Over the last few years, J.R. Hunter lias developed 

 automatic data processing techniques for the quantitative 

 analysis of fish schools from photographs. Use of these 

 techniques has allowed him to study the effects of feed- 

 ing, liglit intensity, fish size, and predators on the behav- 

 ior of schooling fish, and to investigate the communica- 

 tion of velocity changes within fish schools. 



Recent accomplishments include the determination 

 of a visual threshold for schooling in jack mackerel 

 (Traclmms symmetricus). and the determination of some 

 of the mechanisms involved in the communication of ve- 

 locity changes among fish in schools. Tlie visual thresh- 

 old for schooling was between 6X10"' and 6 X 10'° ft.- 

 lambert. Comparison of these data with measurements 

 of liglit in the sea indicated that jack mackerel would be 

 able to maintain schools near the surface on a moonless, 

 starlit night. 



Studies of communication in fish schools revealed 

 that the latency of the response of a fish to an increase 

 in velocity by another fish in a school depends on the 

 extent of apparent movement by the other fish and there- 

 fore upon visual perception of movement. Thus, a fish 

 reacts sooner to changes in velocity by fish to the side 

 and by ones within its binocular field than to changes by 

 fish located elsewhere. Communication was faster and 

 appeared to be more effective, however, among fish in 

 the same rank than among fish in the same file. 



J.R. Hunter has also begun to develop techniques 

 for artificially congregating schools of fish on the high 

 seas. Floating objects attract many species of pelagic 

 fishes, including tuna, and the fish normally remain near 

 the object for many days. The shape and displacement 

 of an object affording maximum attraction has been in- 

 vestigated, and future work will be designed to deter- 

 mine the optimum size and color for attraction, and also 

 to evaluate the effects of olfactory attractants. 



Such studies are obviously desirable because of tiie 

 widely dispersed nature of many important pelagic fish 

 in the open ocean far from land. If artificially aggregated 

 by such means they may become available to the catching 

 gear of the fishing fleets. 



An apparatus for measuring the speed of pelagic 

 marine fish is currently being calibrated, and this, to- 

 gether with high-speed photographic equipment, will per- 

 mit analysis of the swimming movements of fish and the 

 determination of their maximum sustained velocities. In- 

 formation will also be collected on tail-beat amplitudes 

 and frequencies which will be used together with the 

 CTFM sonar in the identification of the fish targets. 

 Data on maximum sustained velocity will be used in de- 

 termining the energy that our local pelagic marine fish 

 require for swimming and will be used by R. Lasker in his 

 energy budget calculations. 



Development of the techniques of rearing pelagic 

 marine fish from the eggs in this Center has permitted 



J.R. Hunter to begin behavioral studies of larval ancho- 

 vies and other pelagic species. He has developed tech- 

 niques for cinephotography of live larval fish as small as 

 7 mm. Photographic and other techniques will be used 

 to investigate swimming abilities, behavior, and schooling 

 activities at various stage of development. 



G Mattson 



Feeding behavior of anchovy- experimental tanks in the 

 aquarium. 



MARINE FISH LARVAE 



G.O. Schumann's investigation of the methodology 

 of rearing the larvae of pelagic fish in the experimental 

 aquarium at the Center culminated during this period in 

 an effective, if empirical, rearing technique. 



G.O. Schumann was able to carry a number of spe- 

 cies through to the subadult stage from fertilized eggs 

 collected in plankton nets at sea; these fish included spe- 

 cies previously impossible to rear because of the very 

 small size of the newly hatched larva (such as Pacific 

 sardine and northern anchovy), together with other spe- 

 cies of pelagic and demersal fish. Particularly spectacular 

 was the development of a large school of Pacific mackerel 

 (Scomber japonicus) which were reared in this way to 

 adult size in circular plastic swimming pools in the 

 aquarium. 



The rearing technique depends for its success on a 

 number of factors but is essentially the building of a 

 model eutrophic ocean in rather large aquarium tanks. 

 Earlier attempts to culture sardine and anchovy larvae in 

 15- to 30-liter tanks did not succeed, because the larvae 

 injured their jaws by repeated contact with the aquarium 

 walls. Subsequently fiberglass aquaria with one plate- 



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