マグロ延繩の漁獲機構に関する研究-I

延繩の構造・寸法と漁獲の関係

抄録

The catch in tuna longline fishing depends chiefly on the knowledge of the behaviour of tuna and the techniques of the gear handling. Biological factors, however, have hitherto often been neglected in the construction of the gear because of few data to be concerned with.
In the present paper, the fishing mechanism of tuna longline is studied from the relation between the behaviour of the fish and the size of the gear, such as hook intervals, mainline, branch line and float line in length. The data used here are of many longline fishing boats which carry various different sizes of gears, and operated in nearly the same fishing ground and at the same period.
The results obtained are as follows. When the catch (C) is assumed to be influenced by the factors that the school density (s) in a fishing ground, the soaking time (t) of the bait, hook intervals (d) and the radius (r) of an estimated spherical surface into which the bait is liable to attract the fish, the relation among them seems to be explained by the following equations:
C=st×d when d<r
C=st×2r when d>r
The depth at which hooks are suspended has practically no effect on the catch.