The use and efficacy of acoustic survey methods as applied to a mixed aquatic community: The deep scattering layer of the California Current.

Abstract

Concurrent acoustic and trawl data were collected in 2008 near Point Conception to compare the abundance estimates of mesopelagic micronekton obtained with these two methods. Acoustic data were obtained with a calibrated EK‐60 equipped with four frequencies (38, 70, 120, and 200 kHz). Animals were collected with a midwater trawl. Target strength (TS) models were created of the animals collected by the trawl, and animals were assigned to acoustic groups based on the frequency spectrum of their modeled TS. The mean spectra of the acoustic groups were used with non‐negative least squares inverse methods to estimate abundance from the multi‐frequency volume scattering. The resulting acoustic abundances of each group were compared to the trawl catches, and capture efficiency of the net was estimated. The accuracy of the inverse method was tested with a Monte Carlo analysis of an artificial echogram. The accuracy of the forward modeling was tested via comparison to single targets recorded by the EK‐60. [Work supported by NASA, CCE‐LTER, and The Moore Foundation.]