グランドロープによる魚の駆集モデルについて

Abstract

The ground rope of drag net has the function of ke ping the net in contact with the sea bottom and herding fishes to the entrance of the bag net. The authors paid attention to fish reaction to ground rope and considered a fish herding model for the ground rope Theoretical probablility of fishes entering a funnel of bag net was calculated, and fishing efficiency of supposed four types of ground rope were compared. The movement of fish can be described as zigzag relative to ground rope. Thinking of a fish herding model of ground rope using plice (body length 30cm), authors considered the assumptions written below; (1) Fishes were distributed on the sea bottom uniformly and remain settled there until coming in contact with the advancing ground rope. (2) When fishes came in contact with the ground rope, they swam inside, in a direction normal to the ground rope. They swam 10 body lengths in 2 seconds, and settled there until coming in contact with the ground rope again. (3) When fishes came in contact with the ground rope, probability p(0〈p〈1) of fishes were not herded and went outside of the ground rope. (4) All of the fishes were distributed in front of the bosom, and fishes which were herded to the area in front of the bosom entered the funnel of the bag net without escaping. Supposed four types of ground rope; triangle, trapezoid, catenary and half ellips were compared using relative herding ratios of ground rope. The catenary type showed the highest fishing efficiency under ordinary towing conditions.