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.

中文翻译：

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比斯开湾欧洲凤尾鱼的异地和原位目标强度测量

本研究测量了欧洲鳀鱼的背侧目标强度 ( TS ; dB re 1 m ² ) 和TS长度（标准长度，SL; cm）关系，在 7 年的两个不同季节获得了非原位和原位的欧洲鳀鱼比斯开湾。测量是在三个常用声频（38、120 和 200 kHz）下进行的。使用 physostome 鱼的反向散射模型来帮助解释结果。获得的 SL 为 3.5–19.5 cm 的凤尾鱼的实验平均TS在 38、120 和 200 kHz 下分别为 -44.6 (±2.3)、-46.9 (±3) 和 -48.4 (±2.7) dB，产生b ₂₀值分别为 -66.4、-68.7 和 -70.4 dB。结果在不同季节以及原地和非原地条件之间是一致的，呈现出TS长度关系与所有频率的统计显着斜率（p 值<0.05）。这项研究代表了一系列计划的一部分，旨在获得全面的TS与长度和深度的关系，以更新比斯开湾欧洲凤尾鱼的声学评估方法。