延縄の枝縄の違いによる漁獲比較と魚の釣糸視認能力

概要

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Fishing operations were conducted to examine the effect of visibility of the branch-lines on the catchability of long-lines in the coastal water of Kagoshima. The visual ability of fish was determined by the conditioning method for the recognition of lines of different thickness and visibilities. Two different branch-lines, brown multifilament and transparent nylon monofilament, caught the same number of green snapper Lethrinus nebulosus and lizard fish Trachinocephalus myops in 27 operations. Long-lines set on the bottom caught twice the number of fishes than those set in mid-water, which was attributed to the feeding habit of the fishes caught. In the transposition test of the conditioning method, girella Lethrinus nebulosusu could recognize brown silk monofilament of 0.06 mm in diameter but could not recognize colorless nylon monofilament of 0.12 mm in diameter, indicating the importance of contrast of thefilament rather than its thickness in the visual recognition by fish.
2009-12-25