Angular measures of dorsal aspect target strength functions of fish

Abstract

Three angular measures of dorsal aspect target strength functions in the pitch plane are computed for previously gathered acoustic data on three gadoid fishes, two clupeoid fishes, and mackerel. These measures are the angle of maximum dorsal aspect backscattering cross section, the central angle of the backscattering cross section, and the dispersion of the cross section about the central angle. Each measure is regressed linearly on fish length. The statistical significances of the estimated regression coefficients are computed. Systematic differences are attributed to fish anatomy: backscattering cross sections of the considered swim bladderbearing fishes are concentrated about negative tilt angles of several degree magnitude, which is attributed to the inclination of the swim bladder axis. Backscattering cross sections of mackerel, which lacks a swim bladder, are appiroximately balanced about the horizontal.