サケ・マスの流網罹網時における網目の伸びと魚体のくびれについて

Abstract

At the moment of capture of salmon with gill-net, twines of the net extended to some extent, and at the same time, body of salmon contracted at netted portion. The extensibility of twines is concerned with the strength of the twines and also with the elasticity of fish body which varies with fish species and duration of time after death. At every fishing operation authors measured the girth length of fishes on netting condition and also after taken off from the net. Mean extension of mesh size of net on netting condition in desirable portion was 3 percent in comparison with original girth length. Load-contraction curves of net twines and load-extension curve of fish body were obtained from the experiments made by using a simple device of meter (Fig. 2). Combining the curve of load-extension of net twine and the curve of load-contraction of fish body, it is presumed that the crossing point of these two curves is the netting point; that is, the point at which contractibility of fish body and extensibility of twine is in an equilibrium keeping the fish body firmly.