Ex situ and in situ target strength measurements of European anchovy in the Bay of Biscay

Abstract

[EN] This study measures the dorsal aspect target strength (TS; dB re 1¿m2) and TS¿length (standard length, SL; cm) relationships for European anchovy, attained both ex situ and in situ in two different seasons across 7 years in the Bay of Biscay. The measurements were made at three frequently used acoustic frequencies (38, 120, and 200¿kHz). A backscattering model for physostome fish was utilized to help interpret the results. The obtained experimental mean TS for anchovies with an SL of 3.5¿19.5¿cm was ¿44.6 (±2.3), ¿46.9 (±3), and ¿48.4 (±2.7) dB at 38, 120, and 200¿kHz, respectively, yielding b20 values of ¿66.4, ¿68.7, and ¿70.4¿dB, respectively. The results were consistent across seasons and between in situ and ex situ conditions, presenting TS¿length relationships with statistically significant slopes (p-values <0.05) for all frequencies. This research represents part of a series of efforts planned to obtain a comprehensive TS vs. length and depth relationship to update the acoustic assessment methodology of European anchovy in the Bay of Biscay.