Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4661
Title: Target strength of two abundant mesopelagic fish species
Author: Benjamin Scoulding, D. Chu, Paul G. Fernandes
Publication Year: 2015
Journal: Canadian Journal of Fisheries and Aquatic Sciences
Pages: 35
Keywords: Acoustic in situ target strength, scattering layers, Myctophidae, Sternoptychidae, swimbladder, x-ray,
Abstract: Mesopelagic fish of the Myctophidae and Sternoptychidae families dominate the biomass of the oceanic deep scattering layers and, therefore, have important ecological roles within these ecosystems. Interest in the commercial exploitation of these fish is growing, so the development of techniques for estimating their abundance, distribution and, ultimately, their sustainable exploitation is essential. The backscattering characteristics for two size classes of Maurolicus muelleri and Benthosema glaciale are reported here, based on swimbladder morphology derived from digitised soft X-ray images, and empirical (in situ) measurements of target strength (TS). A backscattering model based on a gas-filled prolate spheroid was used to predict the theoretical TS for both species. Sensitivity analyses of the TS model to the modelling parameters were performed indicating that TS was sensitive to the viscosity, resulting in substantial changes to the TS around the resonance frequency. Theoretical TS predictions close to the resonance frequency were in good agreement with mean in situ TS derived from sections of the echogram which were spatially and temporally consistent with the trawl information for both species.
Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Develop methods to use physiological and biological information to predict population-level processes.