ber of fish by the volume of the truncated cone 

 between the planes of the largest and smallest fish 

 image. 



In September 1974, 14 camera drops were made 

 in the Santa Barbara Channel on anchovy schools 

 located by sonar. Observation of camera drops 

 revealed that the slow sinking rate and Vi.ooo-s 

 strobe flash did not disturb the fish. A space of 

 about 4 m in diameter opened up in the school 

 below the system as the camera descended. The 

 increase in the school density caused by formation 

 of the open space in the school was not detected in 

 my analysis. 



Anchovy schools appeared on 16 of the 230 

 photographs taken. For the 10 photographs in 

 which the fish seemed to be perpendicular to the 

 camera, the mean density of the school was 114.8 

 fish/m 3 where s = 99.1 fish/m 3 and the mean of the 

 mean distance to the nearest neighbor was 1.2 

 body lengths with s = 0.3 body length (Figure 4, 

 Table 1). 



Photographs 6-10 were of the same school taken 

 over a 10-min period. Excluding photograph 7, in 

 which the fish appeared to be reacting to the cam- 

 era or a predator and are more compact, the den- 

 sities calculated for this school were 60, 56, 51, and 

 55 fish/m 3 with a mean distance to the nearest 

 neighbor of 1 .27, 1 .28, 1 .63, and 1 .42 body lengths, 

 respectively. 



The interfish distances estimated for the schools 

 photographed in this field study are, in general, 

 larger than those reported in laboratory studies. 

 This suggests that the small tanks used in these 

 studies have caused fish to form more compact 

 schools than they typically do under natural 

 conditions. 



The camera and these techniques could be of 

 considerable value in determining the density and 

 species composition of pelagic fish schools for 



TABLE 1 . — Parameters of schooling compaction generated by the 

 computer program for the 10 photographs in Figure 4. 



sonar surveys. They should also be of value in the 

 study of the behavior of schooling fish. School 

 densities are known to change during feeding, 

 predatory attack, and under diminished light 

 intensity (Shaw 1970; Radakov 1973). Using the 

 drop camera, it may now be possible to study the 

 behavior of schools in the sea since interfish 

 distance is as yet the best characteristic to mea- 

 sure changes in schooling tendencies. 



Acknowledgments 



I thank Daniel M. Brown of the Scripps Institu- 

 tion of Oceanography for instructing me in the use 

 of the camera; the California Department of Fish 

 and Game for providing time on the vessel Alaska 

 and the assistance of its crew; John Ford for as- 

 sisting with the camera calibration; John Hunter, 

 Paul Smith, and Roger Hewitt of the National 

 Marine Fisheries Service for helping in various 

 ways; and Evelyn Shaw and Charles Breder for 

 reviewing the manuscript. 



Literature Cited 

 Breder, C. M., Jr. 



1954. Equations descriptive of fish schools and other 

 animal aggregations. Ecology 35:361-370. 



Cullen, J. M., E. Shaw, and H. A. Baldwin. 



1965. Methods for measuring the three-dimensional 

 structure offish schools. Anim. Behav. 13:534-543. 



DAMBACH, M. 



1963. Vergleichende Untersuchungen uber das 

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Hewitt, R. P., P. E. Smith, and J. C. brown. 



1976. Development and use of sonar mapping for pelagic 

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KEENLEYSIDE, M. H. A. 



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Mais, K. F. 



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Radakov, D. V. 



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