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Tohru Mukai, Kohji Iida, Depth dependence of target strength of live kokanee salmon in accordance with Boyle's law, ICES Journal of Marine Science, Volume 53, Issue 2, April 1996, Pages 245–248, https://doi.org/10.1006/jmsc.1996.0029
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Abstract
The target strength (TS) of fish varies with a number of factors, especially the presence or absence of a swimbladder. This study investigated the effect of the swimbladder on the TS of live kokanee (Oncorhynchus nerka) in relation to depth. Experiments were conducted at Lake Kuttara, Hokkaido, Japan, which is abundant with kokanee. Fish samples were caught with a fishing net. The live fish were suspended on the sound beam axis, and tilted from −50° (head-down aspect) to +50° (head-up aspect). The dorsal aspect TS functions were measured at 50 kHz. Measurements were performed when the fish were forced to change depth rapidly. The TS values were measured as a function of tilt angle and depth, and the maximum dorsal aspect TS (TSmax) values and the averaged dorsal aspect TS (TSavg) values were calculated and compared. TSavgvalues were calculated with respect to fish tilt-angle distribution, which was assumed to have a mean value of −5° and a standard deviation of 15°. Both TSmaxand TSavg decreased with depth in accordance with Boyle's law, i.e. a reduction rate of 6.7 dB per 10 atm was observed.