Estimation of Fish Length from Acoustic Target Strengths

Abstract

I show that fish length distributions calculated from acoustic target strengths of cod (Gadus morhua) are in error when target strength–length relationships are used that do not account for the orientation distribution of the fish. The magnitude and statistical significance of the errors vary with the length frequency structure of the fish sample and are thought to be large enough to question the value of acoustically determined lengths in fish surveys if corrections for fish orientation are not applied.