A method for evaluating the effects of biological factors on fish target strength

Hazen, E. L., and Horne, J. K. 2003. A method for evaluating the effects of biologicalfactors on fish target strength. – ICES Journal of Marine Science, 60:555–562.Understanding the relationship between fish biology and target strength potentially im-proves the accuracy of acoustic assessments. The effects of individual biological factors(e.g., length, tilt, and depth) on backscatter amplitude have been examined, but the relativecontribution of each factor has not been quantified. Dimensionless ratios, whichfacilitate comparison of disparate quantities, were used to evaluate the effects of individualbiological factors on echo intensities. Ratios from 25 adult walleye pollock (Theragrachalcogramma) were calculated using a Kirchhoff-ray-mode, backscatter model parameter-ized for each fish. This comparative approach can be used to identify the influence ofbiological factors on backscatter intensity and is potentially a tool for improving accuracywhen converting acoustic size to fish length.