ベーリング海における底曳船の1日の揚網回数の季節変化と漁獲量・昼間の長さとの関係

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The boats showed a tendency of conducting less frequent hauling on the days of better catch2)5). The discrepancy due to the seasonal change of daily catch should therefore be eliminated from the seasonal change of the number of daily hauls in relation to the length of daytime. The daily reports by the 22 Danish seiners of a fish-meal fleet in the Bering Sea during the entire season of 1963 were stratified according to the grade of daily catch and analyzed by the same methods as in the previous report3). And the results obtained are summarized as follows: 1. The number of daily hauls (y) on the days of the same grade of catch in the same fishing ground of Area A or B depended on the length of daytime, log (11-y) keeping very significant linear regression on the length of daytime. 2. In Area C, all the catch grades except the grade 30 tons did not show a significant linear regression of log (ll-y) on the length of daytime (the value in the grade 30 tons decreased with the progress of the autumnal shortening of the daytime).3. The increase in the daily catch made the regression line shift upwards, although the line for the grade 10 tons was located upward of that for the grade 20 tons. 4. These facts meant that 1) the characters of the seasonal change of the number of daily hauls-the differentiation into three seasons, significant linear regression on the length of daytime in Area A or B, and invariableness in Area C-were not attributable to the seasonal change of the daily catch, and that 2) the decrease in the daily catch had the same effect as the elongation of the daytime, both making the boats conduct more frequent hauling.
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ベーリング海における底曳船の1日の揚網回数の季節変化と漁獲量・昼間の長さとの関係

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