Incorporating behavior in backscatter model predictions of walleye pollock target strength

Abstract

Target strength to size relationships for fish and zooplankton are typically based on in situ field or ex situ tethered measurements. Combining backscatter measurements with species-specific backscatter models improves the translation of acoustic data to computations of type, number, and size of aquatic organisms. Variability in acoustic measurements is largely due to the choice of carrier frequency and organism behaviors. Shoaling, schooling, and orientation are three behaviors that influence the amplitude of echoes received from individuals or aggregations of aquatic organisms. Kirchhoff-ray mode (KRM) backscatter models of individual fish were combined with tilt and roll tank observation data to predict and visualize backscatter from individual and groups of walleye pollock (Theragra chalcogramma). Model predictions were compared to in situ target strength measurements at 38 kHz in the Bering Sea. Incorporating behavior in distributions of echo amplitudes should increase accuracy of target strength to length and abundance estimate accuracy. [Work supported by ONR and the Alaska Fisheries Science Center.]