Research on acoustic target strength of Larimichthys crocea in South China Sea based on Kirchhoff Approximation Model

Fisheries acoustics is as an important method for assessing fish abundance and distribution, but the acoustic assessment of Larimichthys crocea is often limited by insufficient Target Strength (TS) data. Thus, we employed the Kirchhoff Approximation Model to measure and calculate the TS of cultured L. crocea in the South China Sea, and analyze the relationship between its attitude inclination, body length (L), acoustic frequency and the target intensity, so as to supplement the target intensity data of L. crocea, and provide scientific references for the acoustic assessment of fishery resources in the South China Sea. The results show that at the frequencies of 38, 70, 120 and 200 kHz, the relationship between TS and body length can be approximated by TS=20 logL−74.12, TS=20 logL−74.34, TS=20 logL−71.98, and TS=20 logL−70.01, respectively. At the same frequencies, the TS of L. crocea increased with increasing body length, with higher values at angles of −20°−−10° and 10°−20°, aligning with their swim bladder orientation, movement posture and behavioral patterns. Moreover, when the frequency was over 70 kHz, the TS of L. crocea increased with increasing frequency but without a direct linear relationship.