南太平洋の大型ビンナガの遊泳層について-II : 改良たて繩によるビンナガの釣獲層

概要

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It is apparent from the former that the albacore is hooked after completion of the sinking of the long-line. In order to further examine the vertical distribution of albacore, a fishing experiment was made by using many baskets of efficient vertical long-lines.The results are summarized as follows;1) Average time taken for hauling of the vertical long-line continuously, was 3.5 minutes, a little more than that of the deep-sea long-line.2) In tests of hooked rate, there was no significant difference between the vertical long-line and the long-line.3) The vertical distribution of albacore catch by the vertical long-line showed a similar tendency with the results reported in the former paper, i.e., the highest hooked rate was 2.2-2.7% at 200-300m layer, and the 1.2% at 380m layer was higher than that at the 150 m layer.4) The greater catch of bigeye tuna at 300m layer, especially in comparison within other layers, the yellowfin tuna catch at 200-300m layer and the marlins catch at 150-300m layer, were obtained in this fishing experiment. These facts exhibit that the vertical distributions of tunas and marlins are quite wide.
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