Comparison of walleye pollock target strength estimates determined from in situ measurements and calculations based on swimbladder form

Abstract

The target strength of walleye pollock (Theragra chalcogramma) at 38 kHz has been determined in each of two ways: (1) in situ measurement with dual-beam and split-beam echo sounders, and (2) theoretical calculation based on the swimbladder form. Respective probability density functions of target strength are compared. The several estimates of mean target strength (T-bar S-bar) determine the relation T-bar S-bar =20 log l–66.0, where l is the fish fork length in centimeters.