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Ex situ and in situ measurements of juvenile yellowfin tuna Thunnus albacares target strength

机译：幼年黄鳍金枪鱼Thunnus albacares目标强度的异位和原位测量

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摘要

To provide target strength (TS) information for estimating the body length of yellowfin tuna Thunnus albacares and its abundance around fish aggregating devices, TS was measured ex situ and in situ. In the ex situ TS measurements, two cameras synchronized with a 200 kHz echosounder were used to obtain the precise orientation of the yellowfin tuna under free swimming conditions. The ex situ TS (dB re 1 m2)–fork length (FL, cm) regression was: TS = 27.06 log (FL) − 85.04. Ex situ TS was found to reach its maximum in the tilt angle range of −15° to −20° after excluding TS samples with insignificant correlation to the tilt angle. The angle between the vertebra and the swim bladder was approximately 25° according to X-ray images, supporting the above tilt range. The relationship between the swim bladder volume (V SB, ml) and the fork length was: V SB = 0.000213 FL3. The results from the in situ TS measurements indicated that the tilt angle was highly concentrated between −10° and 15°. The results from a calculation using the ex situ TS–FL equation with the fork length from biological sampling agreed strongly with the average in situ TS.
机译：为了提供目标强度（TS）信息以估计黄鳍金枪鱼Thunnus albacares的体长及其在鱼类聚集设备周围的丰度，对TS进行了非现场和现场测量。在异地TS测量中，使用两台与200 kHz回声测深仪同步的摄像机来获得黄鳍金枪鱼在自由游泳条件下的精确方向。异位TS（dB re 1 m 2 ）-叉长（FL，cm）回归为：TS = 27.06 log（FL）− 85.04。在排除与倾斜角无关紧要的TS样本后，发现异位TS在-15°至-20°的倾斜角范围内达到最大值。根据X射线图像，椎骨和游泳膀胱之间的角度约为25°，支持上述倾斜范围。游泳膀胱容积（V SB ，ml）与叉子长度之间的关系为：V SB = 0.000213 FL 3 。原位TS测量的结果表明倾斜角高度集中在-10°和15°之间。使用异地TS-FL方程进行计算的结果，生物采样的叉长与平均原位TS高度吻合。

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