Bioacoustic attenuation spectroscopy in the Santa Barbara Channel and Yellow Sea: Inference of anchovy parameters from broadband transmission loss measurements

Synoptic measurements of broadband transmission loss (TL), sound speed profiles, geo-acoustic properties of the bottom, and distributions of lengths, depths, and species of fish permitted isolation of the effects of bio-acoustic attenuation due to fish, the bottom and solitons on TL in the Santa Barbara Channel (SBC). Sound speed and geo-alpha in the bottom were derived from chirp sonar measurements. Differences between TL measurements and PE calculations of TL during a period, which was not affected by solitons, provided measures of excess attenuation due to bio-alpha versus frequency. Trawls revealed that 10.5 cm long anchovies were dominant. Resonances were evident at 1.8 kHz at 18 m and 1.1 kHz at 7 m due to dispersed, one year old, 10.5 cm anchovies, and at 0.5 kHz due to schools of 10.5 cm anchovies. A BAS experiment in the Yellow Sea revealed resonances due to dispersed 1-year old, 11 cm anchovies, the dominant species/length in the Yellow Sea, and schools of 11 cm anchovies. The resonance frequencies were essentially the same (within 0.1 kHz) as in the SBC. Inferred depths of dispersed anchovies are consistent with concurrent echo-sounder data and historical measurements of preferred depths (Sobradillo, et al. 2021).