Sound-scattering spectra of steelhead (Oncorhynchus mykiss), coho (O. kisutch), and Chinook (O. tshawytscha) salmonids

Renfree, J. S., Hayes, S. A., and Demer, D. A. 2009. Sound-scattering spectra of steelhead (Oncorhynchus mykiss), coho (O. kisutch), and Chinook (O. tshawytscha) salmonids. – ICES Journal of Marine Science, 66: 1091–1099. A recently developed method for measuring total target strength (TTS) allows calculation of the absolute scattered energy from fish over a broad-bandwidth signal. This technique uses the ratio of coherent and incoherent sound fields reflected off fish swimming in tanks. In stark contrast to other acoustic methods, this technique works best in reverberant conditions, is self-calibrating, and conveniently provides measurements of sound-scattering spectra for possible target identification. It has been used to successfully characterize the scattering spectra of marine life such as anchovy, sardine, and krill. In this experiment, the broad-bandwidth scattering spectra are characterized for the salmonids steelhead (Oncorhynchus mykiss), coho (Oncorhynchus kisutch), and Chinook (Oncorhynchus tshawytscha). The TTS measurements demonstrate that the scattering spectra for these species are similar, yet discernible. These unique scattering spectra may provide means for acoustically identifying and enumerating such targets in rivers or streams. Having effective acoustic methods for assessing salmon abundance could become a major addition to currently available measurement tools and provide a new, low-impact assessment technique for both commercial and endangered populations.