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Homing behaviour of an inter-tidal fish Oligocottus maculosus girard Khoo, Hong Woo 1971

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THE HOMING BEHAVIOUR OF AN INTER-TIDAL FISH OLIGOCOTTUS MACULOSUS ;GIRARD' by HONG WOO KHOO B. Sc. (Hons.), University of Singapore, 1965 M. Sc.; University of Singapore, 1967 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Zoology We accept t h i s thesis as conforming to the required standard The University of B r i t i s h Columbia January, 1971 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Br i t ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Z .e QV IC ^f/^j The University of Bri t ish Columbia Vancouver 8, Canada Date M /??/ TABLE OF CONTENTS PAGE ABSTRACT i LIST OF TABLES i v LIST OF FIGURES v i LIST OF PLATES v i i ACKNOWLEDGEMENTS v i i i GENERAL INTRODUCTION 1 GENERAL MATERIALS AND METHODS 5 HOME RANGE - Experiments 1-3 19 EVIDENCE OF HOMING IN O. MACULOSUS - Experiment 4 31 FACTORS AFFECTING HOMING PERFORMANCE - Experiments 5-17 40 Experiments 5. Rate of homing 41 6. E f f e c t of season on homing performance 42 7. E f f e c t of d i r e c t i o n on homing performance 48 8. E f f e c t of distance on homing performance 51 9. E f f e c t of 'experience' on homing performance 58 10. E f f e c t of sex and size on homing performance 63 11. Sensory impairment and mortality 66 12 . B i l a t e r a l v i s u a l and ol f a c t o r y impairment and homing performance 72 PAGE 13. Removal of pectoral and p e l v i c f i n s and homing performance 79 14. U n i l a t e r a l v i s u a l and ol f a c t o r y impairment and homing performance 80 15. Homing on cloudy nights 84 16. Homing to pools with destruction of the immediate environment 88 17. Discriminatory a b i l i t y of 0. maculosus to water from d i f f e r e n t sources 94 GENERAL DISCUSSION 113 SUMMARY 124 LITERATURE CITED 127 APPENDICES 130 i ABSTRACT The purpose of the study i s to find out how Oligocottus  maculosus homes and what mechanisms or sensory channels are involved i n the homing process. The species' home range was defined from pool f i d e l i t y and movement observations. Evid-ence was obtained to show that the f i s h homes when displaced to unfamiliar areas. The roles of season, distance and d i r e c t i o n of displacement as well as sex, size and experience of the f i s h i n homing were assessed. The roles of both v i s i o n and o l f a c t i o n and the related environmental cues were also investigated. Some f i s h showed s t r i c t f i d e l i t y to s p e c i f i c tide-pools while others moved from one pool to another but limited them-selves to a r e s t r i c t e d group of neighbouring pools. The range of movement seldom exceeded an area of about one hundred square feet which was defined as the maximum home range. Homing, i . e . s t r i v i n g to return to i t s home range instead of going to other equally habitable areas, was observed through-out the year; homing was most successful between March and August. This seasonal v a r i a t i o n was probably the r e s u l t of mortality owing to the seasonal sea conditions. i i In my study O. maculosus had been shown to home from as far as one thousand feet. A decrease i n homing returns with i n -creasing distances from home was observed. This was a t t r i -buted to the effects of wave action which decreased the chances of survival with increasing distances from home. Direction of displacement did not seem to aff e c t homing per-formance and no difference i n homing performance was observed between the sexes or among f i s h of d i f f e r e n t s i z e s . Fish which were shown to home at least once seemed to home better than naive f i s h though no further improvement i n homing was observed when the former were repeatedly displaced. There i s a strong in d i c a t i o n that there i s inherent v a r i a b i l i t y i n homing a b i l i t y , that some f i s h home better than others and that learning per se i s not important. Displacement experiments conducted with b l i n d and anosmic f i s h had shown that blind f i s h could home better than anosmic f i s h i n d i c a t i n g that o l f a c t i o n , not v i s i o n , i s more important i n homing. Studies on the a b i l i t y to home on cloudy nights, the a b i l i t y to discriminate sea water from d i f f e r e n t sources i n the laboratory and the a b i l i t y to return to pools with the im-mediate environment destroyed further indicated the importance of o l f a c t i o n i n the homing mechanism of 0. maculosus. i i i How the f i s h finds i t s way from the release point to i t s home range i s s t i l l not known with c e r t a i n t y . However, i t i s suggested that the f i s h homed by (i) following odour streams originating from i t s home area or ( i i ) an exploratory search process or ( i i i ) a combination of the two processes. I V LIST OF TABLES TABLE PAGE 1 Movement and f i d e l i t y to home pools i n (a) Study Site A (May 1968) (b) Study Site B (March-May 1969) 24 2 Movement of replaced f i s h within s i t e A using method (b) (29 May 1968) 26 3 Homing returns to home range and home pools from a distance. (a) Home range = A. (b) Home range = B. 35 4 Rate of homing 43 5 Seasonal f l u c t u a t i o n of homing 45 6 Homing performance from d i f f e r e n t directions 50 7 E f f e c t of distance on homing performance 53 8 Summary of the r e s u l t s of experiments conducted to study the e f f e c t of distance of displacement on homing performance (1968-1969) 54 9 Homing performance of 'naive' and 'experienced' f i s h 60 10 Homing performance of repeatedly displaced f i s h 62 11 Homing performance according to sex and size of the f i s h . Summary of displacement experi-ments conducted during 1969. 65 12 Homing performance according to sex and size of f i s h (Selected data from Table 11) 67 13 B i l a t e r a l v i s u a l and o l f a c t o r y impairment and mortality (a) Laboratory study (b) F i e l d study 69 V TABLE PAGE 14 Homing performance of b i l a t e r a l l y b l i n d , b i l a t e r a l l y anosmic and normal (control) f i s h during spring-summer and f a l l - w i n t e r from 100, 300 and 400 f t . 74 15 Results of the three factor G-test of independence on the r e s u l t s of table 14 (a) Homing x Season x Treatment for 0, 100, 300 and 400 f t . (b) Homing x Season x Distance for control, b l i n d , and anosmic f i s h 75 16 Homing performance of f i s h with pelvics (PELV) and pectorals (PECT) removed 81 17 Homing performance of u n i l a t e r a l l y b l i n d , u n i l a t e r a l l y anosmic and normal (control) f i s h from home range (a) A and (b) B 83 18 Homing on dark cloudy nights 86 19 E f f e c t of pool destruction on homing performance 91 20 The homing performance of b i l a t e r a l l y b l i n d , b i l a t e r a l l y anosmic and normal (control) f i s h to destroyed pools 93 21 Response of normal and b l i n d O. maculosus to d i f f e r e n t test water i n the Y-tank choice experiment 99 v i L I S T O F F I G U R E S F I G U R E P A G E 1 M a p of the Study A r e a 6 2 S e a s o n a l f l u c t u a t i o n of h o m i n g p e r f o r m a n c e and sea state c o n d i t i o n s 47 3 Y - m a z e s e t - u p 96 v i i LIST OF PLATES PLATES PAGE I View of S i t e A 9 II View of Site B 10 III view of area between Sites A and B 11 v i i i ACKNOWLEDGEMENTS I wish to express my gratitude to those who have i n one way or another contributed towards the completion of t h i s study as well as the preparation of the t h e s i s . My thanks to members of my research advisory committee, Drs. J . D. McPhail, N. R. L i l e y , H. D. Fisher, T. Carefoot and esp e c i a l l y to Dr. N. J . Wilimovsky, my research supervisor, for t h e i r advice and guidance. My gratitude goes to the Commonwealth and Fellowship Administration of Canada for the f i n a n c i a l support and i t s personnel for t h e i r continued patience. I would l i k e to thank Mr. M. R. Morrell, Mr. S. R. Heizer and Mrs. S. Heizer for t h e i r valuable c r i t i c i s m s and corrections of the manu-s c r i p t . My sincere thanks to Mr. R. A l l e n for h i s help on s t a t i s t i c a l problems and to Dr. R. Nakamura, Mr. P. Breen as well as Mr. J . Himmelman for t h e i r assistance and useful suggestions during the many f i e l d t r i p s we had together. I am also grateful for Mrs. B. Minchin's help i n preparing the map. GENERAL INTRODUCTION R e l a t i v e l y few s t u d i e s have been made on the homing behaviour of i n t e r - t i d a l f i s h e s . Homing has been suggested t o occur i n the f o l l o w i n g i n t e r - t i d a l s p e c i e s : Amphigonopterus  aurora (Hubbs, 1921); Bathyqobius soporator (Beebe, 1931; Aronson, 1951); C l i n o c o t t u s a n a l i s and G i r e l l a n i g r i c a n s (Williams, 1957); Acanthocottus (= Enophrys) b u b a l i s , C i l i a t a mustela, and B l e n n i u s p h o l i s (Gibson, 1967); C l i n o c o t t u s g l o b i c e p s (Green, 1967) and O l i g o c o t t u s maculosus (Gersbacher and Denison, 1930; Eastman, 1962; Green, 1967). In these s t u d i e s the term 'homing' r e f e r s t o three d i f f e r e n t phenomena: (a) p o o l f i d e l i t y , (b) p e r i o d i c r e t u r n t o an area w i t h i n a home range, and (c) r e t u r n from o u t s i d e the home range. Hubbs (1921) and Gersbacher and Denison (1930) i n t e r p r e t e d p o o l f i d e l i t y as homing a b i l i t y . The p e r i o d i c r e t u r n of a f i s h t o an area which i s sm a l l compared t o i t s home range i s r e f e r r e d t o as 'homing' by W i l l i a m s (1957) . Accor d i n g t o Beebe (1931) homing i s d e f i n e d as the r e t u r n of a f i s h t o i t s home range when e x p e r i m e n t a l l y d i s p l a c e d a c o n s i d e r a b l e d i s t a n c e . W i l l i a m s ' (1957) and Beebe's (1931) d e f i n i t i o n s d i f f e r e d i n t h a t the former was concerned with how a f i s h l o c a t e s 2 a certain area within i t s home range while the l a t t e r was concerned with how a f i s h locates i t s home range from outside i t . Aronson (1951), Eastman (1962) and Gibson (1967) have demonstrated the former type of homing while Green (1967) demonstrated the l a t t e r form of homing. In t h i s study homing i s defined as the return of a f i s h to i t s home range when experimentally displaced to unfamiliar areas. I t i s con-cerned with how a f i s h finds i t s way back from outside i t s home range and with how the f i s h recognizes i t s home range. Oligocottus maculosus (Girard), a tide-pool sculpin, i s a common i n t e r - t i d a l f i s h ranging from northern C a l i f o r n i a to the Bering Sea (Clemens and Wilby, 1961) and i s found i n great abundance in tide-pools at the rocky shore near Port Renfrew on the west coast of Vancouver Island, Canada. I t s maximum size i s about eighty millimetres i n standard length and i t spawns during late winter, spring and early summer. The newly hatched larvae are pelagic; they become demersal and populate the tide-pools during summer and f a l l (Atkinson, 1939;; Nakamura, 1970) . Green (1967) was the f i r s t to show that t h i s species at the Port Renfrew marine station, former s i t e of the Minnesota Seaside Station, exhibited homing a b i l i t y . 3 The present study i s a continuation of Green's work at the same s i t e . The purpose of my study was to formulate a mechanism(s) that might explain how 0_. maculosus homes. E v i -dence was obtained from experiments conducted to investigate the e f f e c t s of various factors on the homing a b i l i t y of the tide-pool sculpin. The factors considered were (a) rate of homing, (b) season, d i r e c t i o n and distance of displacement, (c) sex, size and 'experience' of the f i s h , and (d) sensory basis of homing. Attention was focused on the v i s u a l and olfactory senses as the basis of homing since they were known to play important roles i n the orientation of other f i s h e s . Sensory impairment, night homing and pool destruction ex-periments were conducted to determine which of the sense organs and the related environmental cues were involved i n the homing mechanism. Before the factors a f f e c t i n g homing a b i l i t y were con-sidered, evidence was obtained to ascertain the v a l i d i t y of the 'home range' concept and i t s use i n assessing homing performance i n t h i s species. Home range i s defined (modified from Hayne, 1949) as the area covered by the f i s h during i t s normal t r a v e l . The presence of home range i n a number of fishes was reviewed by Gerking (1959) . Home range i n a few i n t e r - t i d a l 4 fishes has been studied by Williams (1957) and Gibson (1967) . The presentation of t h i s study i s i n three parts: Demonstration of the home range i n 0. maculosus (Experiments 1-3), evidence of homing (Experiment 4), and factors a f f e c t i n g homing performance (Experiments 6-117) . 5 GENERAL MATERIALS AND METHODS Description of the Study Area The study area was the i n t e r - t i d a l region at Botany Beach near Port Renfrew on the south-west coast of Vancouver Island, B r i t i s h Columbia, Canada. I t i s situated south of San Juan I n l e t (latitude 48° 32' north, longitude 124° 27' west) . I t i s on the northern shore of the Juan de Fuca S t r a i t and i s r e l a t i v e l y exposed to the P a c i f i c Ocean. The region i s p a r t i c u l a r l y suitable for the present study because of the numerous tide-pools. These pools were formed as the r e s u l t of wave erosion and i n t e r a c t i o n on the varying hardness of the rocky shore. The area consists primarily of sandstone and shale. The northern section of the shore consists mainly of a shale outcrop; the slope i s steeper and the tide-pools present are more isolated from other pools than that of the southern section (Fig.1). The southern section of the study area consists mainly of sandstone rocks with numerous tide-pools close to each other and shallow channels which form pools at low t i d e . The gradient i s gentle except on the southern edge where the • 1 SITE B F i m i P F 1 M A P f)F T H F «1TIIDV A R E A 7 i n t e r - t i d a l shelf drops abruptly into the sub-tidal region. At high tid e several high areas i n t h i s section form islands separated from the main shore. The physical, chemical and b i o l o g i c a l c h a r a c t e r i s t i c s of the area were recorded i n d e t a i l by Green (1967). The tides i n t h i s region are of the mixed semi-diurnal type. The amplitude of the extreme tides i s approximately twelve feet. During the period between September and March the lowest low tides occur i n the late afternoon and evening and the highest high tides occur near mid-day. From March to September the lowest low tides occur during the early morning and the highest high tides occur near midnight. Sea state data recorded on a semi-daily basis from November 1965 to December 1966 was obtained for t h i s region by Green (1967). The sea state was considerably rougher between September to February than between March to August. The benthic biota i s that of an open coastal rocky en v i r -onment. The f l o r a of the lower i n t e r - t i d a l (below the six foot tid e level) i s characterised by kelp and the dominant algae Hedophyllum. The upper i n t e r - t i d a l i s generally devoid of algae cover except i n more exposed areas where P o s t e l s i a occurs 8 and i n sheltered areas where Fucus occurs. Generally the t i d e -pools at most le v e l s , e s p e c i a l l y the upper levels, contain l i t t l e algae cover except for calcareous algae such as C o r a l l i n a , C a l l i a r t h r o n and Bossea. A number of pools at the lower leve l s contain thick mats of eel grass (Phyllospadix scouleri) but those at the upper leve l s r a r e l y contain much, i f any, eel grass. C h a r a c t e r i s t i c t e r r a i n of the region -is.* shown i n Plates I - I I I . Plate I i s a view of the southern section of the study area. Plate II i s a view of the northeast section of the study area and Plate III i s part of a view of the sea flo o r between the above two areas. Five main 's i t e s ' are used i n the study. Site A i s a sandstone f l a t with ten pools situated at the 8.4 f t . l e v e l (Plate I) . This s i t e i s r e l a t i v e l y protected, p a r t i c u l a r l y from southerly swells. Site B i s about one hundred yards north of s i t e A. I t consists of shallow trenches which are connected at the high ti d e , and at low t i d e they form shallow pools (Plate I I ) . They form f i v e discrete pools at the 8.9 - 9.2 f t . l e v e l . The dimensions of the pools are given i n Appendix II . The area Plate I. View of Site A (centre of photograph ) 9 Plate I I . View of Site B (centre of photograph) Plate I I I . View of area between Sites A and B. 11 between s i t e A and B i s r e l a t i v e l y lower and strewn with boulders. This area has many shallow channels which form large shallow pools at low tide (Plate I I I ) . Site C consists of a pool 12 x 10 f t . and about 20 inches deep. This s i t e i s situated i n the shale rocks; on rainy days water from a stream drains i n t o t h i s pool. The pool i s protected and i s o l a t e d from other pools by high ground on a l l sides except on the seaward side. Swells come into t h i s area from the west. This area i s at the 9.8 f t . l e v e l . Site D i s a group of discrete pools arranged l i k e a step-ladder. The upper pool (D-l) drains into the lower pools (D-2, D-3, and D-4). These pools are enclosed by steep walls on each side which form a trench to the south-west at high t i d e . S ite E i s a group of isolated pools i n shale rocks at the 6.1 f t . l e v e l . Other pools used are PD-1, PD-2 and PD-3; the location and dimension are given i n Figure 1 and Appendix II r e s p e c t i v e l y . The above s i t e s and pools were chosen because they are 13 isolated from other pools and because the pools are accessible at a l l low tides during fine weather. Tagging, Capture and Recapture Methods The captured f i s h were i n d i v i d u a l l y tagged with strings of colored embroidery beads. A similar method was used by Williams (1967) and Green (1967). The beads were threaded on two pound te s t monofilament nylon l i n e s and sewn into the dorsal musculature of the f i s h just below the f i r s t dorsal f i n . Use of anaesthetic was unnecessary during tagging since no difference i n mortality between anaesthetised and unanaesth-etised f i s h was observed. There are certain l i m i t a t i o n s to t h i s tagging method. Increasing the number of beads per tag increases the chances of tag loss as well as increasing the burden on the f i s h ' s swimming a b i l i t y . Smaller f i s h have to be tagged with a minimum number of beads. The advantage of colored bead tags i s the ease of v i s u a l i d e n t i f i c a t i o n of i n d i v i d u a l f i s h even when i n the pool. Tag loss (indicated by the number of recoveries of f i s h which had lesions on the dorsal musculature) was not s i g n i f i c a n t 14 for f i s h recaptured within the f i r s t four months after release. The t o t a l number of f i s h recovered with lesions out of the t o t a l number recovered during the entire period of the study (about three thousand fish) was less than one per-cent. To bias the recovery data tag loss must occur within the f i r s t four months after release. There i s no apparent increase i n mortality of the f i s h owing to the tagging procedure. Laboratory survival studies of tagged and untagged f i s h kept for a period of about four months show no differences i n mortality. No tags were l o s t during t h i s period. M o r t a l i t y of the tagged f i s h i n the f i e l d , however, i s not known. Tagged f i s h released into the environment may be more susceptible to predation or wave action. The majority of f i s h were captured by means of metal minnow traps. The traps were baited with mussels (Mytilus  californianus) and placed i n the tide-pools one hour before low tide and removed about three hours l a t e r . In some experiments such as experiment 16 which involved pool destruction, the pools were drained dry using a siphon, bucket or a gas driven pump. The captured f i s h were then transported i n p l a s t i c buckets to the f i e l d laboratory where they were tagged, measured and sexed. Owing to the time taken to tag, sex and measure, the f i s h were often kept, at least, overnight before release i n many of the experiments. A l l the f i s h i n a pool could be recaptured by draining the pool, but t h i s method was not used since i t might disturb the pool habitat. This i n turn might aff e c t the behaviour of the f i s h . Hence recovery data of tagged f i s h were obtained by frequent trapping of the pool and by searching the pool v i s u a l l y . Trapping e f f i c i e n c y for tagged f i s h i s about 67% (95% confidence l i m i t s - 54%-80%). The combined e f f i c i e n c y of the two methods was not known, but i t was assumed that most of the tagged f i s h would be recovered by setting traps and searching at the same time. The cumulative r e s u l t s of f o r t n i g h t l y recapture attempts for a four month period wetfe used i n most experiments; i n t h i s way the f i s h not recovered at any one trapping should be captured i n other attempts. Recovery attempts i n most cases were made during the daytime low t i d e s . Fish above 35mm standard length were used i n most of the experiments. 16 Sensory Impairment Methods Visi o n Three methods of blinding were i n i t i a l l y studied i n the laboratory; these were chemical blinding, surgical r e -moval of the eyes and eye lens removal. The chemical method of blinding involved a solution of phemerol (benzethonium chloride) which was injected into the posterior chamber of the eye . u n t i l the solution oozed out around the needle. A syringe with a No. 26 needle was used. A f i v e percent solution appeared to be the best concentration. However, when treated f i s h were kept i n aquaria the majority regained th e i r v i s i o n after f i v e days. This method was abandoned. Surgical removal of the eyes by severing the optic nerve where i t joined the eyeball proved to be traumatic. Most of the treated f i s h died a few days l a t e r . This method was not used. Lens removal was the most successful method. Removal of the lenses was carried out by making a s l i t with a sharp scalpel on the cornea, and by applying pressure on both sides of the s l i t with a pair of forceps u n t i l the lens "popped" out. I t was found that puncturing the cornea 17 with the point of a red hot needle increased the e f f i c i e n c y of the operation i n the f i e l d . Survival of the f i s h was shown to be good (see experiment 11) . Fish with t h e i r lenses removed may s t i l l detect l i g h t but the i r a b i l i t y to detect s p e c i f i c features of the environment i s d e f i n i t e l y impaired. Ol f a c t i o n Heat cauterisation of the olf a c t o r y rosettes was the method used for olfactory impairment. other methods such as occlusion of the olf a c t o r y p i t s with vaseline and latex and severing of the olf a c t o r y nerve were not possible because of the small size of the f i s h . Heat cautery of the ol f a c t o r y rosette was performed by inse r t i n g the point of a red hot needle into the anterior nares of the f i s h and maneouvering the needle into the approximate position of the ol f a c t o r y rosette. Examination under the microscope showed that most of the rosettes were destroyed by t h i s method. The needles used were thread darners the size of which varied with the size of the f i s h treated. Survival of the f i s h from t h i s treatment was good (see experiment 11). In both v i s u a l and olf a c t o r y impairment treatments the f i s h were not anaesthetised. 18 Types of Experiments Two main types of experiments.were conducted, replace-ment and displacement experiments, which, together evaluate the homing a b i l i t y of 0. maculosus,. Displacements were experiments i n which captured f i s h were tagged and trans-located to areas other than the area i n which they were o r i g i n a l l y captured. The f i s h were released into t i d e pools . at low t i d e . On the other hand i n replacement experiments the captured f i s h were tagged and then returned to the same pools i n which they were o r i g i n a l l y caught. S t a t i s t i c a l Analysis In most cases the 2 x 2 contingency chi square test was used. In some cases when the sample size was small the Fisher's test (Siegel, 1956) was used. Where more than two factors were involved a G-test of independence (Sokal and Rohlf, 1969) was used. The l e v e l of significance adopted i n a l l tests was ninety-five percent. 19 HOME RANGE Introduction According to Gibson (1969) the f i s h inhabitants of the i n t e r - t i d a l zone may be c l a s s i f i e d into four groups (a) true residents: f i s h which remain within the i n t e r - t i d a l zone and are r a r e l y found below low water, (b) p a r t i a l r e -sidents: f i s h whose d i s t r i b u t i o n also extends below low water, (c) t i d a l v i s i t o r s : f i s h which move into the i n t e r -t i d a l zone at high water only, and (d) seasonal v i s i t o r s : f i s h which move into the i n t e r - t i d a l zone during certain seasons. g_. maculosus belongs to the f i r s t group; i t i s a resident f i s h c o n f i n i n g . i t s movement about the i n t e r - t i d a l zone at high tide and remaining i n pools at low t i d e . A number of other resident species have also been observed to move around a c t i v e l y at high tide and return to certain pools at low tide . This has been demonstrated for Clinocottus  analis and G i r e l l a nigricans (Williams, 1957) ; these fishes leave t h e i r pools at high t i d e , follow the high tide l i n e , and return to the i r home pools when the tide ebbs. 20 Other f i s h have been shown to have more r e s t r i c t e d movements over a smaller area as has been attributed to Amphigonopterus  aurora (Hubbs, 1921) . The studies by Gersbacher et a l . (1930) and Green (1967) also implied that Q_. maculosus r e s t r i c t e d i t s movement to a rather small area. They suggested that the f i s h do not move too far from th e i r home pools at high t i d e and that at low tide the f i s h often return to the same home pool. The extent of movement by O. maculosus was assessed by experiments i n which tagged f i s h were returned to the i r o r i g i n a l pools of capture (home pool), and t h e i r movement i n r e l a t i o n to them was followed on successive low tides . Thus the following experiments were concerned with the home range, home pool f i d e l i t y and degree of movement of O. maculosus. Methods Two areas were chosen for t h i s study: s i t e s A and B ( f i g . 1). Two methods of observation were used: (a) Groups of f i s h from a r e l a t i v e l y large area, consisting of several tide-pools were captured, tagged and replaced into t h e i r 'home pools'. Two weeks after release the pools within the selected 21 area were trapped and searched at two-week i n t e r v a l s . The pool i n which the f i s h was recovered was used as an in d i c a t i o n of the extent of movement of the f i s h from i t s home pool. Recovered f i s h were removed and used i n other experiments. Cumulative data from up to four months after release were analysed. Several replacements were conducted for each area and the combined r e s u l t s were analysed. (b) In the second method f i s h from several pools within a r e l a t i v e l y large area were captured, tagged and replaced. The recapture schedule was d i f f e r e n t from that of (a). The pools within the area concerned were searched and trapped d a i l y . The f i r s t recovery attempt was made three days after the release of the f i s h and continued for ten days. The pool of recovery was recorded. The recovered f i s h were immediately returned into the pool from which they were l a s t recovered. Three experiments were conducted. Experiment 1 was conducted on f i s h from area A using method (a); experiment.2 was conducted on f i s h from area B also using method (a). Experiment 3 was conducted, using method (b), on f i s h from area A. 22 Results Experiment 1 Two replacements were conducted i n s i t e A during May 1968. The combined r e s u l t s of the two replacements (Table la) showed that of the seventy-two f i s h replaced, fifty-two f i s h (72.2%) were recovered within s i t e A. Sixteen of those r e -covered i n s i t e A (30.8%) were recaptured i n their home pools. Movement of the f i s h was quite r e s t r i c t e d . Most r e -coveries are from pools nearest the home pools and not i n pools furthest away. For example f i s h i n i t i a l l y from pools 1, 2 and 3 were not found i n pools 8, 9 and 10, which were furthest away, but were recovered i n pools nearer t h e i r home pools (see F i g . 1 for s p e c i f i c -location of the pools) . Si m i l a r l y f i s h from pools 8, 9 and 10 were not found i n pools 1, 2 and 3. This r e s t r i c t e d movement within a group of pools near home pools was also demonstrated by the f i s h i n i t i a l l y from pools 5, 6 and 7. The greatest distance t r a v e l l e d within the study area by t h i s group of f i s h was shown by a f i s h i n i t i a l l y from pool 7. This f i s h was recovered i n pool 2, about for t y feet from pool 7. 23 Experiment 2 Three replacements were made i n s i t e B from March to May 1969. Altogether, f i f t y - t h r e e f i s h were replaced (Table l b ) . T h i r t y of these (56.6%) were recovered within s i t e B. Twenty-four of those recovered i n s i t e B (80.0%) were recaptured i n thei r home pools. The rest (20.0%) were recovered i n neigh-bouring pools. Again movement r e s t r i c t e d to pools nearest the home pools was demonstrated by the majority of the f i s h . The maximum distance t r a v e l l e d by t h i s group was shown by a f i s h o r i g i n a l l y from pool 3. This f i s h was la t e r recovered about a hundred feet away i n pool 5. Experiment 3 A t o t a l of f i f t y - e i g h t f i s h from s i t e A were replaced on May 29, 1968. Thirty-seven of t h i s number (63.8%) were recovered within s i t e A (Table 2). Eighteen f i s h (48.6%, of those recovered i n s i t e A) were recovered at least once i n their home pools. The r e s u l t s showed that most of the f i s h were recovered i n d i f f e r e n t pools on successive low t i d e s . For example eleven f i s h (individuals 5, 9, 11, 13, 14, 15, 20, 22, 28, 31 24 Home Pool of Recovery Number Number recovered Pool 1 2 3 4 5 6 7 8 9 10 Released i n : Home Home Range Pool 1 2 3 4 5 6 7 8 9 10 3 1 1 1 2 1 2 1 1 1 2 2 1 2 3 1 5 3 4 5 2 1 1 5 5 2 13 6 6 26 6 8 4 2 7 5 6 18 4 6 3 0 2 2 2 0 2 5 Tota l 72 52 16 % of number released 72 .2 22 .2 Home Pool Pool of recovery s Number Number recovered 1 2 3 4 5 Released i n : Home ranqe Home pool 1 3 1 1 10 5 3 2 1 1 4 2 0 3 10 1 1 19 12 10 4 1 3 1 1 5 10 17 10 10 Total % of number released 53 30 56.6 24 45 .3 Table 1. Movement and f i d e l i t y to home pools i n (a) Study s i t e A (May 1968) (b) Study s i t e B (March - May 1969) . and 37) were recovered i n d i f f e r e n t pools on each successive low t i d e . Only seven f i s h were recovered on successive occasions i n the same pools (e.g. indiv i d u a l s 3, 4, 24, 25, 27, 29 and 32) and only four of these were i n t h e i r home pools. The r e s u l t s indicated that there was d a i l y movement from pool to pool and that f i d e l i t y to s p e c i f i c pools was an exception rather than the r u l e . The r e s u l t s also indicated that f i s h movement was r e -s t r i c t e d to a few neighbouring pools and that they seldom stay i n the same pool for a prolonged period of time. The most extensive distance t r a v e l l e d between pools was by f i s h i n d i v i -dual 5; i t was i n i t i a l l y from pool 2 but i t was recovered once, about sixt y feet away, i n pool 9. The majority of the f i s h , however, showed less extensive movement. Discussion Contrary to Gersbacher and Denison's (1930) as well as Green's (1967) conclusions, the above studies show that 0. maculosus r a r e l y r e s t r i c t themselves to one par t i c u l a r pool; the majority of the f i s h did not exhibit s t r i c t f i d e l i t y to the i r home pools. The fact that most of the f i s h were found i n a r e s t r i c t e d group of pools on successive low tides, • 26 Release Data Recovery Data Home No. Individual Days After Release Pool Released Fish 4 5 6 7 8 9 10 11 12 13 (Recovery Pool) 1 (6) 1 2 2 2 3 1 1 1 2 (4) 4 4 4 4 5 9 5 3 (12) 6 1. 7 4 8 2 9 3 1 1 1 3 1 10 4 11 3 4 7 12 5 13 4 1 6 14 4 7 15 2 4 16 3 4 (18) 17 3 18 5 19 3 20 4 1 5 21 4 22 4 7 23 6 24 4 25 7 7 26 4 4 9 (18) 27 9 9 28 8 9 29 9 9 30 10 31 9 10 10 9 9 32 9 9 33 9 34 9 35 9 36 7 37 9 8 Table 2. Movement of replaced f i s h within s i t e A using method (b) . (29 May 1968) . implies that there was probably a r e s t r i c t e d area or range within which the f i s h often move around and a group of pools to which the f i s h frequently returned. Movement over a r e s t r i c t e d 'home range' would account for the observations that the f i s h were often recovered i n d i f f e r e n t tide-pools, that sometimes the f i s h were observed i n the i r home pools, and that the pools involved were close to each other. Three categories of f i s h could be recognised from the above r e s u l t s : (a) f i s h which were recovered i n t h e i r home pools, (b) f i s h which were recovered i n pools neighbouring the home pool, and (c) f i s h which were not recovered i n the pools within the study s i t e . The proportion of each category varied i n the three experiments. This was probably due to a number of f a c t o r s . The d i f f e r e n t proportions probably depended on the mobility of the in d i v i d u a l f i s h , the extent of the i n d i v i -dual f i s h ' s home range and the 'centre of a c t i v i t y ' of the in d i v i d u a l home, range. Thus according to Gibson (1967), the three categories observed for a pool population would corres-pond to (i) individ u a l s whose home range was centered on or. near that home pool, ( i i ) others whose home range included the pool within,but not as the centre of,the range, and ( i i i ) f i s h out-side t h e i r normal home range or whose home range r a r e l y included 28 the pool i n question. Disturbances due to trapping and searching might also influence the proportion of each category. However no data were a v a i l a b l e . The size and s p a t i a l d i s t r i b u t i o n of the pools within the study s i t e could also be an important factor deter-mining the proportion observed for each category. I f the pools were small and close together observations of a f i s h i n d i v i d u a l i n more than one tide-pool would be more common than i f the pools were large and more i s o l a t e d . The e f f e c t of pool size and pool d i s t r i b u t i o n could be substantiated from the r e s u l t s of experiments 1 and 2 conducted i n s i t e s A and B, respe c t i v e l y . The pools i n s i t e A were smaller and more aggregated than the pools of s i t e B. The proportion of home pool recover-ies i n s i t e B was higher than the proportion recovered i n s i t e A (BO.0% and 30.8%, of recoveries within the study s i t e , r e s p e c t i v e l y ) . I f the pools were larger than the average home range, then a higher proportion of the f i s h would be recovered i n the i r home pools as demonstrated by the r e s u l t s of experiment 2 for s i t e B, and i f the pools were smaller than the home range of the f i s h , a lower proportion of the f i s h would be recovered i n th e i r home pools as shown by the re s u l t s of experiment 1 for s i t e A. 29 The extent of the home range of 0. maculosus i s d i f f i -c u l t to ascertain, but most probably the home range of the majority of the f i s h was smaller than the areas of si t e s A and B. From the above observations of f i s h movement i t i s probable that the extent of the home range would seldom ex-ceed a hundred feet. However t h i s i s based on the data of f i s h recovered i n the study s i t e s ; no information was available regarding those f i s h which were not recovered again. Fish of t h i s l a t t e r category might have strayed or died, or they might be f i s h with th e i r home range outside the study s i t e s but happened to wander into the two areas. This category might also include those f i s h which were present i n the s i t e s but were undetected because of trapping and searching i n e f f i c i e n c y . Nevertheless, evidence supporting the hypothesis that the extent of O. maculosus's home range was much smaller than a hundred feet was substantiated from Green's (1967) observations which show that most of the f i s h were observed not more than three metres from th e i r home pools and only a few were observed further but not exceeding ten metres. At high tide, the time during which the f i s h were allowed to range around was l i m i t e d . The two study s i t e s are situated above the eight foot l e v e l . The time duration 30 of submergence of pools at t h i s l e v e l i s seldom more than three hours. Hence i t i s quite u n l i k e l y that the f i s h from pools of t h i s l e v e l would range far from their home pools during high t i d e s . In studies subsequent to these f i r s t three experiments, the maximum extent of the home range of the tide-pool sculpin was assumed to be not more than a hundred f e e t . 31 EVIDENCE OF HOMING IN O. MACULOSUS Introduction The following experiments were conducted to test whether or not 0. maculosus i s able to return to i t s home range after i t has been translocated some distance outside the home range. This section also presents the c r i t e r i a used for assessing homing performance. Homing performance i s the percentage of f i s h returning to t h e i r home range of the t o t a l number of f i s h displaced. I t i s a measure of both homing a b i l i t y and motivation to home. No d i s t i n c t i o n be-tween homing a b i l i t y and homing motivation i s possible using t h i s c r i t e r i o n . The c r i t e r i o n of a 'home' for judging whether a d i s -paced f i s h has homed or not d i f f e r s from that used by past authors (Gibson, 1967; Green, 1967). These authors considered only those f i s h which returned to th e i r pools of o r i g i n a l capture (home pool) i n assessing homing performance. Fish which have returned to pools near t h e i r home pools were con-sidered as 'strays'. The study on home range has demonstrated that s t r i c t f i d e l i t y to s p e c i f i c pools i s rare and that movement among a number of pools within t h e i r home range i s 32 common i n the tide-pool sculpin, e s p e c i a l l y i n an area where the pools are small and close to each other. I t i s very l i k e l y , that displaced 0. maculosus may recognize a number of pools and thus return to a number of pools rather than one single pool. The following experiments were conducted to test whether the homing returns to the home range i s a better c r i t e r i o n than the homing returns to home pools i n assessing homing performance. Methods Experiment 4a Newly tagged (naive) f i s h greater than 35 mm i n standard length from s i t e A were displaced to station S-8; about three hundred feet north-east of s i t e A. The f i s h were displaced from May to June 1968. The pools within s i t e A were trapped and searched at two-week in t e r v a l s , and the pool location of the f i s h on f i r s t recovery was recorded. Cumulative data from up to four months after displacement were studied. Experiment 4b This experiment was similar to the above except that f i s h from s i t e B were studied. The f i s h were displaced from March to June 1969. They were displaced to station S-8, the same displacement station as the above experiment. Station S-8 was about a hundred and f i f t y feet from the nearest and about three hundred feet from the furthest pool of home s i t e B . Results Experiment 4a Altogether, seventy-nine f i s h from s i t e A were d i s -placed. Forty-three f i s h (54.4% of the t o t a l number released) were recovered i n s i t e A (Table 3a). Eighteen of these f i s h (41.9%) were recovered i n th e i r home pools. Not a l l the f i s h were recovered i n the i r home pools; a large proportion were recovered i n pools neighbouring the home pools. For example, f i s h from pools 1 to 4 were recovered i n nearby pools 1 to 5, and none of them were recovered i n pools 8, 9, and 10 which were farther away from the home pools. S i m i l a r l y most of the f i s h from home pools 5, 6 and 7 were recovered i n th e i r neighbouring pools (pools 3 to 7). Fish from home pool 8 were recovered mainly i n the i r home pool as well as i n pool 9 which was the pool nearest to the home pool. The r e s u l t s indicate that a large proportion of the 34 displaced f i s h are able to return to a r e l a t i v e l y small area, s i t e A, from a distance of about three hundred f e e t . Some of the f i s h returned to th e i r home pools, but a larger proportion returned to pools neighbouring t h e i r home pools. This implies that the f i s h return to a home range. Recoveries of the f i s h i n pools within an area smaller than the size of the si t e A implies that extent of the home range of the f i s h was probably smaller than the area of s i t e A. Experiment 4b Altogether one hundred and thirty-one f i s h from s i t e B were displaced. About seventy-seven f i s h (58.8%) were recovered within s i t e B (Table 3b); fifty-two of these (80.0%) were recovered i n the i r home pools. In t h i s experiment more f i s h returned to the i r home pools than to pools nearby; perhaps t h i s had to do with the size of the pools i n s i t e B. This experiment again demonstrates the c a p a b i l i t y of the f i s h i n homing to a small area from a considerable distance. Discussion The above r e s u l t s indicate that the percentage returns to the home range, given by the returns to the study s i t e s , are 35 (a) Home Pool of Recovery Number Number recovered Pool 1 2 3 4 5 6 7 8 9 10 Released i n : Home Home Range Pool 1 3 2 1 13 6 3 2 1 1 2 2 0 3 2 1 1 1 6 5 0 4 1 1 1 5 3 1 5 1 2 1 1 10 5 1 6 1 1 1 0 7 1 3 1 1 8 2 1 1 7 3 27 14 7 9 - - -10 1 5 12 6 5 To t a l 79 43 18 % of number released 54.4 22.8 Home Pool Pool of recovery Number Number recovered 1 2 3 4 5 Released i n : Home Home Range Pool (b) 1 13 3 1 31 17 13 2 4 6 4 4 3 1 12 4 1 25 18 12 4 9 8 23 17 8 5 3 3 15 46 21 15 Total 131 77 52 % of number released 58.8 39.7 Table 3. Homing returns to home range and home pools from a distance (a) Home Range = A; Distance displaced = 300 f t . N.E. (May-July 1968) . (b) Home Range = B; Distance displaced= 150-300 f t . S .E . (March - July 1969) . better c r i t e r i a for assessing homing performance than the percentage returns to the home pools . I f returns to home pools are the basis of assessing homing performance then about 22.8% and 39.7% of the f i s h displaced from s i t e s A and B, respectively, are considered to have homed. But i f the returns to the home range are used then about 54.4% and 58.8% from s i t e s A and B, respectively, have homed. Apparently the percentage home range returns are more similar than the percentage home pool returns for the two s i t e s . Recoveries of a large proportion of f i s h i n pools near th e i r home pools as shown by experiment 4a imply that the f i s h also home to other pools i n th e i r home range rather than to th e i r home pools only. Considering also that 0. maculosus possesses home range consisting of several tide-pools, as shown i n the study on home range, i t i s therefore more r e a l i s t i c to use the percentage returns to the home range as a measure of homing a b i l i t y than the use of the percentage returns to home pools. Subsequent experiments use the former c r i t e r i o n for expressing homing performance. The discrepancy i n the percentage home pool returns between the two s i t e s , A and B, i s probably related to the diff e r e n c e . i n pool sizes within each s i t e as well as to the size 37 of the f i s h ' s home range. As suggested i n the section on home range, i f the pools are close to one another and smaller than the home range of the f i s h (as i n s i t e A) then a smaller proportion of f i s h which homed would be observed i n the home pools than i f the pools are less aggregated and larger than the f i s h ' s home range (as i n s i t e B). The r e s u l t s of experiments 4a and b show that 0. maculosus i s capable of returning from about three hundred feet to a r e l a t i v e l y small area. In both experiments, s l i g h t l y more, than f i f t y percent of the f i s h displaced have returned to t h e i r home range. Considering the fact that there are numerous other equally habitable pools i n between the d i s -placement s i t e and th e i r home range, these r e s u l t s imply that there i s some form of homing mechanism i n 0. maculosus, that i s , the f i s h s t r i v e to return to areas formerly occupied rather than to other equally habitable places. That the observed returns are not due to chance a r r i v a l of the f i s h to th e i r home areas i s substantiated by comparing the r e s u l t s of replacement and displacement experiments (experiments 1 to 2 and experiments 3 to 4 respectively.) Both types of experiments have been conducted around the same time of the year and on f i s h from the 38 same s i t e s (A and B). Thus 72.2% and 56.6% of the f i s h r e -placed to s i t e s A and B, respectively, were found to remain within t h e i r home range; 54.4% and 58.8% of the f i s h displaced from s i t e s A and B, respectively, returned. This s i m i l a r i t y between.the homing returns and the home range f i d e l i t y , shown above, indicates that the observed returns obtained i n experi-ments 3 and 4 are not due to random chance. In the displacement experiments, a l l the f i s h l e f t the pools to which they were transplanted, within two weeks. On the other hand most of those f i s h which were replaced (replace-ment experiments) to th e i r pools of o r i g i n a l capture did not leave. This difference i n behaviour between replaced and displaced f i s h indicates that the f i s h are able to d i f f e r e n t i a t e between pools within t h e i r home range and 'foreign' pools. Green (1967) also observed that transplanted f i s h always move out of the transplant pools within a few t i d a l cycles. Ap-parently there i s motivation to home i n displaced f i s h while there i s none i n f i s h replaced within t h e i r home range. What made the transplanted f i s h leave while replaced f i s h remained i n a pool i s not known. Conceivably some topo-graphic or odour features of the pool are detected and these cues stimulate the f i s h to leave or remain according to whether the cues of the pool are fam i l i a r or unfamiliar to the f i s h . Subsequent experiments involving sensory impairment (experiment 12) imply that odour may be the cue involved. Perhaps the f i s h l e f t the transplant pool because of the presence of other f i s h , However Green (1967) shows that the presence of resident f i s h i n the' transplant pool i s not the factor involved. He has depleted pools of the i r resident f i s h and introduced f i s h from other areas. The transplanted f i s h s t i l l l e f t within one t i d a l cycle and eventually returned to thei r home. Probably the same factors which motivate the displaced f i s h to leave the transplant pools may also be the factors which ' i n h i b i t ' the adoption of the other equally habitable pools by the f i s h during t h e i r homeward journey. 40 FACTORS AFFECTING HOMING' PERFORMANCE Introduction In t h i s section several aspects of homing i n O. maculosus and factors a f f e c t i n g homing performance were investigated. They were attempts to find out what homing mechanisms are involved. The main objective of t h i s section i s concerned with the sensory mechanisms of homing. The two most l i k e l y senses, v i s i o n and o l f a c t i o n , were studied. No experiments have been conducted by previous authors to test whether or not v i s i o n and o l f a c t i o n are involved i n the homing mechanism of i n t e r -t i d a l fishes . Attention was focused on the rate of homing (experiment 5); the e f f e c t of season (Experiment 6 ) , d i r e c t i o n (Experiment 7) and distance of displacement on homing (Experiment 8); the difference i n homing performance between newly tagged-:na±-ve-fish and f i s h which have been shown to home at least once—experienced f i s h (Experiment 9); the difference i n homing performance between the sexes and f i s h of d i f f e r e n t sizes (Experiment 10). 41 Experiments concerning the sensory basis of homing are: the e f f e c t s of sensory impairment on the homing performance (Experiments 11 to 14); night homing (Experiment 15); homing to pools with destruction of the immediate environment (Experiment 16); and Y-tank choice experiment (Experiment 17). Fish from s i t e s A, B and C were studied. Experiment 5: Rate of homing This experiment i s concerned with the rate of homing of 0. maculosus. By-'knowing the rate of homing some idea as to the mechanism of homing may be obtained. I f the majority of the displaced f i s h arrived at the same time to t h e i r home range then i t i s possible to maintain that random movement as against other mechanisms involving exploration or directed movement i s probably not involved. Method Naive f i s h from s i t e A were released during May to June 1968 to station S-8, about three hundred feet away. The pools were monitored d a i l y for about a week after each release. Recovery attempts were also conducted thereafter at two-week i n t e r v a l s . The f i r s t recovery attempt was made the day after release of the f i s h . 42 Results Altogether, forty-four f i s h were displaced, and of these sixteen f i s h (36.4%) returned to s i t e A within a week (Table 4). Four of the f i s h returned within a day (two t i d a l c y c l e s ) . Recovery data from up to four months after the release of the f i s h showed that thirty-two f i s h (72.7%) eventually returned. The above r e s u l t s show that some f i s h could home quite r a p i d l y from about three hundred feet, a remarkable rate of return considering that the f i s h could only home during the high tide periods, e s p e c i a l l y when the time period during which the home s i t e and the displacement station were submerged was not more than three hours. The r e s u l t s , however, show that other f i s h took a longer time to return. About h a l f of those which eventually returned took more than a week to return. Experiment 6: E f f e c t of season:; on homing performance This experiment i s concerned with the seasonal v a r i a -t i o n of homing i n 0. maculosus and the factors affecting such a v a r i a t i o n . Date Released Number Days elapsed Number homed Number homed Released 1 2 3 4 5 6 7 i n 7 days eventually 2 9 v 68 7 1 1 1 3 5 3 1 v 68 9 3 2 1 6 8 1 v i 68 10 1 1 3 4 v i 68 8 1 2 3 8 5 v i 68 10 1 2 3 8 Total 44 4 1 8 1 1 1 16 (36.4%) 32 (12.1%) Table 4. Rate of homing. Home range = A; Distance displaced = 300 f t . N .E. 4^ co 44 Method Naive f i s h from s i t e A were displaced re g u l a r l y at about two-week in t e r v a l s from A p r i l 1968 to June 1969. The f i s h were displaced between one and three hundred feet north of the' s i t e . Recovery attempts at the s i t e were con-ducted at two-week i n t e r v a l s . Recovery data from up to four months after the release of the f i s h were analysed. Results The percentage homing returns show a monthly f l u c t u -ation with a maximum i n May 1969 (71.4%) and a minimum i n December 1968 (9.1%)—Table 5. Lower percentage returns were obtained during the period between September 1968 and February 1969 and higher percentage returns were obtained for the rest of the months with the exception of June. This change i n homing performance during the d i f f e r e n t seasons of the year could be related to the f i s h spawning behaviour or i t could be related to environmental factors such as weather conditions. Atkinson (1939) indicates that 0. maculosus of the Puget Sound region spawns between A p r i l to July each year. This time period roughly.corresponds to the higher l e v e l of 45 Month Number Number Released Released Homed % A p r i l 1968 35 16 45.7 May 90 55 61.1 June 2 6 8 30.8 July 95 51 53.7 August 9 4 44.4 September 7 2 28.6 October 15 2 13.3 November - - -December 33 3 9.1 January 1969 7 1 14.3 February 53 20 37.7 March 40 20 50.0 A p r i l 21 10 47.6 May 7 5 71.4 June 48 9 18.8 Table 5. Seasonal Fluctuation of homing. Home range = A; Distance displaced = 100-300 f t . north. 46 homing performance obtained from t h i s experiment, implying a r e l a t i o n s h i p between spawning and homing behaviour.. I t i s more probable that the flu c t u a t i n g homing performance i s due to the seasonal changes i n sea conditions rather than i t s r e l a t i o n s h i p to spawning behaviour. The homing a b i l i t y of the f i s h may be adversely affected by wave action during rough weather months. Green (1967) obtained sea condition data for t h i s area. The per-cent observations of six foot swells for 1966 (Fig. 2) showed that rougher sea conditions occur during September to February than during March to August. These two periods of weather condition correspond to the above observed time periods for d i f f e r e n t l e v e l s of homing performance. The sea state maximum occurred i n December and the minimum i n A p r i l . There seems to be an inverse r e l a t i o n s h i p between sea state and homing performance. In subsequent experiments the terms 'spring-summer' and 'fall-winter' corresponding to March to August and September to February, respectively, are used. 47 100 80 60 90 A 40 / i 35 20 i \ \ 95 i i i \ A 40 / 21 t i \ i \ i V 26 •\ 53 V * I I I f , 97 33 • • A M J J A S O N D J F M A M J 19 6 8 [ ] uKoming performance 1969 [••••] Observations of > 6 ft swel Is -1966 Fig. 2. Seasonal f l u c t u a t i o n of homing performance and sea state conditions. (Sample si2e given f o r each month.) Distance displaced = 100-300 f t $ Home range = A. 48 Experiment 7: E f f e c t of d i r e c t i o n on homing performance. This experiment i s concerned with the homing perfor-mance of displaced f i s h from d i f f e r e n t directions with r e -spect to the i r home range. I f f i s h home equally well from a l l d i r e c t i o n s of t h e i r home then i t i s quite l i k e l y that a fixed-compass d i r e c t i o n mechanism ('dead reckoning') i s not involved. Method Four sub-experiments were conducted: (a) naive f i s h from Site A were displaced i n four d i r e c t i o n s to about two hundred feet (stations S - l , S-2, S-3 and S-4) on 4 A p r i l 1968. (b) Experienced f i s h from s i t e C were displaced to the southeast and to the west about a thousand feet on 12 June 1969. (c) Both naive and experienced f i s h from s i t e A ! were displaced to the southwest and to the northwest about a hundred feet (stations S-5 and S-6) on 9 September 1969. (d) Experienced and naive f i s h from s i t e C were displaced to the west and the southeast about four hundred feet on 9 September 1969 (stations S-8 and D - l ) . In each case recovery data from up to four months after release were used . 49 Results Results of the four sub-experiments (a to d) are presented i n Table 6. (a) Fisher's chi-square t e s t shows that there was no s i g n i f i c a n t difference i n the homing performance among the f i s h displaced to the four d i r e c t i o n s , (b) None of the f i s h displaced to the southeast returned while 71.4% of those displaced to the west returned. This difference was probably due to the difference i n t e r r a i n . The f i s h displaced to the southeast have to swim over a shelf which drops abruptly into the subtidal (southern section of F i g . 1); the steep trenches i n t h i s area could be a major obstacle. The shore to the west of the home s i t e on the other hand was more gradual and continuous. (c) For both naive and experienced categories there were no s i g n i f i -cant differences i n homing returns between the f i s h displaced to the southwest and those displaced to the northwest. (d) The homing returns of naive and experienced f i s h from s i t e C also showed no s i g n i f i c a n t e f f e c t of d i r e c t i o n on the homing performance of 0. maculosus. These r e s u l t s imply that the homing a b i l i t y and probably the homing mechanism are independent of d i r e c t i o n of displace-ment. Apparently rough t e r r a i n may also a f f e c t homing a b i l i t y . Experi- Date Home 'Exper- Distance Direction Release Number Number Chi-ment Released s i t e ience 1 Displaced Displaced Station Released Homed % square 4 i v 68 A naive 200 f t S .E . S .W. W. N.E . S- l S-2 S-3 S-4 7 8 7 11 3 7 4 8 42 .9 87.5 57 .1 72 .7 n.s. 12 v i 69 C exp 1000 f t S .E W. S-12 12 7 0 5 0 .0 71 .4 9 i x 69 A exp. 100 f t naive S .W. N.W. S .W. N.W. S-5 S-6 S-5 S-6 20 11 7 7 9 8 2 3 45 .0 72 .7 28.6 42 .9 n .s n .s 9 i x 69 C exp, 400 f t naive S .E W. S .E W. S-8 D-l S-8 D-l 20 25 3 11 8 9 1 4 40 .0 36.0 33 .3 36.4 n. s n.s. Table 6. Homing performance from d i f f e r e n t d i r e c t i o n s . n.s. = not s i g n i f i c a n t s. = s i g n i f i c a n t * = Fisher's t e s t exp. = experienced o I t i s very l i k e l y that 'dead reckoning' i s not part of the homing mechanism. Experiment 8: E f f e c t of distance on homing performance This experiment i s concerned with the e f f e c t of d i s -tance on homing performance. I f homing involves a random search or a random r a d i a l scattering process then with the release of f i s h at progressively greater distances, the number of successful returns should decrease r a p i d l y . Method (a) In t h i s preliminary experiment, naive f i s h from s i t e A were displaced to three distances about one, three and six hundred feet (stations S-7, S-8 and D-l respectively) to the north on 6 A p r i l 1968. A group of f i s h (control) was returned to the s i t e . (b) The r e s u l t s of replacement . and displacement experiments conducted throughout 1968 and 1969 were compiled according to distance displaced, s i t e s (A, B, and C), time of displacement (spring-summer and f a l l -winter periods) and 'experience' (naive and experienced f i s h ) . In both cases recovery data from up to four months after displacement were analysed. Results (a) The returns of the f i s h displaced to the three distances were 52.4%, 45.0% and 27.3% for 100, 300 and 600 f t . respectively (Table 7). The recoveries for the control (0 f t . ) was 40.0%; t h i s value was lower than the returns of f i s h from 100 and 300 f t . This was probably due to straying. The replaced f i s h might be more prone to abandon th e i r home i f they were disturbed and handled than those f i s h which were displaced. This explanation was suggested for birds and bats (Davis, 1966); the recoveries of these animals i n the i r home areas when replaced had, on occasions, been observed to be lower than those which were displaced. Inspection of the r e s u l t s indicates that there i s a decrease i n homing returns with increasing distance. Further tests were made on accumulated data of other displacement experiments with respect to distance and displacement. (b) This section i s concerned with a further test for the ef f e c t s of distance on homing performance. The com-pi l e d r e s u l t s are given i n Table 8. The re s u l t s of the seven categories again showed, a decrease i n homing returns with the increase i n distance of displacement from the s i t e . Release Distance Number Number si t e Displaced Released Homed % S-7 S-8 D-l 0 f t 100 300 600 10 21 20 11 4 11 9 3 40 .0 52 .4 45 .0 27 .3 Table 7. E f f e c t of distance on homing performance. Naive f i s h from s i t e A displaced on 6 A p r i l 1968. Cate- Season Home 'Exper- Distance Release gory Released Site ience 1 Displaced Site (i) Spring- A Naive 0 f t . Summer 100 S-7 1969 300 S-9 600 D-l ( i i ) " B 0 100 S-9 300 S-7 400 A-4 ( i i i ) " C 0 100 S - l l 300 .S-8 1000 S-12 (iv) " C Exp. 100 S - l l 200 S-10 300 S-8 1000 S-12 (v) F a l l - A Naive 0 Winter 100 S-7 1968 300 S-9 400 B-5 Number Number Regression Test Released Homed % Homing x Distance t - value (see text) 205 139 67.8 -20.95 s 197 101 56.5 218 93 42.7 56 13 23.2 34 24 70.6 -16.38 s 174 118 67.0 125 78 62.4 86 52 60.5 32 20 62.5 - 6.04 s 206 128 62 .1 20 11 55.0 6 3 50.0 58 48 77.6 - 2.18 n.s 100 76 76.0 48 34 70.8 7 5 71.4 5 2 40.0 +19.4 n.s 41 7 11.1 30 5 16.7 51 9 17.6 Continued . . . Cate- Season Home 'Exper- Distance Release Number Number Regression Test gory Released Site ience' Displaced Site Released Homed % Homing x Distance t - value (see text) (vi) F a l l -Winter 1968 Naive 100 f t 200 400 S - l l S-10 S-7 11 10 3 3 4 1 27.3 40 .0 33 .3 + 0.15 n .s ( v i i ) Exp, 100 200 400 S - l l S-10 S-7 46 93 20 26 50 8 56.5 53 .8 40 .0 8.03 s . Table 8. Summary of the res u l t s of experiments conducted to study the effect of distance of displacement on homing performance. (1968-1969) Exp. = experienced m U l A test more rigorous than the chi-square t e s t was used. The t- t e s t on the slope of a regression between percentage hom-ing performance and distance displaced (taking into account the variance and sample size by weighting) was conducted on each of the seven categories. The tests showed s i g n i f i -cant e f f e c t s of distance on homing performance for cate-gories ( i ) , ( i i ) , ( i i i ) and ( v i i ) while no s i g n i f i c a n t e f f e c t of distance was obtained for categories ( i v ) , (v) and (vi) . This discrepancy between the two groups of re s u l t s could be explained i n terms of season during which the experiments were conducted and i n terms of 'experience'of the f i s h . Experiments conducted during the spring-summer period showed a distance e f f e c t for naive f i s h (categories ( i ) , ( i i ) and ( i i i ) ) but not for experienced f i s h (category (vi)). This difference i n distance e f f e c t was probably related to the ' experience 1 of the f i s h . The nature and importance of 'experience' i n homing was tested i n experiment 9. Some-how with increasing displacement distances from the home range the homing performance of the experienced f i s h was r e l a t i v e l y better than the homing performance of the naive f i s h . 57 On the other hand experiments conducted during the fal l - w i n t e r months showed no s i g n i f i c a n t e f f e c t of distance on the naive f i s h (categories (v) and (vi))but a s i g n i f i c a n t e f f e c t of distance was obtained for the experienced f i s h (category ( v i i ) ) . The homing returns of the naive f i s h during these months were very low, thus no s i g n i f i c a n t e f f e c t of distance could be detected. The e f f e c t of d i s -tance was perhaps masked by the ef f e c t of the rough weather conditions. The s i g n i f i c a n t e f f e c t of distance on the ex-perienced f i s h during these months appeared to contradict the r e s u l t s obtained for category ( i v ) , above, which showed no s i g n i f i c a n t e f f e c t of distance on the experienced f i s h . This discrepancy could be due to the fact that the distance e f f e c t on the homing performance of experienced f i s h was enhanced during rough weather conditions and therefore detected i n the experiments conducted during f a l l - w i n t e r months. Apparently the homing a b i l i t y of 0. maculosus decreases with increasing distance from the home s i t e . However t h i s e f f e c t i s modified by the weather conditions and the 'exper-ience' of the f i s h . Though there was some e f f e c t of distance on homing a b i l i t y , the r e s u l t s showed that the f i s h could home from as far as a thousand feet from their home range 58 (categories ( i i i ) and (iv)). Experiment 9: Ef f e c t of 'experience' on homing performance. This experiment i s concerned with the difference i n homing performance between naive and experienced f i s h . Naive f i s h are newly tagged f i s h which have not been d i s -placed previously while experienced f i s h are f i s h which have been displaced and have been shown to home at least once. This experiment i s to tes t whether learning i s involved i n homing or not. I f learning i s involved one would expect an improvement i n homing performance e s p e c i a l l y i n i n d i v i d -uals which were repeatedly displaced to the same areas. Method Two sub-experiments were conducted: (a) Both naive and experienced f i s h from s i t e C were displaced i n six separate displacements during July 1969. These f i s h were displaced to station S - l l about one hundred feet south of the home s i t e . Recovery data from up to four months after r e -lease were analysed. (b) The homing performance of repeatedly displaced f i s h was studied. The f i s h studied were from s i t e C. During June to July 1969 naive f i s h were displaced. Those f i s h which returned were displaced repeatedly. The d i s -placement h i s t o r y of these f i s h \was? followed and their homing performance up to October 1969 was compiled accord-ing to the number of times they have been displaced. In th i s way about two hundred of the i n i t i a l l y naive f i s h (displaced during June-July period) were followed. Most of these f i s h were displaced to between one to three hundred feet south of the home s i t e . Results (a) Altogether, one hundred experienced f i s h and sixty-seven naive f i s h were displaced during July 1969 (Table 9) i n six separate displacements. A chi-square test on the t o t a l showed a s i g n i f i c a n t difference i n homing return between the experienced and the naive categories. However, ind i v i d u a l tests made on each displacement experiment showed that s i g n i f i c a n t differences occurred i n displacement ex-periments 1, 4 and 6 only. The homing returns of the rest, nevertheless, showed higher proportion of returns for the experienced f i s h than for the naive f i s h except for displace-ment 3. Displacement 3 showed higher homing returns for naive f i s h ; t h i s was probably due to sample size and trapping i n e f f i c i e n c y . Displacement 'Experienced ' Experiment Date Number Number No. Released Released Homed % 1 5 v i i 69 17 15 88.2 2 6 v i i 69 11 9 81.8 3 18 v i i 69 13 8 61.5 4 19 v i i 69 15 12 80.0 5 20 v i i 69 13 10 76.9 6 21 v i i 69 31 22 71.0 _ Naive  Number Number x test Released Homed % Experienced x naive 23 11 47.8 s. 7 4 57.1 n.s. * 4 3 75.0 n.s. * 7 1 14.3 s. * 3 2 66.7 n.s. * 23 8 34.8 s. * Total 100 76 76;:0 67 29 43.3 s Table 9. Homing performance of 'naive' and 'experienced' f i s h . Home range = C; Displaced to S - l l (100 f t . ) * Fisher's t e s t . o 61 This difference i n homing performance between the naive and the experienced f i s h could be due to either l e a r n -ing by the l a t t e r or some q u a l i t a t i v e inherent differences i n the homing a b i l i t y of the f i s h . A f i s h which has homed at least once could have become familiar with the environ-ment outside i t s home range thus improving i t s homing a b i l i t y when i t i s displaced again. I f some f i s h have homing a b i l i t y while others have not then after the f i r s t d i s -placement those which have no homing a b i l i t y are selected against. Thus the experienced category would consist mainly of f i s h with homing a b i l i t y while the naive category would consist of both f i s h with homing a b i l i t y and f i s h without such an a b i l i t y . Such a difference i n composition could then account for the differences i n homing performance between the experienced and the naive categories. (b) Of the two hundred naive f i s h displaced for the f i r s t time about 64% returned (Table 10). One hundred and six of those which returned were displaced a second time, about 66% of them returned . Subsequent r e s u l t s of repeated displacement showed that about 65%, 75% and 68% of the f i s h displaced on th e i r t h i r d , fourth and f i f t h displacements, respectively, returned to s i t e C. The r e s u l t s also showed 62 Number of times displaced Number Released Number Homed % 1 200 128 64 2 106 70 66 3 60 39 65 4 28 21 75 5 19 13 68 6 2 2 7 1 1 9 1 1 Table 10. Homing performance of repeatedly displaced f i s h . Home range = C. Release s i t e s = S-8, S-10 and S - l l £300 f t . ) 63 that a few f i s h homed on t h e i r sixth, seventh and ninth displacements . The r e s u l t s indicate that there i s no s i g n i f i c a n t improvement i n homing performance with repeated displace-ments. I f learning of the environment was involved an im-provement would be expected. However, the r e s u l t s seem to indicate that learning was not involved. Nevertheless, no d e f i n i t e conclusions could be made u n t i l more i s known about the f i s h which did not return; about one-third of the f i s h were l o s t i n each repeat displacement. Experiment 10: E f f e c t of sex and size on homing performance. This experiment i s concerned with the difference i n homing performance between f i s h of d i f f e r e n t sexes ;and s i z e s . I f homing performance i s related to sex then i t i s l i k e l y that homing a b i l i t y may be related to some b i o l o g i c a l function. I f larger f i s h home better than smaller f i s h then i t i s possible that improvement i n homing a b i l i t y i s related to learning and experience of the f i s h . Method Two sub-experiments were considered: 64 (a) A l l the recovery data (from up to four months) of displacement experiments conducted on f i s h from s i t e C during the spring-summer period were compiled according to size groups (at 10 mm i n t e r v a l s from 35 mm to 79 mm)' and sex. Both the naive and experienced f i s h were considered together. (b) This section was a reanalysis of the above data. Only the r e s u l t s of displacements of f i s h up to three hundred feet were used. The data were compiled according to sex (male and female) and age (yearlings and greater than one year o l d ) . Green (1967) shows that f i s h less than 55 mm t o t a l length are below one year old; t h i s length i s approximately equivalent to 45 mm standard length. The 45 mm length was used to separate the two age groups. The naive and the experienced f i s h were considered separately. Results (a) A three factor G-test of independence (Sokal and Rohlf, 1969) of the r e s u l t s i n Table 11 was conducted. The three factors were size, sex and homing performance. The r e s u l t s of t h i s test showed no s i g n i f i c a n t differences i n homing performance between the sexes or among the d i f f e r e n t size groups . 65 Size Number Number Per cent groups Released Homed homed of (mm) # released M F M F M F 35-39 16 14 9 9 56 64 (30) (18) (60) 40-44 77 103 40 50 52 49 (108) (90) (50) 45-49 69 60 40 28 58 47 (129) (68) (53) 50-54 53 79 31 59 58 75 (132) (90) (68) 55-59 42 48 27 23 64 48 (90) (50) (56) 60-64 35 29 20 17 57 59 (64) (37) (58) 65-69 14 17 6 1 43 14 (21) (7) (33) 70-74 0 8 0 7 0 88 (8) (7) (88) 75-79 0 1 0 0 0 0 (1) (0) ( 0) Total 306 349 173 194 57 56 (655) (367) (56) Table 11. Homing performance according to sex and size of the f i s h . Summary of displacement experiments conducted during 1969. Home range = C. ( ) = T o t a l . 66 (b) The same s t a t i s t i c a l test was conducted on the compiled data i n Table 12. The r e s u l t of the test also showed no s i g n i f i c a n t differences i n homing performance between the sexes and between one year old f i s h and f i s h greater than one year o l d . The same r e s u l t s were obtained for both naive and experienced f i s h . The above r e s u l t s show c l e a r l y that male and female f i s h home equally w e l l . Size and age of the f i s h do not seem to af f e c t homing a b i l i t y . Experiment 11: Sensory impairment and mortality. This experiment i s concerned with the e f f e c t of sensory impairment on the su r v i v a l of the f i s h . Laboratory and f i e l d experiments were conducted. Method (a) Laboratory study: Fish from the f i e l d were transported back to the laboratory where they were tagged and treated and kept i n an aquarium. The mortality rate of untreated, b i l a t e r a l l y b l i n d and b i l a t e r a l l y anosmic f i s h was observed almost d a i l y . Eleven f i s h of almost equal size (approx. 45 mm standard length) per treatment category Season 'Experience' Size Sex Number Number Group Released Homed % Spring- Experienced ^45mm Summer >45mm Naive 45mm >45mm M 40 22 55.0 F 47 27 57.5 M 109 70 64.2 F 122 82 67.2 M 47 25 53.2 F 54 27 50.0 M 66 43 65.2 F 82 46 56.1 Table 12. Homing performance according to sex and size of f i s h . (Selected data from Table 11) . —I 68 were observed. No food was given to the f i s h throughout the experiment. (b) F i e l d Study: Three treatment categories of f i s h (untreated, b i l a t e r a l l y b l i n d and b i l a t e r a l l y anosmic) were caged i n a minnow trap and kept i n a tide-pool. Ten f i s h per category were observed at two-week i n t e r v a l s . Fish of about the same size were used. Results (a) The laboratory experiment showed that the three categories of f i s h (untreated, b i l a t e r a l l y b l i n d and b i -l a t e r a l l y anosmic) survived equally well up to thirty-one days (Table 13a) . The high mortality after that time was due to the f a i l u r e of the aeration and cooling system of the aquarium i n which the fishv.were kept. (b) F i e l d r e s u l t s showed that a l l three categories survived equally well up to about eighty-one days (Table 13b). 90%, 80% and 100% of the untreated, blind and anosmic f i s h , respectively, survived up to eighty-one days. Between the e i g h t y - f i r s t and the ninety-third days mortality of the blind and anosmic f i s h were high compared to that of the untreated f i s h . This mortality was probably due to starvation. 69 Days Elapsed Numbers Survivinq Control Blind Anosmic a) 0 11 11 11 25 10 10 11 26 10 10 10 31 10 10 9 41 * 2 2 3 b) 0 10 10 10 19 10 10 10 24 10 9 10 42 9 9 10 67 9 8 10 81 9 8 10 93 8 1 3 Table 13. B i l a t e r a l v i s u a l and olf a c t o r y impairment and mortality. (a) Laboratory study (16 i v 69) (b) F i e l d study (28 v i 69) * Mortality due to f a i l u r e of aeration• and cooling system. 70 The r e s u l t s of experiments 11a and b showed that sensory impairment did not seem to affe c t the s u r v i v a l of the f i s h within a short period of time. Survival of the treated f i s h when released i n the f i e l d , however, was not known. I t was assumed that the treated f i s h could survive up to about three months. Recovery data i n la t e r studies involving treated f i s h were based on t h i s time period. Observations i n the f i e l d showed that the immediate response of b l i n d f i s h when released i n a tide-pool was to swim towards the surface of the water, swimming into ob-stacles i n an e r r a t i c manner, u n t i l they arrived at a shallow section of the pool (about two to three inches deep). These f i s h dispersed i n a l l d i r e c t i o n s and there seemed to be no d i r e c t i o n a l preference. They would remain at the same spot and seldom s h i f t t h e i r positions u n t i l the time of high t i d e . They would then swim out of the pool with the f i r s t few waves of the incoming t i d e . Very often they would not swim against the incoming wave but would hold f i r m l y to the ground with t h e i r pectoral f i n s and then swim out with the receding water. Normal and anosmic f i s h would often remain i n the deeper parts of the pool, hiding i n crevices. They would not swim out of the pool with the f i r s t waves which covered the pool. No observations could be made after the f i r s t h a l f hour of the incoming t i d e . However, observations after one t i d a l cycle showed that the majority of the f i s h l e f t . Several days l a t e r none of the displaced f i s h remained. Observations i n the aquaria showed that b l i n d f i s h were able to feed o f f the bottom of the tanks. Anosmic f i s h , however, were unable to feed i n most cases although they could see and swim as well as the normal f i s h . Blind f i s h i n aquaria responded to brine shrimp extracts; they swam around the tank quite a c t i v e l y when the extract was i n t r o -duced . Normally they would s i t q u i e t l y at the bottom of the tank. Anosmic f i s h , however, did not respond to the brine shrimp extract. When charcoal p a r t i c l e s were i n t r o -duced into the tanks, the bl i n d and the anosmic f i s h did not respond, but normal f i s h would swim towards the p a r t i c l e s and attempt to feed. Normal f i s h responded to brine shrimp extracts by a c t i v e l y searching around. Apparently these f i s h feed by smell as well as by sight. However, the reason why anosmic f i s h could not feed could be due to the ef f e c t of trauma from treatment. Experiment 12: B i l a t e r a l v i s u a l and ol f a c t o r y impairment and homing performance. The roles of v i s i o n and o l f a c t i o n i n homing are studied i n t h i s experiment. The homing performance of b i l a t e r a l l y b l i n d and b i l a t e r a l l y anosmic f i s h when displaced was i n -vestigated. I f blind f i s h home then v i s i o n i s not involved i n homing but i f anosmic f i s h home then o l f a c t i o n i s not used for homing. Method Replacement and displacement experiments were con-ducted throughout 1968, 1969 and 1970 on three categories of f i s h : normal (untreated), b i l a t e r a l l y b l i n d and b i l a t e r -a l l y anosmic. Fish from s i t e s A and B were used. In each release an almost equal number of individuals per treatment category were used. The f i s h were released at the same displacement station i n each release. Groups of f i s h con-s i s t i n g of the three treatment categories were displaced to 100 f t . , 300 f t . and 400 f t . from th e i r home range i n the same general d i r e c t i o n on d i f f e r e n t occasions. Owing to sc a r c i t y of captured f i s h and the time required to tag each ind i v i d u a l f i s h , displacements to d i f f e r e n t distances were not conducted on the same day. The size range of the f i s h used for each treatment category i n each release was si m i l a r . The sex of the f i s h was not considered for each release. Recovery data from up to three months after each release were used for anal y s i s . Results Replacement Experiments The home range f i d e l i t y of both bl i n d and anosmic f i s h i s shown by the r e s u l t s of the replacement experiments (Table 14 and Appendix I I ) . A three factor test of indepen-dence (Treatment x Season x Home range f i d e l i t y ) on the t o t a l , the combined r e s u l t s of experiments conducted on Sites A and B, showed no difference i n home range f i d e l i t y between the spring-summer and the fa l l - w i n t e r periods for both treated and untreated f i s h (Table 15a) . However, treated f i s h appeared to be less f a i t h f u l to the i r home range than the normal f i s h ; the s t a t i s t i c a l test showed a s i g n i f i c a n t e f f e c t of treatment (Control x Treated of Table 15a) . S u s c e p t i b i l i t y to removal ..by wave action at high tide or behavioural changes due to treatment may be the cause of the lower degree of home range f i d e l i t y observed for both Release Home Control Blind Anosmic  S i t e Season Site NR NH % NR NH % NR NH % Row # Replaced Spring- A 8 7 87.5 23 1 4.4 27 6 22 .2 1 (Oft) Summer B 43 30 69.8 48 13 27 .1 47 4 8.5 2 Total 51 37 72 .6 71 14 19 .7 74 10 13 .5 3 F a l l - A 4 1 . 25.0 4 1 25.0 4 o: 0 .0 4 Winter B 28 13 46.4 42 4 - 9.5 43 8 18.6 5 Total 32 14 43 .8 46 5 10 .9 47 8 17 .0 6 100 f t .S-7 Spring- A 107 55 51.4 101 28 27.7 98 7 7.1 7 S-9 Summer B 84 32 38.1 88 28 31.8 88 1 1.1 8 Total 191 87 45.6 189 56 29.6 186 8 4.3 9 S-7 F a l l - A 49 7 14.3 44 4 9.1 47 2 4.3 10 S-9 Winter B 86 33 38.4 79 4 5.1 83 6 7 .2 11 Total 135 40 29.6 123 8 6.5 130 8 6.2 12 300 ft.S-8 Spring- A 14 11 78.6 16 10 62 .5 17 0 0 .0 13 S-8 Summer B 25 10 40.0 24 2 8.3 25 1 4.0 14 Total 39 21 53.9 40 12 30.0 42 1 2 .4 15 S-8 F a l l - A 34 7 20.6 30 4 13 .3 27 1 3.7 16 S-8 Winter B 14 2 14.3 3 0 0.0 2 0 0.0 17 Total 48 9 18.8 33 4 12 .1 29 1 3.5 18 400 ft.B-3 Spring- A 42 8 19.1 44 8 18.2 42 0 0 .0 19 Summer F a l l - 14 5 35.7 16 2 12 .5 17 1 5 .9 20 Winter Table 14. Homing performance of b i l a t e r a l l y blind, b i l a t e r a l l y anosmic and normal (control) f i s h during spring-summer and fall-winter from 100, 300 and 400 f t . Home range = A. NR = number released; NH = number homed. 75 Displacement Distance Hypothesis df Oft. 100 f t . 300 f t . 400 f t . Season x Treatment 2 0.01 0 .30 3 .47 0 .21 Season x Homingl 1 3.55 21 .11* 8 .51* 0 .38 Treatment x Homings- 2 60.82* 118 .83* 29 .00* 11 .31* Control x (treated) 1 60.73* 83 .07* 15 .49* 5 .04* Blind x Anosmic 1 0 .09 35 .76* 13 .51* 6 .27* Interaction 2 5 .27 15 .72* 7 .02* 1 .85 Total 7 69.65* 155 .96* 48 .00* 13 .75* (a) Hypothesis df Treatment Control Blind Anosmic (b) Season x Distance 3 Season x Homing 1 Distance x Homing 3 Replaced x Displaced 1 100 f t x (300ft + 400 f t . ) 1 300 f t . x 400 f t . 1 Interaction 3 13 .55* 17.71* 23.82* 18.26* 3 .45 2 .10 11.18* 5 .22 28.45* 1.61 4.78 3 .36 1.08 14.70* 13.76* 0.91 0 .04 0.21 Total 10 66.26* 40.06* 19.36* Table 15. Results of the three factor G-test of independence on the r e s u l t s of Table 14, (a) Homing x Season x Treatment for 0,100, 300 and 400 f t . (b) Homing x Season x Distance for control, b l i n d and anosmic f i s h . ^Home range f i d e l i t y for replaced (0 Ft.) f i s h * S i g n i f i c a n t . the b l i n d and the anosmic f i s h . Due to t h e i r i n a b i l i t y to seek shelter or maintain t h e i r p osition during high tide, treated f i s h may be more e a s i l y dislodged from their pools than normal untreated f i s h . I t i s also possible that the treated f i s h tend to stray more than normal f i s h and t h i s i s probably caused by the handling and the d r a s t i c opera-tions on the f i s h . M o r t a l i t y due to treatment per se or predation does not appear to be the major cause. Experi-ment l i b has shown that both treated and normal f i s h survived equally well within a period of about three months—the period of the experiments. Predators such as mink, otters and f i s h are r a r e l y observed at the study s i t e s . However, mortality due to wave action may be important. Apparently there i s no s i g n i f i c a n t difference i n home range f i d e l i t y between the b l i n d and the anosmic f i s h (Blind X Anosmic of Table ]5a) . Most probably the e f f e c t s of both v i s u a l and o l f a c t o r y treatments are s i m i l a r ; there appears to be no difference i n mortality e f f e c t s between the two treatments. Displacement experiments Displacement experiments were conducted to study the homing performance of both b i l a t e r a l l y b l i n d and b i l a t e r a l l y anosmic f i s h . Homing from 100 f t . , 300 f t . and 400 f t . \wasj studied. The r e s u l t s of i n d i v i d u a l displacement experi-ments are presented i n Appendix I I . A summary of a l l the displacement experiments according to season of release (spring-summer and f a l l - w i n t e r ) , s i t e of study (A and B), distance displaced (100 f t . , 300 f t . , and 400 f t . ) and treatment (normal or control, b l i n d and anosmic) i s shown i n Table 14. The r e s u l t s of the three factor test of independence (Treatment x Season x Homing performance) on the t o t a l , for each displacement distance (100, 300 and 400 ft.) are shown in Table 15a. The homing performance of both the blind and the anosmic f i s h are s i g n i f i c a n t l y lower than that of normal f i s h for a l l three displacement distances (Control x Treated) . The homing performance of anosmic f i s h i s s i g n i -f i c a n t l y lower than that of blind f i s h for a l l three distances (Blind x Anosmic). Apparently b l i n d f i s h home better than anosmic f i s h , thus implying that v i s i o n i s less important than o l f a c t i o n i n the homing process. Although the r e s u l t s of the t o t a l have 78 shown that normal f i s h generally home better than b l i n d f i s h , several examples are available to show that on some d i s -placements b l i n d and normal f i s h homed equally w e l l . One example was the displacements of f i s h from s i t e B to 100 f t . during the spring-summer period (row 8 of Table 14). Another was shown by the homing performance of f i s h from s i t e A displaced to 300 f t . during the same season (row 13 of Table 14). Rows 4 and 19 also show almost equal homing returns for both normal and b l i n d f i s h . That v i s i o n i s not very important i n homing i s substantiated by these examples. Experiment 6 has shown that homing of normal f i s h i s generally lower during f a l l - w i n t e r than during spring-summer. S i m i l a r l y the r e s u l t s of t h i s experiment (12) show that the homing performance of normal as well as bl i n d f i s h i s generally lower during the f a l l - w i n t e r than during the ..spring-summer period (Season x Homing performance of Tables 15a and b ) . At 400 f t . the e f f e c t of season i s not detected; t h i s was probably due to the small sample size for the f a l l -winter period. The e f f e c t of season on the homing performance of b l i n d f i s h i s c l e a r l y shown by the r e s u l t s of ind i v i d u a l displace-ment experiments (Appendix I I ) . The homing performance of 79 b l i n d f i s h was generally low from December to A p r i l but improvement could be detected from May to June. As sug-gested, t h i s change with advancing season i s probably due to the ef f e c t s of sea conditions. The r e s u l t s for anosmic f i s h show no difference i n homing performance between the two time periods (Table 15b) . This i s not unexpected since anosmic f i s h are unable to home. Home range f i d e l i t y and homing performance. A comparison of the re s u l t s between replacement and displacement experiments shows that the homing performance of b l i n d f i s h i s not s i g n i f i c a n t l y d i f f e r e n t from t h e i r home range f i d e l i t y data (Replaced x Displaced of Table 15b). On the other hand the percentage homing returns of anosmic f i s h i s s i g n i f i c a n t l y lower than t h e i r percentage home range f i d e l i t y . This again provides evidence i n support of the hypotheses that v i s i o n i s not important while o l f a c t i o n may be the sensory mechanism involved i n the homing of 0. maculosus. Experiment 13: Removal of pectoral and p e l v i c f i n s and homing performance. This experiment i s to tes t the hypothesis that homing 80 i s through the detection of sea bottom cues . Since the paired f i n s are i n constant contact with the sea f l o o r , the sensory structures involved may be located mainly on the pectoral and p e l v i c f i n s . Method The^homing returns from 100 f t . of f i s h with th e i r pelvics or pectorals removed were observed. Recovery data "up to two months were analysed . Results The removal of the p e l v i c or the pectoral f i n s does not seem to aff e c t homing a b i l i t y of the f i s h (Table 16). The r e s u l t s imply that chemical detection by means of chemi-c a l contact with the sea bottom with the paired f i n s i s not important. Experiment 14: U n i l a t e r a l v i s u a l and olf a c t o r y impairment and homing performance. This experiment i s conducted to study the homing per-formance of u n i l a t e r a l l y b l i n d and u n i l a t e r a l l y anosmic f i s h . I t i s an attempt to determine whether homing requires both the paired organs or not. 81 Treatment Date Number Number % Released Released Homed PELV 16 i 70 29 2 6.9 23 i 70 12 7 58.3 25 v 70 18 6 33 .3 Total 59 15 25.4 PECT 25 v 70 18 7 38.9 Table 16. Homing performance of f i s h with pelvics (PELV) and pectorals (PECT) removed. Home range = 13. Release s i t e = S-9 (100 ft.) . 82 Method Fish from two s i t e s (A and B) were studied. Both replacement and displacement experiments were conducted. Four categories of treatment were released: normal, u n i l a t -e r a l l y b l i n d , u n i l a t e r a l l y anosmic and u n i l a t e r a l l y b l i n d as well as u n i l a t e r a l l y anosmic. Recovery data from up to three months after release were analysed. The distance of displacement was 100 f t . , 300 f t . and 400 f t . Results The homing performance of the normal (control) f i s h and the treated f i s h for both s i t e s A and B (Tables 17a and b respectively) does not appear to d i f f e r . S t a t i s t i c a l test (two factor G-test of independence: treatment and homing performance) on the combined data for f i s h from s i t e A (Table 17a) showed no s i g n i f i c a n t e f f e c t s of treatment. S i m i l a r l y the s t a t i s t i c a l t e s t (three factor G-test: distance, treatment ..and homing performance) on the re s u l t s i n Table 17b also showed no s i g n i f i c a n t e f f e c t of treatment on the homing performance of the f i s h . Apparently f i s h with only one eye or only one o l f a c t -ory organ can home as well as normal f i s h . Comparing the res u l t s of t h i s experiment with that of experiment 12, U n i l a t e r a l impairment Release Date Control Blind Anosmic Blind & Anosmic Si t e Released NR NH % NR NH % NR NH % NR NH % (distance) I • 3 30.0 4.. 1 25.0 I I 12 75.0 1 5 1 1 5 33.3 1 1 2 33 .3 3 1 1 1 33 .3 5 i i : L 1 20.0 5 a 0 0.0 71-'- 0 0.0 5 i v 2 40.0 Total 34 12 35.3 37 17 45.9 29 7 24.1 10 3 30.0 (a) S-7 (100 f t ) 31 i i i 70 10 2 20 .0 10 S-8 (300 f t ) 5 v i 70 14 10 71 .4 16 B-3 (400 f t ) 18 X 68 10 0 0 .0 6 Replaced 11 i v 69 16 10 62 .5 16 9 56 .3 16 8 50 .0 (Oft) 26 i v 69 9 8 88 .9. 10 5 50 .0 10 6 60 .0 Total 25 18 72 .0 26 14 53 .8 26 14 53 .8 S-9 (100 ft) 5 i i i 69 6 2 33 .3 15 i i i 69 3 2 66 .7 2 1 50 .0 3 2 66 .7 2 i v 69 7 4 57 .1 6 5 83 .3 S-8 (300 ft) 27 i v 69 13 9 69 .2 13 5 38 .5 13 5 38 .5 S-7 (400 ft) 15 i i i 69 5 5 100 .0 Total 23 15 65 .2 26 16 61 .5 22 9 40 .9 Table 17. Homing performance of u n i l a t e r a l l y blind, u n i l a t e r a l l y anosmic and normal (control) f i s h from home range (a) A and (b) B. i = ri g h t side impaired; i i = l e f t side impaired; i i i = l e f t eye and ri g h t naris impaired; i v = ri g h t eye and l e f t naris impaired. LO 84 u n i l a t e r a l anosmic f i s h seems to home better than b i l a t e r a l anosmic f i s h . This implies that the f i s h need not require both ol f a c t o r y organs for homing; they can home with one funct-i o n a l organ. In a comparison of homing returns of u n i l a t e r -a l and b i l a t e r a l b l i n d f i s h , the former shows better homing performance than the l a t t e r . This indicates that v i s i o n may be useful i n homing although i t may not be e n t i r e l y needed i n the homing mechanism as shown i n experiment 12. Vi s i o n may be used to maintain the pos i t i o n of the f i s h i n the surging currents, during the homing process. Experiment 15: Homing on cloudy nights. This experiment i s concerned with the homing a b i l i t y of the f i s h during dark cloudy nights. I f the f i s h do not home at night then day-time environmental cues are involved i n the homing process. I f they do home on cloudy nights i t i s possible that v i s u a l cues such as stars and topographic features are not used. Method Fish from s i t e C were displaced to 100 f t . and 400 f t . (stations S - l l and S-8 respectively) at dusk prior to 85 the night high t i d e . The nights involved happened to be dark cloudy nights. No stars could be seen and i t was pit c h black to the human eye. Recovery attempts of the f i s h i n the home s i t e were conducted at the succeeding low t i d e . Subsequent recovery attempts at two-week in t e r v a l s were conducted and the homing returns from up to four months after each release were included for comparison. A straight return from the release s i t e s to the home s i t e by the f i s h was not possible; there i s a rock outcrop or 'ridge' i n between the two s i t e s . The displaced f i s h have to swim seawards, make a ninety degree turn and then swim shorewards. Results An average of about 12.4% of the fi s h Q r e t u r n e d over-night from 100 f t . within one t i d a l cycle (Table 18). At least one f i s h returned from 400 f t . within that same time period. The corrected time and height of the high t i d e s (from the Tofino t i d e data i n the Canadian Tide and Current Tables for 1969) for the nights concerned are given i n the ta b l e . The tides alone could not have completely covered the home s i t e and the displacement station S - l l during those nights. However, two foot swells which are common during t h i s time of the year w i l l e a s i l y cover the two areas at 86 Night Date High Tide Number Number % Total % Released Time Height Released Homed Event-(PST) (feet) Overnight u a l l y Homed Displaced to S - l l (100 feet) 13 v i 69 2159 9.7 27 11.1 24 88.9 15 v i 69 0029 9 .9 40 15 .0 32 80 .0 3 v i i i 6 9 0023 9.4 22 9.1 19 86.4 To t a l 89 11 12 .4 75 84.3 Displaced to S-8 (400 feet) 3 v i i 69 0319 9.4 22 1 4.6 13 59.1 Table 18. Homing on dark cloudy nights. Home range = C. 87 flood t i d e s . Both the home s i t e and the station S - l l are at the nine foot l e v e l . The time of submergence of these two areas could not be more than one hour taking into consider-ation the t i d a l height and the swells during those nights. Nevertheless, eleven f i s h returned from 100 f t . away (S - l l ) and one f i s h returned from 400 f t . (S-8) within that hour. Moreover they returned on dark cloudy nights . These r e s u l t s imply that c e l e s t i a l cues such as stars are not used by the f i s h to home. I t i s probable that other v i s u a l cues are also not involved. However, the vis u a l s e n s i t i v i t y of t h i s species i s not known, and i t i s possible that t h e i r v i s i o n i s more sensitive than that of the human. Hence i t i s quite possible that these f i s h use shoreline cues or even v i s u a l topographic cues of the sea f l o o r i f they have s u f f i c i e n t l y acute and sensitive v i s i o n . The fact that these f i s h have to detour around a ridge also implies that the cues used for homing have to provide the necessary information to the f i s h . A l t e r n a t i v e l y , these overnight returns could be due to random chance. However t h i s i s u n l i k e l y considering the fact that only one hour i s allowed for the f i s h to home as well as the complexity of the route the f i s h has to take i n order to home. 88 Experiment 16: Homing to pools with destruction of the immediate environment. This experiment i s concerned with the homing perfor-mance of displaced f i s h to home pools with destruction of the immediate environment of these pools . This i s an a t -tempt to find out about the nature and the source of the cues used by the f i s h either for ori e n t a t i o n a l purposes i f directed movement i s involved or for recognition of thei r home area. Method The pools to be destroyed were drained and a l l the fauna, f l o r a and debris were removed. The pools were then scrubbed with a st e e l brush and subsequently burnt using gasoline and kerosene. The f i s h from these pools were tag-ged and released only after the pools had ..been further cleaned out by the t i d e s . This took about two days. Two sub-experiments were conducted. (a) In July 1969, three f a i r l y isolated pools—PD-1, PD-2 and PD-3—were destroyed and the f i s h from these pools were displaced to stations S-8 and S-10 (see F i g . 1 for locations of the pools and stations) . Normal f i s h were tested . 89 At the same time normal f i s h from four untreated pools, s i t -uated near to the treated pools, were also displaced to the same stati o n s . These control pools were D-l, E - l , E-2 and E-3. Recovery data i n both the treated and the control (untreated) pools were obtained from trappings and search-ings conducted at two-week i n t e r v a l s . Recovery data from up to four months after release were analysed. (b) During June 1970 pool A-8 i n s i t e A was destroyed (see F i g . 1 for the location of the pool). A four yard s t r i p around the pool was also treated. The pool and the surrounding area were scrubbed, burnt and then treated with IN hydrochloric a c i d . Pool A-7 was used as a control pool. One group of f i s h was replaced and another group was displaced to about 100 f t . (station S-7) . Three treatment categories were released i n each group: normal, b i l a t e r a l l y b l i n d and b i l a t e r a l l y anosmic. At two-week int e r v a l s r e -covery attempts of the f i s h i n a l l the pools within s i t e A were conducted by draining with a gas driven pump. Recovery data from up to two months after release were analysed. Results (a) No s i g n i f i c a n t difference i n the homing perfor-mance of f i s h from the control and \the treated pools was 90 observed (Table 19). The s t a t i s t i c a l test was conducted between the combined data of the three destroyed pools and that of the four control pools. Apparently the f i s h can s t i l l recognise t h e i r home pools even though the pool environment has been destroyed. This implies that the cues used for homing do not come from the plants or the animals of a pool. Chemicals, especi-a l l y organic forms, i n the rock structure of the pools could not be the source of the cues which were most probably destroyed by the heat. I t i s possible, however that the f i s h could s t i l l recognise the home pools either by the i r topographic features or by some other features of the sur-rounding areas. (b) This experiment was i n i t i a l l y conducted to con-firm the r e s u l t s of experiment 16a, above, and to study the e f f e c t of pool destruction on the homing performance of blind and anosmic f i s h as w e l l . Replacement experiments were also conducted to study the home range f i d e l i t y of the treated f i s h to destroyed pools. Results of replacement experiments showed that there i s a general movement out of both the destroyed and the un-91 Release Pool Site Treatment (distance m Home Pool Number Released Number Homed X z test % on t o t a l S-10 Control (160-300) Total D-l E 1-3 5 15 20 2 40.0 Control 10 66.7 x Destroyed 12 60.0 ns Destroyed PD-1 PD-2 PD-3 42 41 79 16 20 22 38.1 48.8 27 .8 Total 162 58 35.8 S-8 Control D-l (400-600) E 1-3 Total Destroyed PD-1 PD-2 PD-3 Total 15 9 60.0 22 6 27.3 Control x 37 15 40.5 Destroyed ns 4 1 25.0 10 8 80.0 18 2 11.1 32 11 34.4 Table 19. E f f e c t of pool destruction on homing performance. (July 1969). 92 treated pools by the bli n d , anosmic as well as the normal f i s h (Table 20). This seems to indicate that both pool destruction and pool draining disturbed the f i s h so much that they moved out. No d e f i n i t e conclusion as to the e f -fect of pool destruction could be made. Most of the normal and the bl i n d f i s h were recovered i n the other pools within s i t e A. I t i s probable that the newly adopted pools are within the home range of the f i s h . Apparently the f i s h can take refuge i n other pools of the i r home range. Somehow pool destruction adversely affected the home range f i d e l i t y of anosmic f i s h . The anosmic f i s h whose home pool was destroyed disappeared from the home area a l -together, although some of the anosmic f i s h from the con-t r o l pool were recaptured within their home range. Results of displacement experiments also showed that pool draining as well as pool destruction affects the pool f i d e l i t y of homing f i s h . As shown by the re s u l t s i n Table 20 most of the f i s h returned to pools other than the home pools. Compared to the r e s u l t s of experiment 4 the proportion of ,normal f i s h returning to the i r home pools i n t h i s experiment (16) i s considerably lower. The former experiment did not Release Pool Home Control B l i n d Anosmic Si t e Treatment Pool NR NHP NHS NR NHP NHS NR NHP NHS Replaced Control A-7 21 1 21 21 2 10 21 0 7 Destroyed A-8 14 1 7 14 0 5 14 0 0 Displaced Control A-7 21 2 15 21 0 6 20 0 2 (S-7;100 ft) Destroyed A-8 14 2 5 14 1 4 14 0 0 Table 20. The homing performance of b i l a t e r a l l y b l i n d , b i l a t e r a l l y anosmic and normal (control) f i s h to destroyed pools. (July 1970) Home Range = A; NR = number released. NHP = number recov-ered i n home pool. NHS = number recovered i n home s i t e . 94 make use of pool draining as the recapture method while the l a t t e r d i d . Perhaps pool draining somehow involved too much pool disturbance which then affects the pool f i d e l i t y of the f i s h inhabitants. The r e s u l t s indicate again that the displaced f i s h do not have to return to one p a r t i c u l a r pool, but can take refuge i n other pools within t h e i r home range. Experiment 17. Discriminatory a b i l i t y of 0. maculosus to water from d i f f e r e n t sources. This experiment i s concerned with the a b i l i t y of the f i s h to discriminate between water from d i f f e r e n t sources. I f f i s h can be shown i n the laboratory to detect differences i n water from d i f f e r e n t sources then perhaps i t i s l i k e l y that the cues involved are odoriferous and water-borne. Extrapolation of laboratory experimental r e s u l t s to f i e l d situations may not be e n t i r e l y v a l i d . They may be useful when used i n combination with other f i e l d evidence. Method Small f i s h (about 20 mm standard length) were brought back to the laboratory i n December, 1969 and kept for three months. The f i s h were reared on frozen brine shrimp. Experimental tests on the discriminatory a b i l i t y of the f i s h were conducted i n March 1970. The apparatus used for the tests was a Y-shaped tank made of plexiglass ( F i g . 3). The terminal arms of the Y-tank were connected to a supply of well aerated and cooled water contained i n a carboy.- The sides of the tank were covered with white paper to avoid the v i s u a l d i s t r a c -t i o n of the f i s h by the observer . Observations were made from above the tank. A s i x t y watt table lamp was placed about s i x inches above the tank. One f i s h was tested at a time. At the st a r t of an experiment, which consisted of a series of test runs (or t r i a l s ) on the same f i s h , the f i s h was allowed to s i t i n the test chamber (T) for about h a l f an hour. A constant flow of sea water from the source (S) was maintained by adjusting the i n l e t and outlet taps ( Tl and T2). The gate (G) was raised and the choice of the f i s h was recorded. A score was given to the arm which the f i s h chose. A score was not given i f the f i s h did not reach the end of j v '-. v . Fig. 3 Y-iiaze set-up . j • -y^y . "; 3 (Ses. v/ater source), B. (Burette), G (Test chamber),-I : - ' . ( f - ; V V.'^'-^" ; .'. Tl &.T2 (Taps),. L(Left arm), .H(Ei-|ht aim), a(Gaee). 97 the arm. The run was repeated by returning the f i s h to the t e s t chamber i f the f i s h only swam h a l f way and turned back. Two types of experiments were made on the same f i s h : a control and a tes t experiment. The control experi-ment was conducted f i r s t and was followed by the tes t experiment. In the tes t experiment, "test" sea water was introduced into one of the arms with a burette (about 30 to 40 ml per minute) and 'control' sea water introduced into the other arm. The 'control' sea water used was the same water as that used for the source (S) . The 'test' sea water used was 'home-tank-water' and 'non-home-tank water'. *Home-tank-water' was the water from the aquaria i n which the experimental f i s h were reared. The water i n the aquaria were i n i t i a l l y obtained from the same source as the water used i n the source (S) . 'Non-home-tank water' was water obtained from other aquaria. In the control experiment no water was introduced through the burettes. Several runs or t r i a l s were made i n each of the pair of experiments consisting of a series of control runs f o l -lowed by a series of test runs oh the same animal. The time i n t e r v a l between runs was about ten minutes during which the Y-tank was flushed with the source water. Altogether, 98 f i v e normal and three b i l a t e r a l l y b l i n d f i s h were tested with 'home-tank' water, and one normal f i s h was tested with 'non-home-tank' water. The purpose of testing b l i n d f i s h i s to see whether discrimination of water from the di f f e r e n t sources i s olfa c t o r y or not. Results The choices of normal f i s h i n the Y-tank were equal-l y d i s t r i b u t e d between the two arms during the control runs (Table 21) . However, introduction of the 'home-tank' water (HTW) into one of the arms, during the test runs, influences the choice of the f i s h i n favour of that arm with the HTW. When HTW was introduced into the l e f t arm (L) a preference for the l e f t arm was shown by Jthe f i s h during the test runs (shown by f i s h A, B and C of Table 21). When HTW was introduced into the r i g h t arm (R) the f i s h chose that r i g h t arm (as shown by f i s h D and E of Table 21) . Sim i l a r l y , b l i n d f i s h (F, G and H) also demonstrated a pre-ference for the arm with the HTW. A sign test (Siegel, 1956) on the f i v e pairs of control and test runs on normal f i s h (A to E) showed that a l l f i v e pairs have a higher proportion of correct choices Test Water Arm Treatment Individual Experiment Pair SIEN TEST with Control Test Proportion of Test Correct Choice Water R L R L Control Test Home-tank L Normal A 5 0 2 3 .0 .6 + Prob water B 7 3 3 7 .3 .7 + of R C 4 6 8 2 .4 .8 + 5 D 2 2 5 0 .25 1.0 + plus E 12 8 7 3 .6 .7 + i n a row • L Blind F 9 1 6 8 .1 .57 + G 6 4 3 7 .4 .7 + R H 9 11 7 3 .45 .7 + Non-Home L Normal I 4 6 5 0 .6 .0 Tank Water Table 21. Response of normal and bl i n d O. maculosus to d i f f e r e n t test water i n the Y-tank choice experiment. control >test + = t e s t > c o n t r o l l e f t arm of Y-tank. rig h t arm of Y-tank. 100 during the test runs than during the control runs. The pr o b a b i l i t y of obtaining f i v e p o s i t i v e scores i n a row i s P = .03, which was s i g n i f i c a n t . (A positive score i s given when a higher proportion of correct choices i s obtained dur-ing the test runs than during the control runs and a negative score i s given to the opposite) . This implies that the f i s h can detect and discriminate the HTW even though the HTW has been diluted several times when mixed with the source water in the Y-tank. This implies that some sort of c h a r a c t e r i s t i c substance i s present i n the HTW which distinguishes i t from other water. The response of the three blind f i s h (F to H) to HTW indicates that perhaps o l f a c t i o n and odoriferous substances were involved. Chi-square t e s t on each experiment pair between the r e s u l t s of control runs and test runs showed a s i g n i f i c a n t positive e f f e c t of HTW for one of the three f i s h (F). The sample size was too small for the sign t e s t . Never-theless the responses indicate that some c h a r a c t e r i s t i c of the HTW i s detected even by the blind f i s h ; thus implying that some sort of odour i s being detected by the olfa c t o r y organs of the f i s h . However, more experiments have to be made to d i s t i n g u i s h t h i s from other chemical senses. 101 When 'non-home-tank' water (NTW) was introduced, the normal f i s h (I) avoided the arm with the NTW. Unfortunately only one set of tests was made; more tests should be made to study the behaviour of the f i s h to water from other sources. Discussion Further evidence of homing The r e s u l t s of the above experiments provide further evidence i n support of the homing hypothesis i n O. maculosus. Results of experiments involving the transplant of f i s h over t e r r a i n to displacement s i t e s from which a straight l i n e return i s obstructed by rock outcrops have indicated that homing i s an active process i n which the f i s h seek th e i r home areas. This i s demonstrated e s p e c i a l l y by experiment 15 (night homing). The rapid rate of return of about 12% of the f i s h within one t i d a l cycle, the large proportion of f i s h which eventually returned and the fact that these f i s h also have to detour around rock outcrops imply that a r r i v a l to the s i t e s of o r i g i n a l capture was not due to chance. The high percentage returns shown by repeatedly d i s -placed f i s h (experiment 9b) indicate that the return to the 102 o r i g i n a l s i t e of capture i s not a passive process. I f the return of a f i s h i n d i v i d u a l to the s i t e from which i t has been displaced i s by chance then one would expect that the prob a b i l i t y of finding that same i n d i v i d u a l i n the same s i t e again on successive displacements would be p n where p i s the pro b a b i l i t y of finding the displaced f i s h within the home area and n i s the number of times of displacement. Thus the pro b a b i l i t y of finding the f i s h on i t s second, t h i r d and fourth displacements, assuming p i s equal to .6 (derived from the f i r s t displacement), would be .6 , .6 , and .6 . Thus a rapid reduction of homing returns would be expected i f the same f i s h from a group were continually displaced. However, t h i s i s not shown by experiment 9b; the proportions of repeat returns are maintained at levels greater than 60%. That more than f i f t y percent of the f i s h displaced to about one thousand feet eventually returned (experiment 8b) also indicates that homing i s an active s t r i v i n g towards home i n O.. maculosus . Factors a f f e c t i n g homing performance Fish displaced i n one d i r e c t i o n have been shown to home as well as f i s h displaced i n the opposite d i r e c t i o n . D i r e c t -ional bias due to the homing mechanism of the f i s h or to 103 environmental factors such as d i r e c t i o n of current flow does not seem to occur. The t e r r a i n of the shore d i f f e r s according to the d i r e c t i o n from the home area; apparently i t does not af f e c t homing performance generally. Physical obstructions i n the path of the home d i r e c t i o n (experiment 15) also Cd-o.-j not appear to affe c t homing a b i l i t y . However, homing over rough and exposed t e r r a i n may be affected (experiment 7b) due most probably to turbulence and wave action. Environmental conditions during the period between March to August (spring-summer) appear to be more conducive to homing than conditions between September-February ( f a l l -winter) . The re l a t i o n s h i p between seasonal homing performance and the seasonal sea state conditions (experiment 6) i n d i -cates that wave action i s probably the main factor for poor homing during f a l l - w i n t e r . The e f f e c t of weather condi-tions during the year i s also shown by'the homing performance of b l i n d f i s h (experiment 12). I t i s conceivable that during rough weather months, the swimming a b i l i t y of the f i s h i s hampered by the d i r e c t e f f e c t s of turbulence and wave action. A small f i s h such as O. maculosus would find d i f f i c u l t y swimming as well as maintaining i t s position i n the turbulent water . Moreover, displaced f i s h may be unfamiliar with th e i r new environment and t h e i r a b i l i t y to seek shelter i s probably • 104 hampered, thus increasing the chances of being swept away or being dashed against the rocks . Even f i s h i n their home pool f i n d d i f f i c u l t y i n maintaining t h e i r positions . This has been indicated by the lower proportion of recoveries of f i s h which have been replaced during f a l l - w i n t e r than those replaced during spring-summer (experiments 8 and 12). Green (1967) also observed that f i s h i n exposed pools have on occasions been swept away during rough sea conditions. Since some f i s h have been observed to home during f a l l - w i n t e r months i t i s u n l i k e l y that there i s a change i n homing a b i l i t y with advancing season. I t i s also u n l i k e l y that the observed seasonal f l u c t u a t i o n of homing performance i s related to the reproductive a c t i v i t y of the f i s h . The longest successful homing observed i s from about one thousand feet. The homing performance from t h i s distance does not appear to d i f f e r d r a s t i c a l l y from the returns from shorter distances (experiment 8). However, a s l i g h t decrease in homing performance with increasing distance has been observed. The decline i s probably due to losses from stray-ing and/or mortality which are l i k e l y to increase with i n -creasing distances from home. The chances of being carried away by the current and waves or predated probably increases 105 with the distance the f i s h have to swim. Experiment 9 shows that homing performance improved between the f i r s t displacement and subsequent displacements but no improvement was observed among the homing returns of repeatedly displaced f i s h . The learning of landmarks at the release point or during the homeward journey was pro-bably not involved. The difference i n homing performance between the naive and the experienced f i s h i s probably due to variations i n homing a b i l i t y among in d i v i d u a l f i s h from the same area. Most probably the better homing performance of the l a t t e r i s pa r t l y the r e s u l t of the weeding out of poor homers. Variation i n homing a b i l i t y has been shown i n birds (Matthews, 1968); perhaps similar variations i n O. maculosus occur. Off-season homing indicates that homing i s probably not related to breeding. This i s further substantiated by the fact that there i s no r e l a t i o n s h i p between homing a b i l i t y and sex as well as size of the f i s h (experiment 10) . Fish below 45 mm standard length are mainly immature f i s h . These immature f i s h home as well as mature f i s h . That the larger, older and probably more experienced f i s h do not show 106 better homing a b i l i t y than smaller, younger and probably less experienced f i s h again indicates that improvement with age i n homing through learning or knowledge of the environ-ment does not occur. Homing a b i l i t y and the related mechanisms may have been acquired or imprinted before the f i s h reached a length of about 35 mm i n standard length. Sensory bases and the related environmental cues involved i n homing Vis i o n Several authors working on i n t e r - t i d a l fishes have suggested that v i s i o n i s the main sensory channel i n homing. Aronson (1951) suggested that the basis of orientation i n Bathygobius soporator i n jumping from one pool to another at low tide i s derived from a memory of the general features of the topography of a limited area around the home pool; the knowledge being acquired from v i s u a l stimulation while swimming over the tide-pools at high t i d e . Similar sensory basis and environmental cues have been implied by Williams (1957) for the homing mechanism of Clinocottus a n a l i s . Gibson (1967) also stated, from h i s studies, that a knowledge of the l o c a l topography and the possession of a memory to 107 r e t a i n i t i s a prerequisite of homing. Contrary to the above hypotheses, homing i n O. maculosus apparently does not depend e n t i r e l y on v i s i o n and v i s u a l topographic features. Data from displacement experiments of b i l a t e r a l l y b l i n d f i s h (experiment 12) and night homing experiments (experiment 15) indicate that v i s i o n i s not necessary i n homing. The r e s u l t s therefore imply that v i s u a l cues such as shoreline features and c e l e s t i a l cues such as stars, the sun and polarised l i g h t may not be involved. U n i l a t e r a l l y b l i n d f i s h have been shown to home better than b i l a t e r a l l y b l i n d f i s h (experiment 14). This implies that v i s i o n may play a secondary r o l e i n homing . V i s i o n may be used to maintain the f i s h ' s position with respect to the substrate so that the f i s h may not be swept away by the waves during high t i d e or from" being stranded on dry land at low t i d e s . I t may be argued that i f v i s i o n i s available a f i s h may make use of a v i s u a l mechanism for homing even though i t i s p a r t i a l l y b l i n d . This i s possible i f based on the hypothesis that the f i s h have several homing mechanisms. Thus on dark cloudy nights a f i s h can switch from a v i s u a l mechanism to some other mechanism. Nevertheless, the above has shown that v i s i o n i s not important 108 and that some other mechanism,perhaps olfaction,may be used for homing by O . maculosus. Olfaction The importance of o l f a c t i o n i n the spawning migration of salmon (Oncorhynchus) has been demonstrated (Hara, 1970) . Gunning (1959) has also shown that homing i n Lepomis  megalotis megalotis involves o l f a c t i o n . Data from displacement experiments of b i l a t e r a l l y anosmic f i s h (experiment 12) indicate that o l f a c t i o n i s important i n the homing of G_. maculosus. This i s substan-tia t e d by the r e s u l t s of laboratory experiments te s t i n g the a b i l i t y of the f i s h to discriminate between water from two d i f f e r e n t sources (experiment 17). Both b l i n d and normal f i s h have been shown to detect and choose c o r r e c t l y the water from t h e i r 'home aquarium'. Homing i s su b s t a n t i a l l y improved when only one of the o l f a c t o r y organs i s impaired (experiment 14). This again supports the o l f a c t o r y hypothesis that o l f a c t i o n i s involved i n the homing of O. maculosus. I t may be argued that the traumatic e f f e c t of ol f a c t o r y impairment i s the major cause of the small homing returns shown by b i l a t e r a l l y anosmic f i s h . This may be disputed by 109 the fact that under laboratory and caged f i e l d conditions, b i l a t e r a l l y anosmic and normal f i s h survived equally well up to three months, the period of most of the impairment experiments (experiment 11). Moreover, i f treatment i s that d r a s t i c the displacements of u n i l a t e r a l l y anosmic f i s h should also r e s u l t i n low homing returns but t h i s was not observed. Thus the e f f e c t of trauma i s probably n e g l i g i b l e . Both the b i l a t e r a l l y b l i n d and the anosmic f i s h when replaced into t h e i r destroyed home pools l e f t within two weeks (experiment 16b). The former non-anosmic, but blinded f i s h moved to nearby pools while the l a t t e r anosmic f i s h completely moved out of the area. Experiment 17 demonstrated the a b i l i t y of the 0. maculosus to detect chemicals i n sea water. Thus, i t i s apparent o l f a c t i o n i s an important factor i n t h i s animal's homing mechanism. Other senses In many fishes taste i s associated with sensory struc-tures i n the p e l v i c or pectoral f i n s . Experiment 13, i n which these f i n s were removed, demonstrated that i f these sensory structures e x i s t i n O. maculosus they are not important i n homing. Therefore chemical contact with 110 bottom features i s not l i k e l y a part of the homing mechanism. The r o l e of the a c o u s t i c o - l a t e r a l i s system i n O. maculosus has not been investigated but Harden-Jones (1968) has suggested that the l a t e r a l - l i n e may be used to recognize the topographic features of home i n longear sunfish. Lowenstein (1957) suggested that the l a t e r a l - l i n e could give a " f a i r l y accurate three-dimensional sensory representation of the topographic features of the immediate environment." Bottom features may also be detected by th e i r e f f e c t on e l e c t r i c f i e l d s produced by the f i s h (Lissmann, 1958). However, these sensory mechanisms are useful only when the f i s h have arrived at th e i r home. The r o l e of sound i n homing cannot be excluded. Recent studies have shown that some f i s h can react d i r e c t i o n a l l y to sound and have the a b i l i t y to l o c a l i s e the sound source from about 20 mm (Bergeijk, 1964; Cahn, 1967 and Kleerekoper and Malar, 1968). However f a r - f i e l d sound detection and l o c a l i s a t i o n a b i l i t y have not been demonstrated yet. I t has been suggested that an animal may be able to remember the number of twists and turns during transportation and that t h i s knowledge i s used by the animal to home. I l l This i s highly u n l i k e l y i n O. maculosus since a l l the f i s h i n each displacement experiment have been transported on a circ u i t o u s route; they were f i r s t transported to the labor-atory, kept overnight and then transported to the release s i t e s . The use of magnetic and other geophysical forces for homing i s most u n l i k e l y to occur i n 0_. maculosus since the sensory bases for detection of such stimuli have yet to be discovered i n vertebrate animals e s p e c i a l l y f i s h . The use of s a l i n i t y or temperature gradients detected by common chemical sense structures or thermal sensors, respectively, does not appear to be l i k e l y considering that steep stable gradients are the f i r s t prerequisite of such mechanisms. Such gradients are not present on the open shore, e s p e c i a l l y the i n t e r - t i d a l areas of Botany Beach. Source of the cues Normal f i s h have been shown to home to destroyed pools (experiment 16a). Apparently these f i s h either recog-nize topographic features or they make use of odour cues from the surrounding areas. Results of impairment experiments indicate that the l a t t e r i s more probable. Experiment 17, 112 which tests the f i s h ' s discriminatory a b i l i t y , implies that the cues are most probably carried by the water. I t i s quite conceivable that the cues come from the f i s h ' s home range. To test t h i s , future experiments involving destru-ction of wider areas have to be made. 113 GENERAL DISCUSSION I t has been established i n the three sections that 0. maculosus s t r i v e to return "to a place formerly occupied instead of going to equally probable places" (Gerking, 1959) and that the precise area to which they return i s the home range. Two basic problems have to be considered when dealing with the mechanism of homing. The f i r s t deals with how the returning f i s h get home, that i s , the orienting mechanism, and the second deals with how the f i s h recognise the home when they have reached i t . The two overlap when the cues used for recognition of the home also serve to guide the f i s h back from a distance. Recognition of the home The f i s h may recognise the home range by means of l o c a l physical or chemical landmarks. Evidence obtained so far strongly supports the hypothesis that the olfa c t o r y organs and odour cues are used for recognition of the home range. However, on the basis that the f i s h may have a number of alternate mechanisms, recognition of the home range by means of v i s i o n and topographic features or other 114 methods cannot be excluded e n t i r e l y . Orientation towards home One or a combination of the following may be involved i n the homing mechanism of 0. maculosus: (i) Passive d r i f t , ( i i ) One-direction compass orientation or true navigation, the a b i l i t y to steer a course using some coordinate or grid systems, ( i i i ) Search, either random or i n a pattern and (iv) Directed movement involving d i r e c t sensory contact with home. Passive d r i f t i s common i n animals which are unable to swim e f f e c t i v e l y against a current. Evidence so far i n d i -cates that such a mechanism i s d e f i n i t e l y not the means with which 0. maculosus return to th e i r home range. This i s sub-stantiated by the fact that the homing performance of the f i s h i s independent of d i r e c t i o n . Moreover passive d r i f t , even i f there i s an o v e r a l l flow of water i n one d i r e c t i o n i n the study s i t e , could not have accounted for the large and similar proportions of returns from d i f f e r e n t d i r e c t i o n s . One-directional orientation systems involving the use of distant cues such as the sun, moon, stars, polarised l i g h t or landmarks such as shore-line features have been suggested for a number of animals. Sun-compass orientation has been observed i n fishes by a number of authors. A summary i s presented by Hasler (1966) . ' Groot (1965) suggest-ed that the sockeye smolts (0. nerka) could find their way out of lake systems during t h e i r migration from the nursery areas to the outlet by means of one-direction orienting mechanisms using the sun and polarised l i g h t during clear days and possibly landmarks on cloudy days as well as some unknown cues the reaction to which he ca l l e d X-orientation. Evidence from sensory impairment and night homing experi-ments indicate that sun-compass orienting mechanisms are not the methods used by O. maculosus. S i m i l a r l y orientation by means of distant landmarks such as shore-line features or sea floor topography outside the home range of the f i s h i s also u n l i k e l y . The importance of one-direction orienta-t i o n mechanisms i n the homing Q_. maculosus i s questionable since the f i s h have been shown to home from d i f f e r e n t d i r e c -tions and moreover they have been able to circumnavigate obstructions which are i n the i r homeward path. A review of the various possible methods of navi-gation has been given by Schmidt-Koenig (1965) and Matthews (1968). Homing involving navigation requires the a b i l i t y to compare the co-ordinates of the position formerly oc-cupied (the home position) with that of the new position to which an animal was displaced so as to arrive at a d i r e c t i o n of orientation as well as to chart a course towards home. Thus navigation using the co-ordinates of the sun such as the sun's a l t i t u d e or i t s azimuth at ce r t a i n times of the day together with a chronometer has been proposed for fishes (Hasler, 1966) . However, i t i s un l i k e l y that such mechanisms are .involved i n the homing of 0. maculosus from distances no further than one thousand feet. Within short distances a very high degree of navigational precision i s required and i t i s doubtful that O. maculosus have such an a b i l i t y . I f homing by means of navigation does e x i s t i n t h i s species i t i s l i k e l y that astronavigation i s not important since b l i n d f i s h can home and also i t has been shown that normal f i s h can home on cloudy nights. Bi-coordinate navigation using information from the earth's magnetic f i e l d s , and c o r i o l i s forces has been, at one time or another, suggested for b i r d s . The sensory bases for perceiving such geophysical forces have yet to be shown i n fishes and thus i t i s u n l i k e l y that navigation using geophysical grids i s involved i n the homing of 0. maculosus. 117 A search or exploratory process may be involved. Search can either be random or i n a pattern. The f i s h using t h i s method i s independent of any cues from the envir-onment . Search proceeds u n t i l the home range i s encount-ered or swimming stops . Simple r a d i a l scatter type of search i n straight l i n e s from the release point, as suggested by G r i f f i n (1952) for birds, could not have accounted for the high homing performance (about s i x t y percent) observed for O. maculosus. Simple calculations based on the formula given by Harden-Jones (1968), assuming random r a d i a l scattering, give homing returns of about sixteen, four and two percent for f i s h displaced to about one hundred, three hundred and one thou-sand feet, respectively, assuming a home area of diameter one hundred feet normal to the d i r e c t l i n e j oining the r e -lease s i t e and the home. Such rapid decrease i n the propor-t i o n of returns with increasing distances i s not observed for O. maculosus. A random search mechanism has been suggested by S a i l a and Shappy (1963) to account for the homing migration of salmon (;Qnoorhynchus) i n the open ocean. In random search 118 the f i s h move i n a straight l i n e for a cert a i n distance, then turn, a l l the angles of turn being equally probable, then move another stretch i n a straight l i n e , turn again and so on. I f such a method i s used by the homing 0. maculosus one would expect that the number of successful returns should decrease r a p i d l y with the release of f i s h at progressively greater distances . A rapid decrease has not been observed from the experiments on the e f f e c t of distance. I t may be argued that random movement of the f i s h i n the i n t e r - t i d a l region i s r e s t r i c t e d to two directions only, that i s , l a t e r a l l y along the shore. The topography of the study area makes i t quite u n l i k e l y that only two directions are possible since the i n t e r - t i d a l features are complicated and f u l l of obstructions such as rock outcrops and deep channels. The same argument that no rapid decrease i n homing returns with distance was observed may also be used to invalidate the use of such a mechanism by 0. maculosus. An expanding s p i r a l , a zig-zag or some other explora-tory search pattern may be involved . Unfortunately no experi-ments were conducted to test t h i s hypothesis. Further work involving tracking the f i s h during the homeward journey 119 might be us e f u l . O. maculosus may :home by means of d i r e c t sensory con-tact with physical or chemical landmarks from the home range. Such a mechanism requires that there are substances "radiating" from the home area. Direct v i s u a l contact with the topogra-phic features of the home area from a distance can be ruled out since b l i n d f i s h can home. I t i s possible that odour may be the d i r e c t i n g cue as strongly implied from the im-pairment experiments. Food detection from a distance i n a number of fishes by means of odour has been observed by several authors as summarised by Kleerekoper (1969). Thus i t . i s possible for f i s h to detect odour o r i g i n a t i n g from th e i r home areas i f i t can be shown that such odour e x i s t s . The Y-tank experimental r e s u l t s show that 0. maculosus can detect as well as discriminate water-borne odour. Thus i t i s possible that t h i s species can be directed towards home by means of some sort of odour stream o r i g i n a t i n g from t h e i r home range . Though there i s strong i n d i c a t i o n that directed movement by means of odour i s the l i k e l y mechanism, more work has to be done before d e f i n i t e conclusions could be made, e s p e c i a l l y on the question of whether odour stream patterns e x i s t on the turbulent i n t e r - t i d a l regions. 120 The most tenable hypothesis appears to be that of an odour directed mechanism for short-distance homing whereas some other mechanism may be used for long-distance homing. There i s also a p o s s i b i l i t y that an exploratory search process may be involved; perhaps a combination of the two mechanisms would be a good working hypothesis. Evidently t h i s study has not come up with a suitable solution regarding the orientation mechanism for the f i s h ' s homeward journey. Nevertheless i t has shown that future studies should take into consideration the importance of o l f a c t i o n , the p o s s i b i l i t y that there may be homers and non-homers i n the f i s h population as well as the importance of sea conditions. Experiments conducted on f i s h selected for t h e i r homing a b i l i t y may give better r e s u l t s and a more pos i t i v e i n d i c a t i o n on the r o l e of o l f a c t i o n than the ones studied. Displacements to distances greater than those -invest-igated i n t h i s study should also be made since i t i s possible that other mechanisms may be involved i n long-distance homing. The role of the a c o u s t i c o - l a t e r a l i s system i n homing should be investigated too. 121 Significance of homing The presence of homing behaviour i n so many species i n the animal kingdom indicates that there must be some select i v e advantage i n having the a b i l i t y to home. I t has been suggested that homing a s s i s t s i n the survival and per-petuation of a species. Thus a return to the natal spawning ground by the salmon ensures an environment favourable to the growth and development of future generations so that "re-productive success i s less dependent upon the chance finding of suitable breeding conditions" (Hasler, 1966). However the function of homing i n the i n t e r - t i d a l f i s h , e s p e c i a l l y 0. maculosus, does not seem to be related to breeding. Williams (1957) suggested that the homing mechanism i n i n t e r - t i d a l f i s h serves to prevent the fi'sh from being strand-ed at low tides i n unfavourable situations such as on dry land or i n pools that disappear through subsurface drainage. Therefore a f i s h with homing a b i l i t y has an advantage i f the f i s h i s accidentally displaced during turbulent sea conditions. Homing behaviour may also be seen as a s t a b i l i s i n g mechanism for population d i s t r i b u t i o n and equitable u t i l i s a t i o n 122 of the resources i n the i n t e r - t i d a l . Since food i s abundant i n t h i s region, space or the a v a i l a b i l i t y of tide-pools appears to be the main f a c t o r . I f dispersal and e s t a b l i s h -ment of home occurs early i n the l i f e of the f i s h and i f s t r i c t f i d e l i t y to the adopted home i s maintained throughout adult l i f e , a l l these coupled with a homing mechanism would ensure an even exp l o i t a t i o n of the environment. F a m i l i a r i t y with the immediate environment as a r e s u l t of frequent f o r -aging t r i p s and returns to the home pool may also be advan-tageous i n avoiding predators. On the other hand an i n f l e x i b l e homing behaviour would be disadvantageous to the species e s p e c i a l l y during turbu-lent sea conditions when whole populations i n an area may be annihilated. Repopulation of the affected area from other populations would require some sort of dispersal mechanism. Such a mechanism appears to be present i n 0. maculosus, as indicated by the high proportion of f i s h which were l o s t i n most of the experiments and the frequent observations of adult r e c r u i t s to a pool. Most probably the 'non-homers' i n the population serve t h i s function. Thus on the one hand homing behaviour prevents over-e x p l o i t a t i o n of the environment and ensures favourable habitat for the in d i v i d u a l while on the other hand the dispersal mech-anism i s an insurance against extinction of the species i n an area. 0. maculosus appears to have both advantages. 124 SUMMARY 1) Individuals of a pool population exhibit d i f f e r e n t de-grees of pool f i d e l i t y and movement. Some f i s h show s t r i c t l o y a l t y to one pool while others move from one pool to another. However movement i s r e s t r i c t e d within a home range, e s p e c i a l l y for short periods of time. 2) The a b i l i t y to return to the home range when experiment-a l l y displaced was demonstrated. This homing process i s not due to chance but i s an active s t r i v i n g by the f i s h to return to the areas formerly occupied. 3) Returns to the home range have been shown to be a better and more r e a l i s t i c measure of homing performance than the returns to s p e c i f i c home pools. 4) O. maculosus homes throughout the year but environmental conditions between March and August are more conducive to homing than the rest of the year . This seasonal v a r i a t i o n i s probably due to sea conditions. 5) 0. maculosus has been shown to home from as far as one thousand f e e t . A s l i g h t decrease i n homing returns with 125 increasing distance i s observed. This i s probably due to accidental mortality due to wave action. G. maculosus homes equally well from d i f f e r e n t d i r e c t i o n s . There i s no difference i n homing a b i l i t y between the sexes and between large and small f i s h . Homing a b i l i t y does not seem to improve with learning. There i s strong i n d i c a t i o n that there may be inherent v a r i a b i l i t y i n homing a b i l i t y i n a f i s h population, that i s , there may be 'homers' and 'non-homers'. /Vision does not seem to be important i n homing. There-i s strong i n d i c a t i o n that o l f a c t i o n i s involved i n the homing mechanism of O. maculosus . 0. maculosus probably recognizes i t s home range by means of an odour or a combination of odours. How the f i s h finds i t s way from a distance i s s t i l l not known for certain,, but i t i s postulated that the f i s h returns home by following odour streams or by an exploratory search process or by a combination of the two processes. 1 2 6 Other mechanisms are also discussed. The significance and function of homing i n i n t e r - t i d a l f i s h such as 0. maculosus are given and discussed. 127 LITERATURE CITED Aronson, L. R. (1951).. Orientation and jumping behaviour i n the gobiid f i s h Bathygobius soporator. Am. Mus. Novit., (1486): 1-22. Atkinson, C. E. (1939) . Notes on the l i f e h i s t o r y of the tide-pool Johnny (Oligocottus maculosus). Copeia, 1939: 23-30. Beebe, W. (1931). Notes on the g i l l - f i n n e d goby, Bathygobius  sopor at or (Cuv. and Val.) . Zoologica, N.Y., 12: 55-56. Bergeijk, W.A. van. (1964). D i r e c t i o n a l and riondirectional hearing i n f i s h . In Marine Bio-acoustics, JL: 281-299. ed. by W.N. Tavolga. Pergamon Press, 413 pp. Cahn, P. H. (1967) . Lateral l i n e detectors. Indiana Univ. Press, London, 496 pp. Clemens, W. A. and Wilby, G. V. (1961) . Fishes of the P a c i f i c coast of Canada. F i s h . Res. Bd. Can. B u l l . , 68: 301-302. Davis, R. (1966). Homing performance and homing a b i l i t y i n bats. Ecological Monographs, 36 (3): 201-237. Eastman, D. S. (1962) . Homing in the tidepool sculpin Oligocottus  maculosus Girard. B. Sc. (Hons) thesis, Univ. B r i t i s h Columbia, 41 pp. Gerking, S. D. (1959). The r e s t r i c t e d movements of f i s h populations. B i o l . Rev ., 34: 221-242 . Gersbacher, W. M. and Denison, M. (1930). Experiments with animals i n tide pools. Pubis. Puget Sound mar. b i o l . Stn., 7.= 209-215. 128 Gibson, R. N. (1967) . Studies on the movements' of l i t t o r a l f i s h . J . Anim. Ecol., 36: 215-234. - r - ^ - - - - - ^ — . (1969) . The biology and behaviour of l i t t o r a l f i s h . Oceanogr . Mar . B i o l . Ann . Rev ., 7_: 367-410. Ed. Barnes, H. Publ. George A l l e n and Unwin Ltd., London. Green, J . M. (1967) .'.A, f i e l d study of the d i s t r i b u t i o n and behaviour of Oligocottus maculosus Girard, a tidepool c o t t i d of the northeast P a c i f i c Ocean. Ph. D. thesis, Univ. B r i t i s h Columbia, 160 pp. G r i f f i n , D. R. (1952). Bird navigation. B i o l . Rev., 27: 359-393. Groot, C. (1965) . On the orientation of young sockeye salmon (Oncorhynchus nerka) during t h e i r seaward migration out of lakes. Behaviour, suppl., (14), 198 pp. Gunning G. E. (1959) . The sensory basis for homing i n the longear sunfish, Lepomis megalotis megalotis (Rafinesque) . Invest. Indiana Lakes Streams, 5_: 103-130. Hara, T. J . (1970) . An elec t r o p h y s i o l o g i c a l basis for o l f a c t -ory discrimination i n homing salmon: a review. J . Fish . Res. Bd. Can., 27 (3): 565-586. Harden Jones, F. R. (1968). Fish migration, Edward Arnold Ltd., London, 525 pp. Hasler, A. D. (1966). Underwater guideposts. Univ. Wisconsin Press. 155 pp. Hayne, D.W. (1949). Calculation of size of home range. J . Mammal, 30: 1-18. Hubbs, C. L. (1921) . The ecology and l i f e h i s t o r y of Amphigonopterus aurora and other viviparous perches of C a l i f o r n i a . B i o l . B u l l . , 40: 181-209. Kleerekoper, H. (1969) Ol f a c t i o n i n f i s h e s . Indiana Univ. Press, London, 222 pp. 129 Kleerekoper, H. and Malar, T. (1968). Orientation through sound i n f i s h e s . In Hearing mechanism i n vertebrates, 188-206. ed. by A. V. S. De Reuck and J . Knight. C h u r c h i l l Ltd., London, 320 pp. Lissmann, H. W. (1958). On the function and evolution of e l e c t r i c organs i n f i s h . J . exp. B i o l . , 35: 156-191. LcTwenstein, O. (1957) . The sense organs: the acoustico-l a t e r a l i s system. In The physiology of fishes, 2_: 155-186. ed. by M. E. Brown. Academic Press, N. Y., 52 6 pp. Matthews, G. V. T. (1968). Bird Navigation. Second edition, Cambridge, 197 pp. Nakamura, R. (1970) . The ecology of two tidepool fishes (Oligocottus maculosus Girard, o . Snyderi Greely) i n r e l a t i o n to the microhabitat and i n t e r - t i d a l d i s t r i b u t i o n patterns. Ph. D. thesis, Univ. B r i t i s h Columbia, 129 pp. S a i l a , S. B. and Shappy, R. A. (1963). Random movement and orientation i n salmon migration. J.'Cons. perm, i n t . Explor. Mer, 28: 153-166. Schmidt-Koenig, K. (1965) . Current problems i n b i r d o r i e n t -ation, In Advances i n the study of Behaviour, 1_: 217-278, ed. by D. S. Lehrman, R. A. Hinde, and E. Shaw, Academic Press, London, 320. pp. Siegel, S. (1956). Nonparametric s t a t i s t i c s for the behaviour-a l sciences. McGraw-Hill, New York, 312. pp. Sokal, R. R. and Rohlf, F . J . (1969). Biometry: the p r i n c i p -les and practice of s t a t i s t i c s i n b i o l o g i c a l research. W. H. Freeman and Co., San Francisco, 77 6 pp. Williams, G. C. (1957) . Homing behaviour of C a l i f o r n i a rocky shore f i s h e s . Univ. C a l i f . Pubis Zool., 59:-249-284. — 130 Appendix I . Detailed r e s u l t s of b i l a t e r a l sensory impair-ment (vision and olfaction) of experiments. The e f f e c t of b i l a t e r a l impairment of v i s i o n (lens removal) and o l f a c t i o n (heat c a u t e r i -sation) on the f i d e l i t y of replaced f i s h as well as on the homing a b i l i t y of displaced f i s h from distances of about 100, 300 and 400 feet. Fish from two home areas (A and B) are studied. NR = Number released. NHS = Number recovered i n home range. NHP = Number recovered i n o r i g i n a l pool, ('home pool') of capture. * Displaced to S - l l (100 f e e t ) . 1 2 3 4 Home Release Date Control _ Site Site Released NR NHS NHP (distance) Replaced 25 ix 68 ,4 1 26 i v 69 8 7 17 iv 70 Displaced 2 x i i 68 13 2 to S-7 19 x i i 68 24 2 (100 feet) 13 i i 69 2 1 2 i i i 69 31 i i i 70 - 10 2 0 17 i v 70 24 8 3 . 3 v 70 15 8 3 23 v 70 10 8 6 27 v 70 15 12 5 26,vi 70 43 19 6 Displaced 24 ix 68 10 4 to S-8 2 x 68 13 2 (300 feet) 3 x 68 3 0 7 i 69 8 1 5 v i 70 14 11 4 Displaced 25 ix 68 3 2 to B-3 1 x 68 8 2 (400 feet) 2 x 68 3 1 26 v i 70 42 8 1 Blind Anosmic  NR NHP NHS NR NHP NHS 4 1 9 1 14 0 0 13 2 21 1 2 1 4 0 4 0 0 14 1 0 14 0 0 14 7 6 14 8 4 45 12 6 5 1 12 1 3 0 10 2 16 10 5 4 0 8 0 4 2 44 8 3 4 0 9 3 18 3 1 14 0 20 0 2 1 3 0 8 1 0 17 3 3 15 0 0 12 2 2 11 0 0 43 2 0 5 0 12 0 3 0 7 1 17 0 0 6 1 8 0 3 0 42 0 0 Continued . . co 2 3 4 5 6 Replaced 26 i i i 69 5 5 3 0 4 2 11 i v 69 16 10 17 2 17 1 26 i v 69 9 8 13 2 13 0 14 v 69 8 5 9 3 9 1 17 i i 70 16 6 4 15 2 1 16 2 2 6 i i i 70 7 2 2 31 i i i 70 24 2 1 23 4 3 27 v 70 10 7 5 9 6 5 8 2 2 Displaced 15 i i i 69 3 2 2 2 2 1 to S-9 11 i v 69 7 4 . 6 0 6 0 (100 feet) 15 v 69* 8 3 10 5 10 0 31 v 69 10 6 13 6 13 . 1 16 i 70 33.. 4 2 30 0 0 32 0 0 23 i 70 12 4 4 10 0 0 12 1 0 2 i i 70 13 6 4 13 0 0 13 0 0 31 i i i 70 25 17 15 24 2 1 24 4 2 17 iv 70 17 8 4 15 0 0 16 0 0 30 i v 70 16 5 3 19 4 3 18 0 0 22 v 70 26 6 6 25 13 10 25 0 0 Displaced 3 i i i 69 2 2 3 0 2 0 to S-8 27 i v 69 13 9 13 0 13 1 (300 feet) 6 i i i 70 12 0 0 4 i v 70 12 1 1 11 2 2 12 0 0 LO t-0 Appendix I I . Dimension and nature of pools and displacement stations . 134 Pool Dimension Maximum Length X Width (feet) Maximum Depth (inches) Tide Level (feet) Remarks Site A A-1 6 x 4 24 8.4 Discrete pools 2 4 x 3 25 on sandstone 3 8 x 1.5 17 f l a t . 4 5.5 x 5 25 5 1.5 x 1 .5 14 6 4 x 3 18 7 8 x 1.5 17 .5 8 7 x 3.5 32 9 10 x 4 20 10 7.5 x 3 .5 13 Site B B - l 37 x 3 14 9 .3 Trench-like 2 28 x 11 10 8.9 pools on sand-3 46 x 3 11 stone f l a t . 4 31 x 8 9 5 33 x 16 13 Site C C . 12 x 10 20 9.8 One pool on sh. rocks. Site D D-l 9 x 4.5 36 10 .2 Step-ladder 2 6 x 4 45 7 .0 series of pool; 3 24 x 6 37 6.2 on shale 4 9 x 3 20 6.2 Site E E - l 4.4 x 3 24 6.1 Discrete pools 2 4.x 4 16 on shale 3 5 x 3 25 Continued 135 Pool Dimension Maximum Length X Width (feet) Maximum Depth (inches) Tide Level (feet) Remarks Other pools PD-1 PD-2 PD-3 3.5 x 3 2.3 x 2.3 6 x 3.5 16 26 34 10.2 11.0 9.6 Shale pools Displacement stations S - l 7.0 Sandstone pool 2 0 .0 Open water 3 0.0 Open water 4 6.1 Sandstone pool 5 9.0 Sandstone pool 6 4.6 Sandstone pool 7 6.1 Sandstone pool 8 6.6 Pool amongst boulders 9 8.4 Sandstone pool 10 7.2 Sandstone pool (14x6x33") 11 9.2 Shale pool 12 0.0 Open water 

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