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首页> 外文期刊>Fisheries Research >Behaviour analysis of undersized fish escaping through square meshes and separating grids in simulated trawling experiment.
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Behaviour analysis of undersized fish escaping through square meshes and separating grids in simulated trawling experiment.

机译：模拟拖网试验中超大尺寸鱼通过方孔和分隔网格逃逸的行为分析。

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Understanding the fish escape behaviour through bycatch reduction devices is the cornerstone of their application as technical conservation measures. To evaluate square meshes and sorting grids as successful size-selective bycatch reduction devices in finfish trawls, we conducted a simulated trawling experiment to assess the effects of illumination, towing speed and mesh or grid orientation on the escape behaviour of undersized fish through square meshes and rigid grids. Juvenile masu salmon (Oncorhynchus masou) with average body length 13 cm were used as the experimental fish. A speed-controllable motor was used to tow the framed net in a circular water tank. An infrared CCD (charge-coupled devices) camera fixed to the towed net by means of a rotary connector was used to observe fish behaviour. In contrast to the active escape seen under lighted conditions, there was no active voluntary escape under dark conditions. As a result, no fish escaped through parallel and backward-sloping meshes, and only 13% of fish escaped through the forward-sloping meshes when the towing speed was increased. On the other hand, the encounter probability and passive escape through the longer openings in the backward-sloping grid increased under the dark condition, resulting in the highest escape ratio. This increased from 67 to 87% on increasing the towing speed from 1 to 1.5 knots, and shortened the swimming time before escaping from 5 to 1.5 min (the highest escape ratio and the shortest swimming time before escaping under the dark condition). Frame-by-frame analysis of some escape events demonstrated easy, passive fish escape through the grids with no change in the normal swimming direction. The results support the backward-sloping grid as an efficient bycatch-reduction device, especially in demersal trawling when placed well ahead of the codend, working in the dark at high towing speeds. [copyright] 2007 Elsevier B.V. All rights reserved.
机译：通过副渔获物减少装置了解鱼的逃逸行为是将其用作技术保护措施的基础。为了评估方形网眼和排序网格作为有鳍拖网中成功的尺寸选择兼捕减少设备的成功性，我们进行了模拟拖网实验，以评估光照，拖曳速度以及网格或网格方向对通过方形网眼逃避超大鱼类的行为的影响。刚性网格。实验鱼的平均体长为13厘米，幼年的马苏鲑（Oncorhynchus masou）。使用速度可控的电动机在圆形水箱中拖曳有框网。使用通过旋转连接器固定在拖网上的红外CCD（电荷耦合器件）摄像机观察鱼的行为。与在光照条件下主动逃生相反，在黑暗条件下没有主动自愿逃生。结果，当拖曳速度增加时，没有鱼通过平行和向后倾斜的网孔逸出，只有13％的鱼通过向前倾斜的网孔逸出。另一方面，在黑暗条件下，通过向后倾斜的格栅中较长的开口的相遇概率和被动逃逸会增加，从而导致最高的逃逸率。在将拖曳速度从1节增加到1.5节的过程中，从67％增加到87％，并且将逃生前的游泳时间从5分钟缩短到1.5分钟（在黑暗条件下逃生率最高，逃生前的游泳时间最短）。对某些逃生事件的逐帧分析表明，容易，被动的鱼通过网格逃逸，而正常游泳方向没有变化。结果支持向后倾斜的栅格作为有效的兼捕减少装置，尤其是在深拖网中，如果将其放置在编码对象之前，则可以在黑暗中以高拖曳速度工作。 [版权] 2007 Elsevier B.V.保留所有权利。

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