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首页> 外文期刊>ICES Journal of Marine Science >Variations in the target strength of Atlantic cod during vertical migration
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Variations in the target strength of Atlantic cod during vertical migration

机译：垂直迁移过程中大西洋鳕鱼目标强度的变化

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Experiments conducted at sea in June 1999 and January 2000 indicated that the mean target strength (TS) of Atlantic cod (Gadus morhua) varies not just with length, but also with pressure (depth) and fish orientation, particularly during vertical migration. In June, when fish were migrating and spawning, vertical migration was pronounced, extending up to 150 m off the seabed, and the associated TS declined by as much as 5 dB. In January, when the fish were located nearer the seabed, mean TS was more stable and matched a conventional model of TS vs. length [L, cm; i.e. TS = 20 log(L) - 66] based on measurements of ex situ fish orientated horizontally and positioned at close range. This paper demonstrates that mean TS is inversely related (ρ< 0.05) to the range off the seabed (r, m), which includes 90% of fish. Based on this finding, a new multivariate TS model is proposed: TS = 20 log(L) - 65- 0.05 r. In this model, r is a proxy for swimbladder volume and fish orientation. A survey in May 2007 found that cod (mean L = 63 cm) dispersed in such a way that single targets could be resolved up to 100 m from the seabed. Measurements of TS of in situ individual fish (TS_(individual)) and mean TS inferred from a comparison of area-backscattering coefficients (s_a) and count-based densities (TS_(indirect)) were positively correlated with a slope not different from unity. Means of these TS estimates were -32.4 and -32.2 dB, respectively, or ～2.3 dB less than that predicted by the conventional model. In contrast, the new multivariate model predicts TS= -32.5 dB, which is nearly identical with the means of TS_(individual) and TS_(indirect).
机译：1999年6月和2000年1月在海上进行的实验表明，大西洋鳕（Gadus morhua）的平均目标强度（TS）不仅随长度变化，还随压力（深度）和鱼向变化，特别是在垂直迁移过程中。 6月，当鱼类迁移并产卵时，垂直迁移明显，延伸至距海床150 m，相关的TS下降了5 dB。一月份，当鱼靠近海床时，平均TS更加稳定，并且与传统的TS与长度[L，cm;也就是TS = 20 log（L）-66]，这是基于水平放置并位于近距离的异地鱼类的测量结果。本文表明，平均TS与海底范围（r，m）呈负相关（ρ<0.05），其中包括90％的鱼类。基于此发现，提出了一种新的多元TS模型：TS = 20 log（L）-65- 0.05 r。在此模型中，r是泳衣体积和鱼向的代理。 2007年5月的一项调查发现，鳕鱼（平均L = 63厘米）的散布方式使得单个目标可以在距海床100 m处分辨。实地单条鱼的TS（TS_（个体））的测量值和通过面积反向散射系数（s_a）和基于计数的密度（TS_（间接））的比较推论得出的平均TS与与单位不变的斜率呈正相关。这些TS估计值的平均值分别为-32.4 dB和-32.2 dB，比传统模型所预测的值低约2.3 dB。相反，新的多变量模型预测TS = -32.5 dB，这与TS_（个体）和TS_（间接）的平均值几乎相同。

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