Studies on the Catch Efficiency Derived from the Difference in the Construction of Tuna Long-Line Gear (I) : On the Catch Difference from the Each Depth of Hook in the Long-Line Gear

As to the tuna long-line gear two facts were already clarified, first, that under the sea water it forms a kind of catenary; and, second, that the sinking degree of each hook is to be influenced by the shifting position of the connecting point of the hook on the main line. By making a statistical research on the catch data from some examination facilities, the following results were obtained: 1) In case of using the gear consisted of the same build, though this is a quite natural process, the more its sinking degree increases in depth the more became large its catch rates. 2) The main factor of the above mentioned phenomenon was considered to be attributed to the varying degree of eating reaction of tuna to the each hook of gear rather than to the different density in the swimming rayer