FISHERY BULLETIN: VOL. 76, NO. 2 



1.0 



1.5 2.0 



RATIO- SCHOOL 



2.5 3.0 4.0 5.0 

 LENGTH TO WIDTH 

 Figure 3. — Regression plot for the ratio estimated anchovy 

 school size to actual size compared with the school length to 

 width ratio. 



For simulated sonar observations of school 

 widths used in the calculation of school area, the 

 preliminary examination of these data indicates a 

 possible 1.72:1 average overestimate ofarea due to 

 school shape deviations from a circle or ellipse. 



Fish schools, being highly variable in horizontal 

 profile, are probably equally complex in vertical 

 structure; the relationship of horizontal complex- 

 ity to vertical complexity is not known. Also un- 

 known is the question of whether the individual 

 school's axis is oriented in the same general direc- 

 tion within a group of schools, a possible factor 

 which, if it occurs, could provide a source of sub- 

 stantially higher or lower school area error esti- 

 mates from sonar track line surveys. 



The problem of accurately estimating the per- 

 centage of school area within view of a low-light- 

 level viewer is difficult, as the examples of school 

 shapes within the target circle would indicate. 

 Parameters of human viewing error could be es- 

 tablished for this survey technique. However, the 



conduct of surveys using a low-light-level televi- 

 sion system where the video signal can be recorded 

 and later electronically analyzed with the aid of an 

 image analyzer, should result in a higher degree of 

 survey accuracy. 



School shapes were taken from photographs 

 randomly selected from an aerial photo file. Many 

 of the photos were taken in the nearshore areas. 

 There is the possibility that schools may be 

 slightly more elliptical in shape over deep water 

 than in the nearshore areas, but this is not 

 documented. If this were true the error estimate 

 would be reduced. This and other aspects of school 

 profile and orientation should be investigated 

 further and estimates of length to width ratios 

 from aerial surveys, done in conjunction with each 

 acoustic survey, may be useful for determination 

 of a correction factor for the acoustic data. 



ACKNOWLEDGMENTS 



The suggestions of Reuben Lasker and Paul 

 Smith and the assistance of Jim Zweifel in the 

 calculation of the weighted linear regression are 

 appreciated. 



LITERATURE CITED 



Cram, D. L. 



1974. Rapid stock assessment of pilchard populations by 

 airrraft-bome remote sensors. Proc. 9th Int. Symp. on 

 Remote Sensing. Ann Arbor, 15-19 April, p. 1043-1050. 



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



1976. Development and use of sonar mapping for pelagic 

 stock assessment in the California Current area. Fish 

 Bull, U.S. 74:281-300. 



Mais, K. F. 



1974. Pelagic fish surveys in the California Cur- 

 rent. Calif Dep. Fish Game, Fish Bull. 162, 79 p. 

 RADAKOV, D. V. 



1972. Schooling in the ecology offish. [In Russ.] Izdatel. 

 "Nauka," Moscow. (Engl, transl., 1973. 173 p. Isr. Pro- 

 gram Sci. Transl. Publ, John Wiley and Sons, N.Y.) 



Smith, P, E. 



1970. The horizontal dimensions and abundance of fish 

 schools in the upper mixed layer are measured by so- 

 nar. In G. B. Farquhar (editor), Proc. International 

 Symposium on Biological Sound Scattering in the Ocean, 

 p. 563-591. Maury Cent. Ocean Sci., Dep. Navy, Wash., 

 D.C. 



Squire, J, L., jr. 



1972. Apparent abundance of some pelagic marine fishes 

 off the southern and central California coast as surveyed 

 by an airborne monitoring program. Fish. Bull., U.S. 

 70:1005-1019. 

 VOGLIS, G. M., AND J. C. COOK 



1966. Underwater applications of an advanced acoustic 

 scanning equipment. Ultrasonics 4:1-9. 



448 



