Comparison of Tilt Variation in the Otter Board and Codend of Bottom Trawl Gear during Fishing Operations
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The motion of the otter board on a trawl can affect the motion of trawl nets, and the motion of the codend can affect fish selectiv- ity. Preliminary measurements of the tilt of bottom trawl gear were carried out to compare the tilts of the otter board and codend. The tilt of the otter board was measured by Vector and tilt at 1.5 m anterior to the end of the codend, and the middle upper panel was measured with a micro-DST-tilt logger. Tilt data such as yaw, pitch, and roll were analyzed by the fast Fourier transforma- tion method and global wavelet and event analyses for the period or amplitude. The mean period ± standard deviation of the tilt in the otter board, (5-6) ± 2 s, was similar to the period of the codend, (4-6) ± (2-3) s, whereas the amplitude of the codend was greater than that of the otter board. The yaw and pitch periods were not significantly different between the otter board and codend, but roll was different. Furthermore, the tilt period frequencies of the otter board and codend were not significantly dif- ferent. Accordingly, the tilt motion of the codend was mostly related to the tilt of the otter board.
Abstract
The motion of the otter board on a trawl can affect the motion of trawl nets, and the motion of the codend can affect fish selectiv- ity. Preliminary measurements of the tilt of bottom trawl gear were carried out to compare the tilts of the otter board and codend. The tilt of the otter board was measured by Vector and tilt at 1.5 m anterior to the end of the codend, and the middle upper panel was measured with a micro-DST-tilt logger. Tilt data such as yaw, pitch, and roll were analyzed by the fast Fourier transforma- tion method and global wavelet and event analyses for the period or amplitude. The mean period ± standard deviation of the tilt in the otter board, (5-6) ± 2 s, was similar to the period of the codend, (4-6) ± (2-3) s, whereas the amplitude of the codend was greater than that of the otter board. The yaw and pitch periods were not significantly different between the otter board and codend, but roll was different. Furthermore, the tilt period frequencies of the otter board and codend were not significantly dif- ferent. Accordingly, the tilt motion of the codend was mostly related to the tilt of the otter board.
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