The Selectivity of the Sunray Surf Clam Dredge

Abstract

The dredge for catching sunray surf clam Mactra chinensis carneopicta pilsbry is known to be highly selective. In this paper, the various factors affecting the selective actin of the dredge are analyzed, and the probabilities of the sunray surf clam not sifting through gaps between the teeth and the mesh of netting bag are calculated for various shell lengths. Considering that the probability of making a catch is the product of both probabilities, and that this probability is proportional to the relative catching efficiency, the selectivity curves for the sunray surf clam dredge were estimated for various gaps between the teeth and for various mesh sizes of the netting bag.
The relative catching efficiencies for the present dredge, with which the smallest sunray surf clam that can be caught has a length of 6cm, were calculated by using selectivity curves. Because the relative catching efficiency for a limited size was 0.62, it is hoped that the distance between teeth can be increased a little, and that the relative efficiency for the limited size can be decreased.