The development and evaluation of a three-dimensional, echo-integration method for estimating fish-school abundance

• Published in: ICES Journal of Marine Science
• Main Authors: Nishimori, Yasushi, Iida, Kohji, Furusawa, Masahiko, Tang, Yong, Tokuyama, Kozo, Nagai, Sanae, Nishiyama, Yoshihiro
• Format: Text
• Language: English
• Published: Oxford University Press 2009
• Subjects: Articles; Norwegian Sea
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/66/6/1037; https://doi.org/10.1093/icesjms/fsp053

<qd> Nishimori, Y., Iida, K., Furusawa, M., Tang, Y., Tokuyama, K., Nagai, S., and Nishiyama, Y. 2009. The development and evaluation of a three-dimensional, echo-integration method for estimating fish-school abundance. – ICES Journal of Marine Science, 66: 1037–1042. </qd>A three-dimensional, echo-integration method (3DEI) which uses scanning-sonar observations of a fish school to estimate its backscattering cross section ( σ bss = Nσ bs ) was developed. Coupled with a modelled estimate of the average backscattering cross section of individual fish ( σ bs ), the 3DEI theoretically allows estimation of the number of fish in a school ( N ). To test the practicality of the method, measurements were made of a metal sphere simulating fish, and several spheres simulating a fish school. The 3DEI correctly measured the σ bss of each target. Next, the 3DEI was applied to echo data from a herring school in the Norwegian Sea, to estimate its σ bss . Several values of σ bs were estimated with a prolate-spheroid model, each assuming different distributions of fish orientations relative to the sonar beam. Dividing the 3DEI-estimated σ bss by these modelled σ bs shows that the resulting estimates of N were closer to the skipper's estimate than those estimated using the apparent school volume. The 3DEI measurements of σ bss , modelled σ bs , and resulting accuracy of N depend largely on the assumed orientations of the fish relative to the acoustic beam.