スケトウダラの餌と餌付き釣針に対する行動と釣針形状

概要

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The response of pollock to a bait tied to snood and a baited hook were examined in a cylindrical tank using two video cameras from Dec., 1987 to Mar., 1988.General features of the hooking process were as follows: pollock swam quickly toward the bait and quickly decelerated in it's immediate vicinity, followed by which a majority of the fish touched the bait, then either sucking it into their mouths or turning away. After sucking the bait into the mouth, hooking took place at the moment the fish made any powerful movement such as jerking or rushing in order to pull the bait off the hook. To be exact, hooking requires a force sufficient to allow the hook point to fully penetrate the inside of the mouth cavity. This force generated at the boundary where a fish's movements are limited by snood length and the velocity difference between the fish's head and the hook in it's mouth. These forces confidence at 95% level ranged from 3.9-5.4 N, with mean value of 4.5 N, as measured by using a steel ring attached to strain gauges placed between the mainline and the snood.According to analyses of the video tapes, the time interval between frames was 1/30s, the velocity vector of the fish head at the moment of hooking was described by a jerking move-ment in most cases. However in the case where the bait tied to snood was stolen, the velocity vector consisted mainly of rushing movement.
日本水産學會の論文