Effect of thin twine on gill net size-selectivity analyzed with the direct estimation method |
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| Authors: | Kosuke Yokota Yasuzumi Fujimori Daisuke Shiode Tadashi Tokai |
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| Institution: | Department of Marine Science and Technology, Tokyo University of Fisheries, Minato, Tokyo 108-8477 and; Division of Marine Environment and Resources, Graduate School of Fisheries Science, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan |
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| Abstract: | ABSTRACT: To analyze the effect of thin twine on gill net size selectivity, a series of fishing experiments using gill nets of two twine thicknesses (no. 0.8 of 0.16 mm diameter and no. 3 of 0.28 mm diameter) and three nominal mesh sizes (41 mm, 46 mm and 51 mm) was conducted in outdoor water tanks containing a rainbow trout ( Oncorhynchus mykiss ) population of known size frequency. For nets of the same nominal mesh size, mesh openings of the no. 0.8 twine nets were approximately 2 mm larger than those of the no. 3 twine nets. The effects of both mesh opening and twine thickness are combined in the conventional analysis with the selectivity curve against fish length. Selectivity against the ratio of fish girth to mesh perimeter was calculated to avoid the direct effect of changes in mesh openings due to twine diameter at the same nominal mesh size. Results demonstrated that the thinner twine gill net was more likely to capture rainbow trout of smaller girth than the mesh perimeter. Fish with girths smaller than the mesh perimeter were often retained by the net with its body tangled by the thinner twine, possibly due to the increased flexibility of the thinner twine. |
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| Keywords: | direct estimation method gill net girth mesh perimeter rainbow trout size selectivity twine thickness |
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