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Factors affecting timing and size of runs of hilsa shad (Hilsa ilisha) in Bangladesh and Pakistan Das, Nitya Nanda 1985

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Factors Affecting Timing and Size of Runs of Hilsa Shad (Hilsa ilisha) in Bangladesh and Pakistan b y Nitya Nanda Das A thes is submit ted in p a r t i a l fu l f i l lment of the r e q u i r e m e n t s for the degree of Master of Science in T h e F a c u l t y of G raduate S t u d i e s (Depar tment of Zoology) We accept t h i s thes i s as con fo rming to the r e q u i r e d s t a n d a r d T h e U n i v e r s i t y of B r i t i s h Co lumbia Apri l 1985 © N i t y a Nanda Das, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Nitya Nanda Das Department of zoology  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 22 April 1985 ABSTRACT Data were ga thered in 1983 and 1984 on the H i l s a f i s h e r y in the Meghna R i v e r in B a n g l a d e s h , and on fac to rs re lated to i ts seasonal v a r i a t i o n , i n c l u d i n g e f fo r t as est imated by weekly c o u n t s of f i s h i n g b o a t s , and l a n d i n g s as est imated by c o u n t s of f i s h of f loaded at C h a n d p u r . H i s t o r i c a l d a t a were also ana l yzed c o n c e r n i n g f a c t o r s i n f l u e n c i n g annua l v a r i a t i o n s in H i l s a l a n d i n g s f rom the Padma R i v e r of the Ganges (1967-1974) and f rom the I n d u s R i v e r of P a k i s t a n (1968 -1982) . Ra i l sh ipments were good i n d i c a t o r s of l a n d i n g s . No s i g n i f i c a n t r e l a t i o n s h i p was o b s e r v e d between r i v e r i n e H i l s a l a n d i n g s and f i s h i n g i n t e n s i t y . R a i n f a l l , mean water leve l and maximum a i r t e m p e r a t u r e had no obv ious i n f l u e n c e on annua l v a r i a t i o n s in seasonal t iming of H i l sa r u n s in the Padma r i v e r of the G a n g e s . R a i n f a l l two y e a r s e a r l i e r had a s i g n i f i c a n t negat ive r e l a t i o n s h i p w i th annua l v a r i a t i o n of H i l sa l a n d i n g s , in both the Padma R i v e r and in the Indus R i v e r . Mechanisms r e g u l a t i n g th i s negat ive assoc iat ion between l a n d i n g s and r a i n f a l l may be that H i l sa are 1 + yea r old when t h e y are f i r s t r e c r u i t e d to the f i s h e r y , and the s u r v i v a l of eggs and f r y is minimum in y e a r s when t h e r e is a v e r y h i g h r a i n f a l l . In the Ganges and Indus r i v e r s , a n n u a l l a n d i n g s were not c lose ly c o r r e l a t e d , and appear to be dependent in p a r t on e a r l i e r ra in fa l l c o n d i t i o n s w i t h i n each r e g i o n . T h i s d e p e n d e n c y o f f e r s a means of r o u g h fo recas t of a n n u a l h a r v e s t on the bas is of p r e v i o u s r a i n f a l l d a t a . - i i -TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES V LIST OF FIGURES vn ACKNOWLEDGEMENTS viii 1. INTRODUCTION 1 2. STUDY AREAS 3 2.1 Ganges River 3 2.2 Indus River 7 3. KNOWN FEATURES OF BIOLOGY OF Hilsa i l i s h a 10 3.1 Migration 10 3.2 Maturity.and reproduction 16 3.3 Spawning season 17 3.4 Factors influencing spawning 19 3.5 Spawning grounds 20 3.6 Eggs 21 3.7 Larval history 22 3 .8 Age and growth 23 3.9 Food 23 4. SEASONAL VARIATIONS IN Hilsa IN THE PADMA AND MEGHNA RIVERS IN BANGLADESH 24 4.1 Description of fishery 24 4.2 Relations of landings to effort 32 4.2.1 Method of estimating effort 32 4.2.2 Method of estimating landings 36 4.2.3 Marine versus freshwater landings 36 4.2.4 Results and discussion 40 4.3 Relationship of landings to environmental factors 43 4.3.1 Sources of data 43 4.3.2 Relationship of landings to rainfal l 49 4.3.3 Relationship of landings to mean water level 52 4.3.4 Relationship of landings to minimum discharge 57 4.3.5 Relationship of landings to maximum air temperature 57 4.3.6 Discussion 60 5. ANNUAL VARIATIONS IN Hilsa IN THE PADMA AND MEGHNA RIVERS OF BANGLADESH AND IN THE INDUS RIVER OF PAKISTAN 67 5.1 Sources of data 67 5.2 Results 70 5.2.1 Relationship of landings to rainfal l in the Padma River of the Ganges at Goal undo in Bangladesh 70 5.2.2 Relationship of rainfal l to maximum water level in the Padma River of the Ganges at Goal undo in Bangladesh . . . 77 5.2.3 Relationship of landings to rainfal l in the Meghna River at Chandpur in Bangladesh 77 5.2.4 Relationship of landings to rainfal l in the Indus River of Pakistan 80 5.2.5 Correlations between the Ganges and the Indus Hilsa landings with a two-year lag in rainfal l 80 5.2.6 Relationship of landings to mean air temperature in the Padma River of the Ganges at Goal undo in Bangladesh . . . 85 5.2.7 Relationship of landings to mean air temperature in the Indus River of Pakistan 85 5.3 Discussion 90 6. CONCLUSIONS 94 LITERATURE CITED 96 APPENDIX 104 LIST OF TABLES TABLE 1. Number of different types of Hi 1sa fishing gear/day that were in operation during different months of the year, the Meghna River between Chandpur and Nilkamal from January 1984 to August 1984. The values reported are the mean and their standard errors. Each monthly mean is based on four observations 34 TABLE 2. TABLE 3. TABLE 4. TABLE 5. TABLE 6. TABLE 7. TABLE 8. TABLE 9. TABLE 10. Mean catch/day of Hi 1sa (kg) by two types of gear in different months in the river stretch from Chandpur to Nilkamal of the Meghna River (after Bangladesh Fisheries Resources Survey System, 1984) 35 Monthly freshwater landings of Hilsa and fishing intensity (calculated as described in text) for the River Meghna at Chandpur during the period of January to August 1984. Monthly freshwater landings are calculated from eight daily observations. Regression stat is t ics shown below Rail trans-shipment records, and observed riverine and marine Hi 1sa landings in metric tonnes for the Meghna River at Chandpur from January 1984 to August 1984. The values reported are the mean and their standard errors. Each monthly mean of freshwater and marine water Hi!sa is based on eight observations and trans-shipment on 30/31 days of observation 37 41 Estimated yie ld (y-j) in tonnes and effort in thousands of man-hours (g-j) of Hilsa i l i sha in Godavari River by dr i f t g i l l nets in the monsoon months of the years 1963-69 (after Rajyalakshmi et a l . 1972). Regression stat is t ics shown below 42 Monthly trans-shipment of Hilsa through Goalundo Railway Station (1967-74) in metric tonnes 48 Landings of Hilsa i l i sha from 1967 to 1974 of the Padma River at Goalundo, with rainfal l and mean a ir temperature of Faridpur from 1962 to 1974 68 Annual landings of Hilsa and rainfal l at Chandpur during the period 1933-1940 69 Catch of Hilsa i l i sha from 1968 to 1982 of the Indus River, ra infal l and mean a ir temperature of Hyderabad from 1962 to 1982 71 Regressions of Hilsa landings from 1967 to 1974 of the Padma River at Goalundo with rainfal l for different lag periods 72 - :v -TABLE 11. Rainfall of Faridpur during the period 1930-40 75 TABLE 12. Output of ice (* bundles) in Rajbari (near Goalundo) Ice Factory (after Nayudu, 1939) 76 TABLE 13. Regressions of Hi 1sa landings from 1968 to 1982 of the Indus River, with rainfal l for different lag periods 81 TABLE 14. Summary of landings of Hi 1sa, and of rainfal l two years previously in the Ganges and in the Indus River 84 TABLE 15. Regressions of Hi 1 sa landings from 1967 to 1974 of the Padma River of the Ganges at Goalundo with mean a ir temperature for different lag periods 86 TABLE 16. Regressions of Hi 1 sa catch from 1968 to 1982 of the Indus River of Pakistan with mean air temperature for different lag periods 89 APPENDIX TABLE 1. Development of a r t i f i c i a l l y f er t i l i z ed eggs (after Kulkarni 1950) 105 APPENDIX TABLE 2. Relationship between mean air temperature (°C) of Calcutta (near Hooghly area) with mean water temperature of Hooghly River of the Ganges 106 - vt LIST OF FIGURES FIGURE 1. Map of the Ganges 4 FIGURE 2. Map of lower Indus River 8 FIGURE 3. Area of distribution of Hilsa indicated by heavy dots. . . 11 FIGURE 4. Diagram of Shangla jal in operation (after Jones 1959) 25 FIGURE 4a. Photograph of open mouth of Shangla j a l , at Chandpur. . . . 26 FIGURE 5. Chandi jal 28 FIGURE 6. Hi 1sa offloaded by standard basket at Chandpur landing centre 38 FIGURE 7. Relationship between riverine Hilsa landings with rai l shipment record of Hi!sa in the Meghna River at Chandpur 44 FIGURE 8. Relationship of Hilsa landings in metric tonnes (MT) of the Padma River of the Ganges at Goalundo to rainfal l of Faridpur (near Goalundo) 50 FIGURE 8a. Relationship of freshwater Hilsa landings of the Meghna River at Chandpur to rainfal l of Chandpur 53 FIGURE 9. Relationship of Hi 1sa landings of the Padma River at Goalundo to mean water level of the Padma River at Goalundo 55 FIGURE 10. Relationship of Hi 1sa landings of the Padma River at Goalundo to minimum discharge of the Padma River at Goalundo 58 FIGURE 11. Relationship of Hi 1sa landings of the Padma River at Goalundo to maximum air temperature of Faridpur (near Goalundo) 61 FIGURE 12. Relationship of Hi 1sa landings of the Padma River at Goalundo with two-year lag in rainfal l 73 FIGURE 13. Relationship of rainfal l to maximum water level in the Padma River of the Ganges at Goalundo 78 FIGURE 14. Relationship of Hilsa landings with two-year lag in ra infa l l in the Indus River 82 FIGURE 15. Relationship of Hi 1 sa landings of the Padma River at Goalundo with two-year lag in mean air temperature of Faridpur (near Goalundo) 87 - V | j -ACKNOWLEDGEMENTS It gives me much pleasure to record here my deep sense of gratitude, sincere appreciation and profound regard to my research supervisor, Dr. C.C. Lindsey, for his constant and untiring help, scholarly guidance and constructive criticism in all phases of this research work. I am grateful to Dr. T.G. Northcote for his invaluable counsel and comments, and Dr. N.R. Liley for his constructive criticism. I have also benefitted considerably from discussions with Drs. N.J. Wilimovsky, J.D. McPhail and C.J. Walters. Much of the field work would not have been completed without the hard work, enthusiasm and perseverance of Dr. Melvin, Md. M. Hossain, Md. Sanaullah, Mr. Bibhuti Das, Md. Sattar, Mr. Indra Mohan, Md. Nurul Islam and of Md. Abbas Patwari. E r i c Taylor and Michael Lapointe provided patient assistance with com-puter handling, programming and their open-door policy regarding my f r e -quent queries on the nuances of various statistical analyses. Eric Taylor also read the f i r s t draft of this thesis and provided many constructive comments. Deepest and most sincere gratitude are also due to my parents, wife, brothers and sisters for their blessings. I received utmost encouragement and appreciation from my wife in completing this work. I am grateful to the International Development Research Centre for awarding me a pre-project fellowship during the tenure of which this work was carried out. Last but not least, I would like to thank Linda Duncan for her con-siderable secretarial assistance. - vi | | -I dedicate this thesis to my dearest people. - IX : -I 1. INTRODUCTION The Hilsa shad Hilsa ilisha (Hamilton) is the most important single species of food fish caught in Bangladesh and is a major source of protein in the people's diet. The Hilsa catch comprises about 22% of the total catch in Bangladesh, while no other single species contributes more than 5%. Employing 50,000 to 100,000 fishing boats, the fishery for Hilsa is also a major source of employment. The importance of Hilsa as a food source is such that the demand for Hilsa far exceeds its supply, and may necessitate management of the harvest to prevent overexploitation. Unfor-tunately, the fishery is as yet almost totally uncontrolled and undocu-mented. Currently, the Hilsa fishery resource is threatened by the con-struction of Farakka Barrage in India which diverts water from entering Bangladesh, and by irrigation, flood control measures and industrial effluents in Bangladesh. Basic life history knowledge of Hilsa is so rudimentary that measures to protect or expand the catch cannot yet be formulated. Successful stock management requires a good understanding of the major factors affecting survival and subsequent run size. Although studies have been published on several aspects of the biology of Hilsa ilisha (Day 1873, Hora 1938, 1940, 1941, 1942, Hora and Nair 1940, Jones 1957, Jones and Menon 1951, Pillay 1952, 1954, 1955, 1957a, 1957b, 1958, Pillay and Rosa 1963, Quddus et al. 1984a, 1984b, 1984c), little is known of the impact of environmental para-meters such as rainfall on timing of runs, or on annual variations in this important commercial fishery. Nor has an attempt been made previously to correlate this information from different countries where Hilsa occurs (extending from the Persian Gulf to the Bay of Bengal). 2 T h e p r i m a r y goals of the p r e s e n t r e s e a r c h were : (1) to e s t a b l i s h to what ex tent r e c o r d s of ra i l t r a n s h i p m e n t s of H i l sa r e f l e c t e d c h a n g e s of a b u n d a n c e of H i l s a in the r i v e r s , i n d e p e n d e n t of v a r y i n g f i s h i n g e f f o r t ; (2) to s t u d y seasonal v a r i a t i o n s in abundance of H i l s a in the Padma and M e g h n a R i v e r s in B a n g l a d e s h , and t h e i r re la t ionsh ip to ra in fa l l or o t h e r e n v i r o n m e n t a l f a c t o r s , and (3) to s t u d y annua l v a r i a t i o n s in H i l sa in the Padma and Meghna R i v e r s of B a n g l a d e s h and in the Indus R i v e r of P a k i s t a n . A n attempt is made , u s i n g t h i s in format ion to deve lop a r u n p r e d i c t i o n m o d e l . 3 2. STUDY AREAS 2 . 1 Ganges R i v e r T h e G a n g e s - B r a h m a p u t r a R i v e r sys tem forms in the B e n g a l B a s i n a d e l t a of 25,000 s q u a r e miles e x t e n t . It is the l i fe l ine and main s o u r c e of s u p p l y in B a n g l a d e s h . The r i v e r s e r v e s as a source of i r r i g a t i o n , nav igat ion and f i s h p ro te in fo r u r b a n and r u r a l s e t t l e -m e n t s . T h e Ganges R i v e r bas in s u p p o r t s a c o n c e n t r a t i o n of 300 mil l ion p e o p l e . T h e G a n g e s , one of the major r i v e r s of the w o r l d , has a l e n g t h of 1570 miles down to the mouth of the Meghna R i v e r ( R a s h i d 1977) . It r i s e s at an e levat ion of about 23,000 feet in G a n g o t r i on the s o u t h e r n s lope of the Himalayan r a n g e . A l o n g t h i s b o u n d a r y are located the t h r e e h ighes t mountain p e a k s : M t . E v e r e s t , K a n c h a n j a n g h a and M a k a l u . F r o m i ts h e a d w a t e r s , the Ganges f lows in a s o u t h - e a s t e r l y d i r e c t i o n a n d , f u r t h e r d o w n s t r e a m , in an e a s t e r l y d i r e c t i o n t h r o u g h Ind ia to the b o r d e r of B a n g l a d e s h ( F i g . 1 ) . Amongs t the major t r i b u t a r i e s which feed the G a n g e s , t h r e e v i z . the K a r n a l i ( G h a g h a r a ) , the Gandak and the K o s i , f low down f rom Nepal a n d together c o n t r i b u t e about 41% to the annua l f low and about 71% to the d r y season f low of the Ganges ( A b b a s , 1982) . T h e r i v e r B h a g i r a t h i - H o o g h l y , on which the Por t of C a l c u t t a is s i t u a t e d , b r a n c h e s off f rom the south bank of the Ganges at F a r a k k a a s h o r t d i s -tance above the point w h e r e the Ganges e n t e r s B a n g l a d e s h ( F i g . 1 ) . It i s at F a r a k k a that a b a r r a g e was c o n s t r u c t e d ac ross the r i v e r b y the e n d of 1974 which d i v e r t e d a l a r g e por t ion of the Ganges water in to 4 FIGURE 1. Map of the Ganges. 6 the B h a g i r a t i - H o o g h l y C h a n n e l . A f t e r r e a c h i n g the I n d o - B a n g l a d e s h b o r d e r , the Ganges forms the b o u n d a r y of the two c o u n t r i e s fo r a d i s -tance of about e ight m i l e s , whereupon it d i v e r g e s complete ly into B a n g l a d e s h . At t h i s p o i n t , it f lows for another 70 miles before j o i n i n g the r i v e r B r a h m a p u t r a - J a m u n a (which f lows southwest t h r o u g h Assam) at G o a l u n d o . T h e combined c o u r s e of the Ganges and B r a h m a p u t r a - J a m u n a , t a k i n g the name of P a d m a , is jo ined f rom the east b y another r i v e r , the Meghna off C h a n d p u r . T h e Meghna rece ives the o ld B r a h m a p u t r a on i t s r i g h t bank at B h a i r a b B a z a r . A l i t t le above t h e c o n f l u e n c e , the Meghna has a w id th of half a mi le . T h e mean d i s -c h a r g e at t h i s p o i n t , f rom late May to m i d - O c t o b e r , is about 250,000 c u s e c s wi th a r e c o r d e d maximum of 431,500 c . f . s . in 1960. A v e r a g e a n n u a l d i s c h a r g e is est imated to be 92 mil l ion a c r e - f e e t . T e n miles f rom S h a i t n o l , where the combined Ganges and B r a h m a p u t r a - J a m u n a , as t h e Padma R i v e r , meets the M e g h n a , the c o n f l u e n c e is seven miles wide i n the ra iny s e a s o n . F rom th is p o i n t , the combined c o u r s e of the t h r e e r i v e r s c o n t i n u e s as the Lower Meghna into the B a y of B e n g a l . T h e e s t u a r y of the Lower Meghna is usua l l y t a k e n to s t r e t c h f rom t h e R a b n a b a d Is lands to the K u m i r a C o a s t , a d i s tance of 95 mi les . The water i s , h o w e v e r , sa l ine f rom half the y e a r as f a r no r th as a l ine d r a w n f rom the middle of B h o l a to the nor th of S h o n d i p . T i d a l i n f l u e n c e e x t e n d s as f a r ups t ream as C h a n d p u r , but t h e r e is no t i d a l i n f l u e n c e at G o a l u n d o . T h e e s t u a r y of the Lower Meghna may be c o n -s i d e r e d to be the I lsa (or Te tu l ia ) and S h a h b a z p u r R i v e r s , wh ich t o g e t h e r have a w id th of twenty miles at the s e a - f a c e . T h e e s t u a r i n e d i s c h a r g e is not k n o w n , but at C h a n d p u r the mean d i s c h a r g e f rom J u n e 7 to October is a r o u n d 2 .5 mil l ion c . f . s . ( c u b i c feet p e r s e c o n d ) . T h e mean maximum in t h i s pe r iod of the y e a r is about 4 mil l ion c . f . s . In w i n t e r , the flow is about o n e - e i g h t h as m u c h , but the r i v e r e v e n t h e n i s s e v e r a l miles w i d e . In maximum f l o o d , the Lower Meghna's f low is not less t h a n f i ve mil l ion c . f . s . It is also est imated that f rom May to O c t o b e r , i ts da i l y load of sediments is near l y f o u r mi l l ion t o n s . T h e annua l load of sed iments c a r r i e d by it is about 1,500 mi l l ion tons and annua l water d i s c h a r g e about 875 mi l l ion a c r e - f e e t . 2 .2 Indus R i v e r In P a k i s t a n , on ly the R i v e r Indus s u p p o r t s a r u n of H i l s a . A b o u t 5000-7000 f i shermen c a t c h about 8000 metr ic tonnes of H i l sa a n n u a l l y . T h e Indus is the longest Himalayan r i v e r , about 2000 miles in l e n g t h . T h e Indus a r i s e s in T i b e t , f lows nor thwest fo r about 800 miles between r a n g e s of the Himalayan M o u n t a i n s , and then a b r u p t l y t u r n s s o u t h w e s t , f l ow ing fo r almost 1000 miles t h r o u g h P a k i s t a n before e m p t y i n g into the A r a b i a n Sea about 65 miles southeast of the major seaport c i t y of K a r a c h i . At S u k k u r (about 475 miles u p s t r e a m f rom the m o u t h , F i g . 2 ) , t h e volume of water f low ing into t h i s r i v e r v a r i e s f rom a low of about 30 ,000 c . f . s . d u r i n g the w in ter to about 410,000 c . f . s . d u r i n g i ts peak flow in A u g u s t . T h e r i v e r is nav igab le in on ly i ts lower 750 mi les . In most of t h i s lower a r e a , the r i v e r f lows t h r o u g h a r i d c o u n t r y where i r r i g a t i o n is n e c e s s a r y to s u p p o r t f a r m i n g , the major land use of the r e g i o n . 8 FIGURE 2. Map of lower Indus River. 9 10 3. KNOWN FEATURES OF BIOLOGY OF Hilsa ilisha O w i n g to i t s h igh consumer p r e f e r e n c e and h igh tonnage l a n d e d , the H i l s a shad ( H i l s a i l i sha) r a n k s as a va luab le commercial f i s h in the w e s t e r n d i v i s i o n of the I n d o - P a c i f i c f a u n i s t i c r e g i o n . H i l sa i l i s h a be longs to the subfami l y A l o s i n a e of the fami ly C l u p e i d a e and is genera l l y t h o u g h t to be a n a d r o m o u s . G e o g r a p h i c a l l y , t h i s spec ies ranges f rom the A r a b i a n Sea to the B a y of B e n g a l ( F i g . 3 ) , but is c o n c e n t r a t e d in the wate rs of B a n g l a d e s h , I n d i a , P a k i s t a n and B u r m a (P i l l ay and R o s a , 1963) . T h e f i s h e r y fo r H i l s a i l i s h a and i t s b io logy have been u n d e r i n v e s t i -gat ion fo r ove r one h u n d r e d y e a r s . T h e e x i s t i n g knowledge about t h i s spec ies stems l a r g e l y f rom o b s e r v a t i o n s of commercial f i s h i n g o p e r a t i o n s . A l t h o u g h these o b s e r v a t i o n s o f f e r on ly a l imited data set fo r d e d u c t i o n s , t h e y n e v e r t h e l e s s form a bas i s on which to b u i l d f u r t h e r r e s e a r c h . A c lea r k n o w l e d g e of the l i fe h i s t o r y of t h i s f i s h is an essent ia l p r e r e q u i s i t e in a n y programme of i ts f i s h e r y r e s e a r c h and management . 3 . 1 M ig ra t ion H i l s a i l i s h a are r e p o r t e d to be la rge l y anadromous ; a d u l t s m i g r a t e in to f r e s h w a t e r f rom the sea fo r s p a w n i n g ; the y o u n g upon h a t c h i n g r e a r in the r i v e r c h a n n e l s and e s t u a r i e s before d e s c e n d i n g to the sea fo r f u r t h e r f e e d i n g and g r o w t h . T h u s , t h e r e are t h r e e phases f o r potent ia l e x p l o i t a t i o n : d u r i n g the b r e e d i n g m i g r a t i o n , the f r e s h -water r e a r i n g s t a g e , and the mar ine phase (Raja 1984) . G e n e r a l l y , it is be l ieved that t h e r e a re t h r e e e c o t y p e s : i) f l u v i a l anadromous s t o c k s wh ich move between coasta l waters and the lower reaches of r i v e r s and breed in the a rea above the leve l of t i d a l i n f l u e n c e ; i i ) f l u v i a l r e s i d e n t s t o c k s that l i ve and b r e e d on ly in the n FIGURE 3. Area of distribution of Hi 1sa indicated by heavy dots. 13 midd le and u p p e r reaches of r i v e r s , and i i i ) p u r e l y mar ine s t o c k s . In add i t i on to these t h r e e t y p e s , a recent development is the e s t a b l i s h -ment of a s e l f - g e n e r a t i n g s tock in the c o n f i n e d waters of U k a i r e s e r v o i r in G u j r a t , Ind ia ( R a j a , 1984) . T h e d e s c r i p t i o n s by many w o r k e r s of the m i g r a t o r y b e h a v i o u r of H i l s a i l i s h a are based almost e n t i r e l y on i ts o c c u r r e n c e in commercial c a t c h e s . T h e on ly s t u d i e s on the migrat ion of H i l s a , t h r o u g h t a g g i n g e x p e r i m e n t s , are those of P i l l a y et a l . (1962) in the G a n g e s . T h e i r f i n d i n g s , a l though not c o n c l u s i v e , i nd ica te that H i l s a m a r k e d in the lower Ganges descended to e s t u a r i n e areas t h r o u g h the main Padma R i v e r that l ies in B a n g l a d e s h . T h e movement of adul t H i l s a f rom the sea to f r e s h w a t e r is c h a r a c -t e r i z e d by a r a p i d inc rease in f r e s h w a t e r c a t c h of s e x u a l l y mature f i s h . In the Ganges Del ta S y s t e m , t h i s i n c r e a s e in l a n d i n g s c o r r e s -p o n d s to the commencement of the s o u t h - w e s t monsoon r a i n s (May) and c o n s e q u e n t f l o o d i n g of a l l r i v e r s of B a n g l a d e s h and I n d i a . T h e v a r i a -t i o n s in the i n t e n s i t y of the monsoon d u r i n g the b r e e d i n g season a p p e a r to be re lated to the c o n s i d e r a b l e f l u c t u a t i o n s in a b u n d a n c e of t h e f i s h and ca tches in d i f f e r e n t a r e a s . A c c o r d i n g to Day (1873) , the b r e e d i n g migrat ion in the Indus and the u p p e r I r r a w a d y t a k e s p lace when r i v e r s are f looded by mel t ing s n o w , not b y monsoon r a i n s . In the I n d u s R i v e r of P a k i s t a n , H i l s a beg in to en te r f r e s h w a t e r in J a n u a r y , and in some years remain in the r i v e r as late as N o v e m b e r . Peak l a n d i n g s o c c u r d u r i n g J u n e , J u l y and A u g u s t . A l t h o u g h i n c r e a s e d s t ream flow does not appear to be the st imulus that a t t r a c t s H i l sa i n t o the I n d u s , as r e p o r t e d for o ther s t r e a m s , the peak of the r u n does o c c u r d u r i n g peak f lows ( Islam and T a l b o t , 1968) . 14 Water t e m p e r a t u r e has been g i ven l i t t le a t tent ion as an e n v i r o n -mental s t imulus fo r H i l sa m i g r a t i o n , yet t h i s fac to r is k n o w n to p lay a c r i t i c a l role in many aspec ts of c l u p e i d l i fe h i s t o r y , i n c l u d i n g anadromous s p e c i e s . T h e i n f l u e n c e of t e m p e r a t u r e on the movement of H i l s a i l i s h a is not k n o w n , but o b s e r v a t i o n of ca tches at C I F R I , Ind ia s u g g e s t some assoc iat ions wi th tempera tu re v a r i a t i o n ; H i l s a show v e r y r e s t r i c t e d m i g r a t o r y movements d u r i n g the cold season ( Jones and S u j a n s i n g h a n i , 1951) . Jones (1957) o b s e r v e d that f rom November to F e b r u a r y , H i l s a move in la rge shoals at the mouths of e s t u a r i e s and a long the f o r e s h o r e areas of the B e n g a l - O r i s s a Coast and as f a r south as the M e r g u i A r c h i p e l a g o on the B u r m a Coast ( K y a w 1953) . T h e genera l r i s e in t e m p e r a t u r e in the r i v e r s o c c u r s d u r i n g the la t te r par t of w i n t e r when H i l s a mig ra t ion also t a k e s p l a c e , s u g g e s t i n g that t e m p e r a -t u r e is a c o n t r i b u t o r y f a c t o r to in i t ia t ion of the r u n . Jones (1957) s u g g e s t e d that the u p s t r e a m migrat ion of H i l sa in the la t te r par t of w i n t e r in the Hooghly R i v e r is s t imulated by i n c r e a s i n g water t e m p e r a -t u r e . H o r a (1940) and Hora and Na i r (1940) have su rmised that t h e r e is a f i v e - y e a r p e r i o d i c i t y in the H i l s a f i s h e r i e s of the Ganget ic R i v e r s . In B a n g l a d e s h w a t e r s , D u n n (1982) o b s e r v e d the sugges t ion of a f i v e -y e a r p e r i o d i c i t y in the H i l s a ca tch which c o r r e s p o n d s to the i n d e x of monsoon s e v e r i t y . Ups t ream migrat ion of H i l s a may be e x t e n s i v e . In B a n g l a d e s h r i v e r s , t h e y ascend the e n t i r e l eng th of the Ganget ic De l ta S y s t e m ; i . e . , about 500 km ( P i l l a y and R a s a 1963) . In the I r rawady R i v e r of B u r m a , H i l s a are k n o w n to ascend into u p p e r B u r m a to M a n d a l a y , a d i s -tance of about 724 km f rom the s e a . On the Ganges in I n d i a , p r i o r to 15 the commission of the F a r a k k a B a r r a g e in 1975, H i l sa were c a p t u r e d i n l a n d as f a r u p r i v e r as D e l h i , about 1287 km (P i l lay and Rosa 1963) . In the Indus R i v e r of P a k i s t a n , the migrat ion e x t e n d s to the Ghulam Mohammad B a r r a g e , about 161 km f rom the s e a . It has of ten been o b s e r v e d that d u r i n g y e a r s of great a b u n d a n c e of H i l sa the u s u a l l imits of ups t ream migrat ion may be e x t e n d e d . S u c h i n s t a n c e s have been r e c o r d e d in the B r a h m a p u t r a R i v e r where H i l sa c a t c h e s were made even in areas above T e z p u r d u r i n g 1955 (P i l l ay and Ghosh 1958) and in the small t r i b u t a r i e s of the G a n g e s , t h r o u g h wh ich t h e f i s h ascended in to L a k e Mahasrata l d u r i n g 1954 ( B a n e r j i 1955) . Day (1873) c o n s i d e r e d it essent ia l to p r o v i d e f i sh passes to f a c i l i t a t e the migrat ion of H i l sa to the u p p e r reaches of r i v e r s in w h i c h a r t i f i c i a l o b s t r u c t i o n s have been c o n s t r u c t e d . H o w e v e r , the f i s h passes c o n s t r u c t e d ac ross the Coleroon and Mahanadi R i v e r s (Southwe l l and P r a s h a d 1918) were found not su i tab le for H i l s a . D e v a n e s a n (1942) o b s e r v e d that m i g r a t i n g f i s h gather below the o b s t r u c t i o n s and f i shermen t a k e l a r g e c a t c h e s , g rea t l y r e d u c i n g the s p a w n i n g escapement . La te r i n v e s t i g a t o r s have al l c o n c l u d e d that it i s not feas ib le to erect su i tab le f i s h passes in Indian r i v e r s (Na i r 1 9 5 4 ) . Ghosh(1976) est imates that the p r o d u c t i o n of the f i s h e r y above t h e F a r a k k a B a r r a g e d r o p p e d f rom 176.1 k g / k m p r e - c o n s t r u c t i o n to less t h a n 1 k g / k m p o s t - c o n s t r u c t i o n . B i l g r a m i and M u n s h i (1982) also r e p o r t e d the de le te r ious ef fect of the F a r a k k a B a r r a g e on the H i l sa f i s h e r y . In the Ganges R i v e r sys tem in B a n g l a d e s h , the major f i s h i n g a c t i v i t y is now in the lower reaches of the main r i v e r s and e s t u a r i n e 16 a r e a s . T h e r e is l i t t le f i s h i n g in ups t ream areas of B a n g l a d e s h s u c h as G o a l u n d o , P a k s e y and R a j s h a h i , once c o n s i d e r e d to be c e n t r e s of the i n d u s t r y . Ganapat i (1973) assoc iates the r e d u c e d migrat ions of H i l s a u p Indian r i v e r s wi th the lack of h i g h d i s c h a r g e s to the s e a , caused b y dams or i r r i g a t i o n d i v e r s i o n s . In P a k i s t a n , the Ghulam Mohammed B a r r a g e was c o n s t r u c t e d in 1954, t h e f i s h l a d d e r s p r o v i d e d in the B a r r a g e were ine f fec t i ve also ( H o s s a i n and S u f i 1962) . 3 . 2 M a t u r i t y and r e p r o d u c t i o n C o n f l i c t i n g v iews have been e x p r e s s e d on the minimum size of H i l s a at f i r s t m a t u r i t y . Day (1873) o b s e r v e d that H i l s a may at ta in f i r s t m a t u r i t y at the end of the f i r s t y e a r , o r at the b e g i n n i n g of t h e second y e a r . Jones and Menon (1951) reached a s imi la r c o n c l u s i o n b a s e d on t h e i r o b s e r v a t i o n s in the H o o g h l y , the Mahanadi and C h i l k a L a k e s . T h e y have r e c o r d e d that males become mature when 2 1 . 6 - 2 5 . 4 cm in l eng th and s u g g e s t e d they were ove r one y e a r o l d , whi le females became mature in the second year when 2 6 . 7 - 3 0 . 5 cm l o n g . H o w e v e r , P i l l a y (1958) found s t i l l smal ler s izes in the Hooghly R i v e r at f i r s t m a t u r i t y ; some males mature at 16-17 cm and females at 19-20 cm in to ta l l eng th when they are both about 1 1/2 years o l d . Some w o r k e r s have e x p r e s s e d the view that males mature e a r l i e r t h a n females , but c r i t i c a l e v i d e n c e is not ava i lab le (P i l l ay and Rosa 1963) . F o r the Ganges at A l l a h a b a d / V a r a n a s i , Mathur (1964) r e p o r t e d that 50% of the females mature at 35 c m , whi le the smallest s ize at m a t u r i t y were 33 cm in A l l a h a b a d and 31 cm at V a r a n a s i . He also 17 r e c o r d e d that males mature at a l e n g t h of about 20 c m . In the u p p e r s t r e t c h e s of the H o o g h l y , De (1980) o b s e r v e d that females f i r s t reach m a t u r i t y at a s ize of 3 4 . 1 c m . Raja (1984) r e p o r t e d that female H i l sa a t t a i n f i r s t m a t u r i t y at the s ize of 32 c m . T h e smallest mature male H i l s a o b s e r v e d in the G o d a v a r i b y P i l l a y and Rao (1962) was 25.6 c m , a n d the smallest mature female 37 .0 cm l o n g . T h e y c o n c l u d e d that the modal s ize of 35 .5 cm in the l e n g t h f r e q u e n c y s t u d i e s r e p r e s e n t s the g r o u p at f i r s t m a t u r i t y . T h i s mode was s u g g e s t e d to r e p r e s e n t f i s h aged 1 + y e a r . In al l o t h e r c a s e s , the age of the f i r s t m a t u r i t y was p laced at 2 y e a r s . In c o n t r a s t to the f o r e g o i n g , H o r a (1940) and Hora and Na i r (1940) s u g g e s t e d that H i l s a must be 5 y e a r s old before a t t a i n i n g m a t u r i t y . D u n n (1982) r e p o r t e d that almost al l r e p r o d u c t i v e H i l sa were at least 4 + in age and t h u s he c o n c l u d e d that t h e r e is l i t t le s p a w n i n g below t h i s a g e . T h i s age g r o u p c o r r e s p o n d s to a l e n g t h of about 40 cm ( r e f e r to age and g rowth s e c t i o n ) . 3 . 3 S p a w n i n g season T h e s p a w n i n g season of H i l sa i l i s h a has been repor ted to v a r y f rom a few months to y e a r - r o u n d , d e p e n d i n g on the r i v e r . Hora and N a i r (1940) and Hora (1940) s u g g e s t e d that in the Hooghly R i v e r , H i l s a p r o b a b l y b reed y e a r r o u n d wi th a major peak in J u l y - A u g u s t and a minor peak in May . On the o ther h a n d , Jones and Menon (1951) contended that the b r e e d i n g in the Hooghly is v e r y r e s t r i c t e d , if not s u s p e n d e d d u r i n g the w in te r months of December and J a n u a r y . T h e i r content ion was based on the low d e n s i t y of p r e - and p o s t - l a r v a e of the spec ies in r o u t i n e p l a n k t o n hauls d u r i n g w i n t e r . T h i s i n d i c a t e d , h o w e v e r , that 18 some w in te r b r e e d i n g may o c c u r lower down in the e s t u a r y where t e m p e r a t u r e s are h i g h e r . Bhanot (1973) con f i rmed by co l lect ion of l a r v a e in the Hooghly R i v e r that H i l s a spawns t h r o u g h o u t the y e a r wi th peak a c t i v i t y in F e b r u a r y - M a r c h , J u l y - A u g u s t , and O c t o b e r - N o v e m b e r . P i l l a y (1958) s u g g e s t e d that t h e r e may be two d i s t i n c t s p a w n i n g s e a s o n s : one wh ich beg ins at the s ta r t of the southwest monsoon and c o n t i n u e s t h r o u g h to N o v e m b e r , and a second peak o c c u r s f rom J a n u a r y to M a r c h . B a s e d on gonadosomatic i n d i c e s , Q u d d u s et_ a l . (1984a) d e s c r i b e d two t y p e s of H i l s a f rom B a n g l a d e s h w a t e r s ; t y p e " A " b r e e d s f rom J u l y to October and t y p e " B " f rom J a n u a r y to M a r c h . T h e y c la imed tha t the two t y p e s of shad are also c h a r a c t e r i z e d by d i f f e r e n c e s in m o r p h o l o g y ; t y p e A is " d e e p - b o d i e d " and t y p e B is " s l e n d e r " . Motwani et a l . (1957) r e p o r t e d that the b r e e d i n g of H i l s a in the Ganges appears to commence wi th the onset of the monsoon season in J u l y , w i th peak b r e e d i n g f rom September to December . Ghosh and N a n g p a l (1970) found that w i n t e r s p a w n i n g is r e s t r i c t e d to the r e s i -dent s l e n d e r va r ie t y in the f r e s h w a t e r sect ion of the G a n g e s , whi le N a i r (1958) o b s e r v e d that oogenesis reached i ts peak in March and the o v a u n d e r g o a t res ia and r e s o r p t i o n . Na i r ' s o b s e r v a t i o n s appear to i n d i c a t e that t h e r e is no w i n t e r s p a w n i n g of H i l s a in the f r e s h w a t e r sec t ion of the G a n g e s . A h m e d (1954) o b s e r v e d that some g r a v i d H i l s a have been found t h r o u g h o u t the y e a r in B a n g l a d e s h w a t e r s , but the major i ty of i n d i v i -d u a l s w i th well deve loped gonads are ava i lab le d u r i n g monsoon m o n t h s . It appears f rom Ahmed's s t u d y that H i l sa spawn t h r o u g h o u t the y e a r , b u t the peak season comes d u r i n g the ra iny s e a s o n . On the bas is of o v a maturat ion s t u d i e s , P i l l a y (1958) c o n c l u d e d that H i l sa b r e e d s 19 i n t e r m i t t e n t l y d u r i n g the b r e e d i n g season in the Hooghly R i v e r . T h e o v a that were l i k e l y to be spawned d u r i n g the season had a s ize r a n g e of 252 to 882 m i c r o n s . S i n c e no d i s t i n c t s ize g r o u p i n g cou ld be o b s e r v e d among the s a m p l e s , s p a w n i n g t h r o u g h o u t the y e a r was s u g g e s t e d . In s u m m a r y , o b s e r v a t i o n s wh ich s u p p o r t two s p a w n i n g s , one d u r i n g monsoon and the o t h e r d u r i n g w i n t e r - s p r i n g , come f rom the i n v e s t i g a -t i o n s of M a t h u r (1964) w i th respect to the G a n g e s , and Q u a r e s h i (1968) a n d Q u d d u s et a l . (1984a) f rom the Padma and Meghna R i v e r s . 3 . 4 F a c t o r s i n f l u e n c i n g s p a w n i n g On the bas is of o b s e r v a t i o n s on development s tages co l lected f rom the s p a w n i n g g r o u n d s , Jones and Menon (1951) sugges ted that the s p a w n i n g time of H i l s a is towards the a f te rnoon and e v e n i n g . V e r y l i t t le is k n o w n about the f a c t o r s that i n d u c e s p a w n i n g in H i l s a . Southwel l (1914) s u g g e s t e d that the c h a n g e s i n v o l v e d in the t r a n s i t i o n f rom the sea to f r e s h w a t e r i n d u c e s p a w n i n g . Na i r (1958) s t u d i e d the va r ia t ion in water tempera tu re of the Ganges near B a n a r a s and the gonadia l a c t i v i t y t h r o u g h o u t the y e a r , and s u g g e s t e d that v e r y h i g h t e m p e r a t u r e s have p e r h a p s an i n h i b i t o r y ef fect on maturat ion of t h e o v a r i e s . T h e f loods d u r i n g the r a i n y s e a s o n , wh ich make the water t u r b i d and the c u r r e n t f low f a s t e r , were c o n s i d e r e d b y Na i r to be most f a v o u r a b l e fo r s p a w n i n g . 20 3 . 5 S p a w n i n g g r o u n d s Southwe l l and P r a s h a d (1918) e x p r e s s e d the op in ion that t h e r e a re no f i x e d s p a w n i n g g r o u n d s f o r H i l sa in the genera l l y accepted use of the t e r m , and that they p r o b a b l y b r e e d d u r i n g the r a i n s w h e n e v e r c o n -d i t i o n s s u c h as w e a t h e r , t e m p e r a t u r e and o t h e r undetermined f a c t o r s a r e s u i t a b l e . T h e f i r s t pos i t i ve e v i d e n c e of the locat ion of s p a w n i n g g r o u n d s was d i s c o v e r e d by Hora (1938) when he i d e n t i f i e d the y o u n g of the spec ies f rom the P u l t a Water Works t a n k s , in to wh ich they would have ga ined access on ly in the form of eggs or e a r l y l a r v a e , because of the v e r y nar row suc t ion space in the c e n t r i f u g a l pumps at the i n t a k e s . He i n f e r r e d that the s t r e t c h of Hooghly R i v e r near P u l t a Water Works formed one of the s p a w n i n g g r o u n d s of H i l s a . T h i s was con f i rmed by f u r t h e r o b s e r v a t i o n s made by H o r a and N a i r (1940) and Jones and Menon (1951) . P i l l ay (1958) , on the bas is of o v a s t u d i e s , i n f e r r e d that the lower limit of the s p a w n i n g g r o u n d s of H i l s a in Hooghly R i v e r is B a g h B a z a r in C a l c u t t a . T h e r e is e v i d e n c e to show that they b r e e d u p s t r e a m u p to M e d g a c h i , a d i s t a n c e of about 251 km f rom the s e a . T h e H i l s a of C h i l k a Lake spawn in the lower reaches of the Daya R i v e r ( Jones and S u j a n s i n g h a n i 1951) . K a r a m c h a n d a n i (1961) c o n c l u d e d that H i l s a b r e e d s also in the f r e s h w a t e r reg ions of the r i v e r , below the most u p s t r e a m limit of i t s mig ra t ion (about 161 km f rom the sea) in a s t r e t c h of about 29 to 3 2 k m . From o b v e r v a t i o n s on the s ize composi t ion of c a t c h e s , he o b s e r v e d that on ly o lde r H i l s a (males 31 .5 cm to 4 8 . 5 cm and females 4 1 . 5 cm to 55 .5 cm) migrate to the f r e s h w a t e r zones f o r b r e e d i n g and tha t the y o u n g e r H i l sa b reed in the t i d a l z o n e . Southwel l (1914) has 21 also s u g g e s t e d s u c h a p o s s i b i l i t y in the r i v e r s of e a s t e r n I n d i a . M o t w a n i , J h i n g r a n and K a r a m c h a n d a n i (1957) have d e s c r i b e d the s p a w n i n g g r o u n d s of H i l sa in the Ganges as the s t r e t c h of the r i v e r between P a t n a ( B i h a r ) and A l l a h a b a d ( U t t a r P r a d e s h ) . T h e p resence of l a r v a e i n the s t r e t c h of La lgo la of the Ganges ind ica tes the p r o b a b i l i t y of H i l s a s p a w n i n g in that a r e a . The p resence of spent H i l s a in the sea off the S a u r a s h t r a C o a s t , where t h e r e are no l a r g e r i v e r s up which H i l s a might a s c e n d , has i n d i c a t e d the p o s s i b i l i t y of the s tock in the a r e a b r e e d i n g in the sea (P i l l ay 1963) . A h m e d (1952) has r e c o r d e d that H i l s a b reed in the Indus R i v e r near Nawabshah and in the s t r e t c h of the r i v e r immediately below the S u k k u r B a r r a g e . T h e s p a w n i n g g r o u n d s have been r e s t r i c t e d b y the c o n -s t r u c t i o n of the Ghulam Mohammed B a r r a g e in 1954, below wh ich H i l s a now s p a w n . In B a n g l a d e s h , Q u r e s h i (1968) o b s e r v e d H i l s a s p a w n i n g g r o u n d s in the Padma and Meghna R i v e r s and t h e i r t r i b u t a r i e s . 3 . 6 E g g s T h e diameter of the f u l l y - r i p e o v a r i a n e g g has been r e c o r d e d as 0 . 7 0 mm to 0 .75 mm b y Jones and Menon (1951) , 0 .89 mm by P i l l ay (1958) and 0.76 mm to 0.87 mm by De (1980) . T h e e g g , when la id in water and f e r t i l i z e d , swel ls to 2 . 1 mm to 2 .3 mm in diameter and is demersal in s t i l l w a t e r ; but as i t s d e n s i t y is v e r y c lose to that of w a t e r , it is e a s i l y buoyed up and d r i f t e d by s l i g h t c u r e n t s ( K u l k a r n i 1950) . T h e e g g membrane is e las t i c and the v i te l l ine space is w i d e . T h e yo lk is segmented and has numerous oi l g lobules of v a r y i n g s i z e s , which coalesce la ter to form a l a r g e and c o n s p i c u o u s g lobule ( Jones and 22 Menon 1951) . K u l k a r n i (1950) and M o t w a n i , J h i n g r a n , and K a r a m c h a n d a n i (1957) s tated that the H i l s a e g g has a d o u b l e - l a y e r e d membrane , but Jones and Menon (1951) o b s e r v e d that the d o u b l e - l a y e r i n g t a k e s p laces as a resu l t of pos t -mor tem c h a n g e s . T h e r e is no in format ion ava i lab le on the p a r a s i t e s and p r e d a t o r s of H i l s a e g g s in n a t u r e . 3 . 7 L a r v a l h i s t o r y K u l k a r n i (1950) has g i v e n the fo l lowing account of the d e v e l o p -ment of a r t i f i c i a l l y f e r t i l i z e d eggs of H i l s a ( A p p e n d i x Tab le 1 ) . The t e m p e r a t u r e of the water in wh ich the e g g s were hatched was between 28°C and 2 8 . 5 ° C . T h e h a t c h i n g time v a r i e d f rom 18 h o u r s to 26 h o u r s , d e p e n d i n g on the t e m p e r a t u r e and o x y g e n a t i o n of the w a t e r . O b s e r v a -t i o n s by Jones and Menon (1951) on d e v e l o p i n g e g g s , co l lec ted f rom the Hoogh ly R i v e r , showed a l o n g e r i n c u b a t i o n pe r iod wh ich might have been due to the low water t e m p e r a t u r e (23°C) in which they were r e a r e d . T h e y s u g g e s t e d c o n s i d e r a b l e r e t a r d i n g of g rowth wi th d r o p in water t e m p e r a t u r e . Motwan i , J h i n g r a n and K a r a m c h a n d a n i (1957) r e c o r d e d the i n c u b a t i o n time to be 24 to 28 h o u r s . T h e newly hatched l a r v a i s 3 . 1 mm a c c o r d i n g to K u l k a r n i (1950) and 2.3 mm a c c o r d i n g to Jones and Menon (1951) . Motwan i , J h i n g r a n and K a r a m c h a n d a n i (1957) f o u n d the leng th of newly hatched l a r v a e to be 2 . 5 mm to 2.55 mm and K a r a m c h a n d a n i (1961) o b s e r v e d it v a r y i n g between 2 .4 mm and 3 . 0 mm. 23 3 . 8 A g e and g rowth One of the major l imi tat ions in the s t u d y of H i l s a popu la t ions is t h e lack of a su i tab le method f o r age and g rowth d e t e r m i n a t i o n . A g i n g f rom h a r d p a r t s , s u c h as scales and o t o l i t h s , has been a t t e m p t e d , but the r e s u l t s have not been e n c o u r a g i n g . T h e most p r o m i s i n g s t r u c t u r e s f o r a g i n g are the o t o l i t h s , wh ich are u n d e r inves t iga t ion by M d . Mokammel Hossa in ( p e r s . c o m m . ) . S i n c e the s t o c k s of H i l s a are exp lo i ted mostly by s ize se lect ive g e a r , a g i n g b y l eng th f r e q u e n c y a n a l y s i s is of l imited u s e . T h e lack of re l iab le a g i n g t e c h n i q u e s has led to many d i f f e r e n t v iews of age and g rowth in H i l s a . H i l s a is t h o u g h t to l i ve a maximum of 5 to 7 y e a r s , a l though age g r o u p s 2 to 4 appear to c o n t r i b u t e most to the f i s h e r y . 3 . 9 Food H i l s a i l i s h a is a p l a n k t i v o r e e x p l o i t i n g both zoop lankton and p h y t o p l a n k t o n . In the y o u n g s t a g e s , diatoms dominate the d i e t . A s t h e f i s h g r o w , h o w e v e r , the composi t ion of the diet s h i f t s towards c r u s t a c e a n i t e m s , espec ia l l y c o p e p o d s . Spent f i s h a re be l ieved to be b e n t h i c f e e d e r s as c o n s i d e r a b l e q u a n t i t y of mud and sand are i n g e s t e d . T h e i n t e n s i t y of f e e d i n g is v e r y h i g h d u r i n g the p o s t - s p a w n i n g p e r i o d . Some a u t h o r s have o b s e r v e d a decrease o r cessat ion of f e e d i n g a c t i v i t y d u r i n g the s p a w n i n g r u n . 24 4. SEASONAL VARIATIONS IN HILSA IN THE PADMA AND MEGHNA RIVERS IN BANGLADESH 4 . 1 D e s c r i p t i o n of f i s h e r y " T h e H i l s a be ing by f a r the most important f o o d - f i s h in the G a n g e s , and i t s f i s h e r y one that engages the at tent ion of the v o c a -t i ona l f i s h e r - c a s t e s f a r beyond any o t h e r , it is n a t u r a l that e x t r e m e l y ingen ious and e f f e c t i v e methods have been e v o l v e d b y a race noted fo r i t s i n v e n t i v e n e s s in t h i s a r t " ( H o r n e l l 1950) . T h e cho ice of the net depends upon the depth of water to be f i s h e d , ve loc i ty of the c u r r e n t , t ime of the year and above al l the f i n a n c i a l c o n d i t i o n of t h e owner of the net (Ahmed 1960) . T h e fo l lowing t h r e e t y p e s a re v e r y common and genera l l y used in the Meghna R i v e r : (1) S h a n g l a j a l , (2) C h a n d i , and (3) D o r a . (1) S h a n g l a jal ( F i g . 4 and 4a) T h i s is a p u r s e - s h a p e d net w i th h i n g e d mouth which can be s h u t i n s t a n t l y when d e s i r e d . It is also ca l led a c lap n e t . It can be used f rom the s u r f a c e to a d e p t h of s e v e r a l f a t h o m s , as the c l o s i n g rope may r u n to a l e n g t h of 15 f a t h o m s . In out l ine t h e mouth is s e m i c i r c u l a r , the two f l e x i b l e bamboo l i p s o f ten o v e r 8 meters in l e n g t h , bent in to a deep g r a c e f u l c u r v e that g i v e s an easy h i n g i n g motion when the mouth has to be s h u t . T h e bag is about 3 to 4 meters d e e p . T h e n e t t i n g is of ny lon twine and the mesh is f rom 8 to 11 c m , knot to knot d i a g o n a l l y . T h e mouth is k e p t open b y a b r i c k o r stone weight of 8 to 10 k g t ied to the c e n t r e of the lower l i p . T h e boat is al lowed to d r i f t in the d i r e c t i o n of the c u r r e n t w i th the mouth of the net f a c i n g 25 FIGURE 4. Diagram of Shangla ja l in operation (after Jones 1959). 25a 26 FIGURE 4a. Photograph of open mouth of Shangla j a l , at Chandpur. 26a 27 downst ream t r a p p i n g any f i s h coming u p . T h e r e is a f ine fee ler c o r d , d i v i d i n g into t h r e e b r a n c h l ines at i ts lower end a t tached at t h r e e po in ts on the u p p e r por t ion of the net to t ransmi t the d i s t u r b a n c e caused by the e n t r a n c e of a f i s h into the n e t . T h e o t h e r end of the l ine is held taut in the f i sherman's left h a n d ; the s l i gh t je rk or q u i v e r it t r a n s m i t s when a f i s h e n t e r s the net i s s u f f i c i e n t s i g n a l ; the net is i n s t a n t l y c losed by a je rk of the h a u l rope in the r i g h t h a n d . T h e net i s then hauled up and e m p t i e d . T h e net is opera ted r o u n d the y e a r , but peak operat iona l season is d u r i n g monsoon . Occas iona l l y when the net is operated at bottom leve l it gets e n t a n g l e d in submerged o b s t r u c t i o n s and if e f f o r t s to e x t r i c a t e it a re of no ava i l t h e rope is c u t and the net a b a n d o n e d . When two nets are operated s imul taneous ly f rom a boat a minimum of t h r e e p e r s o n s are r e q u i r e d fo r the p u r p o s e , one at the helm and two o t h e r s to operate the nets and ass i s t in rowing ( Jones 1959) . T h e boats used fo r o p e r a t i n g S h a n g l a jal a re k n o w n as d i n g h i s . A d i n g h i is a p lank bu i l t r o u n d - b o t t o m e d shal low boat most common in the G a n g e s , about 5 to 8 meters in l eng th and about 1 - 1 . 5 meters w i d e , wi th long po inted bow and s t e r n . T h e boat is s t r e n g t h e n e d by r i b s and c r o s s - b e a m s wi th detachable h a l f - s p l i t bamboo pieces in the i n t e r s p a c e s . Long padd les are used also wh ich se rve in s t e e r i n g . When s a i l i n g , a bamboo mast is c a r r i e d i n the f r o n t w i th t h i n sp l i t sa i l s u p p o r t e d by a d iagona l bamboo y a r d s tepped f a r in f r o n t . FIGURE 5. Chandi 29 30 (2) C h a n d i jal ( F i g . 5) T h i s is a p o w e r f u l d r i f t g i l l net and employed c h i e f l y when r i v e r s are in f lood - May to O c t o b e r . T h e C h a n d i jal is made l i k e al l l a r g e d r i f t nets in a number of shor t l e n g t h s , which are t ied together into a long f leet when about to be s h o t . T h e s ize of each p iece var ies c o n s i d e r a b l y , but g e n e r a l l y each piece measures 12 meters in length by 8 meters d e e p . T h e nets are of ny lon t w i n e , and have a mesh of f rom 6 to 10 c m , knot to k n o t . F loats of bamboo are used to buoy the h e a d -l ine at i n t e r v a l s of about 3 - 5 m e t e r s , whi le the f o o t - r o p e is we igh ted at s imi la r i n t e r v a l s , u s u a l l y wi th t h i c k d i s c - s h a p e d b u r n t - c l a y s i n k e r s each of about 10 to 15 cm in diameter h a v i n g an e c c e n t r i c a l l y p laced h o l e , or wi th f ragments of b r i c k . T h e net c a n be ad justed to float v e r t i c a l l y at any d e s i r e d d e p t h . F o r opera t iona l p u r p o s e s s e v e r a l p ieces of n e t , f rom 25 to 7 5 , a re t ied toge ther d e p e n d i n g on the l e n g t h r e q u i r e d and the r e s o u r c e s of the f i s h e r m e n . To one end of the head rope a small ra f t of bamboo is a t tached and the net is pa id out ac ross the r i v e r , the o ther end b e i n g t ied to a b o a t . T h e net as wel l as the boat d r i f t s down in the c u r r e n t , g i l l i n g any a s c e n d i n g H i l s a . When f i s h i n g is done at n i g h t , a l i gh t is kept b u r n i n g on the raf t so that the f i shermen in the boat can get an idea of the pos i t ion of the o ther e x t r e m i t y of the n e t . F o r d a y - t i m e f i s h i n g , the raft i s sometimes s u b s t i t u t e d b y a long pole or any c o n s p i c u o u s f l o a t i n g ob jec t . T h o u g h the net is employed mainly fo r c a t c h i n g H i l s a , o ther f i s h e s also sometimes get g i l led o r en tang led in i t . 31 T h e boat used fo r the operat ion of t h i s net is known as the C h a n d i n a u k a . T h i s is a shal low p l a n k - b u i l t boat wi th a r o u n d e d b o t t o m , longer and wider t h a n the d i n g h i . It is about 12 to 20 meters in l eng th and about 2 . 5 - 3 . 5 meters in w i d t h . T h e boat is p r o v i d e d wi th a hood and t h e r e is p r o v i s i o n for a mast and s a i l . T h e r e are u s u a l l y 5 to 8 p e r s o n s in a b o a t . T h e net is employed r o u n d the y e a r , but c h i e f l y used f rom May to O c t o b e r . (3) Dora jal T h i s net is s imi lar to C h a n d i j a l , but of smal ler mesh (5 to 8 cm) and is mainly employed fo r c a t c h i n g H i l s a . T h i s net goes by the name of I l ish jal in the d i s t r i c t s of K h u l n a and B o g r a of B a n g l a d e s h (Ahmed 1962) . The net may r u n f rom about 60 to ove r 300 meters and the d e p t h f rom about 5 to 8 meters a c c o r d i n g to the w i d t h and depth of the r i v e r . T h e net is employed r o u n d the y e a r , but mainly opera ted a f te r the Pooja (Oc tober ) fo r a pe r iod of about 6 months u n t i l M a r c h - A p r i l . T h e H i l s a c a u g h t in the Dora jal are s e v e r a l cm smaller t h a n those c a u g h t in the C h a n d i j a l . T h e boat used for the oper ta ion of t h i s net is k n o w n as the D o r a n a u k a . It is the same t y p e of boat as C h a n d i n a u k a , but smal ler in s i z e . G e n e r a l l y f i she rmen c a t c h H i l s a e v e r y d a y . T h e y t a k e l i t t le r e s t , on ly when p r e p a r i n g and t a k i n g t h e i r mea l . T h e r e are a few b r a v e f i s h e r m e n who p r e f e r n igh t f i s h i n g to day f i s h i n g , and who 32 t a k e rest d u r i n g d a y t i m e . D u r i n g the lean f i s h i n g season some of them seek a l te rnate employment . Few f i shermen d e l i v e r t h e i r ca tches d i r e c t l y to the f i s h l a n d i n g c e n t r e s . Most of the r i v e r f i she rmen appear to use no ice and have no means of main ta in ing the q u a l i t y of the f i s h . Most ly t h e y sel l t h e i r ca tches on the r i v e r to a f a r i a ( c o l l e c t o r ) . T h e c o l l e c t o r b u y s the f i s h f rom the f i s h e r m e n , and t r a n s p o r t s them to the l a n d i n g c e n t r e s where they are o f f - l o a d e d from the co l lec tor boats to the wholesale m a r k e t . F rom t h e r e , fo l lowing a u c t i o n , most are t r a n s - s h i p p e d e lsewhere by t r u c k o r by r a i l , u s u a l l y p a c k e d wi th i c e . A t C h a n d p u r , the co l lec tor boats b r i n g i n g f i s h f rom f r e s h w a t e r areas operate b y sa i l o r o a r s , and can t h e r e f o r e be d i s t i n g u i s h e d f rom the l a r g e r mechanized boats wh ich d e l i v e r H i l s a of mar ine o r i g i n . 4 . 2 Re lat ions of l a n d i n g s to e f fo r t 4 . 2 . 1 Method of es t imat ing e f fo r t A s s u m i n g the amount of H i l sa t r a n s h i p p e d is a f a i r i n d i c a -t i o n of the actua l amount of f i s h c a u g h t (as is d i s c u s s e d l a t e r ) , the c h a n g e s in f r e s h w a t e r ca tch cou ld be due e i t h e r to c h a n g e s in a v a i l a b i l i t y of H i l sa or to c h a n g e s in f i s h i n g i n t e n s i t y . S i n c e t h e r e were no data on f i s h i n g i n t e n s i t y , I c o n d u c t e d a r e g u l a r f i s h i n g boat count fo r two c o n s e c u t i v e d a y s i n e v e r y f o r t n i g h t o v e r an 8 -month p e r i o d , i n o r d e r to est imate the number of boats d u r i n g the h i g h and low t ide f i s h i n g o p e r a -t ion on a p a r t i c u l a r segment of the Meghma R i v e r [ f rom C h a n d p u r 33 to N i lkamal f i s h i n g g r o u n d ( F i g . 1 ) ] . T h i s 10-mile s t r e t c h of the Meghna R i v e r p r o v i d e s a r e g u l a r s o u r c e of H i l s a s u p p l y to the C h a n d p u r l a n d i n g c e n t r e . T h u s , f i s h i n g i n t e n s i t y (boat c o u n t s ) and l a n d i n g s can be compared f rom t h i s s t r e t c h of r i v e r . H i l s a f i s h i n g boat c o u n t s s t a r t e d in J a n u a r y 1984 and c o n -t i n u e d u n t i l August 1984 in t h i s se lected segment of the Meghna R i v e r . On the f i r s t week of e v e r y month I and a f ie ld a s s i s -t a n t counted the number of boats engaged in H i l s a f i s h i n g f rom C h a n d p u r to N i lkamal b y a schedu led f e r r y . T h e f leet c o n s i s t e d of small b o a t s , medium boats and la rge b o a t s , as d e s c r i b e d in the f o r e g o i n g s e c t i o n . While go ing to N i lkamal b y the f e r r y d u r i n g h igh t i d e , I r e c o r d e d the number of f i s h i n g boats a long the near s ide of the r i v e r b y naked e y e , and boats a long the o t h e r s ide was counted t h r o u g h a b i n o c u l a r by an a s s i s t a n t . T h e next d a y , whi le r e t u r n i n g f rom Ni lkamal to C h a n d p u r by the s c h e d u l e d f e r r y d u r i n g low t i d e , the c o u n t s were repeated ( T a b l e 1 ) . In o r d e r to combine the e f f o r t of the t h r e e s izes of f i s h i n g boats into a s ing le i n d e x , each size was ass igned a weight a c c o r d i n g to the est imated a v e r a g e da i l y ca tch p e r boat . Smal l boats were est imated to take 1 k g / d a y on the bas is of p e r s o n a l o b s e r v a t i o n and d i s c u s s i o n s wi th f i s h e r m e n . Medium boats were est imated to t a k e 6 .33 k g / d a y , and la rge boats 17 .6 k g / d a y , t h e la t te r two f i g u r e s based on r e c o r d s of monthly ca tch/boat ove r a t e n - m o n t h pe r iod ( Tab le 2 ) . T h u s , the tota l i n t e n s i t y of f i s h i n g e f fo r t fo r each time was ca lcu la ted by TABLE 1. Number of different types of Hi 1sa fishing gear/day that were in operation during different months of the year, the Meghna River between Chandpur and Nilkamal from January 1984 to August 1984. The values reported are the mean and their standard errors. Each monthly mean is based on four observations. MONTH High Tide Low Tide Mean of High and Low Tide Counts Clap Net Dora Chandi Clap net Dora Chandi Clap Net Dora Chandi January 22.0 347.0 56.0 15.0 211.0 22.5 18.5+2.2 279.0+43.4 39. 3+9.9 February 16.5 344.0 76.5 14.0 167.5 22.5 15.3+2.3 255.8+54.1 49.5+ 17.1 March 12.5 300.0 72.0 9.0 279.0 85.0 10.8+1.1 289.5+28.6 78.5+ 13.1 April 45.5 223.0 404.0 37.5 167.0 94.0 41.5+10.4 195.0+30.6 249.0+ 93.1 May 35.5 178.5 191.0 16.5 174.5 123.0 26.0+6. 5 176.5+17.5 157.0+ 20.2 June 60.a 124.0 330.5 52.0 102.5 178.5 56.0+8.0 113.3+23.0 254.5+ 44.7 July 299.5 62.5 297.5 97.0 50.0 123.0 198.3+58.8 56.3+3.8 210.3+ 51.9 August 101.0 31.5 186.0 50.0 29.0 127.0 75.5+15.9 30.2+3.5 156.5+ 24.6 35 TABLE 2. Mean catch/day of Hilsa (kg) by two types of gear in different mouths in the river stretch from Chandpur to Nilkamal of the Meghna River (after Bangladesh Fisheries Resources Survey System, 1984). Month Chandi Dora May 1982 6.15 4.10 May 1982 10.03 6.12 September 1982 33.82 9.40 October 1982 25.90 6.33 January 1983 10.50 6.00 February 1983 7.75 3.25 April 1983 7.67 3.25 July 1983 13.64 7.35 October 1983 28.67 8.50 December 1983 31.67 9.00 Mean 17.58 kg/day 6.33 kg/day 36 a d d i n g together the c o u n t s of each boat t y p e each mul t ip l ied by t h e w e i g h t i n g f a c t o r f o r that t y p e ( Tab le 3 ) . 4 . 2 . 2 Method of es t imat ing l a n d i n g s T h e number of b a s k e t s of r i v e r i n e H i l s a landed at C h a n d p u r l a n d i n g c e n t r e d u r i n g the l a n d i n g time ( f rom 6 a . m . to 8 p . m . ) were counted b y two f ie ld ass is tant and by me fo r each day of f i s h i n g boat c o u n t s ( F i g . 6 ) . T h e c a t c h is usua l l y of f loaded b y s t a n d a r d s ize b a s k e t s and the weight of f i s h per basket is k n o w n . T h e da i l y total weight of r i v e r i n e H i l s a o f f - l o a d e d f rom co l lec tor ' s/ f i shermen 's boats wh ich had been o p e r a t i n g in t h e r i v e r was t h e r e f o r e est imated by basket c o u n t s supplemented b y weight data when a v a i l a b l e . Est imates may have been s l i g h t l y low due to a few f i s h r e a c h i n g the l a n d i n g c e n t r e a f t e r 8 p . m . , but the e r r o r is s l i g h t . F r e s h w a t e r H i l s a l a n d i n g data obta ined in t h i s way were also c h e c k e d against t r a n s - s h i p m e n t d a t a . 4 . 2 . 3 Mar ine v e r s u s f r e s h w a t e r l a n d i n g s A n attempt was made fo r the f i r s t time to f i n d out the ra t io between r i v e r i n e o r f r e s h w a t e r v e r s u s mar ine ca tches d e l i v e r e d to C h a n d p u r l a n d i n g c e n t r e . T h e method of es t imat ing mar ine H i l sa was the same as fo r H i l s a o r i g i n a t i n g f rom f r e s h -w a t e r , except that mar ine H i l s a were those b r o u g h t u p s t r e a m to t h e l a n d i n g c e n t r e b y mechanized b o a t s . It was o b s e r v e d that 2319 metr ic t o n n e s , i . e . about 54% of the total H i l s a , was f r e s h w a t e r , whi le 1999 metr ic t o n n e s ; i . e . , 46% were c o n t r i -37 TABLE 3. Monthly freshwater landings of Hilsa and fishing intensity (cal-culated as described in text) for the River Meghna at Chandpur during the period of January to August 1984. Monthly freshwater landings are calculated from eight daily observations. Regression s tat i s t ics shown below. Month Freshwater Landings (metric tonnes) Fishing Intensity January 57. 7+.1 2475.4 February 57.2+.3 2503.0 • March 220.7+1.8 3223.4 April 203.9+1.4 5653.7 May 231.8+1.5 3904.6 June 506.8+2.2 5248.6 July 434.6+2.2 4251.7 August 606.1+1.9 3018.6 Y = 59.5 + .06 * Fishing intensity r 2 = .1286 P = .61 38 FIGURE 6. HiIsa offloaded by standard basket at Chandpur landing centre . 3 9 40 b u t e d by the mar ine H i l s a ( Tab le 4 ) . On ly the r i v e r i n e ca tches at C h a n d p u r are c o n s i d e r e d in the fo l lowing c a l c u l a t i o n s . 4 . 2 . 4 R e s u l t s and d i s c u s s i o n T h e r e g r e s s i o n was ca lcu la ted of month ly l a n d i n g s on f i s h i n g i n t e n s i t y ( Tab le 3 ) . F i s h i n g i n t e n s i t y accounted fo r o n l y 12% of the va r ia t ion in f r e s h w a t e r H i l s a l a n d i n g s at C h a n d p u r , and the r e g r e s s i o n was not s i g n i f i c a n t . T h e month of h i g h e s t f i s h i n g i n t e n s i t y (5654 in A p r i l ) p r o d u c e d a moderate ly low l a n d i n g (204 t o n n e s ) ; the h ighes t l a n d i n g s (606 tonnes in A u g u s t ) were p r o d u c e d by only moderate f i s h i n g i n t e n s i t y (3018) . E v i d e n t l y , v a r i a t i o n s in l a n d i n g s are not cont ro l led b y v a r i a t i o n s in e f f o r t , among the monthly samples at C h a n d p u r . T h e only o ther ava i lab le r e c o r d s on l a n d i n g s and e f fo r t were f rom G o d a v a r i R i v e r on the east coast of Ind ia d u r i n g the monsoon months of the y e a r s 1963-1969 ( R a j y a l a k s h m i et_ a l . 1 9 7 2 ) . R e g r e s s i o n ca lcu la t ions showed that here again f i s h i n g e f f o r t accounted for only 14.6% of the var ia t ion in y i e l d of t h e G o d a v e r i R i v e r , and the r e g r e s s i o n was not s i g n i f i c a n t ( T a b l e 5 ) . One f u r t h e r ques t ion a r i s e s : to what ex ten t are t r a n s -sh ipment r e c o r d s (wh ich are u s u a l l y the on ly h i s t o r i c a l data ava i lab le ) a re l iab le ind i ca t ion of ac tua l l a n d i n g s . S ince both sets of data were ava i lab le f rom C h a n d p u r fo r the months of J a n u a r y to A u g u s t 1984 (Tab le 4 ) , t h e i r c o r r e l a t i o n was c a l c u l a t e d . Month ly t r a n s - s h i p m e n t s were v e r y h i g h l y c o r r e -41 TABLE 4. Rail trans-shipment records, and observed riverine and marine Hi 1sa landings in metric tonnes for the Meghna River at Chandpur from January 1984 to August 1984. The values reported are the mean and their standard errors. Each monthly mean of freshwater and marine water Hilsa is based on eight observations and trans-shipment on 30/31 days of observation. Month Rail Trans-shipment Ri veri ne Landing Marine Water Landing Observed Total Landing (Riverine o marine water landings) January 108.4 57.7+.1 124.7+2.2 182.4 February 232.2 57.2+.3 167.2+1.1 224.4 March 397.9 220.7+1.8 76.9+1.1 297.6 April 427.1 203.9+1.4 31.6+0.7 235.5 May 360.8 231.8+1.5 25.1+0. 5 256.9 June 918.4 506.8+2.2 372.8+4.3 879.6 July 1081.6 434.6+2.2 261.5+1.5 696.1 August 2337.3 606.1+1.9 939.7+7.3 1545.8 TOTAL 5863.8 2318.8 1999.5 4318.3 42 TABLE 5. Estimated y ie ld (y-j) in tonnes and effort in thousands of man-hours (g-j) of Hi Isa i i i sha in Godavari River by dr i f t gi l lnets in the monsoon months of the years 1963-69 (after Rajyalakshmi et a l . 1972). Regression s tat i s t ics shown below. Year 9 i 1963 7.5 63.7 1964 43.9 306.2 1965 36.3 105.2 1966 15.0 165.3 1967 9.6 221.7 1968 14.3 226.7 1969 18.9 198.0 8.73 + .06 * Effort .1465 .60 Y = 2 r = P = 43 la ted with o b s e r v e d f r e s h w a t e r H i l sa l a n d i n g s (p=.003) v a r i a b i -l i t y in the fo rmer accounted fo r about 80% of the va r ia t ion in t h e la t te r ( F i g . 7 ) . T h e r e f o r e , c h a n g e s in e i the r can be t a k e n as a reasonable i n d i c a t o r of c h a n g e s in H i l s a ca tch at C h a n d p u r . It has been assumed that the same c lose re la t ionsh ip was t r u e between t r a n s - s h i p m e n t s and l a n d i n g s at G o a l u n d o . A s the f o r e g o i n g sect ion has e s t a b l i s h e d that t r a n s - s h i p -ments (or l a n d i n g s ) seem to v a r y p r i m a r i l y a c c o r d i n g to a b u n d -ance of f i s h , not to e f f o r t , I am now go ing to examine monthly c h a n g e s in sh ipments and t r y to re late them to env i ronmenta l f a c t o r s . 4 . 3 R e l a t i o n s h i p of l a n d i n g s to e n v i r o n m e n t a l f a c t o r s 4 . 3 . 1 S o u r c e s of data R e c o r d s of ca tch s t a t i s t i c s of any f i s h e r y are v i ta l fo r i t s j ud ic ious exp lo i ta t ion and d e v e l o p m e n t . T h e r e are many d i f f i c u l t i e s in the way of co l lect ion of s u c h s t a t i s t i c s r e l a t i n g to the H i l s a f i s h e r i e s of B a n g l a d e s h r i v e r s . T h e s e d i f f i c u l t i e s i n c l u d e the v e r y d i f f u s e and sca t te red na tu re of t h e i n d u s t r y , lack of f i x e d l a n d i n g c e n t r e s , and d i v e r s e t r a d e p r a c t i c e s . F u r t h e r , co l lec t ion of H i l s a l a n d i n g data is compl icated by the t r a d i t i o n a l n a t u r e of the i n d u s t r y in that n e i t h e r f i she rmen nor government agenc ies keep deta i led r e c o r d s of l a n d i n g s . F o r these reasons i n d i r e c t methods of est imat ion of l a n d i n g s must be employed such as t r a n s - s h i p m e n t r e c o r d s ( i . e . , sh ipment of H i l sa by r a i l w a y ) . 44 FIGURE 7. Relationship between riverine Hilsa landings with r a i l shipment record of Hi 1sa in the Meghna River at Chandpur. 2 5 0 0 n Y = - 1 9 2 . 2 +3.2*riverine hilsa landings 46 Of al l the t r a n s - s h i p m e n t r e c o r d s a v a i l a b l e , those of the B a n g l a d e s h Rai lway are most re l iab le and the most u s e f u l fo r a n a l y s i s of seasonal and annua l va r ia t ion in l a n d i n g s . T h e a d v a n t a g e of t h i s source of r e c o r d s l ies in the deta i l w i th w h i c h they have been kept ( D u n n 1982, Melv in 1984) . Fo r i n s t a n c e , da i l y r e c o r d s of H i l sa t r a n s - s h i p m e n t at Goalundo have been kept s ince 1967. T h i s sometimes al lows detect ion of o b v i o u s e r r o r s by c o m p a r i n g day to day w e i g h t s . The second and most s i g n i f i c a n t advantage is that r e c o r d s are kept of w e i g h t , n u m b e r of p a c k a g e s , and t r a n s - s h i p m e n t c h a r g e s . If an e r r o r o c c u r s in the w e i g h t , an approx imat ion can be made f rom e i t h e r of the o ther var iab les and the e r r o r can be c o r r e c t e d . U s i n g t h i s s t r a t e g y has led me to u n c o v e r s e v e r a l e r r o r s in Dunn 's (1982) ca tch i n d e x . Dunn 's index documented l o n g - t e r m t r e n d s i n the H i l sa l a n d i n g s . A t Goalundo on the u p p e r reaches of the r i v e r Padma the number of p a c k a g e s s h i p p e d was e r r o n e o u s l y p r e s e n t e d as the w e i g h t . T h i s e r r o r has made l a n d i n g s appear r e l a t i v e l y s table between 1976-1981 whereas l a n d i n g s have a c t u a l l y been i n c r e a s i n g . T h e r e are however some prob lems wi th t r a n s - s h i p m e n t r e c o r d s as a measure of l a n d i n g s . F o r i n s t a n c e , the weight i n c l u d e s p a c k i n g ice wh ich is used in va r iab le quant i t i es a c c o r d i n g to s u p p l y and d i s tance to m a r k e t . A l s o , a small p o r -t ion of H i l s a landed which are consumed by the local people has not been t a k e n into a c c o u n t ; h o w e v e r , consumpt ion b y f i shermen i s small because of the h i g h cash value of H i l s a wh ich may be 47 almost t h e i r on ly source of income. M o r e o v e r , the use of c e r t a i n ra i lway s ta t ions f o r sh ipment of H i l sa have v a r i e d o v e r t h e y e a r s fo r both economic and n a t u r a l reasons ( c losure of l a n d i n g c e n t r e s due to s i l t a t i o n ) . F o r i n s t a n c e , the r i s i n g cost of ra i l t r a n s - s h i p m e n t , and improved road c o n s t r u c t i o n , have r e s u l t e d in r e l a t i v e l y g reate r t r a n s - s h i p m e n t of H i l s a by t r u c k s ince 1975. F r o m B a n g l a d e s h waters the on ly seasonal and i n t e r - a n n u a l r e c o r d s of r i v e r i n e H i l sa ca tch data are ava i lab le f rom the t r a n s - s h i p m e n t of the f i s h of Goalundo on the Padma r i v e r . S u b s e q u e n t to 1974, h o w e v e r , the t r a n s - s h i p m e n t data f rom t h i s s i te are not r e p r e s e n t a t i v e of r i v e r i n e H i l s a c a t c h . F i r s t l y , a f t e r 1974 t r a n s - s h i p m e n t s of H i l s a at Goa lundo have i n c l u d e d s i g n i f i c a n t but u n k n o w n p r o p o r t i o n s of both r i v e r i n e and mar ine c a t c h e s . S e c o n d l y , the impact of complet ion of the F a r a k k a B a r r a g e in 1975 on the s u b s e q u e n t H i l s a f i s h e r y of the lower Ganges is qu i te ev ident ( A b b a s 1982, B i l g r a m i and M u n s h i 1982) . H i l s a l a n d i n g s d e c l i n e d above the b a r r a g e in India a l though c a t c h e s of n o n - m i g r a t o r y spec ies d i d n o t , whi le the H i l s a f i s h e r y in India below the b a r r a g e has been s teady and ac tua l l y r e c o r d e d in 1981 a bumper c r o p t h r e e t imes the a v e r a g e c a t c h of t h e e a r l i e r y e a r s s ince c o n s t r u c t i o n ( A n o n y m o u s 1984b) . T h i r d l y , s u b s e q u e n t to 1974 these r e c o r d s ref lect the s tead i l y d e c r e a s i n g impor tance of ra i lway f r e i g h t as the nat ional road t r a n s p o r t network improved ( D u n n 1982) . I have used Goalundo t r a n s - s h i p m e n t data on ly f rom 1967 to 1974 (Tab le 6) because of TABLE 6. Monthly trans-shipment of Hilsa through Goalundo Railway station (1967-74) in metric tonnes. Year/Month Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Total 1967 243.0 507.0 402.0 188.0 131.0 124.0 199.0 159.0 334.0 229.0 190.0 196.0 2875.0 1968 107.0 102.0 143.0 223.0 282.0 257.0 131.0 132.0 205.0 183.0 166.0 412.0 2323.0 1969 239.0 529.0 734.0 718.0 843.0 1524.0 1006.0 1128.0 1652.0 410.0 207.0 419.0 9409.0 1970 471.0 489.0 1250.0 206.0 893.0 1406.0 380.0 269.0 240.0 124.0 93.0 268.0 6089.0 1971 NR1 NR NR NR NR NR NR NR NR NR NR NR NR 1972 30.0 26.0 22.0 22.0 35.0 257.0 255.0 9.0 30.0 90.0 103.0 42.0 921.0 1973 206.0 237.0 240.0 294.0 365.0 975.0 514.0 1269.0 6289.0 613.0 489.0 523.0 12014.0 1974 163.0 235.0 420.0 342.0 495.0 535.0 52.0 31.0 72.0 45.0 42.0 3.0 2435.0 NR = no record 49 t h e above r e a s o n s . A l l data on t r a n s - s h i p m e n t s f rom C h a n d p u r have been e x c l u d e d f rom y e a r - t o - y e a r c o m p a r i s o n s , because t h e y i n c l u d e a va r iab le but u n k n o w n p r o p o r t i o n of mar ine f i s h . It has also been n e c e s s a r y to e x c l u d e f rom ca lcu la t ions t h e H i l sa l a n d i n g s in B a n g l a d e s h d u r i n g the l i b e r a t i o n (March to December 1971) , because of seve re d i s r u p t i o n s in f i s h i n g e f f o r t . While f i s h i n g was d r a s t i c a l l y r e d u c e d in B a n g l a d e s h , f i s h e r m e n in the H o o g h l y - M a t t a h e s t u a r i n e sys tem of India h a r v e s t e d a bumper c r o p ( D u t t a et a l . 1973) . The seasonal p a t t e r n of l a n d i n g s in the e s t u a r i n e sys tem was more or less s imi la r in al l y e a r s except March 1971 to F e b r u a r y 1972, when u n u s u a l l y h i g h l a n d i n g s were made in A u g u s t and September [ c o n -t r i b u t i n g 31% of the a n n u a l l a n d i n g s in 1971-72 as against on ly 2-7% in o ther y e a r s ( M i t r a and Ghosh 1 9 7 9 ) ] . C l e a r l y in t h i s i n s t a n c e , geograph ic s h i f t s in e f fo r t p r o d u c e d marked c h a n g e in d i s t r i b u t i o n of the c a t c h . R a i n f a l l and maximum ai r t e m p e r a t u r e data were co l lected f rom the B a n g l a d e s h Meteorology D e p a r t m e n t , whi le water l eve l and minimum d i s c h a r g e data were co l lected f rom the B a n g l a d e s h Water Development B o a r d , D h a k a . These data a re be l ieved to be r e l i a b l e . 4 . 3 . 2 R e l a t i o n s h i p of l a n d i n g s to r a i n f a l l Month ly H i l s a l a n d i n g s of the r i v e r Padma at Goalundo f rom 1967 to 1974 are shown in F i g . 8 a , a long wi th monthly ra in fa l l d a t a of F a r i d p u r (near G o a l u n d o ) . (Month ly ra in fa l l data of 50 FIGURE 8. Relationship of Hilsa landings in metric tonnes (MT) of the Padma River of the Ganges at Goalundo to ra infa l l of Faridpur (near Goalundo). 52 1974 are not complete . ) T h e month of September 1973 was the most p r o d u c t i v e (6289 metr ic t o n n e s ) , whi le the poorest c a t c h was in December 1974 (3 metr ic t o n n e s ) . T h e r e were major d i f f e r e n c e s between y e a r s in the p a t t e r n of l a n d i n g s , and also i n the p a t t e r n of r a i n f a l l , but no o b v i o u s r e l a t i o n s h i p between v a r i a t i o n s in the t w o . In t h r e e y e a r s , the l a n d i n g s showed two d i s t i n c t peaks ( J u n e and September in two y e a r s , J u n e and March i n o n e , and in o ther y e a r s on ly a s l i g h t peak in May or J u n e ) . In f o u r y e a r s , r a i n f a l l showed two d i s t i n c t p e a k s , and in the o t h e r y e a r s a s ing le p e a k , w i th peaks o c c u r r i n g in any month f rom May to A u g u s t . Peak l a n d i n g s cou ld o c c u r e i t h e r before o r a f t e r the month of peak r a i n f a l l . T h e on ly o t h e r set of data on H i l sa l a n d i n g s and ra in fa l l were those co l lec ted d u r i n g the p r e s e n t s t u d y f rom J a n u a r y to J u l y 1984. Month ly H i l sa l a n d i n g s of the Meghna R i v e r at C h a n d p u r f rom J a n u a r y to J u l y 1984 are shown in F i g . 8 b , a long w i th monthly r a i n f a l l da ta of C h a n d p u r . F rom a simple l i n e a r r e g r e s s i o n , r a i n f a l l accounted fo r about 67% of the va r ia t ion i n f r e s h w a t e r H i l s a l a n d i n g s , and the two were s i g n i f i c a n t l y p o s i t i v e l y c o r r e l a t e d (p < 0 . 0 3 ) , but the time se r ies is s h o r t . 4 . 3 . 3 R e l a t i o n s h i p of l a n d i n g s to mean water leve l Month l y H i l sa l a n d i n g s at Goalundo are shown in F i g . 9 , a long wi th monthly mean water leve l of the Padma at G o a l u n d o . T h e r e was much more r e g u l a r i t y between y e a r s in seasonal 53 FIGURE 8a. Relationship of freshwater Hilsa landings of the Meghna River at Chandpur to ra infa l l of Chandpur. 54 r -V) O z Q Z < < 8000-7000-6000 H 5000-4000-3000-2000-1000 ' 1 ' I / I / \ / I / I \ \ X 1400 1300 • 1200 • 1100 1000 • 900 | • 800 -I ,< 700 £ < r 600 500 400 300 200 100 ~ i — — i — r J A N F E B MAR APR i r MAY J U N J U L -O HILSA LANDINGS X -X RAINFALL 55 FIGURE 9. Relationship of Hilsa landings of the Padma River at Goalundo to mean water level of the Padma River at Goalundo. 56 57 p a t t e r n s of water leve l t h a n of r a i n f a l l . E v e r y y e a r , water l eve l was lowest in F e b r u a r y and rose to a h i g h in A u g u s t . H o w e v e r , as t h e r e were major d i f f e r e n c e s between y e a r s in H i l sa l a n d i n g s , as d e s c r i b e d a b o v e , t h e r e was no obv ious re la t ionsh ip between v a r i a t i o n s in water leve l and in l a n d i n g s . 4 . 3 . 4 R e l a t i o n s h i p of l a n d i n g s to minimum d i s c h a r g e Month ly H i l s a l a n d i n g s at Goalundo are shown in F i g . 10 a long with monthly minimum d i s c h a r g e of the Padma r i v e r at G o a l u n d o . Seasonal p a t t e r n s of d i s c h a r g e showed somewhat more v a r i a t i o n between y e a r s t h a n d i d water l e v e l s , wi th g reate r d i f f e r e n c e s in the rates of r i se and f a l l , but the peak a lways o c c u r r e d in e i t h e r A u g u s t o r S e p t e m b e r . A g a i n , t h e r e was no o b v i o u s re la t ionsh ip between v a r i a t i o n s in d i s c h a r g e and in l a n d i n g s . 4 . 3 . 5 R e l a t i o n s h i p of l a n d i n g s to maximum a i r t e m p e r a t u r e Water t e m p e r a t u r e data of the Padma r i v e r at Goalundo are not a v a i l a b l e , but a i r tempera tu re data are a v a i l a b l e . H o w e v e r , water t e m p e r a t u r e s were ava i lab le fo r 13 consecut i ve months fo r the Hooghly R i v e r of the G a n g e s , and also a i r t e m p e r a t u r e s at C a l c u t t a (near H o o g h l y ) . A h i g h l y s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n (p < 0.01) was f o u n d between a i r and water t e m p e r a t u r e ( A p p e n d i x T a b l e 2 ) . A s s u m i n g "that a i r t e m p e r a t u r e of F a r i d p u r (near Goalundo) s i m i l a r l y has a c lose assoc iat ion wi th water tempera tu re of Padma r i v e r at G o a l u n d o , I have p lot ted month ly H i l s a l a n d i n g s 58 FIGURE 10. Relationship of Hilsa landings of the Padma River at Goalundo to minimum discharge of the Padma River at Goalundo. 59 60 at Goalundo in F i g . 1 1 , a long wi th monthly maximum a i r t e m p e r a -t u r e of F a r i d p u r . It is o b s e r v e d that h ighest tempera tu res were r e c o r d e d in A p r i l o r M a y , and lowest t e m p e r a t u r e s d u r i n g D e c e m b e r , J a n u a r y and F e b r u a r y . V a r i a t i o n s f rom year to y e a r i n seasonal changes of tempera tu re are s l i g h t , and bear no o b v i o u s r e l a t i o n s h i p to those of l a n d i n g s . 4 . 3 . 6 D i s c u s s i o n " In fo rmat ion f rom the env i ronment rece i ved b y the s e n s o r y s y s t e m of a f i s h can act in two ways to af fect i ts m i g r a t o r y b e h a v i o u r . F i r s t l y , an e n v i r o n m e n t a l s t imulus s u c h as r a i n -f a l l , water c u r r e n t , t e m p e r a t u r e may a l ter f i s h o r ien ta t ion and t h e r e b y act as a " d i r e c t o r " of movement . S e c o n d l y , s u c h s t i m u -l u s may i n c r e a s e or decrease the i n t e n s i t y of movement , r e g a r d -less of o r i e n t a t i o n , and so se rve as a ' regu la to r ' of m i g r a -t i o n . " (Nor thcote 1984) . T h e e n v i r o n m e n t a l c o n t r o l of te leost r e p r o d u c t i v e c y c l e s has been s tud ied e x t e n s i v e l y (de V laming 1972) , i n c l u d i n g s e v e r a l f r e s h w a t e r spec ies in India ( S u n d a r a r a j 1981) , but l i t t l e of t h i s work has been d i r e c t e d to H i l s a i l i s h a . T h e c loses t re la t i ve whose s p a w n i n g r u n s have been s tud ied in deta i l is the A m e r i c a n shad A l o s a s a p i d i s s i m a (Legget t 1977) , i n wh ich t e m p e r a t u r e has been shown to be an important e n v i r o n -mental s t imu lus c o n t r o l l i n g r u n t i m i n g . In t r o p i c a l and s u b t r o p i c a l c l i m a t e s , monsoon ra ins and s u b s e q u e n t i n c r e a s e d st ream flow appear to t r i g g e r many 61 FIGURE 11. Relationship of HiIsa landings of the Padma River at Goalundo to maximum a i r temperature of Faridpur (near Goalundo). 63 b e h a v i o u r a l responses in f i s h . R e s e a r c h e r s sugges t that seasonal and/or annua l va r ia t ion in ca tch of r i v e r i n e H i l sa a r e , to some e x t e n t , t r i g g e r e d by seasonal and/or l o n g - t e r m e n v i r o n m e n t a l c h a n g e s . Data s u p p o r t i n g t h i s h y p o t h e s i s a r e , h o w e v e r , l a r g e l y c i r c u m s t a n t i a l . T h e r e seems to be no c lose assoc iat ion between the seasonal t iming of H i l sa l a n d i n g s and of r a i n f a l l in the r i v e r Padma at G o a l u n d o , o v e r the 7 - y e a r pe r iod e x a m i n e d . B o t h l a n d i n g s and r a i n f a l l may show e i the r two peaks o r one in a y e a r , and t h e r e is wi th no s u g g e s t i o n of c a u s a l re la t ionsh ip between t h e m . A b o u t the on ly commonality in al l y e a r s is that r a i n f a l l and l a n d i n g s are both low f rom November to J a n u a r y . While t h e r e was a c o r r e l a t i o n between ra in fa l l and l a n d i n g s at C h a n d p u r on the Meghna R i v e r as measured in the p r e s e n t c o n t e x t , on l y 7 months' data in one year were a v a i l -a b l e , d u r i n g most of wh ich time r a i n f a l l and l a n d i n g s were r i s i n g m o n t h l y . Much the same t r e n d appeared at Goalundo ( F i g . 8) fo r the same months in 1969. S i n c e the much more e x t e n s i v e data base fo r Goalundo demonst rates no s u c h c o r r e l a -t i o n in some y e a r s , the c o r r e l a t i o n d u r i n g the shor t se r ies fo r C h a n d p u r is p r o b a b l y f o r t u i t o u s . T h e reason that r a i n f a l l showed more e r r a t i c f l u c t u a t i o n s t h a n d id water leve l is that flow in the lower G a n g e s -B r a h m a p u t r a is determined by the summation of e v e n t s ( p r e c i p i -ta t ion p l u s snow-mel t ) t h r o u g h o u t the immense area of the w a t e r s h e d . Water leve l and d i s c h a r g e r e c o r d s were f a i r l y 64 r e g u l a r f rom y e a r to y e a r in t h e i r seasonal p a t t e r n . L a n d i n g s , w h i c h d i s p l a y e d s h a r p l y d i f f e r e n t p a t t e r n s f rom y e a r to y e a r , a re t h e r e f o r e e v i d e n t l y not t ied c lose ly to r i v e r f l o w . T h e o ther env i ronmenta l v a r i a b l e s t u d i e d , t e m p e r a t u r e , aga in showed a f a i r l y c o n s i s t e n t seasonal p a t t e r n f rom year to y e a r . S i n c e peak l a n d i n g s d i d n o t , it does not seem that t e m p e r a t u r e is r e s p o n s i b l e in any simple way fo r annua l d i f f e r e n c e s in r u n t i m i n g . T h e c o n c l u s i o n must be that seasonal v a r i a t i o n s in t iming of the l a n d i n g s of H i l s a do not seem to be d i r e c t l y a t t r i b u -tab le to any of the e n v i r o n m e n t a l v a r i a b l e s s t u d i e d ( r a i n f a l l , water l e v e l , d i s c h a r g e s , a i r t e m p e r a t u r e ) . L a n d i n g s a re a lways r e l a t i v e l y low in November to J a n u a r y , and t h i s w in te r season a lways e x p e r i e n c e s r e l a t i v e l y low r a i n f a l l , s t ream flow and t e m p e r a t u r e . B u t in o ther m o n t h s , l a n d i n g s in the Meghna R i v e r show an e r r a t i c b e h a v i o u r both w i th in and between y e a r s a p p a r e n t l y i n d e p e n d e n t of the local c o n d i t i o n s s t u d i e d . T h e s e v a r i a t i o n s in l a n d i n g s have been shown not to be due to v a r i a -t i o n s in f i s h i n g e f f o r t . P e r h a p s the s o u r c e s of var ia t ion l ie in the e s t u a r i n e o r mar ine c o n d i t i o n s a f f e c t i n g the t iming of e n t r y in to f r e s h w a t e r ; f l u c t u a t i o n s in numbers of f i s h a r r i v i n g at C h a n d p u r may p r i n c i p a l l y ref lect env i ronmenta l i n f l u e n c e s c o n s i d e r a b l y removed in time and d i s t a n c e f rom where the f i s h a r e l a n d e d . T h e p r e s e n c e in some y e a r s of two peaks of H i l sa r u n s s u g g e s t s that t h e r e may be two (or more) rac ia l l y d i s t i n c t 65 g r o u p s i n v o l v e d . P r e s e n c e of a monsoon r u n ( J u n e to October ) and a w in te r r u n (November to March) has been sugges ted in Ind ia (Motwani et a L 1957, N a i r 1958, P i l l ay 1958, P i l l ay and R o s a 1963) . In B a n g l a d e s h , Q u d d u s et_ a l . (1984a) be l ieved t h e r e are two t y p e s of H i l s a : t y p e " A " b road form r e p r e s e n t a -t i v e of monsoon s p a w n i n g , and t y p e " B " s l e n d e r form r e p r e s e n t a -t i v e of w i n t e r s p a w n i n g . On the o ther h a n d , in G o d a v a r i R i v e r on ly a s ing le wave of migrat ion has been o b s e r v e d ( June to Oc tober ) by C h a c k o and Ganapat i (1949) (as is ev ident also in c e r t a i n y e a r s at G o a l u n d o ) . If t h e r e are indeed more t h a n one race of H i l sa r e a c h i n g Meghna R i v e r , it may be n e c e s s a r y to f i r s t d i s t i n g u i s h between them before a t t r i b u t i n g f l u c t u a t i o n s i n t h e i r t iming to p a r t i c u l a r e n v i r o n m e n t a l f a c t o r s . P r e v i o u s o b s e r v e r s of f a c t o r s c o n t r o l l i n g u p s t r e a m move -ment of H i l s a p r o v i d e c o n f l i c t i n g i n t e r p r e t a t i o n s . Hora and N a i r (1940) s u g g e s t e d that the ups t ream movement of H i l sa was l a r g e l y dependent on two main f a c t o r s ; v i z . , monsoon and the s tate of s e x u a l m a t u r i t y . T h e fact that mature H i l sa ascend t h e r i v e r d u r i n g the w i n t e r s e a s o n , when water leve ls are l o w , s u g g e s t s however that f lood c o n d i t i o n s are not n e c e s s a r y for i n d u c i n g the f i s h to move u p s t r e a m . In c o n t r a s t , Day (1873) o b s e r v e d in the w in te r that a secondary migrat ion of H i l s a o c c u r s in the Indus and I r rawady R i v e r s and is i n d u c e d by minor f loods caused by the melt ing of snow in the u p p e r r e a c h e s . H o w e v e r , K u l k a r n i (1951) o b s e r v e d that the summer migrat ion of H i l s a in the N a r b a d a R i v e r cannot be e x p l a i n e d by any s u c h 66 s e c o n d a r y f l o o d i n g . Islam and Ta lbot (1968) o b s e r v e d that i n c r e a s e d st ream flow does not appear to be a s t imulus that a t t r a c t s H i l s a , a l though the peak of the r u n does o c c u r d u r i n g peak f l o w s . On the o t h e r h a n d , Jones and S u j a n s i n g h a n i (1951) i n d i -ca ted a d i rec t c o r r e l a t i o n between f lood water leve ls and H i l sa l a n d i n g s in C h i l k a lake and the Mahanadi R i v e r in O r i s s a . T h e y a lso su gges t that o ther h y d r o l o g i c a l f a c t o r s ( i . e . , low s a l i n i t y and h i g h e r temperatu re ) i n f l u e n c e the ups t ream m i g r a -t i o n of adul t H i l s a . R a m a k r i s h n a i a h (1972) , h o w e v e r , f o u n d no d e s c e r n i b l e t r e n d between water f low and f i s h e r y l a n d i n g s . In c o n t r a s t , Ganapat i (1973) assoc iated the reduced migrat ions of H i l s a up South Indian r i v e r s wi th the lack of h i g h d i s c h a r g e s to the sea caused b y dams or i r r i g a t i o n d i v e r s i o n s . T h e g e n e r a l r i se in tempera tu re in the r i v e r s which o c c u r s d u r i n g the la t te r pa r t of the w in ter when H i l s a mig ra t ions are u n d e r w a y has been s u g g e s t e d as a fac to r c o n t r i b u t i n g to i n i t i a -t i o n of the r u n ( Jones 1957, Kyaw 1953) . In v e r y genera l t e r m s , t h i s is c o n s i s t e n t wi th the p resent d a t a , in that each y e a r it is on ly a f te r the s ta r t of r i s e in tempera tu re in F e b r u a r y that l a n d i n g s may s ta r t to i n c r e a s e . T e m p e r a t u r e r i se may be the t r i g g e r wh ich i n d u c e s the f i r s t movement into the r i v e r mouth from the o c e a n , but ne i ther it nor the o ther e n v i r o n m e n t a l f a c t o r s examined can as yet be i n v o k e d to e x p l a i n t h e s u b s e q u e n t l a r g e monthly f l u c t u a t i o n s in f i s h r e a c h i n g the u p s t r e a m f i s h e r y . 67 5 . ANNUAL VARIATIONS IN Hilsa IN THE PADMA AND MEGHNA RIVERS OF BANGLADESH AND IN THE INDUS RIVER OF PAKISTAN In addition to seasonal variations in Hilsa, the total annual landings may vary considerably from year to year. The purpose of this part of the study was to document levels of variation of landings betwen years and to try to uncover causes of such variation. Although precise and comparable spatial and temporal data are not available, it appears that Bangladesh waters contribute about 150,000 metric tonnes (mt) of Hilsa (Melvin 1984). This total may include up to about 50,000 mt realized by the mechanized gill netters operating on the sea front (Raja 1984). In comparison, India contributes about 25,000 mt, Burma about 3,000-4,000 mt (Druzhinin 1970), and Pakistan about 7,000-8000 mt. Data suitable for analysis were available only from Bangladesh waters and from the Indus River. 5.1 Sources of data For the river Padma at Goalundo the sources, methods and time periods of data collection were outlined in the foregoing chapter. Landings of Hilsa from 1967 to 1974 of the Padma River at Goalundo, with rainfall and mean air temperature of Faridpur from 1962 to 1974, are shown in Table 7. Landings of Hilsa from 1937-1940 of the Meghna River with rainfall from 1933-1940 are shown in Table 8. For the Indus River I collected Hilsa catch data of 1968 to 1982 from the FAO Yearbook of Fishery Statistics - Catches and Landings. The rainfall and mean air temperature of Hyderabad which represents the rainfall and water temperature of Indus were collected from 68 TABLE 7. Landings of Hilsa i l i sha from 1967 to 1974 of the Padma River at Goalundo, with ra infa l l and mean a ir temperature of Faridpur from 1962 to 1974. Year Landings (mt) Rain (mm) Mean A i r Temp. (°C) 1961 - 1892 24.73 1962 - 1615 24.72 1963 - 1676 23.33 1964 - 2045 22.22 1965 - 2007 25.28 1966 - 1519 25.28 1967 2875 1246 25.00 1968 2323 1762 24.72 1969 9409 1526 25.00 1970 6089 2220 25.28 1971 - 1365 24.17 1972 921 1706 24.72 1973 12014 2918 25.28 1974 2435 2920 23.89 TABLE 8. Annual landings of Hilsa and rainfal l at Chandpur during the period 1933-1940. Year Landings (mt) Rain f a l l (mm) 1933 - 2142 1934 - 2073 1935 - 1494 1936 - 2224 1937 (456.78) 1736 1938 298.55 1907 1939 975.97 2204 1940 826.02 1791 70 Monthly Climatic Data for the World and 25 Years of Pakistan in Statistics. Landings of Hilsa of the Indus, rainfall and mean air temperature are shown in Table 9. These data are believed to be reliable. 5.2 Results 5.2.1 Relationship of landings to rainfall in the Padma River of the Ganges at Goalundo in Bangladesh I calculated a simple linear regression of the landings of Goalundo with rainfall over different lag periods of from 1 to 6 years (Table 10) for the years 1967-1974 using MISP (Hilborn 1980). A two year lag in rainfall is significant (p<0.05) with negative slope, and variability of rainfall accounted for 57.6% of the variation in landings at Goalundo (Fig. 12). The only other regression verging on significance was a positive regres-sion for the 5-year lag (p=0.0812). An interesting record which indirectly supports a negative relationship between Hilsa catch and rainfall two years earlier is the record of packing ice use. Before the Bengal was parti-tioned into East and West there was unrestricted trade between the two Bengals. Further, in view of the high demand for fish in the cities of Calcutta and Howrah and their suburbs, most of the Hilsa catches were preserved in ice and dispatched to West Bengal. The quantity of ice required to pack a unit weight of fish varies from season to season. In summer more ice is used than in winter. On an average it is observed that a bundle of TABLE 9. Catch of Hilsa i l i sha from 1968 to 1982 of the Indus River, ra infa l l and mean a ir temperature of Hyderabad from 1962 to 1982. Year Catch ( i n mt) Ra i n f a l l ( i n mm) Mean A i r Temp. (°C) 1962 - 394 27.46 1963 - 65 28.13 1964 - 387 27.11 1965 - - -1966 - 79 . 28.38 1967 - 348 27.23 1968 2,500 22 27.43 1969 2,900 17 28.19 1970 12,700 271 27.92 1971 11,100 56 28.05 1972 10,828 27 27.65 1973 11,795 49 27.75 1974 9,098 22 27.75 1975 9,474 145 27.55 1976 9,545 335 27.50 1977 9,129 268 28.40 1978 4,813 416 27.55 1979 9,036 153 27.80 1980 4,427 119 28.20 1981 3,923 117 28.10 1982 6,032 54 27.65 72 TABLE 10. Regressions of Hilsa landings from 1967 to 1974 of the Padma River at Goalundo, with ra infa l l for different lag periods. Lag Period (Year) F Total DF Probability 2 r Slope Intercept 0 0.63 6 .5358 .1134 2.11 839.42 1 0.00 6 .9897 .0000 - 0.02 5201.40 2 6.77 6 .0474* .5755 - 9.15 20612.13 3 0.32 6 .5947 .0616 2.73 498.53 4 0.88 6 .6080 .1507 - 5.94 15977.29 5 4.69 6 .0812 .4845 10.47 -12622.89 6 0.48 6 .5292 .1075 - 5.49 14562.13 73 FIGURE 12. Relationship of Hilsa landings of the Padma River at Goalundo with two-year lag in r a i n f a l l . 14000 - i TABLE 11. Rainfall of Faridpur during the period 1930-40. Year R a i n f a l l (mm) 1930 1954 1931 2179 1932 -1933 1987 1934 1813 1935 1415 1936 1977 1937 1691 1938 2148 1939 2225 1940 1507 TABLE 12. Output of ice (* bundles) in Rajbari (near Goalundo) Ice Factory (after Nayudu, 1939) . Month/Year 1935 1936 1937 1938 January 1,933 748 1,191 -February 3,130 3,277 3,313 -March 2,130 4,251 3,714 -April 2,229 2,028 4,235 3,020 May 2,164 3,297 9,469 8,970 June 5,347 3,208 5,989 9,496 July 4,923 2,739 2,555 5,569 August 3,988 2,710 3,111 2,915 September 3,255 2,928 4,015 2,957 October 1,530 2,934 3,255 1,704 November 1,859 2,250 1,683 -December 1,879 1,852 4,014 -Total 34,367 32,222 46,544 * The above figures are in bundles of ice , each containing 1 1/2 mounds approximately (one mound = 82.28 lbs.) 77 1.5 mounds of ice is used to pack about 2.5 mounds of HIisa. Even without converting the output of ice in terms of Hilsa weight, the figures should give a rough index of the trend in the Hilsa fishery in the Goalundo area of the Ganges. In 1935 the rainfall was very low, 1415 mm, (Table 11), while in 1937 (Table 12), the production of ice bundles were the maximum (46,544 bundles, Nayudu 1939), which also suggests that landings of Hilsa in the Padma river at Goalundo has a negative relationship with 2-year lag in rainfall. 5.2.2 Relationship of rainfall to maximum water level in the Padma River of the Ganges at Goalundo in Bangladesh In order to find to what extent water level is controlled by local rainfall, I calculated a simple linear regression of the rainfall of Faridpur (near Goalundo) with maximum water level of the Padma River at Goalundo for 1967 to 1974. The regression is significant (p<.02) with positive slope; and variability in rainfall accounted for 71% of the variation in maximum water level (Fig. 13). 5.2.3 Relationship of landings to rainfall in the Meghna River at Chandpur in Bangladesh Trans-shipment data of Hilsa at Chandpur of the Meghna River for the period of 1937-1940 suggests that landings have a negative relationship with 2-year lag in rainfall (Table 8). In 1936 there was a heavy rainfall (2224 mm) which was followed by a very low landings in 1938 (298.55 mt) at Chandpur; in 1937 78 FIGURE 13. Relationship of ra infa l l to maximum water level in the Padma River of the Ganges at Goalundo. 80 t h e r e was a low r a i n f a l l (1736 mm) fol lowed in 1939 b y a bumper H i l s a l a n d i n g s (975.97 m t ) . 5 . 2 . 4 R e l a t i o n s h i p of l a n d i n g s to ra in fa l l in the Indus R i v e r of P a k i s t a n From Indus r i v e r of P a k i s t a n I also ca lcu la ted simple l i n e a r r e g r e s s i o n of H i l sa l a n d i n g s wi th ra in fa l l ove r d i f f e r -ent lag p e r i o d s ( Tab le 13) for the y e a r s 1968 to 1982. From these ana l yses I again found that l a n d i n g s wi th 2 - y e a r lag in r a i n f a l l was s i g n i f i c a n t (p<0.05) w i th negat ive s lope and v a r i a b i l i t y of r a i n f a l l accounted fo r 28.7% of the va r ia t ion in l a n d i n g s at Indus R i v e r ( F i g . 1 4 ) . One o t h e r r e g r e s s s i o n was s i g n i f i c a n t (p<0.05) - a 4 - y e a r l a g , wi th negat ive s l o p e . 5 . 2 . 5 C o r r e l a t i o n s between the Ganges and the Indus H i l s a l a n d i n g s w i th a t w o - y e a r lag in r a i n f a l l A ques t ion comes to the mind w h e t h e r ca tch f l u c t u a t i o n s a re c o r r e l a t e d in the Ganges and in the Indus R i v e r . C o m p a r -able data are ava i lab le f o r on ly the y e a r s 1968, 1969, 1970, 1972, 1973 and 1974. C a t c h and r a i n f a l l , g i v e n p r e v i o u s l y f o r d i f f e r e n t l o c a l i t i e s , a re summarized in s impl i f ied form in T a b l e 14 . In genera l a n n u a l r a i n f a l l fo l lowed the same t r e n d s in the two r e g i o n s (except in 1969, when r a i n f a l l 2 - y e a r s e a r l i e r had been low in the Ganges and v e r y h i g h in the I n d u s ) . L a n d i n g s , on the o ther h a n d , d i d not : t r e n d s were oppos i te in t h r e e y e a r s (1969, 1972, and 1974) and were the same in the o ther t h r e e y e a r s . In 1969 when r a i n f a l l 2 - y e a r s e a r l i e r had been 81 TABLE 13. Regressions of Hilsa landings from 1968 to 1982 of the Indus River, with ra infa l l for different lag periods. Lag Period (Year) F Total DF Probability 2 r SI ope Intercept 0 0.20 14 .6606 .0156 3.32 7360.26 1 0.65 14 .5625 .0480 - 5.47 8683.66 2 5.23 14 .0377* .2869 -13.27 9878.62 3 0.31 13 .5923 .0253 - 3.56 8761.91 4 5.02 13 .0428* .2950 -11.34 10151.16 5 1.43 13 .2535 .1066 - 7.53 8597.42 6 0.24 13 .6333 .0220 3.16 7083.90 82 FIGURE 14. Relationship of HiIsa landings with two-year lag in ra infa l l in the Indus River. 14000 -i Y = 9878.6 - 13.3*RAIN 12000 H r = 0.29 C § 10000-P = 0.038 (/) 8000 O 6000-4000-2000-50 100 150 200 250 300 350 2 YEAR LAG ANNUAL RAINFALL (mm) 400 450 TABLE 14. Summary of landings of HiIsa, and of ra infa l l two years previously in the Ganges and in the Indus River. R i v e r 1968 1969 1970 1972 1973 1974 Landings Ganges very low very high high very low very high very low Indus very low very low very high very high very high very high Rainfall Ganges low low low very high very low low Indus low very high very low very high very low very low 85 different in the two regions, landins were also different in the two regions. Evidently annual variations of landings of Hilsa in the Ganges and in the Indus are not synchronous; they seem to be associated with environmental events which may vary indepen-dently in the two regions. 5.2.6 Relationship of landings to mean air temperature in the Padma River of the Ganges at Goalundo in Bangladesh I calculated a simple linear regression of the landing of Goalundo with mean air temperature (using data in Table 7) over different lag periods from 1 to 6 years (Table 15) for the years 1967 to 1974. Regression on mean air temperature 2-years earlier is significant (p=0.05) with negative slope; and variability of mean air temperature accounted for 56.2% of the variation in landings at Goalundo (Fig. 15). A multiple regression of landings with rainfall and temperature was calculated with a 2-year lag period. The regression was not significant (p=0.15), and variability of rainfall combined with temperature accounted for less of the variation (42%) than did rainfall alone. 5.2.7 Relationship of landings to mean air temperature in the Indus River of Pakistan I calculated a simple linear regression of the landings of Indus River with mean air temperature over different lag periods from 1968 to 1982 (Table 16). There was no lag period TABLE 15. Regressions of Hilsa landings from 1967 to 1974 of the Padma River of the Ganges at Goalundo with mean a ir temprature for different lag periods. Lag Period F Probability 2 r Slope 0 2.80 .1533 .3596 5239.67 1 0.05 .8197 .0105 -1105.73 2 6.42 *.0515 .5623 -7527.59 3 0.88 .6077 .1505 1443.43 4 1.26 .3117 .2024 1562.61 5 0.45 .5334 .0836 -1075.92 6 0.55 .5072 .1004 -1203.42 87 FIGURE 15. Relationship of HiIsa landings of the Padma River at Goalundo with two-year lag in mean a ir temperature of Faridpur (near Goalundo). H O O O - i Y = 192750.7 - 7527.6*TEMP 12000 H r = 0.56 £ 10000 8000 H 6000H 4000H 2000-P = 0.05 24 24.2 24.4 24.6 24.8 25 25.2 25. 2 YEAR LAG IN TEMPERATURE ( C) 89 TABLE 16. Regressions of Hilsa catch from 1968 to 1982 of the Indus River of Pakistan with mean a ir temperature for different lag periods. Lag Period F Probability r 2 Slope 0 0.05 0.81 0.00 -743.41 1 0.24 0.64 0.02 1381.35 2 0.12 0.73 0.00 911.55 3 2.36 0.15 0.16 -3641.89 4 0.95 0.65 0.07 2199.00 5 0.21 0.65 0.02 1053.96 6 0.06 0.80 0.01 -649.96 90 of air temperature which gave a significant regression. The 2-year lag period of air temperature, which had given a signi-ficant negative slope for the Goalundo data in the preceding section, was now significant but with a positive slope for the Indus River data. Multiple regression of landings with rain-fall and temperature also was non-significant. 5.3 Discussion Changes in environmental conditions may influence the spawning success of the Hilsa fishery from year to year. Dunn (1982) suggested that there was a correlation between landings and rainfall with a 5-year lag, and that this supported the contention that Hilsa first recruit to the fishery when they are 5 years old. Some errors are however, present in the data he used. After calculation of the modified data, as shown here no significant correlation was found between landings with 5-year lag in rainfall, and the hypothesis of Dunn (1982) is not supported by my analysis. Hora (1940), and Hora and Nair (1940), also postulated a five- year cycle in Hilsa landings, but his evidence was rather circumstantial. Day (1873) suggested that Hilsa may attain first maturity at the end of the first year, or at the beginning of second year. Day's (1873) hypothesis was supported by Jones and Menon (1951) based on their observations in the Hooghly River, Mahamadi River, and Chilka Lake. Jones and Menon (1951) reported that males become mature when they are 21.6-25.4 cm in length and 1 + in age. Females become mature in the second year when they are 26.7-30.5 cm long (Jones and Menon 1951). 91 Also, Pillay (1958) observed still smaller sizes in the Hooghly river at first maturity males at 16-17 cm and females at 19-20 cm in total length when Hilsa are both about 1 1/2 years old. De (1980) suggested that female Hilsa attained first maturity when they are at a size of 34.1 cm in the upper stretches of the Hooghly River. Raja (1984) reported female Hilsa attains first maturity at the size of 32 cm. As can be seen from the above, there is disagreement among researchers as to size at first maturity of Hilsa. This may be due in part to the lack of uniformity in the length measurement used (total, fork or standard length), and or ecological differences between different rivers studied. Although there is even less agreement on age at first maturity, the weight of observations suggest that Hilsa first recruit to the fishery well before 5 years of age, a view supported by the current research of M. Hossain (pers. comm.). From my analysis I suggest that abundance of adult Hilsa has a moder-ately strong negative correlation with rainfall two years previously. Mechanisms regulating this negative significant association between rainfall and landings (both in the Padma River and the Indus River) may be that Hilsa are 1 + year old when they are first recruited to the fishery and the survival of the spawn and fry are optimum when there is a very low rainfall of that year. On the other hand, heavy rainfall may wash out eggs and larvae and consequently after 2 years the catch is comparatively low. In Bangladesh waters, rainfall has been shown here to be positively correlated with water level (in Padma River at Goalundo, p=.05). My hypothesis is consistent with that of Wickett (1958) and Vernon (1958) who showed that the survival of spawn 92 and fry of pink and chum salmon is much less in years of severe floods. In the Indus River there was a significant negative regression of Hilsa landings with rainfall not only 2-years earlier but also 4-years earlier (Table 13). No such trend regarding the 4-year lag was evident in the Ganges (Table 15), where that regression was non-significant. A possible explanation is that extreme environmental conditions in one year may affect strength of a year-class so sharply as to be reflected 4 years later even in the return of the offspring of that year class. Such a 4 year regularity would be quickly dampened. There is no convincing evidence of a sustained "cycle" in any of the available data series on Hilsa landings. Although the negative correlations between landings and rainfall 2-years earlier are statistically significant (in each of two widely separated river systems), there is still a large residual variation in landings unaccounted for by rainfall. Considering the nature of the data and the possible complexity of the Hilsa life history, this resi-dual variation is not surprising for several reasons. Firstly, rainfall has been used as an index of river discharge, and while the two were shown to be significantly correlated at Goalundo, they are not tightly coupled. Only local rainfall was recorded, while river discharge may also be affected by weather condi-tions or snow melt farther upstream. Secondly, environmental factors other than river discharge are likely also to affect early survival. Some evidence of a negative correlation has been found between landings and temperature two years 93 e a r l i e r , but as this occurred only in data for the Ganges and not for the Indus, its implications are conjectural. T h i r d l y , although most fish may return two years after hatching, the commmercial landings probably include a mixture of more than one age, and possibly of more than one race with somewhat differernt life history patterns. F u r t h e r , it is not known whether some Hilsa may s u r v i v e spawning and return in subsequent years. For these and other reasons the dependency between landings and earlier rainfall cannot be expected to offer more than a rough means to forecast annual harvest. Nevertheless, even this possibility has not been detected until now. The other principal new observation regarding annual changes in Hilsa catch is that annual variations in landings are not necessarily synchronous in the Ganges and in the Indus Rivers. They seem to be associated with environmental events which may vary independently in the regions. Hilsa from the two river systems if they are anadromous presumably spend their sea-life in two separate marine areas (Bay of Bengal and the Arabian Sea). However, the negative association beween landings and rainfall two years earlier suggest that it is events d u r i n g the freshwater phases, rather than oceanographic conditions, which are dominant in determining year-class strength. On the other hand, the failure in the first section of this study to detect any clear relationship between short term seasonal changes in riverine landings and local environmental conditions suggest that the details of timing of entry of fish into river mouths may be controlled by events in the estuaries or the oceans. 94 6. CONCLUSIONS (1) Month ly v a r i a t i o n s in f i s h i n g e f fo r t at C h a n d p u r on R i v e r Meghna in B a n g l a d e s h , and annua l va r ia t ions in f i s h i n g e f fo r t in G o d a v a r i in I n d i a , were not s i g n i f i c a n t l y c o r r e l a t e d wi th H i l s a l a n d i n g s in e i ther p l a c e . V a r i a t i o n in l a n d i n g s p r o b a b l y depend p r i n c i p a l l y on changes in a b u n d a n c e of H i l s a r a t h e r t h a n on changes in e f f o r t . (2) Seasonal c h a n g e s i n r e c o r d e d r a i l sh ipments f rom C h a n d p u r showed a c lose pos i t i ve c o r r e l a t i o n wi th o b s e r v e d l a n d i n g s of r i v e r i n e H i l s a , a n d can t h e r e f o r e be used as an i n d i c a t o r of l a n d i n g s in y e a r s fo r w h i c h no d i r e c t o b s e r v a t i o n s are a v a i l a b l e . (3) H i s t o r i c a l e v e n t s wh ich may affect i n t e r p r e t a t i o n of ra i l sh ipment r e c o r d s i n c l u d e the i n f l u x of m a r i n e - c a u g h t H i l sa into r i v e r i n e l a n d i n g s i t e s wi th the advent of mechanized v e s s e l s , the sh i f t f rom ra i l to road t r a n s p o r t a t i o n of H i l sa between l a n d i n g s i tes and consumer c e n t r e s , c o n s t r u c t i o n of F a r a k k a B a r r a g e wh ich d i v e r t e d water f rom B a n g l a d e s h to Ind ian w a t e r s , and the d i s r u p t i o n of f i s h i n g in B a n g l a d e s h d u r i n g l i be ra t ion in 1971. (4) Seasonal t iming and i n t e n s i t y of H i l s a r u n s in the Ganges var ied m a r k e d l y f rom year to y e a r , and bore no e v i d e n t assoc iat ion wi th seasonal t iming of r a i n f a l l , mean water l e v e l , minimum d i s c h a r g e o r t e m p e r a t u r e . T h e only seasonal r e g u l a r i t y was that in al l y e a r s few f i s h were t a k e n i n w i n t e r months (November to J a n u a r y ) . 95 (5) Annual variations in Hilsa landings showed a significant negative correlation with local rainfall 2 years previously. This was true both in the Ganges River in Bangladesh and in the Indus River in Pakistan. (6) The mechanism regulating the negative association between landings and rainfall 2 years earlier may be that heavy rainfall may wash away eggs and larvae, and that Hilsa are 1 + years old when they are recruited to the fishery. (7) Annual landings sometimes vary in opposite directions in the Ganges and the Indus Rivers. In each region annual landings are dependent in part on rainfall 2-years earlier in that region. This dependency offers a means of rough forecast of annual harvest on the basis of previous rainfall data. 96 LITERATURE CITED A b b a s , B . M . 1982. The Ganges Waters D i s p u t e . 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A preliminary note on the spawning grounds and bionomics of the so-called Indian shad, Hilsa ilisha (Ham.) in the River Ganges. Rec. Indian Mus. 40:147-148. Hora, S.L. 1940. Life-history and wanderings of Hilsa in Bengal waters. J. Asiatic Soc. Beng. Sci. 6:93-112. Hora, S.L. 1942. Effects of dams on the migration of Hilsa. Curr. Sci. , Bangalore 11:470-471. 99 H o r a , S . L . and K . K . N a i r . 1940. F u r t h e r o b s e r v a t i o n s on the bionomics and f i s h e r y of the Indian S h a d , H i l s a i l i s h a (Ham.) in B e n g a l w a t e r s . R e c . Indian M u s . 4 2 : 3 5 - 5 0 . H o r n e l l , J . 1950. F i s h i n g In Many Waters . C a m b r i d g e U n i v e r s i t y P r e s s , L o n d o n . 207 p p . H o s s a i n , Z . and S . M . K . S u f i . 1962. B i o l o g i c a l and economic e f fec ts of b a r r a g e s on H i l sa i l i s h a (Ham.) and i t s f i s h e r i e s in the I n d u s . A g r i . P a k . 1 3 : 3 4 6 - 3 5 9 . I s l a m , B . N . and G . B . T a l b o t . 1968. F l u v i a l m i g r a t i o n , s p a w n i n g and f e c u n -d i t y of Indus R i v e r H i l s a , H i l s a i l i s h a . T r a n s . A m e r . F i s h . S o c . 9 7 : 3 5 0 - 3 5 5 . J o n e s , S . 1957. On the late w i n t e r and e a r l y s p r i n g migrat ion of the Ind ian s h a d , H i l s a i l i s h a ( H a m i l t o n ) , in the Ganget ic d e l t a . Ind ian J . F i s h . 4 : 3 0 4 - 1 4 . J o n e s , S . 1959. F i s h i n g methods f o r the Ind ian S h a d , H i l s a i l i s h a (Ham.) i n the Indian r e g i o n . Par t I. J . Bombay N a t . H i s t . S o c . 5 6 : 2 5 0 - 2 7 5 . J o n e s , S . and K . H . S u j a n s i n g a n i . 1951. The H i l s a f i s h e r y of the C h i l k a L a k e . J . Bombay N a t . H i s t . S o c . 5 0 : 2 6 4 - 2 8 0 . J o n e s , M S . and P . M . G . M e n o n . 1951. O b s e r v a t i o n s on the l i f e - h i s t o r y of the Ind ian S h a d , H i l s a i l i s h a ( H a m i l t o n ) . P r o c . 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O b s e r v a t i o n on the b io logy and f i s h e r y of H i l s a i l i s h a (Ham. ) of r i v e r G o d a v a r i . P r o c . I n d o - P a c i f . F i s h . C o u n . 1 0 : 3 7 - 6 1 . P i l l a y , S . R . K . V . R a o , and P . K . M a t h u r . 1962. P r e l i m i n a r y repor t on the t a g g i n g of h i l s a , H i l s a i l i s h a ( H a m . ) . P r o c . I n d o - P a c i f . F i s h . C o u n . 1 0 : 2 8 - 3 9 . P i l l a y , T . V . R . 1952. A p r e l i m i n a r y b iometr ic s t u d y of c e r t a i n popu la t ions of h i l s a , H i l sa i l i s h a ( H a m . ) . P r o c . I n d o - P a c i f . F i s h . C o u n . 4 : 1 8 1 - 1 9 4 . P i l l a y , T . V . R . 1954. Morpho log ica l and sero log ica l c h a r a c t e r s of the h i l s a , H i l sa i l i s h a (Ham.) wi th spec ia l re fe rence to rac ia l i n v e s t i g a -t i o n . J . A s i a t i c S o c . S c i . 2 0 : 6 9 - 7 4 . P i l l a y , T . V . R . 1955. 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S o u t h w e l l , T . and B . P r a s h a d . 1918. On h i l s a i n v e s t i g a t i o n in B e n g a l , B i h a r and O r i s s a . B u l l . D e p . F i s h . B e n g . 1 1 : 1 - 1 2 . S u n d a r a r a j , B . I . 1981. R e p r o d u c t i v e p h y s i o l o g y of teleost f i s h e s . A rev iew of p r e s e n t knowledge and needs f o r f u t u r e r e s e a r c h . F A O A q u a c u l t u r e Development and C o o r d i n a t i o n Programme A D C P / R E P / 8 1 / 1 6 . 82 p p . V e r n o n , E . H . 1958. A n examinat ion of f a c t o r s a f f e c t i n g the a b u n d a n c e of p i n k salmon in the F r a s e r R i v e r . A p r o g r e s s repor t p r e p a r e d f o r the In te rna t iona l Pac i f i c Salmon F i s h e r i e s C o m m i s s i o n . p p . 4 9 . New Westmins te r , B . C . , C a n a d a . W i c k e t t , W . P . 1958. Rev iew of c e r t a i n env i ronmenta l f a c t o r s a f f e c t i n g the p r o d u c t i o n of p i n k and chum sa lmon . J . F i s h . R e s . B d . C a n a d a 1 5 : 1 1 0 3 - 1 1 2 6 . 104 APPENDIX 105 APPENDIX TABLE 1. Development of a r t i f i c a l l y - f e r t i 1 i z e d eggs (after Kulkarni 1950). Time i n Hours After Development Features F e r t i l i z a t i o n Within 1/2 hour Blasto-disc is formed. Within 4 1/2 hours Segmentation of blasto-disc, forming a cap of ce l l s covering half of the yolk. After 8 1/2 hours Embryonic shield v i s ib le . After 12 hours Embryo is dist inct with head and free t a i l . A few myotomes v is ib le but the optic vericle is not discernible. After 15 hours Contrations of the embryo begin. After 18 hours Hatching takes place. 106 APPENDIX TABLE 2. Relationship between mean a ir temperature (°C) of Calcutta (near Hooghly area) with mean water temperature of Hooghly River of the Ganges. Month/Year A i r Temperature Water Temperature Sept. 1952 29.1 30.0 Oct. 1952 27.7 31.0 Nov. 1952 24.2 29.5 Dec. 1952 20.4 22.5 Jan. 1953 19.7 22.7 Feb. 1953 24.4 26.0 Mar. 1953 29.7 28.0 Apr. 1953 32.1 31.3 May 1953 31.9 33.0 June 1953 30.2 30.5 July 1953 29.4 31.5 Aug. 1953 29.3 30.5 Sept. 1953 29.1 31.2 

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