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

Abstract Understanding the relationship between fish biology and target strength potentially improves 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 relative contribution of each factor has not been quantified. Dimensionless ratios, which facilitate comparison of disparate quantities, were used to evaluate the effects of individual biological factors on echo intensities. Ratios from 25 adult walleye pollock (Theragra chalcogramma) were calculated using a Kirchhoff-ray-mode, backscatter model parameterized for each fish. This comparative approach can be used to identify the influence of biological factors on backscatter intensity and is potentially a tool for improving accuracy when converting acoustic size to fish length.