マグロ延繩の揚繩速力-II.

Abstract

It is one of the characteristics of the tuna longlining that the simple and repetitious hauling work extends over very long hours. And many of the conditions change with the lapse of time. The present report dealt, accordingly, with the change of the hauling speed with the altitude of the sun till the astronomical twilight and that with the lapse of time after it; and the results obtained were summarized as follows: 1. The difference of the average hauling speed of the sections during the astronomical twilight and at night from that in the daytime was not larger than 15%. This was far smaller than our impression during the work on board, because the results did not concern with the effort paid by the fishermen. 2. It took a little longer time to haul up the first and the last several sections than the time to do so their adjacent sections, because these sections were meandering severer than those in the other parts. 3. The hauling speed was the fastest when the altitude of the sun was not smaller than 20°. 4. The speed was slightly reduced when the altitude of the sun was smaller than 20°, and was the smallest during the astronomical twilight especially when the estimated altitude of the sun was -10° to -15°. 5. The speed at night took the similar value to that during the declining sun and civil twilight (20° to -5°), and did not show reduction with the long lapse of working time.