北東太平洋東部海域資源調査におけるマグロ延縄の漂流形状と短縮率

概要

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The shortening ratio, defined as the ratio of the horizontal distance between two neighboring floats to the mainline length, is one of the important factors in settled hook depth in tuna longline. Because it was difficult to measure the distance between floats, apparent shortening ratio was estimated from a log in shooting. The purpose of this study is to investigate the drift pattern and actual shortening ratio of a tuna longline using GPS buoys to determine the position of floats of a longline during drifting. The longline research cruise was conducted by Japanese R/V Shoyo-Maru in eastern area of northeastern Pacific Ocean in the period between September and November 2004. In this study, a total of 583 GPS buoys were used which measured the distance of 179 given baskets. Drift patterns of a longline are classified into two types. One is a parallel track to the shooting course, and the other is a meandering track. There is no relationship between the drift pattern and the variation in actual shortening ratio. Actual shortening ratio on 70 to 90% of total 179 baskets shows a different value from apparent shortening ratio without relation to drift pattern.
日本水産工学会の論文
2009-07-15