三枚網の内網のたるみ,内網の網目の変化と漁獲

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The experimental operations concerning the catching efficiency and the fish selectivity for bottom gillnet and trammel net were examined with 3 different mesh sizes and 3 different slack-nesses (the ratio of the height of inner net to that of outer net) in the Tokyo Port during 1981 to 1982. The results obtained are summarized as follows: 1) The catch pattern of gizzard shad Clupanodon punctatus, sardine Sardinops melanostictus, and big eyed herring Herklotsichthys zunasi changes due to difference of mesh size of inner net. 2) The slackness of trammel net seems to affect to some degree the catches, while in the case where the mesh size of inner net is suitable for the size of fish, the slackness of inner net does not affect the catches of trammel net so much. 3) In the case where both the mesh size of inner net of trammel net and the mesh size of bottom gillnet are suitable for the size of fish, it seems that the catching efficiency of gizzard shad by bottom gillnet exceeds that by trammel net. 4) It follows from the selection curves of trammel net and bottom gillnet obtained by this experiment that when the slackness is 1.1, the sharpness of selection curve for the trammel net has the same tendency as that of the bottom gillnet. In the case where the slackness is more than 1.5, it is expected that the larger size of fish is caught more easily by trammel net than by bottom gillnet. 5) The selection curve of the trammel net has the same character as that of bottom gillnet. This means that the smaller size of fish is selected severely by the mesh sizes.
日本水産學會の論文

三枚網の内網のたるみ,内網の網目の変化と漁獲

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