6.5 5.1 5.2 8.0 11.1 12.3 10.4 10.4 10.6 10.8 11.6 10.1 10.8 10.9 10.8 11.7 14.1 14.2 15.4 14 14.3 10.6 11.4 13.8 11.4 11.5 10.8 11.1 9.9 9.9 0 11.4 0 0.6 1 0.7 0.4 3.7 0.9 2.1 2.4 6.3 6.1 5.7 13.7 15.8 22.0 16.7 21.7 14.7 15.9 MEAN 57896 14357 455 0.8 24.4 %variation 43 46 37 14 20 % of worldwide elasmobranch catch, 1987-1991 % importance of elasmobranchs in country, 1987-1991 (p) data from Secretaria de Pesca (s) data from SEAFDEC (s/fl data from SEAFDEC and FAO (t/f) data from Fishery Yearbooks for Taiwan Area and FAO 9.8 76 3.57 0.42 17.4 72 4.88 2.36 16.4 55 3.69 3.00 11.7 72 2.71 0.29 8.8 59 2.54 3.19 22.7 75 1.75 0.11 25.7 14 3.31 2.63 4.3 80 1.03 3.03 21.4 56 1.21 0.44 9.8 57 2.65 1.22 19 Table 2.2 Continued YEAR ITALY FRA NIG PKST INDIA SRILK THAI (si MALAY (s) INDONE Is/f) S KOR JAPAN PHILIPP (s) TAIWA (t/f) AUST N ZEL 1947 20.5 1 73.2 1948 16 1.5 2 14.6 86.1 1949 16.7 9.1 3 118.5 1950 13.7 2 100.7 1951 13.5 2 85.7 1952 13.1 9.8 0.6 2 89.1 1953 14.4 10.8 15.9 0.7 2.2 10.5 97.4 10.7 1954 13.7 9.8 16 3.1 2.3 9.2 102.9 1955 14.9 11.7 20.4 2.5 1.6 10.8 97.2 1956 15.2 9.7 21.9 3 1.6 14.8 92.6 1957 15.2 17.6 23.1 3.9 3.1 12.2 93.8 1958 15.2 9.5 24.3 4.3 2.7 10.2 82.9 1959 15.1 9.8 23.5 4.3 2.8 7.6 86 16.5 1960 16.7 11.3 35.6 7.1 4.3 10.9 83.9 17.1 1961 34.3 9.4 33.6 8.5 4 3.2 8.7 78.3 18.9 1962 33.1 22 40.8 10.3 4.5 3.2 9.9 81.5 19.7 1963 35.5 0.3 25.2 43 12.1 5.1 4.4 9.4 77.4 17.1 1964 37.4 0.3 26.2 34.9 11.2 5.8 4.7 12.6 69 18.8 1965 29.5 28.2 31.4 11.8 12.4 4.6 66.9 20.2 1966 36.3 37.2 37.4 11.6 12.8 6.4 6.3 71.1 22.9 1967 33.1 38.4 29.6 16.3 8 7 5.6 67.5 26.0 1968 27.4 40.3 31.2 14.7 12.3 6.5 18 56 33.1 1969 39 42.5 8.75 18.8 59.3 32.8 1970 4.8 28.2 30.4 39.8 44.1 12.5 22.4 3.6 14.2 61.8 6.9 36.3 7.8 2.6 1971 5.0 25.2 9.4 41.8 41.3 9.8 12.5 6.4 10.3 12.3 50.2 7.3 39.7 7.4 3.1 1972 5.4 25.7 10.2 62.9 45.2 11.5 14.4 6.7 9.2 7.2 52.2 8.2 41.4 7.4 2.4 1973 4.6 27.3 10.4 74 60 17.9 13.6 7.7 16.3 19.3 49.4 9.0 38.1 3.0 2.6 1974 5.1 25.6 11.2 34.8 60.1 15.7 13.7 8.2 18.5 18.9 45.7 9.4 45.8 4.3 3.5 1975 4.8 23.9 12.5 36.6 61 13.1 12.1 8.5 27 22.5 46.2 10.4 62.4 2.9 3.0 1976 5.6 26.8 19.4 40.3 49.1 15.6 11.4 12.2 28.7 18.7 52.9 9.1 59.9 4.5 4.4 1977 5.6 23.2 19.9 64.1 45.6 11.3 12.2 12.2 29.5 17.4 59.7 8.9 56.4 6.9 5.3 1978 4.8 27.8 20.3 71.9 49.9 12.6 9.8 13.7 30.3 18.2 51.2 21.2 48.1 8.0 4.2 1979 4.5 31.9 20.9 74.7 40.9 12.8 9.3 11.9 33.3 19.0 53.0 9 43.7 7.5 4.4 1980 5.1 35.0 21.5 65.0 49.7 14.2 9.5 10.9 42.9 18.0 54.3 9.7 52.3 9.4 6.6 1981 3.9 42.0 11.9 62.9 50.0 21.3 10.2 11.5 43.2 21.5 49.0 12.6 43.7 9.5 7.3 1982 4.8 32.8 14.0 68.8 47.8 20.1 9.6 9.9 45 20.5 47.6 11.4 47.2 9.6 8.0 1983 6.5 39.2 12.0 18.2 51.4 19.2 8.5 10.3 49.9 22.3 43.7 8.2 43.5 9.4 9.9 1984 12.2 34.1 13.0 20.9 54.0 14.7 8.1 10 52.8 20.5 45.7 11.3 48.5 7.1 11.5 1985 14.3 33.1 14.2 29.5 50.5 15.1 9.2 10.3 54.3 22.9 39.4 10.9 55.8 7.5 11.1 1986 13.4 36.4 9.3 27.4 49.1 15.5 13.5 11.2 55.1 21.0 44.4 18.1 46 10.6 8.3 1987 9.8 36.6 9.5 28.6 57.9 16.1 14.4 11.7 58.2 16.2 42.9 16.2 50.1 13.5 9.5 1988 10.4 34.4 9.5 30.3 73.5 16.7 11.4 16.8 63.9 21.7 28.6 17.9 43.9 14.2 13.0 1989 8.4 34.0 6.9 27.6 66.3 17.0 11.2 13.4 74.9 20.8 33.9 19.0 54.8 8.3 10.8 1990 9.6 34.0 8.4 40.0 51.2 15.3 11.0 16.8 73.3 15.7 32.1 18.4 75.7 6.7 12.3 1991 13.7 25.7 7.2 45.1 52.9 18.4 11.8 16.9 79.8 17.3 33.8 19.0 68.6 7.6 13.7 7.4 26.7 12.6 33.0 41.6 11.9 8.4 9.4 42.7 15.2 65.2 12.4 39.9 7.9 7.2 47 33 54 63 36 47 62 43 49 34 34 37 42 36 53 1.51 4.79 1.21 4.99 8.78 2.42 1.74 2.20 10.18 2.67 4.98 2.63 8.52 1.46 1.73 1.89 3.78 2.92 7.42 1.72 8.76 0.43 2.46 2.41 0.66 0.31 0.85 3.50 4.80 2.19 20 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 80 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 ~° 40 NIGERIA •( f \ A / * / \ — - - — PAKISTAN . '. ' , / ' / \ • / / \ INDIA SRI-LANKA ' f \ ' '• I \ tv... • ; v , / i / . .„ - —.i.* 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 80 -THAILAND • MALAYSIA INDONESIA 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 Years -ARGENTINA 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 19 80 • AUSTRALIA -NEW ZEALAND 1947 1951 1855 1959 1963 1967 1971 1975 1979 1983 1987 1991 SOUTH KOREA - J A P A N \ / , . ' x PHILIPPINES —TAIWAN ' .\.. .ry ISfc j J \/ 1947 1951 1955 1959 1963 1967 1971 1975 1979 1983 1987 1991 Years Figure 2.2 Historical catches of elasmobranchs for the 25 major elasmobranch-fishing countries, arranged by geographical area. 21 e i ther s h a r k s o r rays with the a i d o f anc i l l a ry informat ion from s e c t i o n 2 .2 .2 . , a n d then spli t t ing the r e m a i n i n g 9 4 , 1 3 9 t/yr of "var ious e l a s m o b r a n c h s " in e q u a l parts , a total of 393 ,741 t/yr (about 59 .5 % of total e l a s m o b r a n c h s ) c a n be at t r ibuted to s h a r k s a n d 2 6 2 , 0 4 6 t/yr to s k a t e s a n d rays (about 39 .5 %) w h e r e a s o n l y l e s s t han 1% a re c h i m a e r a s a n d e l e p h a n t f i shes . 2 .2 .2 M a j o r F i s h e r i e s for E l a s m o b r a n c h s . T w o m a i n s o u r c e s w e r e u s e d for the informat ion in this s e c t i o n . First , l i terature o n the subject w a s c o n s u l t e d for e a c h c a s e a s e x t e n s i v e l y a s p o s s i b l e . M u c h informat ion p robab ly r e m a i n s in the form of u n p u b l i s h e d reports from different g o v e r n m e n t a l off ices a r o u n d the w o r l d . S e c o n d l y , in a n a t tempt to fill in s o m e o f the m a n y g a p s o f informat ion , a ques t i onna i r e w a s d e s i g n e d a n d sent to officers o r sc ien t i s t s in a l l the major e l a s m o b r a n c h - f i sh ing coun t r i e s . H o w e v e r the s u c c e s s of this a p p r o a c h w a s poor . T h e extent of p u b l i s h e d w o r k o n e l a s m o b r a n c h s in e a c h coun t ry a n d the l eve l o f r e s p o n s e to the ques t i onna i r e is ref lected in the quant i ty o f informat ion that is p r e s e n t e d u n d e r e a c h coun t ry ' s a c c o u n t . 2.2.2.1 A m e r i c a . U S A . G e n e r a l o v e r v i e w . T h e U S A is o n e o f the few coun t r i e s with r e a s o n a b l y de t a i l ed informat ion o n e l a s m o b r a n c h f i she r ies . N e v e r t h e l e s s , no c o m p r e h e n s i v e a c c o u n t o f t h e s e f i she r i es o n a na t iona l b a s i s s e e m s to exis t . M a i n f i sher ies for e l a s m o b r a n c h s o f the U S A h a v e t radi t ional ly b e e n cen t r ed o n s h a r k s , a l t h o u g h ba to ids h a v e a l s o b e e n f i shed th rough his tory. R a y s a n d ska t e s w e r e r e c o r d e d in U . S . c o m m e r c i a l c a t c h e s a s ea r ly a s 1916 (Mar t in a n d Z o r z i , 1993) , ma in ly a s a b y c a t c h o f m o r e important f i sher ies . H o w e v e r , the first d i r ec t ed f i sher ies for e l a s m o b r a n c h s in this coun t ry s e e m to h a v e b e e n t hose for the soupf in s h a r k Galeorhinus galeus (then zyopterus) in C a l i f o r n i a , a n d the f i shery for la rge s h a r k s off S a l e r n o in F l o r i d a . B o t h f l ou r i shed a s a c o n s e q u e n c e o f the h igh d e m a n d for sha rk l iver o i l in the 40 ' s -50 ' s a n d d i e d m a i n l y b e c a u s e o f the labora tory s y n t h e s i s o f v i t amin A in 1 9 5 0 . 2 2 Unti l recent ly a n d a c c o r d i n g to F A O stat is t ics , the c o m m e r c i a l c a t c h e s o f e l a s m o b r a n c h s in the U S A w e r e toge the r with t hose o f A r g e n t i n a , the leas t impor tan t a m o n g major e l a s m o b r a n c h - f i s h i n g coun t r i e s in A m e r i c a . H o w e v e r , this s i tua t ion h a s c h a n g e d s i n c e the ea r ly 90 ' s . E l a s m o b r a n c h p roduc t ion h a s v a r i e d c o n s i d e r a b l y for the last 4 0 y e a r s osc i l l a t ing a r o u n d 1 0 , 0 0 0 t/yr until the late 80 ' s . T w o p e r i o d s of v e r y l ow c a t c h e s w e r e 1 9 5 2 - 1 9 5 6 a n d 1 9 7 0 - 1 9 7 7 , w h i l e 1 9 5 8 - 1 9 6 0 s a w s o m e of the h ighes t y i e l d s . T h e p o s t - w a r p e a k o f 17 ,000 t h a s b e e n b r o k e n s i n c e 1 9 8 8 (fig. 2 .2) . C a t c h e s rapid ly i n c r e a s e d d u r i n g the m i d 70 ' s a n d s o a r e d in the mid -80 ' s . S t i l l , e l a s m o b r a n c h s a re o n l y a m i n o r f i shery in the U S A a s c a t c h e s dur ing 1987 -1991 a v e r a g e d on ly to 0 .42 % of the total f i she r i es p roduc t ion w h i l e they con t r ibu ted 3 . 5 7 % of the total repor ted e l a s m o b r a n c h c a t c h in the w o r l d (table 2 .2) . A c c o r d i n g to C o m p a g n o (1990) , the recent r ise in c a t c h e s might reflect a c h a n g e in c o n s u m e r p r e f e r e n c e s that h a s m a d e sha rk mea t f a s h i o n a b l e a n d a c c e p t a b l e to the pub l i c a s a di rect result of the i n f amous " J a w s " f i lms . T h i s w o u l d h a v e p r o m p t e d a w h o l e n e w g roup o f f i she r i es d i r ec t ed to s h a r k s in the U S A . A c c o r d i n g to C o o k (1990) , recen t c h a n g e s in in te rna t iona l shark-f in marke t s h a v e further i n c r e a s e d the d e m a n d for s h a r k s in the U S A . A m o n g s t t h e s e n e w f i sher ies , t hose for the t h r e s h e r shark , Alopias vulpinus, the P a c i f i c a n g e l s h a r k Squatina californica a n d the shortfin m a k o Isurus oxyrinchus, a re the mos t important in the w e s t coas t . F o r the G u l f of M e x i c o a n d eas t c o a s t o f U S A , mos t o f the recent ly r i s ing s h a r k f i sher ies h a v e a d ive r se c a t c h o f c o a s t a l s h a r k s , r epor ted a s unc l a s s i f i ed s h a r k s . T h i s difference in de ta i l o f the repor ted c a t c h e s o n both s i d e s o f the U S A p r o b a b l y fo l lows b e c a u s e o f the e x i s t e n c e of w e l l de f ined m a r k e t s a n d p r i ces for m a n y s p e c i e s o f e l a s m o b r a n c h s o n the w e s t coas t , w h i c h a re l a c k i n g in the eas t coas t . A c c o r d i n g to the N a t i o n a l O c e a n i c a n d A t m o s p h e r i c A d m i n i s t r a t i o n ( N O A A 1991) , in the eas t c o a s t f i sher ies o n l y m a k o s h a r k s h a v e a s e p a r a t e pr ice from the r e m a i n i n g "unc la s s i f i ed sharks" . D a t a from F A O s h o w s that up until 1 9 8 0 e l a s m o b r a n c h c a t c h e s in the U S A w e r e abou t e v e n l y d is t r ibuted in both s i d e s of the count ry . S i n c e 1981 h o w e v e r , the eas t c o a s t h a s con t r ibu ted the bulk of the c a t c h e s t h a n k s to a la rge e x p a n s i o n o f f i she r i es for s h a r k s a n d rays (fig. 2 .3) . T h i s n e w growth l ed to the recent imp lemen ta t i on o f m a n a g e m e n t s t ra teg ies for la rge s h a r k f i sher ies in the eas t coas t . O v e r a l l , the t w o m o s t important e l a s m o b r a n c h g r o u p s in the f i she r i es o f the U S A are the 23 40,000 35,000 5,000 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Years Sharks NE Sharks NW Sharks SE H | Skates NE Sharks SW • Batoids W Figure 2.3 Elasmobranch catches of the USA by major groups and regions as reported by FAO, during 1977-1991. 9,000 8,000- 7,000- w 6,000 <D C 2 5,000- X5 c w 4,000 3 O ^ 3,000- 2,000- 1,000- 0- mm m m 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 Years Skates N. Engl. — Dogfish N. Engl. G. of Mex. fJM] S. Atlant. Mid-Atlant. New Engl. | id-Atlant. £ Figure 2.4 Elasmobranch catches from the east coast of the USA during 1980-1989. Bars represent shark fisheries. (Data from FAO and Hoff 1990). 2 4 d o g f i s h e s (main ly Squalus acanthias) a n d the ska t e s . D o g f i s h a n d ska te c a t c h e s from the wa t e r s wi th in F A O A r e a 21 ( roughly c o r r e s p o n d i n g to the N e w E n g l a n d a n d M i d - A t l a n t i c r eg ions of the N a t i o n a l M a r i n e F i s h e r i e s S e r v i c e [ N . M . F . S . ] o f the U S A ) a n d dogf ish c a t c h e s in F A O A r e a 6 7 ( roughly c o r r e s p o n d i n g to the c o a s t s o f W a s h i n g t o n a n d O r e g o n ) h a v e d o m i n a t e d the e l a s m o b r a n c h p roduc t ion o f the coun t ry until v e r y recent ly . D o g f i s h c a t c h e s off the N o r t h e a s t U S A ( A r e a 21) w e r e the major part o f total e l a s m o b r a n c h c a t c h e s dur ing 1 9 7 9 - 1 9 8 3 , fell d o w n in 1984 a n d s l o w l y r e c o v e r e d s i n c e 1 9 8 5 . S k a t e c a t c h e s in this reg ion h a v e i n c r e a s e d t r e m e n d o u s l y s i n c e 1 9 8 3 , a n d w e r e the s e c o n d m o s t important g roup in 1 9 8 9 with a l m o s t o n e third of the total e l a s m o b r a n c h c a t c h e s o f the coun t ry (figs. 2.3 a n d 2.4) . D o g f i s h c a t c h e s off the nor thwes t U S A ( taken ma in ly in W a s h i n g t o n ) h a d fairly va r i ab l e y i e ld s , con t rac t ing du r ing the m i d 80 ' s , part ial ly r e c o v e r i n g in 1 9 8 6 - 1 9 8 7 on ly to s u b s e q u e n t l y fa l l . M o s t o f the dogf i sh o n the eas t c o a s t a n d s k a t e s o n both s i d e s o f the coun t ry a re t a k e n by t rawlers , w h i l e dogf i sh in the nor thwes t c o a s t a r e a p p a r e n t l y h a r v e s t e d with gi l lnets a n d t rawl nets . A l t h o u g h both rays a n d dogf i sh a re l ow p r i c e d r e s o u r c e s w h e n c o m p a r e d with s o m e o ther e l a s m o b r a n c h s (i.e. m a k o o r t h r e s h e r s h a r k s ) they a re a v a i l a b l e in s u c h la rge quant i t ies that they b e c o m e profitable for f i sh ing en te rp r i se s . T h e dogf i sh a n d ray r e s o u r c e s o f the U S A a p p e a r to be wi thout spec i f i c m a n a g e m e n t r e g i m e s . In the bes t c a s e s , s o m e s t o c k s a re i n c l u d e d in g e n e r a l m a n a g e m e n t s c h e m e s for g r o u n d fish r e s o u r c e s . G r u l i c h a n d D u P a u l (1987) es t imate that the s p i n y dogf i sh s t o c k s of the U S A eas t c o a s t c o u l d suppor t a harves t of abou t 2 4 , 0 0 0 t/yr in the mid -80 ' s . H o w e v e r , recent s tud ie s s u g g e s t that the b i o m a s s o f the Squalus acanthias s t ock s u s t a i n i n g mos t o f this f ishery, a l t h o u g h i n c r e a s i n g recent ly , is h igh ly va r i ab l e from y e a r to y e a r ( S i l v a 1993) . T h i s c o u l d m e a n that h igh l eve l s o f explo i ta t ion w o u l d not be s u s t a i n a b l e , p r even t ing s t e a d y s u p p l y to a la rge marke t . T h e E a s t C o a s t . T h r o u g h o u t this cen tury , the s ing le mos t important f i shery for s h a r k s in the E a s t C o a s t of U S A w a s that for la rge s h a r k s o f S a l e r n o F l o r i d a dur ing the p e r i o d 1 9 3 5 - 1 9 5 0 (major a c c o u n t s in S p r i n g e r [ 1 9 5 1 , 1 9 6 0 ] ) . T h e f i shery w a s c e n t r e d o n p roduc t ion o f v i t amin A from sha rk l iver o i l a n d w a s c l o s e d a s a c o n s e q u e n c e of the indus t r ia l s y n t h e s i s o f this v i t amin . F i n s a n d h i d e s w e r e a l s o u t i l i sed . T h e fleet w a s c e n t r e d at S a l e r n o but it u s u a l l y e x t e n d e d 2 5 o p e r a t i o n s w e s t to the M i s s i s s i p p i r iver dur ing s u m m e r , a n d after 1 9 4 5 it e x p a n d e d to i nc lude boa t s in the C a r o l i n a s , the F l o r i d a k e y s a n d the G u l f c o a s t o f F l o r i d a . T h e C a r i b b e a n a n d W e s t Indies a l s o p r o v i d e d c a t c h e s to this f ishery. In the later y e a r s , a p p r o x i m a t e l y half o f the c a t c h e s c a m e from the G u l f of M e x i c o . T h i s f i shery h a d up to 16 boa t s o f 12-15 .5 m ope ra t i ng concur ren t ly , e a c h f i sh ing with two bot tom l o n g l i n e s o f at leas t 2 0 0 h o o k s , in dep ths up to 91 m . F loa t i ng l ong l ines a n d bot tom gi l lnets w e r e a l s o u s e d o c c a s i o n a l l y . S a n d b a r s h a r k s , Carcharhinus plumbeus, c o m p o s e d m o s t o f the c a t c h e s , w h i c h p e a k e d at 10 ,514 s h a r k s in 1 9 4 7 . In recen t t imes , the s e c o n d mos t important e l a s m o b r a n c h f i sher ies in the U S A after dogf i sh a n d rays , a re the g r o w i n g f i sher ies for la rge s h a r k s in the G u l f o f M e x i c o a n d S o u t h At lan t i c . W h i l e c a t c h e s of la rge s h a r k s h a v e r e m a i n e d prac t ica l ly u n c h a n g e d in the M i d - A t l a n t i c a n d N e w E n g l a n d r eg ions , s h a r k c a t c h e s in the G u l f o f M e x i c o a n d S o u t h A t l a n t i c r eg ions u n d e r w e n t r ad i ca l c h a n g e s , wi th a n e ightfold i n c r e a s e in y i e l d from 1 9 8 4 to 1 9 8 9 (fig. 2.4) . T h i s t rend , c a u s e d ma in ly by the d e v e l o p m e n t o f a s tab le marke t , b e g a n in 1 9 8 5 w h e n f i s h e r m e n s tar ted to target s h a r k s with gi l lnets a n d l ong l ine s . T h e l a n d i n g o f p r e v i o u s l y d i s c a r d e d s h a r k b y c a t c h e s from o ther f i sher ies a l s o b e c a m e at t ract ive. A c c o r d i n g to N O A A (1991) , d i rec ted f i sher ies for s h a r k s in the ea s t c o a s t i nc lude : a monof i l amen t 18-64 c m m e s h driftnet f i shery appa ren t l y d i r ec t ed to s c h o o l i n g b lack t ip s h a r k s (Carcharhinus limbatus) in F lo r ida ; a M a y - N o v e m b e r gil lnet f i shery in the eas t c o a s t of F l o r i d a c a t c h i n g mos t ly g ray s h a r k s Carcharhinus spp . ; a driftnet f i shery for tunas , bi l l f ishes a n d s h a r k s in the At lan t i c , G u l f o f M e x i c o a n d C a r i b b e a n ; p e l a g i c l o n g l i n e s for tunas , bi l l f ishes a n d s h a r k s in the At lan t i c , C a r i b b e a n a n d G u l f o f M e x i c o (this f i shery d e p l o y s g e a r in a m e c h a n i s e d ope ra t i on invo lv ing large v e s s e l s a n d t h o u s a n d s o f h o o k s ) ; a recent f i shery for s h a r k s wi th bot tom long l i ne s se t s m a n u a l l y up to 100 h o o k s from e a c h s m a l l boat; a n d a p e l a g i c h o o k a n d l ine f i shery for tunas , bi l l f ishes a n d s h a r k s in the G u l f o f M a i n e , S o u t h N e w E n g l a n d a n d the M i d At lan t i c . L a w l o r a n d C o o k (1987) report that the s e a s o n a l E a s t F l o r i d a long l ine f i shery for s h a r k s is c a r r i ed out f rom boa t s 11-15 .5 m long wi th 2-4 f i s h e r m e n u s i n g bot tom a n d / o r sur face long l ines in 1-2 d a y s ope ra t i ons . T h e long l ine ' s ma in l i ne v a r i e s from 1.6 to 10 k m in length a n d is m a d e o f 4 .8-6 .4 ha rd - lay ta r red ny lon , f rom w h i c h 3 0 0 - 5 0 0 g a n g i o n s o f 3.6 m long 26 mul t i s t rand s t ee l c a b l e fal l , a r m e d with a 3/0 o r 3.5/0 s h a r k h o o k e a c h . B u o y s a re a t t ached to the m a i n l i n e o n 2 8 - 3 0 m l e a d e r s for bot tom long l i ne s a n d for p e l a g i c l o n g l i n e s with 10-30 m l e ade r s . B l u e f i s h , boni to , m a c k e r e l , mul le t a n d s q u i d a re the m o s t c o m m o n bait. A p p a r e n t l y , abou t 110 boa t s w o r k full-time a n d y e a r - r o u n d in this f i shery fo l l owing migra t ing s h a r k s a l o n g the coas t . A d d i t i o n a l informat ion ( N O A A 1991) i nd i ca t e s that 124 v e s s e l s target s h a r k s in the U S A eas t coas t , wi th long l ine r c a t c h e s du r ing 1 9 8 9 a d d i n g up to 6 ,140 t w h i l e gi l lnet ters c a u g h t 621 t. S o m e s h a r k s in the eas t c o a s t o f U S A are a l s o l a n d e d a s b y c a t c h in the fo l lowing f i sher ies : the G u l f o f M e x i c o t u n a f i sher ies ; the G u l f o f M e x i c o a n d sou th A t l a n t i c c o a s t s n a p p e r - g r o u p e r b o t t o m long l ine f ishery; swordf i sh gil lnet f i shery o f M a s s a c h u s e t t s a n d R h o d e Is land (up to 15 v e s s e l s ) a n d the gil lnet f i sher ies o f M a i n e , V i r g i n i a , N e w Y o r k a n d N e w J e r s e y . A c c o r d i n g to the repor ts o f Hoff (1990) a n d N O A A (1991) , the m a i n s p e c i e s c a u g h t in the S o u t h A t l an t i c a n d G u l f of M e x i c o with gi l lnets a re Carcharhinus plumbeus, C. limbatus, C. leucas, C. altimus, C. brevipinna, Galeocerdo cuvieri, Carcharias taurus, Negaprion brevirostris, Sphyrna lewini a n d S. mokarran. T h o s e c a p t u r e d wi th l o n g l i n e s a re ma in ly C . plumbeus, C. limbatus, C. isodon, C. acronotus, C. leucas, C. brevipinna, C. obscurus, Rhizoprionodon terraenovae, Carcharias taurus a n d Sphyrna lewini (a g l o s s a r y of e n g l i s h a n d latin s p e c i e s n a m e s is g i v e n in a p p e n d i x 1). R u s s e l l (1993) repor ts C . limbatus, Mustelus canis a n d Rhizoprionodon terraenovae a s the mos t c o m m o n s p e c i e s in sha rk long l ine r s in the nor thern G u l f o f M e x i c o . D a t a from N O A A (1991) s h o w s that e x - v e s s e l p r i ces for s h a r k s in the G u l f o f M e x i c o a n d sou theas t U S A a l m o s t d o u b l e d from a n a v e r a g e pr ice in cons t an t U S do l l a r s o f $ 0 . 5 7 / k g in 1 9 7 9 to $ 1 . 1 2 / k g in 1 9 8 6 , the a v e r a g e s i n c e 1983 b e i n g a p p r o x i m a t e l y $ 1.00/kg. M e a n w h i l e , the p r i ces for f ins h a v e r i sen nea r ly a n o r d e r of m a g n i t u d e s i n c e 1 9 8 5 . In g e n e r a l , h i g h e r p r i ces a re p a i d for d r e s s e d c a r c a s s e s a n d a l s o for s h a r k s f i shed in w a t e r s m o r e than 3 mi l e s from the c o a s t a s o p p o s e d to t hose caugh t ins ide the 3-mi le S ta te wa t e r s limit. O n l y the m a k o s h a r k a t ta ins a h i g h e r pr ice than the rest of the s p e c i e s w h i c h a re t rea ted a s "unc lass i f i ed shark". Hoff (1990) s t r e s s e s that important b y c a t c h e s o f s e v e r a l s p e c i e s o f s h a r k s a re t a k e n regular ly by the s h r i m p t rawl ing f i sher ies o f the north G u l f o f M e x i c o . Unfor tunate ly , mos t o f the c a t c h e s a re d i s c a r d e d b e c a u s e o f a l ack o f marke t for t h e m ( G M F M C 1980) . T h e on ly p u b l i s h e d e s t i m a t e s ( N O A A 1991) indica te that the inc iden ta l c a t c h o f s h a r k s in the G u l f o f 2 7 M e x i c o s h r i m p f i shery is o f abou t 2 , 8 0 0 t/yr. M o s t i nd iv idua l s a re j u v e n i l e s c a u g h t in nur se ry a r e a s a n d this kill might r ep resen t a n important threat for recru i tment to the b r e e d i n g s t o c k s in future y e a r s . E s c a p e m e n t o f l a rger s p e c i m e n s wi l l p r o b a b l y i n c r e a s e if the regu la t ions for the m a n d a t o r y u s e o f turtle e x c l u d e r d e v i c e s ( T E D ) are a p p r o v e d . O v e r a l l , total yea r ly d i s c a r d s o f s h a r k s in a l l f i sher ies o f the eas t c o a s t of U S A a v e r a g e d 1 6 , 0 0 0 1 ( N O A A 1 9 9 1 ) . T h e great i n c r e a s e in s h a r k explo i ta t ion both by c o m m e r c i a l a n d r ec rea t iona l f i s h e r m e n in the eas t c o a s t of the U S A l ed to the e s t a b l i s h m e n t of a m a n a g e m e n t r e g i m e b a s e d o n c a t c h quo t a s a n d b a g l imits s i n c e apr i l 1 9 9 3 . T h i s m a n a g e m e n t r e g i m e t ook a n ou t s t and ing 10+ y e a r s for i m p l e m e n t a t i o n d u e to, a m o n g o ther th ings , l a ck o f app rop r i a t e da ta o n a b u n d a n c e , b io logy , d is t r ibut ion, life his tory a n d c a t c h e s o f s h a r k s , n e e d e d for s tock a s s e s s m e n t . G i v e n c o n c e r n s abou t p o s s i b l e ove rexp lo i t a t ion of s h a r k s t o c k s du r ing the late 80 ' s , a n a s s e s s m e n t w a s pe r fo rmed with the v e r y l imited a v a i l a b l e in format ion . T h e s h a r k F i s h e r i e s M a n a g e m e n t P l a n d i v i d e s sha rk s p e c i e s in three m a n a g e m e n t units a c c o r d i n g to their habitat , a s s h o w n in tab le 2 .3 . T h e e s t ima ted l eve l s o f M S Y , w h i c h a p p e a r rather s m a l l w h e n c o m p a r e d wi th c a t c h e s in n e i g h b o u r i n g M e x i c o , a re a b o u t 3 ,400 t for la rge c o a s t a l s h a r k s a n d a b o u t 3 ,600 t for s m a l l c o a s t a l s h a r k s ( P a r r a c k 1 9 9 0 , N O A A 1991) . A n u m b e r of m a n a g e m e n t m e a s u r e s in effect s i n c e A p r i l 1 9 9 3 inc lude : 1 9 9 3 c o m m e r c i a l quo t a s (in d r e s s e d we igh t s ) o f 2 , 4 3 6 t for la rge c o a s t a l s h a r k s a n d 5 8 0 t for p e l a g i c s p e c i e s ; r ec rea t iona l b a g l imits of four sha rks /vesse l / t r ip for la rge c o a s t a l a n d p e l a g i c s h a r k s c o m b i n e d , a n d five s h a r k s / p e r s o n / d a y for s m a l l c o a s t a l s p e c i e s ; c o m m e r c i a l f i sh ing on ly by permit; fins l a n d e d in propor t ion to c a r c a s s e s ; r e l e a s e of s h a r k b y c a t c h e s e n s u r i n g m a x i m u m probabi l i ty of su rv iva l ; c o m p u l s o r y s u b m i s s i o n o f s a l e s r ece ip t s a n d l o g b o o k s from s e l e c t e d c o m m e r c i a l a n d rec rea t iona l opera tors ; a c c o m m o d a t i o n o f o b s e r v e r s in s e l e c t e d c o m m e r c i a l boa ts ; a n d b a n n i n g of s h a r k c a t c h e s for fore ign v e s s e l s in U S A wa te r s ( N M F S 1993) . T h e W e s t C o a s t . Ho l t s (1988) a n d Ca i l l i e t et a l . (1993) r ev i ew the s h a r k f i she r i es o f the w e s t c o a s t of the U S A . A s i d e from the s p i n y dogf i sh f i sher ies w h i c h d o m i n a t e the c a t c h e s o f the w e s t coas t , a n important g r o u p o f d i rec ted f i sher ies for s h a r k s s u d d e n l y ro se in C a l i f o r n i a at the e n d of the 70 ' s . H o w e v e r , s o m e o f t he se f i sher ies d e c l i n e d wi th in the fo l l owing ten y e a r s . T h e s e 28 Table 2.3 Sha rks spec ies cons idered in each of the U S A east coas t management unit (from N O A A 1991). F A O C o m m o n Name Scientif ic Name Large Coasta l Sharks Small Coasta l Sharks Pelagic Sharks Sandbar Blacktip Dusky Spinner Silky Bull B ignose Coppe r Ga lapagos Night Car ibbean reef Tiger Lemon Sandtiger Bigeye sand tiger Nurse Sca l loped hammerhead Great hammerhead Smooth- hammerhead Whale Basking Great White Atlantic sharpnose Car ibbean sharpnose Finetooth B lacknose Smalltail Bonnethead Sand devil Shortfin mako Longfin mako Porbeagle Thresher Bigeye thresher Blue Ocean ic whitetip Sharpnose sevengil l Bluntnose sixgill B igeye sixgill Carcharhinus plumbeus Carcharhinus limbatus Carcharhinus obscurus Carcharhinus brevipinna Carcharhinus falciformis Carcharhinus leucas Carcharhinus altimus Carcharhinus brachyurus Carcharhinus galapagensis Carcharhinus signatus Carcharhinus perezi Galeocerdo cuvier Negaprion brevirostris Carcharias taurus Odontaspis noronhai Ginglymostoma cirratum Sphyrna lewini Sphyrna mokarran Sphyrna zygaena Rhincodon typus Cetorhinus maximus Carcharodon carcharias Rhizoprionodon terraenovae Rhizoprionodon porosus Carcharhinus isodon Carcharhinus acronotus Carcharhinus porosus Sphyrna tiburo Squatina dumeril Isurus oxyrinchus Isurus paucus Lamna nasus Alopias vulpinus Alopias superciliosus Prionace glauca Carcharhinus longimanus Heptranchias perlo Hexanchus griseus Hexanchus vitulus 2 9 f i sher ies o r ig ina t ed m a i n l y a s a r e s p o n s e to c h a n g e s o f t r ends in c o n s u m e r p re fe rence w h i c h i n c r e a s e d d e m a n d a n d s p a r k e d a s o a r in p r i ce s for s o m e s p e c i e s . T o t a l c a t c h e s ( exc lud ing dogf ish) i n c r e a s e d th rough the late 70 ' s to a p e a k o f a b o u t 1,800 t in 1 9 8 2 but h a v e s i n c e v a r i e d wi th a d e c r e a s i n g t rend (table 2 .4) . Ca i l l i e t et a l . (1993) c o n s i d e r marke t f luctuat ions a n d suscep t ib i l i ty to overexp lo i t a t ion o f s o m e s t o c k s a s the m a i n r e a s o n s for d i m i n i s h i n g c a t c h e s . T h e first f i shery to r ise w a s that for the c o m m o n th re she r (Alopias vulpinus). T h i s w a s cen t r ed b e t w e e n S a n D i e g o a n d C a p e M e n d o c i n o , a n d ini t iated o p e r a t i o n s with 15 l a rge- m e s h driftnet v e s s e l s in 1 9 7 7 . E x - v e s s e l p r i ce s for this s p e c i e s i n c r e a s e d from U S $ 0 . 6 4 / k g in 1977 to U S $ 3 . 5 2 / k g in 1 9 8 6 . S o o n , the t h r e she r s h a r k f i shery w a s d i s p l a c e d by the m o r e v a l u a b l e sword f i sh f i shery a n d the t h r e she r sha rk b e c a m e a s e c o n d a r y target. T h i s l e a d to pol i t ical u p h e a v a l a n d s p u r i o u s m a n a g e m e n t o f the f i shery a n d r e su l t ed in the l o s s o f the t h r e she r p o p u l a t i o n s ( see B e d f o r d 1987 for a de t a i l ed a c c o u n t ) . C a t c h e s p e a k e d in 1 9 8 2 at 1 ,0831 w h e n m o r e than 2 0 0 v e s s e l s w e r e ope ra t ing , but s l o w l y d e c l i n e d thereafter. D u r i n g 1986 , a l imi ted a r e a a n d s e a s o n leg i s la t ion w a s p a s s e d , c a u s i n g a further d e c l i n e in c a t c h until the d i r ec t ed f i shery for this s p e c i e s w a s o u t l a w e d in O c t o b e r 1 9 9 0 . A t present , o n l y inc iden ta l c a t c h e s in the swordf i sh f i shery are permi t ted , a n d they a c c o u n t for a l m o s t 3 0 0 t/yr (D . Ho l t s , N M F S S o u t h w e s t F i s h e r i e s C e n t r e , pers . c o m m . , J u l y 2 2 , 1991) . T h r o u g h o u t mos t o f the f i shery c a t c h e s w e r e c o m p o s e d ma in ly o f y o u n g s h a r k s 1-2 y e a r s o l d , but a l s o i n c l u d e d a few A. superciliosus a n d A. pelagicus. B e d f o r d (1987) repor ts that marke t s a m p l i n g da t a s h o w e d d e c r e a s i n g m o d a l s i z e s th rough t ime a l o n g wi th d r o p p i n g C P U E i n d i c e s s i n c e the mid -80 ' s . U n p u b l i s h e d da t a (Hol ts , pers . c o m m . o p . cit.) s h o w s the m e a n length o f c a t c h e s c l ea r ly d e c l i n e d dur ing the s a m e p e r i o d . A n o t h e r important recen t d e v e l o p m e n t in the w e s t c o a s t w a s the f i shery for P a c i f i c a n g e l sha rk (Squatina californica). T h i s b e g a n a s a v e r y l o c a l i s e d ope r a t i on in S a n t a B a r b a r a in 1977 (166 kg l anded) , u n d e r w e n t great e x p a n s i o n in 1981 (158 t l a n d e d ) , r e a c h e d a p e a k in 1986 ( 5 6 3 1 l anded) a n d suffered a s t eady fall in the fo l lowing three y e a r s (121 t in 1989) (table 2.4; Ca i l l i e t et a l . 1993) . E x - v e s s e l p r i ces c l i m b e d from U S $ 0 . 3 3 / k g in 1978 to U S $ 0 . 9 9 / k g in 1984 (Hol ts 1988) . P a c i f i c a n g e l s h a r k s w e r e t a k e n initially a s b y c a t c h of the Pac i f i c hal ibut f i shery with bot tom set t r a m m e l nets . A s m a r k e t s a n d d e m a n d e x p a n d e d , they b e g a n to be t a rge ted with s i n g l e - w a l l e d gi l lnets m a d e o f ny lon twine ( N o . 2 4 to N o . 3 0 ) 30 CO cn CD CD -*—' CD -*—' CD CO o E p T3 CD •s. CO T J 3, < co Z) -•—« </) CO o o -I—» (/> </> 0) D) c c CO CO _c CO CN (D _Q CO LU < T - O C O O L O C O - T - C O O ^ N W I O T - O O CM" S-" -r-" <D h-" CO" CM" © in O) N S S CM T -CT) W r- i- OStMlO^T-CDCOS^ T-TtOT-inoo)TfOW Tt O CO" CM CD co" co" m" h-" O CD CM CM CO i-rj- CM CM CM S N CO T - LO CO CO CD T -LO i- OOJNOO'-Wt-(D O) If) i- N CM O ) CO i- co OWlf)Si-'tCOCO^OOTfOrN(OCOmoW r̂ CNî Lor̂ -h-cocococvj CM ̂  s <o r CM •<-mtocococoh-i-Ti-coco coo T - T - tn LO* oi co" N-" co* in* T -" in i-" o" G ) CM O CNJ T— CO CO CO Tf CM T- co" -i-incococM^mcocMh-o ( D c o s m i -o icoton ' tn co_ o in CM co cn T - to CM O ) i- CO r-» O ) i-co in co o — co m m CM CM" cn cn co in cn CM CO T - O CM CJ) CM T * V- T - O O O O CO CM CM r O (O N CM CO CO CO CO CM N O O) CO tO CM" T - " r-" o~ T - CJ) CD CJ) T— m CD m coco^o-i-mo>T-coi-cvjcoiotoojo) coco-i-r-coi-cMCM lO ^ if) O) CM O CO o)-«tcococj)a)-r- inco-i-cocooocomoT-Tfoco T - CO •<- TI- TI- o (OCOOi-'tCO^^CM o n T - w s ^ o i m o o" cj)" CD" of co" in co" co" io cn m s "3- -3-r-- -i- lOOr-ir)COCOCM(DO)N 0)T-lf)CDNlf)COCOCO't C M i n c o m o c M O T f c o c o O CO CJ) CO i— ^ J - CM CO IT) CO N O CM CM co r- m T - o CO Tl- CO o o i- CM" T - " WCD̂ NCDCDOCOCOCO cnr-LOCMcoT-T-cococM 0)(OOCMCOrfNNO CO" CT)" co" m" co" CM CM" o" 0) r- i- CM i- CJ) CM T- T- CO i- i- 1- iTtlDONOWOOOO) O C O C J ) O O O O O T J - C T ) C O T-inocoojr̂ o>CMin COCMinCMCMCMOCMCM CMCDO)LOCNJCMi-0)CO CM" CJ) cn" o" r--" K co" TI-" CM" omco«tfor*-oo^rmoi- N CO CO T - co CM CO CO CM LO i- CO CO CD CO TJ- i- CM Tf CO O ) r O S r M T-" co" co" to" O " CO" CM" TJ- co in •<- o co i- co CO T- CO CO CJ) CT) o o co CD in co r T - T f If) O T-" m" CT)" T -" O O CT) O rf oooTj-moTi-oococoocDOr^in Tl- T- Tf Tf CT) CO CO o co ro cj) Tt CM in o o co co i-CT)" co* TI-" o" S t T - O O T I - O L O O O O O L O O O C M L O TI- co co cn m -c o _ o O) ! i D. O tn o 01^1^0^^000(00000 O OO CVJ CVJ CVJ CO CVJ CO Tf" CD 2 •£ = f II o £ E ^ o E S O ffl o 0) fu I £ = ? o o 3 O Ol O .= o = 5 .i? [ o m J j m i i K / j o x o i d i U u i i a o i Q D o E 31 3 6 6 - 5 4 9 m long a n d 13 m e s h e s d e e p ( m e s h s i z e s b e t w e e n 3 0 . 5 a n d 4 0 . 6 c m ) ( R i c h a r d s 1987) . V e s s e l s w e r e u s u a l l y t hose of the hal ibut f ishery, w h i c h u s e h y d r a u l i c g e a r re t r ievers . O p e r a t i o n s w e r e c e n t r e d in the S a n t a B a r b a r a - V e n t u r a r eg ion a n d the C h a n n e l I s lands in wa t e r s l e s s t han 2 0 m d e e p , no m o r e than 1.6 k m from s h o r e . In the o p i n i o n o f Ca i l l i e t et a l . (1993) , the d rop in c a t c h e s s i n c e 1986 is d u e to a c o m b i n a t i o n o f d e c l i n i n g ava i lab i l i ty o f the s p e c i e s a n d c h a n g e s in the marke t a s c h e a p e r impor t s o f s h a r k mea t b e c a m e a v a i l a b l e . T h e o n l y r egu la t ions a p p l i e d to th is f i shery a re still t h o s e w h i c h per ta in to the set- net f i shery for hal ibut in C a l i f o r n i a , neg l ec t i ng the n e e d for s e p a r a t e m a n a g e m e n t o f this e l a s m o b r a n c h r e s o u r c e . A shortfin m a k o (Isurus oxyrinchus) f i shery a l s o s tar ted in C a l i f o r n i a a s a v a l u a b l e b y c a t c h of the driftnet f i shery for swordf i sh a n d c o m m o n th re she r s h a r k o f the late 70 ' s . C a t c h e s i n c r e a s e d s t ead i ly from 1 9 7 7 th rough 1 9 8 2 w h e n they r e a c h e d 2 3 9 t, t hen u n d e r w e n t a pe r iod of l o w e r c a t c h e s p o s s i b l y at t r ibuted to c h a n g e s in f i sh ing s t ra tegy o r e n v i r o n m e n t a l cond i t i ons (Hol t s 1988) , but p e a k e d a g a i n in 1987 at 2 7 7 t. S i n c e then , c a t c h e s h a v e d e c l i n e d o n c e m o r e (table 2 .4) . T h e b y c a t c h of m a k o s in the driftnet f i shery is l ow a n d s i n c e 1988 a c l o s e l y con t ro l l ed e x p e r i m e n t a l f i shery w a s s tar ted wi th l o n g l i n e s target ing this s p e c i e s . U n d e r t h i s r eg ime , s ix v e s s e l s u s i n g 4 .8-8 .2 k m s t a in l e s s s t ee l c a b l e l ong l i ne s n e a r the sur face , a re a l l o w e d to fish in t ime /a r ea c l o s u r e s a w a y from spor t f i sh ing g r o u n d s . A d d i t i o n a l l y , a n 8 0 1 T A C h a s b e e n e s t a b l i s h e d a n d a marke t for the subs t an t i a l b lue sha rk b y c a t c h mus t be d e v e l o p e d to uti l ise this r e s o u r c e . B y c a t c h e s o f shortfin m a k o in the driftnet f i shery a re a l s o a l l o w e d . A l t h o u g h the shortfin m a k o f ishery is m a i n l y s u s t a i n e d by ve ry y o u n g s h a r k s a v e r a g i n g 9-14 kg d r e s s e d weight , there is no a p p a r e n t d e c l i n e in the m e a n s i z e o f the c a t c h e s , popu la t i ons look hea l thy a n d e v e n might be re la t ive ly u n e x p l o i t e d (Holts 1988 , Ca i l l i e t et a l . 1993) . In add i t ion to the three f i sher ies m e n t i o n e d a b o v e w h i c h const i tu te the m a i n "new" sha rk f i sher ies in the last 15 y e a r s o n the w e s t coas t , m a n y o ther e l a s m o b r a n c h s a re a l s o t a k e n c o m m e r c i a l l y , m a i n l y a s a b y c a t c h o f o ther f i sher ies . Mar t in a n d Z o r z i (1993) r e v i e w the ska te f i sher ies o f C a l i f o r n i a . S k a t e s (main ly Raja binoculata, R. inornata a n d R. rhina) h a v e b e e n f i shed in C a l i f o r n i a s i n c e at leas t 1916 , a v e r a g i n g 96 t a n d 1 1 . 8 % of the total c o m m e r c i a l e l a s m o b r a n c h c a t c h e s in C a l i f o r n i a pe r a n n u m . S a n F r a n c i s c o a n d M o n t e r e y a re the m a i n l a n d i n g ports m a k i n g o v e r 7 0 % of the total . T e c h n i c a l cons t ra in t s in the 32 p r o c e s s i n g limit m a r k e t a b l e s k a t e s to s i z e s o f up to 1 kg , therefore m o s t o f the l a n d i n g s o f R. binoculata a n d R. rhina a re c o m p o s e d of immatu re i nd iv idua l s . R o e d e l a n d R i p l e y (1950) s u g g e s t e d that the ska t e r e s o u r c e might be underu t i l i s ed , but it a l s o s e e m s to be p resen t ly mi s su t i l i s ed . A marke t for l a rger s k a t e s s h o u l d be d e v e l o p e d in o r d e r to o p t i m i s e u s e a n d m a n a g e m e n t o f t he se r e s o u r c e s . A n o t h e r s p e c i e s o f interest is the b lue s h a r k (Prionace glauca). Ho l t s (1988) a n d Ca i l l i e t et a l . (1993) s u m m a r i s e the a v a i l a b l e informat ion . T h e b lue s h a r k is a major inc iden ta l c a t c h of the driftnet f i shery o f C a l i f o r n i a a n d a m i n o r b y c a t c h o f the set-net f i she r i es for hal ibut a n d a n g e l s h a r k s . Morta l i ty e s t ima te s fo r the driftnet f i shery w e r e o f 1 5 , 0 0 0 - 2 0 , 0 0 0 (3001) s h a r k s a n n u a l l y in the ea r ly pe r iod , a l t hough c h a n g e s in g e a r d e s i g n h a v e a c c o u n t e d for r educ t ions in this mortal i ty. T h e e x p e r i m e n t a l long l ine f i shery for m a k o s h a r k s a l s o t a k e s inc iden ta l c a t c h e s o f b lue s h a r k s at a rate o f four b lue s h a r k s for e a c h m a k o . N e v e r t h e l e s s , the en fo rcemen t o f r ap id r e l e a s e o f l ive s h a r k s is e x p e c t e d to d e c r e a s e mortal i ty. A s m a l l e x p e r i m e n t a l l ong l ine f i shery with o n e v e s s e l took p l a c e du r ing 1 9 8 0 - 1 9 8 2 a n d c a t c h e s of b lue s h a r k s p e a k e d a r o u n d 90 t in 1 9 8 0 a n d 1981 (table 2 .4) . T h e m a i n cons t ra in t for the d e v e l o p m e n t o f a la rge s c a l e f i shery for b lue s h a r k s is the l ack o f a marke t . B l u e sha rk mea t is repor ted ly l e s s pa la t ab le than that o f o ther e l a s m o b r a n c h s . A t t e m p t s to initiate a f i shery for s a l m o n s h a r k s Lamna ditropis in A l a s k a n wa t e r s w a s repor ted by P a u s t (1987) but no further r e c o r d s of this w e r e found . T h e s i ng l e mos t important f i shery for e l a s m o b r a n c h s in the h is tory o f the w e s t c o a s t w a s the C a l i f o r n i a f i shery for soupf in s h a r k Galeorhinus galeus du r ing the 1 9 3 0 ' s - 1 9 4 0 ' s . R i p l e y (1946) g i v e s a de t a i l ed desc r ip t ion of this f i shery . S t i m u l a t e d by the d i s c o v e r y in 1937 that the soupf in s h a r k s o f that a r e a w e r e the r iches t s o u r c e o f h igh p o t e n c y v i t amin A in the w o r l d , the s u b s e q u e n t four y e a r s m a r k e d a t r e m e n d o u s i n c r e a s e in c a t c h e s w h i c h r e a c h e d o v e r e ight t i m e s t hose o f p r e - b o o m leve l s a n d a v e r a g e d a p p r o x . 3 ,400 t/yr. V e s s e l s from the nor thern hal ibut f i shery s w i t c h e d to sha rk f i sh ing a n d in a v e r y short p e r i o d a l l sorts of v e s s e l s mod i f i ed their ope ra t i ons a n d j o i n e d the f i shery to ta l l ing abou t 6 0 0 boa t s by 1 9 3 9 . Swift c h a n g e s in g e a r s from drift a n d set g i l lnets to m a c h i n e - h a n d l e d hal ibut l ong l ines a n d b a c k to "diver" g i l lnets a n d the pos te r io r m e c h a n i s a t i o n o f thei r o p e r a t i o n o c c u r r e d in a p e r i o d o f l e s s t han 3 y e a r s (de ta i led desc r ip t ion of g e a r in R o e d e l a n d R i p l e y 1950) . Nor the rn C a l i f o r n i a w a s the m a i n f i sh ing a r e a with m o r e than 7 0 % of the c a t c h e s , a l t hough 33 f ishing o c c u r r e d th roughou t the entire c o a s t mos t ly wi th in 7.8 k m from s h o r e in wa t e r s up to 144 m d e e p . S i n c e 1 9 4 1 , c a t c h e s p l u m m e t e d a n d n e v e r r e c o v e r e d the i r p e a k l eve l s . T h e d i s c o v e r y o f syn the t i c v i t amin A p r e v e n t e d efforts to rev ive this f i shery to its fo rmer glory, a l t hough a s m a l l f i shery h a s r e m a i n e d up to p resen t t imes . C a t c h e s s i n c e 1 9 7 6 f luctuated b e t w e e n 6 6 a n d 2 5 3 t/yr (table 2 .4) . Ac t iv i t i e s a re n o w c e n t r e d a r o u n d S a n D i e g o a n d O r a n g e c o u n t i e s (Hol ts 1988) w h e r e c a t c h e s are appa ren t l y a n inc iden ta l p roduct o f net f i sher ies for hal ibut a n d a n g e l shark . O n l y the g e n e r a l r egu la t ions for the latter f i sher ies "protect" soupf in s h a r k popu la t i ons . H o l d e n (1977) e s t i m a t e d the north P a c i f i c unexp lo i t ed s tock at 2 9 , 4 0 0 t, but it a p p e a r s that s t o c k s h a v e not yet r e c o v e r e d to the fo rmer l eve l s (Hol ts 1988) . H o w e v e r , no recent a s s e s s m e n t s h a v e b e e n d o n e for this s p e c i e s . F ina l ly , a short l ived s m a l l - s c a l e h a r p o o n f i shery for b a s k i n g s h a r k s (Cetorhinus maximus) took p l a c e dur ing the late 40 ' s in P i s m o B e a c h ( R o e d e l a n d R i p l e y 1950) but p e r i s h e d a l s o a s a c o n s e q u e n c e o f the fall of the l iver o i l industry. M e x i c o . S i n c e the mid -70 ' s , M e x i c a n e l a s m o b r a n c h f i sher ies h a v e b e e n the la rges t in A m e r i c a (fig. 2 .2) . A c c o r d i n g to F A O stat is t ics , there h a s b e e n a g e n e r a l t r end o f i n c r e a s e d c a t c h e s of e l a s m o b r a n c h s in M e x i c o , from the typ ica l 5 ,000 t/yr o f the 50 ' s to the recent y i e l d s v a r y i n g a r o u n d 3 0 , 0 0 0 t/yr s i n c e the ea r ly 80 ' s . J u d g i n g from the t r end o f the last ten y e a r s , M e x i c a n f i sher ies for s h a r k s a n d rays h a v e a t ta ined relat ive stabil i ty. E l a s m o b r a n c h s a re a re la t ively important r e s o u r c e in M e x i c o , m a k i n g 2 .36 % of the total na t iona l c a t c h e s dur ing 1 9 8 7 - 1 9 9 1 . T h i s is c o m p a r a b l e to o ther major e l a s m o b r a n c h - f i s h i n g coun t r i es , but is subs tan t ia l ly h ighe r than the 0.8 % cont r ibu t ion o f e l a s m o b r a n c h s to w o r l d f i sher ies in the last 10 y e a r s . E l a s m o b r a n c h explo i ta t ion in M e x i c o c a n be t r a c e d b a c k to at leas t the 1930 ' s , but de t a i l ed stat is t ics a re difficult to f ind before the mid -70 ' s . W a l f o r d (1935) repor ts " seve ra l tons" of sha rk fins from the w e s t c o a s t of M e x i c o b e i n g impor ted to C a l i f o r n i a e a c h y e a r a n d R i p l e y (1946) refers to M e x i c a n f i sher ies s u p p l y i n g s h a r k l iver o i l to the U S A indust ry . M a z a t l a n a n d G u a y m a s w e r e the m a i n l and ing points in the w e s t coas t . C a t c h e s p e a k e d at 9 ,000 t in 1944 but d e c l i n e d to 4 8 0 t in 1 9 5 3 , after the fall o f the s h a r k l iver o i l indust ry (Cas t i l lo 34 1990) . In the ea s t c o a s t du r ing the 40 ' s , a fleet ta rge t ing s h a r k s b a s e d at P r o g r e s o , Y u c a t a n h a d cha rac t e r i s t i c s s imi l a r to the fleet o f S a l e r n o , F l o r i d a , a n d c a u g h t up to 3 ,200 t/yr s i n c e 1950 ( G M F M C 1980) . M e x i c a n f i sher ies for e l a s m o b r a n c h s are c e n t r e d o n s h a r k s . B a t o i d s a r e s e l d o m exp lo i t ed but c o n s i d e r a b l e ( and u n k n o w n ) a m o u n t s a re d i s c a r d e d in the e x t e n s i v e t r awl ing ope ra t i ons for s h r i m p f i she r ies . A c c o r d i n g to da t a t a k e n from the M e x i c a n Min i s t ry o f F i s h e r i e s y e a r b o o k s for the p e r i o d 1 9 7 7 - 1 9 9 1 , s h a r k s a c c o u n t for 94 .8 % (29 ,036 t/yr) of e l a s m o b r a n c h c a t c h e s w h i l e ba to ids o n l y represen t 4 .2 % (1 ,272 t/yr). B e c a u s e o f its l a rge r sho re l i ne , the P a c i f i c c o a s t con t r ibu tes 6 0 % o f total s h a r k c a t c h e s w h i l e the r e m a i n i n g 4 0 % c o m e s from the G u l f o f M e x i c o a n d C a r i b b e a n . N o da t a o n c a t c h e s by s p e c i e s a re a v a i l a b l e . O n l y s m a l l s h a r k s ( those m e a s u r i n g l e s s t han 1.5 m T L w h e n c a u g h t a n d k n o w loca l ly a s c a z o n ) a n d large s h a r k s ( those l a rge r t han 1.5 m T L ) are r e c o r d e d in the s tat is t ics . L a r g e s h a r k s a re 6 0 % of total s h a r k c a t c h e s a n d 2/3 o f t he se a re c a u g h t in the P a c i f i c w h i l e on ly 1/3 are c a u g h t in the G u l f of M e x i c o a n d C a r i b b e a n . T h e r e m a i n i n g 4 0 % of the total sha rk c a t c h e s are s m a l l s h a r k s , 6 4 % c o m e from the P a c i f i c a n d 36 % from the eas t coas t . T h e r e is s o m e var iabi l i ty in the c a t c h e s o f la rge a n d s m a l l s h a r k s from e a c h coas t , but ove ra l l , M e x i c a n f i sher ies s e e m to h a v e r e a c h e d a n equ i l ib r ium dur ing the last 10 y e a r s (fig. 2 .5) . M e a n w h i l e , ba to id c a t c h e s a re s l o w l y a n d s t ead i ly e x p a n d i n g . M e x i c a n s h a r k f i she r i es a re la rge ly a r t i sana l , m u l t i s p e c i e s , mu l t i gea r f i she r ies . Bonf i l e t a l . (1990) , C a s t i l l o (1990) a n d Bonf i l (in press) s u m m a r i s e mos t o f the a v a i l a b l e informat ion o n e l a s m o b r a n c h f i she r i es in M e x i c o . It is e s t ima ted that a p p r o x i m a t e l y 2/3 o f the sha rk c a t c h is t a k e n by s m a l l - s c a l e f i she r ies . V e s s e l s a re g e n e r a l l y f i b r eg l a s s boa t s 7-9 m long with o u t b o a r d moto r s u s i n g e i ther gi l lnets o r l ong l ines d e p e n d i n g o n the c u s t o m s o f e a c h r eg ion . S o m e v e s s e l s of 14-20 m a re a l s o u s e d w h e r e a s o n l y a few v e s s e l s in e x c e s s o f 2 0 m take part in the f i shery . S ign i f ican t quant i t ies o f s h a r k s a n d r ays a re a l s o t a k e n a s inc iden ta l c a t c h e s o f l a r g e - s c a l e t rawl f i sher ies for s h r i m p or d e m e r s a l f i shes in both s i d e s of the count ry . L a r g e s c a l e f i sher ies for t unas a n d bi l l f ishes in both c o a s t s a l s o cont r ibute to the total c a t c h e s . S h a r k s a n d rays a re t radi t ional ly u s e d for f o o d in M e x i c o , e i ther f resh , f rozen o r m o r e c o m m o n l y , sa l t -d r ied . S h a r k fins a re a n important export , h i d e s a r e a l s o in tens ive ly u t i l i sed a n d m o s t offal is b u r n e d d o w n to fish m e a l . 35 40,000 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Years Pacific, large sh. Gulf/Car; large sh. %%%\ Pacific, small sh. | | Gulf/Car, small sh. H i Both; Batoids Figure 2.5 Elasmobranch catches in the Pacific and Gulf of Mexico/Caribbean coasts of Mexico during 1977-1991 (sh = sharks). (Data from Secretaria de Pesca, Mexico). 36 T h e m a i n f i sh ing g r o u n d s in the P a c i f i c a re c e n t r e d in the G u l f o f C a l i f o r n i a in the north a n d the G u l f of T e h u a n t e p e c in the sou th . H o w e v e r , mos t o f the a v a i l a b l e informat ion abou t t he se f i sher ies c o m e s from the nor thern coas t . Little is k n o w from the s h a r k f i sher ies in the G u l f of T e h u a n t e p e c apar t from the total c a t c h e s . In the nor thern r eg ion , s h a r k s are ma in ly c a u g h t with monof i l amen t l ong l i ne s of 1-2 k m a n d a p p r o x i m a t e l y 3 5 0 h o o k s , a l t hough s m a l l c a t c h e s a re t a k e n with v a r i o u s gi l lnets o f up to 2 k m in length . T h e r e a r e repor ts that s o m e 17 v e s s e l s , 4 4 m l o n g a n d u s i n g long l ines o f up to 2 , 0 0 0 h o o k s t a rge t ed s h a r k s a n d bi l l f ishes in the P a c i f i c c o a s t du r ing 1 9 8 7 . It is u n k n o w n if t h e s e v e s s e l s a re still in ope ra t ion . Hol t s (1988) s ta tes that a s imi l a r n u m b e r o f J a p a n e s e - M e x i c a n joint ven tu re long l ine r s c a u g h t 2 3 4 t/yr o f s h a r k s in B a j a C a l i f o r n i a dur ing 1 9 8 1 - 1 9 8 3 . O n the eas t , f i sh ing g r o u n d s s p a n the entire coa s t l i ne . D u r i n g 1 9 7 6 - 1 9 8 8 , V e r a c r u z a n d C a m p e c h e s h a r e d 58 % of the total s h a r k c a t c h w h i l e T a m a u l i p a s a n d Y u c a t a n m a d e ano the r 30 % . L o n g l i n e s a re preferred in V e r a c r u z a n d T a m a u l i p a s . G i l l n e t s o f 11-40 c m m e s h s i z e a r e the m a i n f i sh ing g e a r in the B a n k o f C a m p e c h e . A d d i t i o n a l l y , there is a subs tan t i a l b y c a t c h of ma in ly j uven i l e s h a r k s in the s e m i - i n d u s t r i a l i s e d long l ine f i sher ies for red g r o u p e r a n d red s n a p p e r of the C a m p e c h e B a n k but no e s t i m a t e s o f the b y c a t c h are a v a i l a b l e . T h e s p e c i e s c a u g h t in the different r eg ions o f the M e x i c a n c o a s t a n d the structure of s u c h c a t c h e s a re o n l y part ial ly k n o w n . M o s t r e s e a r c h h a s b e e n d o n e in the mouth of the G u l f of C a l i f o r n i a in the w e s t c o a s t a n d in the sou the rn S t a t e s o f C a m p e c h e , Y u c a t a n a n d Q u i n t a n a R o o in the eas t coas t . Important l a n d i n g s in o ther a r e a s of both c o a s t s h a v e b e e n ve ry poor ly s t ud i ed . A t leas t 4 4 s p e c i e s of s h a r k s are repor ted in the c o m m e r c i a l c a t c h e s o f M e x i c o . A v a i l a b l e informat ion ind ica te s 12 a s the mos t important for their cont r ibu t ion to the c a t c h e s in the a r e a of L a P a z , B a j a C a l i f o r n i a S u r a n d S i n a l o a , w h e r e a s there a r e 15 m a i n s p e c i e s in the G u l f of M e x i c o a n d C a r i b b e a n (table 2 .5) . M o s t o f the c a t c h e s o f l a rge s h a r k s cons i s t of Carcharhinus s p p , Sphyrna s p p a n d o ther c a r c h a r h i n i d s , w h i l e the s m a l l s h a r k c a t c h e s a re a mixture o f Mustelus s p p . a n d Rhizoprionodon spp . , wi th j u v e n i l e s o f the large s h a r k s s o m e t i m e s con t r ibu t ing a n important part o f the total . F o r the S i n a l o a c o a s t in the cen t ra l Pac i f i c Rhizoprionodon longurio, Sphyrna lewini, Nasolamia velox, Carcharhinus limbatus, C. falciformis, C. leucas a n d Galeocerdo cuvieri, a re the mos t impor tant s p e c i e s . G a l v a n - M a g a n a et a l . (1989) report Mustelus lunulatus, Heterodontus mexicanus a n d Sphyrna lewini Table 2.5 Shark species found in the commercial fisheries of Mexico. GULF OF MEXICO FAMILY SPECIES PACIFIC /CARIBBEAN Hexanchidae 1 Heptranchias perlo X 2 Hexanchus griseus X 3 Hexanchus vitulus X Echinorhinidae 4 Echinorhinus cookei X Squalidae 5 Centrophorus granulosus X 6 Centrophorus uyato X 7 Squalus cubensis X 8 Squalus mitsukurii X Squatinidae 9 Squatina californica X * Heterodontidae 10 Heterodontus mexicanus X * Ginglymostomatidae 11 Ginglymostoma cirratum x X * Rhiniodontidae 12 Rhiniodon typus X X Alopiidae 13 Alopias vulpinus X * 14 Alopias superciliosus X X Lamnidae 15 Isurus oxyrinchus x X Triakidae 16 Mustelus californicus x 17 Mustelus canis X * 18 Mustelus lunulatus X * 19 Mustelus sp. ? X 20 Triakis semifasciata X Carcharhinidae 21 Carcharhinus acronotus X* 22 Carcharhinus altimus X X 23 Carcharhinus brevipinna X * 24 Carcharhinus falciformis X * X * 25 Carcharhinus leucas X * X * 26 Carcharhinus limbatus X * X * 27 Carcharhinus longimanus X 28 Carcharhinus obscurus X X * 29 Carcharhinus perezi X 30 Carcharhinus plumbeus X * 31 Carcharhinus porosus X X 32 Carcharhinus signatus X 33 Galeocerdo cuvieri X * X * 34 Nasolamia velox X * 35 Negaprion acutidens X 36 Negaprion brevirostris X * 37 Prionace glauca X * 38 Rhizoprionodon longurio X * 39 Rhizoprionodon terraenovae X * Sphyrnidae 40 Sphyrna lewini X * X * 41 Sphyrna media X 42 Sphyrna mokarran X X * 43 Sphyrna tiburo X X * 44 Sphyrna zygaena X * Main species in the commercial catches. 38 a s the mos t important s h a r k s in the a r e a o f L a P a z , B . C . E x p e r i m e n t a l c a t c h e s o f long l ine r s in the P a c i f i c c a u g h t ma in ly pre-adul t a n d adul t Alopias vulpinus a n d Carcharhinus limbatus ( V e l e z et a l . 1989) . F o r the eas t coas t , the mos t important s p e c i e s a re Carcharhinus falciformis, C. leucas, C . obscurus, C . plumbeus, C. limbatus, Rhizoprionodon terraenovae, Sphyrna tiburo, Mustelus canis, C. brevipinna, Negaprion brevirostris, Sphyrna mokarran, Sphyrna lewini, Galeocerdo cuvieri a n d Ginglymostoma cirratum. W i t h the e x c e p t i o n s o f C . obscurus, C. plumbeus a n d Ginglymostoma cirratum, a l l the impor tant s p e c i e s of the eas t c o a s t a re k n o w n to be heav i ly exp lo i t ed a s j u v e n i l e s a n d s o m e t i m e s e v e n a s n e w b o r n s at least in s o m e part o f thei r r ange . T h e r e a r e o n l y a few p re l imina ry a s s e s s m e n t s o f the s ta tus of s o m e s h a r k s tocks for the eas t coas t . A l v a r e z (1988) reports that a c c o r d i n g to su rp lus p roduc t ion m o d e l s , the s t o c k s of Sphyrna tiburo a n d Rhizoprionodon terraenovae in Y u c a t a n a re c l o s e to op t ima l explo i ta t ion l eve l s ; resul ts o f the y ie ld-per- recrui t m o d e l s u g g e s t Sphyrna tiburo is at the o p t i m u m explo i ta t ion l eve l w h e r e a s Rhizoprionodon terraenovae s e e m s to be a l r e a d y o v e r e x p l o i t e d . F o r the p roduc t ion m o d e l s , c a t c h a n d effort w e r e e s t i m a t e d in a ve ry rough w a y a n d f o r t h e d y n a m i c m o d e l , g rowth a n d mortali ty w e r e e s t i m a t e d v i a length f r equency a n a l y s i s . Bonf i l (1990) , e s t i m a t e d growth v i a ve r t eb rae r e a d i n g s a n d u s i n g the y ie ld -pe r - recruit m o d e l d i a g n o s e d growth over f i sh ing for the Carcharhinus falciformis s tock of the C a m p e c h e B a n k . T h i s resul ts ma in ly from the v e r y h igh b y c a t c h e s o f n e w b o r n s a n d j u v e n i l e s o f this s p e c i e s in the l oca l red g r o u p e r f i shery . T h e r e h a v e b e e n a n u m b e r of p e r m a n e n t r e s e a r c h p r o g r a m m e s for s h a r k f i sher ies in M e x i c o s i n c e the ea r ly 80 ' s . D e s p i t e this , to date there is n o spec i f i c m a n a g e m e n t for e l a s m o b r a n c h f i she r i es in M e x i c o . A n u m b e r o f c o n c e r n s h a v e b e e n e x p r e s s e d abou t s o m e u n d e s i r a b l e p rac t i ces in the f i sher ies . A t least , Carcharhinus falciformis, C. acronotus, Rhizoprionodon terraenovae a n d Sphyrna tiburo a re b e i n g h e a v i l y e x p l o i t e d a s j u v e n i l e s in C a m p e c h e a n d Y u c a t a n , h e n c e o p e n i n g the poss ib i l i ty o f a future c o l l a p s e o f the s t ocks . Add i t i ona l l y , there a re s u g g e s t i o n s that s t rong d e c r e a s e s in the a b u n d a n c e of j u v e n i l e s of C . leucas, C. limbatus, C. acronotus, C. perezi a n d Negaprion brevirostris h a v e o c c u r r e d in s o m e c o a s t a l l a g o o n s o f the Y u c a t a n P e n i n s u l a d u e to h e a v y f i sh ing wi th set nets (Bonfi l in press). It is v e r y l ikely that this s i tuat ion is c o m m o n p l a c e in m o s t c o a s t a l l a g o o n s a l o n g the c o a s t o f M e x i c o . A d d i t i o n a l l y , the ki l l ing o f la rge quant i t ies o f p regnan t f e m a l e s of 39 Rhizoprionodon longurio in S i n a l o a , o n the w e s t coas t , is a n o t h e r c a u s e for c o n c e r n . A l t h o u g h informat ion is l imi ted , it is l ikely that m a n y s t o c k s in the G u l f s o f C a l i f o r n i a a n d T e h u a n t e p e c a r e c l o s e to the o p t i m u m explo i ta t ion l eve l o r e v e n o v e r f i s h e d . H o w e v e r , no a s s e s s m e n t s a re k n o w n to date in t hose a r e a s . L i m i t e d o r non-ex i s ten t informat ion abou t the s i z e o f the s t o c k s a n d abou t the ac tua l l eve l s o f mortal i ty m a k e s the a d e q u a t e a p p r a i s a l of the s ta tus o f M e x i c a n f i sher ies difficult. A s in o ther coun t r i e s , s o c i o - e c o n o m i c a n d heal th p r o b l e m s re la ted to the f i sher ies further c o m p l i c a t e the m a n a g e m e n t o f e l a s m o b r a n c h s in M e x i c o . T h e c h a n c e s o f cur ta i l ing the f i sh ing o f j u v e n i l e s h a r k s in M e x i c o wi l l be c o n s t r a i n e d by the p r o b l e m s re la ted to the a r t i sana l nature of m a n y of the f i sh ing fleets ( loss o f i n c o m e for la rge n u m b e r s of f i she rmen) a n d the h igh e s t e e m that s m a l l s h a r k s h a v e o n the M e x i c a n t ab le . T h e h i g h e r concen t r a t i on of h e a v y me ta l s in o l d e r s h a r k s a l s o m a k e s the ha rves t i ng of j u v e n i l e s preferab le . P e r u . F r o m the mid-s ix t i e s a n d until v e r y recent ly , the e l a s m o b r a n c h c a t c h e s o f P e r u w e r e the third la rges t in A m e r i c a a n d con t r ibu ted 2.71 % of the w o r l d e l a s m o b r a n c h c a t c h . N e v e r t h e l e s s , e l a s m o b r a n c h s a re of m i n o r impor t ance in P e r u v i a n f i she r i es a n d represen t o n l y 0 .29 % of the total f i shery p roduc t ion (table 2 .2) . T h e e l a s m o b r a n c h f i sher ies of P e r u h a d a fairly s t e a d y t rend o f s l o w d e v e l o p m e n t in the 50 ' s a n d ea r ly 60 ' s . S i n c e the mid-60 ' s c a t c h e s h a v e o s c i l l a t e d a r o u n d 1 8 , 0 0 0 t, p e a k i n g at m o r e t han 3 0 , 0 0 0 t in 1984 a n d u n e x p e c t e d l y c r a s h i n g in 1990-1991 (fig. 2 .2) . T h e r e m a y be a l ink b e t w e e n recent ly d e c l i n i n g e l a s m o b r a n c h c a t c h e s a n d the erupt ion o f c h o l e r a in P e r u d u r i n g 1 9 9 0 . A c c o r d i n g to F A O stat is t ics , e l a s m o b r a n c h y i e l d in P e r u is s t rongly d o m i n a t e d by s m o o t h - h o u n d s . D u r i n g the p e r i o d 1 9 7 7 - 1 9 9 1 , s m o o t h - h o u n d s of the g e n u s Mustelus w e r e the mos t important s p e c i e s in the e l a s m o b r a n c h c a t c h e s m a k i n g 56 % (10 ,219 t/yr) o f the total a n d a c c o u n t e d for 2 5 , 0 0 0 1 in 1984 w h e n r eco rd e l a s m o b r a n c h c a t c h e s o f P e r u r e a c h e d 3 4 , 4 0 0 t (fig. 2 .6) . S e v e r a l u n s p e c i f i e d rays m a k e 2 5 % (4 ,640 t/yr) o f the total c a t c h e s . T h e i r l a n d i n g s h a v e i n c r e a s e d s ignif icant ly s i n c e 1984 , m a k i n g t h e m the s e c o n d mos t important e l a s m o b r a n c h g roup in P e r u . Rhinobatosplaniceps a n d a n g e l s h a r k s Squatina s p p . a re a l s o important s p e c i e s in the c a t c h e s with a v e r a g e s o f 10 % (1 ,908 t/yr) a n d 3 % (560 t/yr) 4 0 re spec t ive ly . T h e y i e l d s o f t he se two g r o u p s s h o w e d v a r i a b l e t r ends in this pe r iod . A n a s s o r t e d g r o u p o f e l a s m o b r a n c h s m a d e the r e m a i n i n g 6 % (1 ,133 t/yr). A p a r t from F A O stat is t ics , no th ing e l s e is k n o w n abou t the e l a s m o b r a n c h f i she r i es o f P e r u . B r a z i l . B r a z i l i a n e l a s m o b r a n c h c a t c h e s a re the third h ighes t in A m e r i c a , after M e x i c o a n d the U S A . It a p p e a r s that B r a z i l i a n e l a s m o b r a n c h f i sher ies h a v e a t t a ined a re la t ive stabil i ty. Af ter a n s l o w but s t e a d y start t h rough the s ix t ies a n d a brief fall in the 70 ' s , the c a t c h e s o f s h a r k s a n d rays from B r a z i l s h o w a major l eap in the ea r ly 80 ' s . Y i e l d s h a v e v a r i e d s i n c e then , up to a 3 0 , 0 0 0 t m a x i m u m (fig. 2 .2) . S h a r k s a n d r ays con t r ibu ted 3 % to the total f i sher ies of B r a z i l du r ing 1987 -1991 w h i l e m a k i n g 3 .69 % of the w o r l d c a t c h e s o f e l a s m o b r a n c h s (table 2 .2) . B r a z i l i a n f i sher ies s tat is t ics d o not differentiate e l a s m o b r a n c h s by s p e c i e s . A t leas t 3 0 e l a s m o b r a n c h s a re c o m m o n in the c o m m e r c i a l c a t c h e s in the sou theas t , but m o s t o f the l a n d i n g s c o m e d r e s s e d wi thout guts , h e a d o r f ins, m a k i n g it difficult to sort by s p e c i e s ( T o m a s 1987) . S o m e o f the s p e c i e s repor ted for the c o m m e r c i a l c a t c h e s a re : Mustelus schmitti, Galeorhinus galeus, Prionace glauca, Isurus oxyrinchus, Squatina guggenheim, Squatina sp , Pristisspp., Rhinobatos percellens, R. horkelii, Dasyatis spp , Gymnura s p p a n d Myliobatis s p p . A c c o r d i n g to F A O da ta , du r ing the pe r iod 1 9 7 7 - 1 9 9 1 , B r a z i l i a n l a n d i n g s w e r e d o m i n a t e d by a n a s s o r t e d g r o u p of s p e c i e s c o r r e s p o n d i n g to 7 2 % (17 ,919 t/yr) o f the e l a s m o b r a n c h c a t c h . Y i e l d s for this g r o u p o f e l a s m o b r a n c h s g r e w rapid ly from l e s s t h a n 1,000 t in 1978 to m o r e than 2 3 , 0 0 0 t in 1 9 8 2 a n d h a v e r e m a i n e d c l o s e to 2 0 , 0 0 0 t/yr s i n c e then (fig. 2 .7) . A l l the s h a r k s k n o w n to o c c u r in B r a z i l i a n c a t c h e s a re i n c l u d e d in this g r o u p . A c c o r d i n g to Ba t i s t a (1988) , l a n d i n g s of Galeorhinus galeus h a v e i n c r e a s e d s i n c e 1 9 7 0 d u e to g r o w i n g act iv i t ies of t r awle r s in sou th eas t B r a z i l . T h e s e c o n d mos t impor tan t g r o u p du r ing this pe r iod w e r e the s k a t e s a n d rays cont r ibu t ing 17 % (4 ,254 t/yr) o f the c a t c h e s . L a n d i n g s of this g r o u p e x p a n d e d s lowly , a s w e l l a s t h o s e o f gui ta r f i shes Rhinobatos s p p . w h i c h a v e r a g e d 7 % (1 ,683 t/yr) o f the total e l a s m o b r a n c h c a t c h . S m a l l c a t c h e s o f s a w f i s h e s Pristis s p . h a v e b e e n s tead i ly l a n d e d a v e r a g i n g 4 % (1 ,014 t/yr) o f the c a t c h e s . 41 35,000 30,000 25,000 <g 20,000 c £ 15,000 10,000 5,000 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Year s Smoo th -hound H i A n g e l Shark Rays v a r - e lasm. Guitarfish Figure 2.6 E la smobranch ca tches of Peru , by spec ies groups, during 1977-1991 (Data from F A O ) . 35,000 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Years Var. Elasm. f^ffl Skates & rays Guitarfish Sawfish Figure 2.7 E la smobranch ca tches of Braz i l , by spec ies groups, during 1977-1991. (Data from F A O ) . 4 2 V o o r e n a n d Bet i to (1987) report o n at leas t 2 5 s p e c i e s o f s m a l l s h a r k s a n d 2 4 o f ba to ids for wa t e r s l e s s t han 100 m d e e p in the sou theas t e rn con t inen ta l shelf . S w e p t a r e a b i o m a s s e s t ima tes ind ica te 2 0 , 0 0 0 t a v a i l a b l e in win te r a n d 1 3 , 0 0 0 t in s u m m e r o f w h i c h 9 0 % are c o m p o s e d of 16 s m a l l s h a r k s a n d 8 ba to id s p e c i e s o f c o m m e r c i a l v a l u e . A p p a r e n t l y , the o n l y t radi t ional u s e for e l a s m o b r a n c h s in B r a z i l h a s b e e n for food , but G o c k s (1987) a n d J a c i n t o (1987) not s o m e efforts for the ut i l isat ion of h i d e s a n d o ther par ts . In the north o f B r a z i l , at leas t two k inds o f f i sher ies l a n d e l a s m o b r a n c h s (R . L e s s a , pers . c o m m . F e b r u a r y 1992) . A n indust r ia l long l ine f i shery for t u n a s wi th up to 5 0 % b y c a t c h e s of s h a r k s , c a p t u r e s m a i n l y Prionace glauca, Carcharhinus longimanus, Carcharhinus spp. , Sphyrna spp . , Isurus spp. , Alopias spp. , Pseudocarcharias kamoharai a n d Galeocerdo cuvieri. T h i s f i shery l a n d e d a n a v e r a g e of 144 t/yr of s h a r k s b e t w e e n 1 9 8 5 - 1 9 9 0 . A b o u t 6 0 % of t he se w e r e s h a r k s l e s s than 1.5 m T L . A r t i s a n a l f i sher ies for Cynoscium acoula a n d Scomberomorus s pp . c a t c h Carcharhinus porosus, Rhizoprionodon spp. , Sphyrna spp. , Isogomphodon oxyrhynchus a n d Pristis peroretti. T h e r e is a h igh i n c i d e n c e of j u v e n i l e s in this f i shery w h i c h is c a r r i e d out u s i n g s m a l l driftnets o f abou t 1 k m long a n d 6 m d e e p . O n the north s h o r e , b e t w e e n the A m a z o n r iver a n d Rec i f e , e l a s m o b r a n c h c a t c h e s m a y be a s high a s 6 0 % of the total in this a r t i sana l f ishery. Incidenta l c a t c h e s o f s m a l l s h a r k s a n d rays in the Brachyplatystoma, s h r i m p a n d s n a p p e r f i sher ies o f the north o f B r a z i l a re repor ted by E v a n g e l i s t a (1987) . A p p a r e n t l y mos t of the b y c a t c h e s w e r e fo rmer ly d i s c a r d e d but a re n o w b e g i n n i n g to be u t i l i sed . V o o r e n et a l . (1990) s u m m a r i s e informat ion o n d e m e r s a l f i she r i es for e l a s m o b r a n c h s dur ing 1 9 7 3 - 1 9 8 6 o n the con t inen ta l she l f off the sou the rn port o f R i o G r a n d e . E l a s m o b r a n c h s a c c o u n t for 7.3 % of the total c a t c h e s , 13.1 % of the otter t r awle r s c a t c h e s , 7.1 % of the p a i r e d t rawlers c a t c h e s a n d 5.4 % of s m a l l - s c a l e f i sher ies c a t c h e s . O t t e r t r a w l i n g ope ra t ions are c a r r i e d out wi th 4 4 0 - 4 8 0 H P boa t s in 11-13 d a y tr ips at d e p t h s b e t w e e n 4 0 - 1 0 0 m , w h i l e pa i r ed t r awl ing is d o n e by 3 4 0 - 3 7 0 H P boa t s in 9-11 d a y tr ips at d e p t h s l e s s than 4 0 m . S m a l l - s c a l e f i sher ies i nc lude b e a c h s e i n i n g a n d t r a m m e l nets in w a t e r s l e s s than 10 m d e e p a n d gi l lnet t ing by 11-16 m boa t s with 1 0 0 - 1 3 0 H P motors in w a t e r s 8-40 m d e e p . S m a l l s h a r k s a v e r a g e 4 6 . 3 % of e l a s m o b r a n c h c a t c h e s , w h i l e a n g e l s h a r k s , gui tar f i shes a n d rays a c c o u n t for 2 4 . 8 5 % , 2 4 . 5 % a n d 5 % respec t ive ly . Mustelus schmitti a n d Galeorhinus galeus m a k e mos t of the c a t c h e s of " c a c o e s " o r s m a l l s h a r k s , w h i c h s h o w i n c r e a s e d 4 3 l a n d i n g s from 1,414 t in 1 9 7 3 to 3 ,217 in 1 9 8 6 , but, a c c o r d i n g to S U D E P E (1990) l a n d i n g s d r o p p e d to 2 , 0 2 3 1 in 1 9 8 9 . T h e propor t ion o f s m a l l s h a r k s in the c a t c h e s o f the s m a l l - s c a l e a n d pa i r t r awle r f i shery i n c r e a s e d dur ing this p e r i o d but d e c r e a s e d in the otter t rawl f ishery. T h i s r e su l t ed in a n a l m o s t e q u a l propor t ion o f l a n d i n g s by e a c h type o f f i shery in 1 9 8 3 - 1 9 8 6 . T h e C P U E of s m a l l s h a r k s in t/trip of both t ypes o f t rawlers t e n d e d to i n c r e a s e th roughout the p e r i o d o f the s tudy. A n g e l sha rk (Squatina guggenheim a n d Squatina sp.) l a n d i n g s i n c r e a s e d from 8 2 2 1 in 1 9 7 3 to 1 ,7771 in 1986 . A s with the s m a l l s h a r k s , the propor t ion of c a t c h e s con t r ibu ted by s m a l l - s c a l e f i sher ies a n d pa i r t r awlers i n c r e a s e d w h i l e that o f otter t rawlers d e c r e a s e d . S t i l l , abou t 5 0 % of the total l a n d i n g o f a n g e l s h a r k s c o m e s from the latter. W h i l e C P U E o f a n g e l s h a r k s in otter t rawlers s h o w e d a n o v e r a l l i n c r e a s e , pa i r ed t rawlers ' C P U E i n c r e a s e d until 1 9 8 3 a n d d e c r e a s e d a f te rwards . L a n d i n g s o f gui tar fish Rhinobatos horkelii, v a r i e d b e t w e e n 6 0 0 t a n d 1,925 t. M o s t o f t h e s e c a m e from the s m a l l s c a l e f i sher ies (50 %) a n d pa i r ed t rawlers (32 % ) , w h i l e otter t r awle r s con t r ibu ted v e r y s m a l l c a t c h e s (13 % ) . D a t a o f C P U E s h o w e d a sl ight d e c r e a s e up to 1 9 8 2 for both t ypes of t rawlers , i n c r e a s i n g to 1984 a n d fa l l ing a g a i n af terwards . L a n d i n g s o f rays , ma in ly g e n u s Dasyatis a n d Gymnura a n d to a l e s s e r extent Myliobatis, g r e w from 36 t in 1 9 7 3 to 4 8 4 t in 1986 . S m a l l - s c a l e f i sher ies a v e r a g e d 18 % of t he se c a t c h e s , p a i r e d t r awl ing 53 % a n d otter t r awl ing 34 % . C P U E for rays in t rawl f i sher ies w e r e v a r i a b l e wi th a n i n c r e a s i n g t rend . T h e a p p a r e n t d e c l i n e o f s o m e o f t he se popu la t i ons in the last p e r i o d o f the a b o v e s tudy s e e m s to be c o n f i r m e d by a swi tch from t rawl ing to bot tom l o n g l i n e s a n d gi l lnets (the latter spec i f i ca l ly a i m e d at Squatina a n d Galeorhinus) w h i c h s tar ted in 1 9 8 6 d u e to d e c r e a s i n g C P U E ' s . T h i s swi tch w a s a l s o c o u p l e d with add i t i ona l f i sh ing for a n g e l s h a r k s by sh r imp t rawlers f rom o ther a r e a s du r ing the s h r i m p off s e a s o n ( C M . V o o r e n , U n i v e r s i d a d de R i o G r a n d e , pers . c o m m . D e c . 2 3 1991) . A m o r i m a n d Arfe l l i (1987) a n d Arfe l l i et a l . (1987) , report s o m e b y c a t c h e s o f la rge s h a r k s t a k e n in sou th a n d sou theas t wa t e r s by t u n a long l ine r s . Prionace glauca ( a ccoun t i ng for 33 % of total c a t c h e s o f this fleet in 1985) a n d Isurus oxyrinchus ( a c c o u n t i n g for 3.2 % of total c a t c h e s of this f i shery 1 9 7 1 - 1 9 8 5 ) a re c a u g h t th roughout the y e a r but m a i n l y du r ing A p r i l - J u l y a n d M a y - N o v e m b e r r e spec t ive ly . L a n d i n g s of b lue s h a r k s a r e c o m p o s e d ma in ly o f 2 0 - 4 0 kg s h a r k s d r e s s e d w e i g h t (no h e a d , fins o r guts) a n d a c c o u n t e d for 5 5 3 t a n d 4 6 2 t in 1984 a n d 1 9 8 5 r e spec t ive ly . B l u e sha rk C P U E h a s v a r i e d from 0.4 k g / 1 0 0 h o o k s in 1971 44 (when their c ap tu re w a s a v o i d e d by sk ippe r s ) to 27 .6 k g / 1 0 0 h o o k s in 1 9 8 5 . Short f in m a k o c a t c h e s v a r i e d b e t w e e n 21 t (1971) a n d 7 3 1 (1981) , thei r m e a n w e i g h t in the c a t c h v a r y i n g b e t w e e n 4 2 kg a n d 6 0 kg th roughout 1 9 8 5 . T h e i r mea t is the m o s t v a l u e d a m o n g e l a s m o b r a n c h s in B r a z i l , a n d is u s e d loca l ly a s w e l l a s e x p o r t e d to U S A . A g o o d d e a l o f r e s e a r c h o n e l a s m o b r a n c h s is d o n e by s e v e r a l B r a z i l i a n Un ive r s i t i e s , g o v e r n m e n t a l a n d n o n - g o v e r n m e n t a l o r g a n i s a t i o n s . H o w e v e r , a c c o r d i n g to L e s s a (pers. c o m m . , op.ci t . ) , at p resen t there a re no m a n a g e m e n t m e a s u r e s for e l a s m o b r a n c h s in B r a z i l , a l t hough s o m e l o c a l g r o u p s in tend to ra i se g o v e r n m e n t a l a t tent ion into the s ta tus o f t he se f i sher ies . S o m e p l a n s to i m p l e m e n t repor t ing by s p e c i e s a r e a l s o u n d e r w a y . L e s s a points out that e l a s m o b r a n c h s t o c k s exp lo i t ed in the north c o a s t a r t i s ana l f i shery a re thought to be u n d e r e x p l o i t e d , t h o s e u t i l i sed by the t u n a long l ine f i shery a re s u s t a i n a b l y exp lo i t ed , w h e r e a s the sou th B r a z i l d e m e r s a l s t ocks a re a l m o s t su re ly o v e r e x p l o i t e d . A r g e n t i n a . A r g e n t i n a h a s s o m e o f the few e x p a n d i n g f i sher ies a m o n g major e l a s m o b r a n c h - f i s h i n g coun t r i e s in A m e r i c a . Af ter a t e m p o r a r y d rop in the late 40 ' s , a t t r ibuted to the g e n e r a l c o l l a p s e o f s h a r k l iver oi l f i sher ies a r o u n d the w o r l d , sha rk a n d ray y i e l d h a d a s l o w but s t e a d y growth from the ea r ly 50 ' s to the m i d 60 ' s (fig. 2 .2) . S i n c e 1 9 6 7 , y i e l d s f luctuated c l o s e l y to 1 0 , 0 0 0 1 but h a v e i n c r e a s e d s i n c e 1 9 8 1 . D e s p i t e the re la t ive ly l ow c a t c h e s , w h i c h a c c o u n t o n l y for 2 .54 % of the w o r l d e l a s m o b r a n c h c a t c h du r ing 1 9 8 7 - 1 9 9 1 , e l a s m o b r a n c h s a re r e a s o n a b l y important for A r g e n t i n e a n f i sher ies cont r ibu t ing 3 .19 % of the total y i e l d s dur ing this p e r i o d . T h i s is the h ighes t relat ive impor t ance for e l a s m o b r a n c h s in A m e r i c a n major e l a s m o b r a n c h - f i s h i n g coun t r i e s . D u r i n g the p e r i o d 1977-1991 the mos t important s p e c i e s in the e l a s m o b r a n c h c a t c h e s w e r e : Mustelus schmitti w h i c h a v e r a g e d 4 9 % (6 ,790 t/yr) o f the total e l a s m o b r a n c h c a t c h ; s e v e r a l rays at 2 0 % (2 ,722 t/yr), unc l a s s i f i ed e l a s m o b r a n c h s with 2 3 % (3 ,160 t/yr) a n d e l e p h a n t f i shes (Callorhinchus s p j wi th 8 % (1 ,048 t/yr). O f t he se g r o u p s , the s m o o t h - h o u n d s a n d "var ious e l a s m o b r a n c h s " h a d a g r o w i n g t rend in c a t c h e s w h i l e the e l e p h a n t f i shes a n d rays h a d a t e n d e n c y to d e c r e a s e . A r g e n t i n a is o n e of the few coun t r i e s wi th impor tant c a t c h e s of c h i m a e r i f o r m e s in the w o r l d (fig. 2 .8) . 4 5 C r e s p o a n d C o r c u e r a (1990) g ive a ve ry de t a i l ed desc r ip t ion o f the f i she r i e s for s h a r k s of C l a r o m e c o a n d N e c o c h e a , B u e n o s A i r e s P r o v i n c e . In this nor thern A r g e n t i n a f ishery, Galeorhinus galeus, Mustelus schmitti, Carchariastaurus a n d Squatina argentina a re caugh t with g i l lne ts . A b o u t 2 3 w o o d e n a n d iron v e s s e l s from 8-44.9 m in length t ake part in the f ishery. T h e y u s e ny lon monof i l amen t g i l lnets (2-3 m m twine) wi th m e s h s i z e s 19-21 c m a n d d i m e n s i o n s 55-71 m long 3.8 m d e e p pe r p a n e l (8-25 pane l s ) . T h e s e gi l lnets a r e set o n the bot tom b e t w e e n 0.5 a n d 2 5 n m from the c o a s t in dep ths v a r y i n g from 2 -70 m . T y p i c a l abou t 6-15 Squatina argentina a n d 1-20 o f the o ther s h a r k s a re c a u g h t pe r p a n e l . E x - v e s s e l p r i ces a re U S $ 3 - 4 / k g for u n d a m a g e d Galeorhinus d e s t i n e d for expor t (ma in ly to Italy) a n d U S $ 1 - 2 .5 /kg for d a m a g e d o n e s that a re c o n s u m e d sa l t -dr ied in the l o c a l marke t . In a n u n u s u a l note, t h e se au tho r s report e x t e n s i v e d a m a g e to sha rk c a t c h e s by m a r i n e m a m m a l s ! S e a l ions bite off the be l ly o f e n t a n g l e d s h a r k s ea t ing on ly the l iver . M e n n i et a l . (1986) ind ica te the p r e s e n c e of m o r e s h a r k s s p e c i e s in nor thern A r g e n t i n a . In add i t ion to the s p e c i e s m e n t i o n e d a b o v e , they report Mustelus canis, M. fasciatus, Squalus blainvillei, S. cubensis a n d Notorhynchus cepedianus in the c o m m e r c i a l c a t c h e s of B u e n o s A i r e s p r o v i n c e . Mustelus schmitti a c c o u n t s for 9 2 % of the i r s h a r k s a m p l e s , at c o m m e r c i a l l and ing s i tes . T h e r e m a i n i n g s p e c i e s a re l e s s than 1 % of the s h a r k c a t c h e s e x c e p t S. cubensis w h i c h m a d e up 2 % . G o v e r n m e n t s tat is t ics o f s h a r k l a n d i n g s at M a r de l P l a t a port a v e r a g e d 5 ,890 t du r ing 1 9 7 1 - 1 9 8 0 , this is abou t 1/2 o f the a v e r a g e total e l a s m o b r a n c h c a t c h o f A r g e n t i n a du r ing that p e r i o d . A b o u t 9 3 % of this c a t c h is m a d e o f ' ga tuzos ' (p redominan t ly Mustelus schmitti, with s o m e quant i t ies o f M. canis a n d s m a l l n u m b e r s of M. fasciatus). ' C a z o n e s ' (main ly Galeorhinus galeus but i n c l u d i n g s o m e la rge M. canis) contr ibute the r e m a i n i n g 7 % . A p p a r e n t l y , the r e m a i n i n g s p e c i e s a re not r e c o r d e d in the s tat is t ics . 2 .2 .2 .2 E u r o p e . N o r w a y . N o r w a y h a s h a d s o m e o f the mos t important sha rk f i sher ies in the Nor th A t l an t i c . N o r w e g i a n c o m m e r c i a l f i she r i es for e l a s m o b r a n c h s h a v e b e e n quite v a r i a b l e s i n c e the e n d of W o r l d W a r II, wi th a n i n c r e a s i n g t rend up to 1 9 6 3 , f o l l o w e d by a g e n e r a l d e c r e a s e to l eve l s a r o u n d 46 7 ,500 t/yr s i n c e 1981 (fig. 2 .2) . C a t c h e s rose a g a i n in the last th ree y e a r s o n r eco rd . J u d g i n g from recent t rends , e l a s m o b r a n c h s a re not a n impor tan t f i shery r e s o u r c e for N o r w a y . S h a r k s a n d rays r ep resen t o n l y 0 .44 % of the total f i she r i es p roduc t ion of this count ry . M o r e o v e r , N o r w e g i a n e l a s m o b r a n c h f i sher ies o n l y cont r ibute 1.21 % to the w o r l d e l a s m o b r a n c h y i e l d 1987 -1991 (table 2 .2) . T h e larges t part o f the e l a s m o b r a n c h c a t c h e s h a s typ ica l ly b e e n s p i n y dogf i sh Squalus acanthias. N e v e r t h e l e s s , there w e r e important f i sher ies for p o r b e a g l e s in the 60 ' s a n d for b a s k i n g s h a r k s until the m i d 80 ' s . W h i l e m a r k e t i n g a n d e c o n o m i c a l cons t ra in t s have t radi t ional ly inh ib i ted b a s k i n g sha rk f i sher ies ( M a x w e l l 1 9 5 2 ; O ' c o n n o r 1 9 5 3 ; K u n s l i k 1988) , appa ren t l y the p o r b e a g l e , Lamna nasus, f i shery d e c l i n e d at leas t in part a s a result o f ove r - explo i ta t ion ( G a u l d 1 9 8 9 , M y k l e v o l l 1 9 8 9 a , A n d e r s o n 1990) . N o r w e g i a n e l a s m o b r a n c h f i sher ies s e e m to be r e c o v e r i n g after a p r o l o n g e d d e c l i n e . F o r t h e first t ime in a l m o s t 2 0 y e a r s , c a t c h t r ends are o n the r i se . F A O d a t a for the pe r iod 1 9 7 8 - 1991 (fig. 2.9) s h o w c a t c h e s of s p i n y dogf i sh d e c l i n i n g from m o r e than 1 2 , 0 0 0 t in 1978 to 2 ,986 t in 1 9 8 6 then r ise up to 9 ,627 t in 1991 a n d a v e r a g i n g 5 ,715 t/yr (53 % of e l a s m o b r a n c h c a t c h e s for this per iod) . C a t c h e s o f b a s k i n g s h a r k s , Cetorhinus maximus, s h o w a pat tern s imi l a r to that of s p i n y dogf i sh c a t c h e s , a l t h o u g h the i r r e c o v e r y is more m o d e s t . B a s k i n g s h a r k c a t c h e s fell f rom 1 1 , 3 3 5 1 in 1 9 7 9 to o n l y 3 5 2 t in 1 9 8 7 , but w e r e of 1,932 t in 1 9 9 0 a n d a v e r a g e d 3 ,929 t/yr (36 %) du r ing this p e r i o d . R a y s c a t c h e s a re fairly s tab le at a r o u n d 1,115 t/yr (10 % ) . S m a l l quant i t ies o f p o r b e a g l e s a re still c augh t , a v e r a g i n g 6 7 t/yr ( less t han 1 % ) . A l t h o u g h there a re s o m e i n c o n g r u e n c i e s a m o n g different s o u r c e s o f da t a o n the N o r w e g i a n d i rec ted f i shery for p o r b e a g l e s o f the 60 ' s ( G a u l d 1989 ; A n d e r s o n 1990) , it is c l e a r that this f ishery c a u g h t la rge a m o u n t s o f s h a r k s . T h e s u m m a r y o f this f i shery is b a s e d o n A a s e n (1963) a n d M y k l e v o l l (1989a) . O p e r a t i o n s s tar ted a s a c o a s t a l act ivi ty but, s i n c e 1930 , the f i sh ing g r o u n d s s t ead i ly e x p a n d e d from N o r w e g i a n wa t e r s nor thwes t to the O r k n e y - S h e t l a n d a r e a a n d the F a r o e Is lands , then sou ther ly into Irish w a t e r s a n d f inal ly s t r e t ched to the A t l an t i c c o a s t s of C a n a d a a n d nor theas te rn U S A . Dis tan t w a t e r o p e r a t i o n s w e r e c a r r i e d out by s p e c i a l i s e d f r eeze r v e s s e l s 4 3 - 5 0 m long , d e p l o y i n g l ong l i ne s wi th up to 5 ,000 h o o k s in wa t e r s 10-30 m d e e p . S h a r k s l e s s than 10 kg in w e i g h t w e r e d i s c a r d e d b e c a u s e o f a l ack 47 (D C c o 25,000' 20,000 15,000 10,000 5,000 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Years Smooth-hound H Rays Elephant fish Var. elasm. Figure 2.8 E lasmobranch catches of Argentina, by spec ies groups, during 1977-1991. S c h o o l shark catches, too smal l to show (Data from F A O ) . 35,000- 30,000- 25,000- 5,000- N O R W A Y 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 Years Sp iny dogfish E H | Rays B a s k i n g shark Figure 2.9 E la smobranch catches of Norway, by spec ies groups, during 1978-1991. Porbeagle catches, too smal l to show (Data from F A O ) . 4 8 of marke t . T h e c o a s t a l fleet w a s c o m p o s e d o f w o o d e n boa t s 2 3 - 3 0 m l o n g w h i c h kept the c a t c h o n i ce . D r e s s e d c a r c a s s e s o f p o r b e a g l e s w e r e e x p o r t e d f rozen to Italy, w h i l e fins w e r e m a r k e t e d to the F a r Eas t . O n c e the N W At l an t i c p o r b e a g l e s t o c k s r e a c h e d unprof i table s i z e in 1 9 6 5 , the fleet m o v e d out to c a t c h m a k o s h a r k s in Nor th W e s t A f r i c a . P r e sen t ly , on ly b y c a t c h e s o f p o r b e a g l e s from p u r s e - s e i n i n g , t r awl ing a n d gi l lnet f i she r i es a re l a n d e d . N o r w e g i a n s d o not e v e n take their 2 0 0 t p o r b e a g l e T A C in E C w a t e r s . T h e b a s k i n g s h a r k f i shery ( d o c u m e n t e d by K u n z l i k 1988 a n d M y k l e v o l l 1 9 8 9 b ) h a s roots in the 16th cen tu ry w h e n the d r i ed str ips o f mea t w e r e u s e d a s f o o d . T h i s h a s t radi t ional ly b e e n a n impor tant d i r ec t ed f i shery in N o r w a y . Inspi red by a grea t d e m a n d for l iver o i l , the b ig e x p a n s i o n o f the f i shery s tar ted in 1 9 6 0 . S m a l l w o o d e n v e s s e l s 15 -25 m l o n g a n d a r m e d with h a r p o o n s , o p e r a t e d ma in ly du r ing A p r i l - A u g u s t . E x p e r i m e n t s to u s e the f lesh of b a s k i n g s h a r k s into f i s h m e a l a n d to g ive v a r i o u s u s e s to the h i d e s f a i l ed . C o n s e q u e n t l y , in a n attitude c o m p a r a b l e to that o f the "f inning" f i s h e r m e n o f o the r a r e a s , N o r w e g i a n f i s h e r m e n took just the l iver for o i l ex t rac t ion a n d d i s c a r d e d the c a r c a s s e s at s e a . L a t e l y they a l s o take the fins a n d expor t t h e m to the Or ient . D u r i n g the p e r i o d 1 9 5 9 - 1 9 8 0 , c a t c h e s r a n g e d b e t w e e n 1,266 a n d 4 , 2 6 6 s h a r k s pe r year , but h a v e d e c l i n e d s i n c e . E E C a g r e e m e n t s with N o r w a y l imi ted their c a t c h e s to a T A C of 4 0 0 t/yr of l ivers s i n c e 1 9 7 8 . T h i s c o r r e s p o n d s a p p r o x i m a t e l y to 2 , 4 0 0 t/yr w h o l e we igh t c o n s i d e r i n g l ivers to be 1/6 o f w h o l e weigh t . S o c i o - e c o n o m i c cons t ra in t s i nc lud ing l imited marke t s a n d a n a g e i n g fleet, a n d the errat ic dis t r ibut ion o f the s h a r k s a re identif ied a s r e a s o n s for the d e c l i n e o f the f i shery . T h e N o r w e g i a n f i shery for b a s k i n g s h a r k s d o e s not e v e n t ake the a l l o w e d c a t c h in E E C wa te r s . T h e oi l from the l ivers is s o l d for ex t rac t ion of s q u a l e n e , a h y d r o c a r b o n u s e d in c o s m e t i c a n d av ia t ion indus t r ies , but s i n c e r icher s o u r c e s h a v e b e e n f o u n d in d e e p - s e a s h a r k s of the g e n u s Centrophorus, the marke t for b a s k i n g s h a r k s is s h r i n k i n g . In g e n e r a l , the d y n a m i c s of N o r w e g i a n e l a s m o b r a n c h f i sher ies s e e m to be s t rongly i n f luenced by e c o n o m i c a n d s o c i a l factors ( M y k l e v o l l 1 9 8 9 a , 1 9 8 9 b , 1989c ) . M a n y of t he se f i sher ies in N o r w a y h a v e d e c l i n e d in part o r totally b e c a u s e of r e a s o n s ex te rna l to the d y n a m i c s o f the r e s o u r c e (e .g. marke t forces) . H o l d e n (1977) a n d M y k l e v o l l (1989d) s u m m a r i s e mos t o f the N o r w e g i a n f i shery for s p i n y dogf i sh Squalus acanthias in the nor theas t At lan t i c , w h i c h da t e s b a c k to 1 9 3 1 . E x p a n s i o n of the marke t s l ed to c a t c h e s of 8 ,767 t by 1 9 3 7 , a n d a p e a k o f a l m o s t 3 4 , 0 0 0 t in 1 9 6 3 . 4 9 S i n c e then , c a t c h e s h a v e s l o w l y fa l len to a l eve l o f l e s s t han 6 , 0 0 0 t in the 80 ' s . D u r i n g the pe r iod 1 9 5 0 - 1 9 7 0 , N o r w e g i a n long l ine r s f i shed ma in ly in the i r c o a s t a l w a t e r s dur ing win te r a n d in S c o t t i s h w a t e r s du r ing s u m m e r - a u t u m n . T h e f ishery a i m e d at expo r t i ng mos t o f the c a t c h e s to f ish a n d c h i p s s h o p s in E n g l a n d . Unt i l the ea r ly 70 ' s , this f i shery c o n s t r a i n e d the e x p a n s i o n o f the Br i t i sh f ishery, d u e to m o r e compe t i t i ve p roduc t s wi th l a rge r s i z e , better a p p e a r a n c e a n d l o w e r p r ice . In recent y e a r s , the migra t ion o f la rge n u m b e r s o f s p i n y dogf i sh into u n u s u a l l y nor thern par ts of N o r w a y h a s p r o d u c e d a n incen t ive for the f i shery . T h i s might a c c o u n t for the i n c r e a s e in c a t c h e s o b s e r v e d dur ing 1 9 8 9 - 1 9 9 1 . D u r i n g the first hal f o f this century , N o r w a y h a d a f i shery for g r e e n l a n d s h a r k s , Somniosus microcephalus, both a s a s p e c i a l i s e d act ivi ty a n d in c o m b i n a t i o n with s e a l i n g . J u d g i n g from the da ta r epor ted by M y k l e v o l l (1989c) , this f i shery p e a k e d in 1 9 1 7 , w h e n 1 7 , 0 4 9 hectol i t res o f l ivers w e r e l a n d e d . P r o b a b l y b e c a u s e of fal l ing marke t p r i ce s for the product , the f i shery c e a s e d in 1 9 6 0 . F i s h e r i e s for s k a t e s a n d rays h a v e n e v e r b e e n d e v e l o p e d a s a t a rge ted act ivi ty in N o r w a y , a l l c a t c h e s a re inc iden ta l to sp iny dogf i sh , l ing , ha l ibut a n d t rawl f i sher ies ( M y k l e v o l l 1 9 8 9 e ) . S k a t e s a n d rays of no c o m m e r c i a l v a l u e a n d s m a l l s p e c i m e n s are c o m m o n l y d i s c a r d e d D e s p i t e h a v i n g d e v e l o p e d s e v e r a l spec i f i c f i sher ies for s h a r k s , N o r w e g i a n r e s e a r c h in e l a s m o b r a n c h s h a s b e e n re la t ively poor . O u t of the three mos t impor tan t s h a r k f i sher ies of N o r w a y ( sp iny dogf i sh , p o r b e a g l e a n d b a s k i n g sha rks ) , o n l y the s p i n y dogf i sh w a s s tud ied in a n y dept in a r e s e a r c h p r o g r a m m e w h i c h l a s t ed from 1 9 5 8 to 1 9 8 0 . T h i s effort p r o d u c e d the first k n o w n a s s e s s m e n t of a n e l a s m o b r a n c h f i shery ( A a s e n 1964) . A a s e n e s t ima ted a m a x i m u m equ i l i b r ium y i e l d of 5 0 , 0 0 0 t/yr for w h a t he c o n s i d e r e d a s i n g l e s tock of sp iny dogf i sh for Nor the rn a n d W e s t e r n E u r o p e . B y 1 9 6 1 , this y i e l d l eve l w a s a l r e a d y s u r p a s s e d . P o r b e a g l e s w e r e briefly s t ud i ed w h i l e the f i shery w a s in e x p a n s i o n a n d this p r o d u c e d o n e of the first a t tempts to es t imate g rowth in s h a r k s from ver teb ra l r ings ( A a s e n 1963) . O n l y ve ry l imited r e s e a r c h w a s e v e r d o n e o n b a s k i n g s h a r k s . T h e r e is e v i d e n c e that N o r w e g i a n v e s s e l s t ake part in the o r a n g e r o u g h y f i sher ies o f N e w Z e a l a n d . H o w e v e r no de ta i l s abou t t he se act ivi t ies c o u l d be f o u n d . T h e f inal u s e g i v e n to the p r o b a b l y la rge b y c a t c h e s o f d e e p s e a s h a r k s in this f i shery is u n k n o w n ( see s ec t ion 2 .2 .3 .4 . ) . 5 0 F o r m e r U S S R . A l t h o u g h the U S S R d o e s not exis t a n y m o r e a s s u c h , the e l a s m o b r a n c h f i she r i es o f w h a t u s e d to be the S o v i e t U n i o n a re t rea ted here b e c a u s e o f the i m p o r t a n c e o f its c a t c h e s . F o r the s a k e o f s impl i f i ca t ion , the n a m e ' former U S S R ' wi l l be u s e d . F o r m e r U S S R f i she r i es for e l a s m o b r a n c h s w e r e not r e c o r d e d s e p a r a t e l y from the rest of the f i sher ies c a t c h e s o f this coun t ry before 1 9 6 4 in F A O y e a r b o o k s . S i n c e the b e g i n n i n g of r ecords , the c a t c h e s s o a r e d r e a c h i n g a total o f 5 9 , 0 0 0 1 in 1 9 7 5 , o n l y to fall d o w n a s sha rp ly a s they s o a r e d to a l eve l of abou t 2 0 , 0 0 0 t in 1 9 7 7 . S i n c e t hen , c a t c h e s h a v e b e e n quite uns tab le , v a r y i n g rough ly b e t w e e n 1 0 , 0 0 0 - 2 0 , 0 0 0 t/yr (fig. 2 .2) . D u e to the d i s a p p e a r a n c e of the S o v i e t U n i o n , c a t c h e s p l u m m e t e d in 1 9 9 0 - 1 9 9 1 . B e c a u s e o f the h u g e f i sher ies p roduc t ion o f the fo rmer U S S R , e l a s m o b r a n c h s con t r ibu ted o n l y 0.11 % of the total c a t c h e s for 1 9 8 7 - 1 9 9 1 , w h i c h is the lowes t a m o n g major e l a s m o b r a n c h - f i sh ing coun t r i e s . T h e former U S S R cont r ibu t ion to w o r l d e l a s m o b r a n c h f i sher ies w a s o f o n l y 1.75 % in the s a m e pe r iod . T h e e l a s m o b r a n c h c a t c h e s of the fo rmer U S S R w e r e m a d e up from con t r ibu t ions o f its e n o r m o u s f i sh ing fleet, w h i c h w o r k e d a r o u n d the w o r l d . A grea t va r i e ty o f s p e c i e s a re m a s k e d u n d e r the two m a i n h e a d i n g s that w e r e repor ted : r ays a n d v a r i o u s e l a s m o b r a n c h s . T h e e v e r c h a n g i n g cha rac te r i s t i c s o f fo rmer U S S R f i she r i es w h i c h d e p e n d e d la rge ly o n a g r e e m e n t s wi th v a r i o u s na t ions , m a k e s their a n a l y s i s difficult. D a t a from F A O (fig. 2 .10) s h o w that from 1978 to 1 9 9 1 , r ays a c c o u n t e d for 6 6 % (8,