Estimation of size selectivity for oval squid Sepioteuthis lessoniana in the squid jigging fishery of Tokushima Prefecture

This paper examines size selectivity in the squid jigging fishery for the o val squid Sepioteuthis lessoniana in Tokushima Prefecture using an extended SELECT model for analyzing size frequency distributions of squid caught by the squid jigging and by set nets. The SELECT model is extended to utilize size frequency distributions constructed from repeat measurements of catch in the squid jig as the test gear and the set nets as the control gear whe re data on the fishing efforts is not available with variable fishing effic iencies. As a result, size selectivity r(l) of squid jigs of a body size fr om 12 to 15 cm is expressed as a logistic function of the mantle length I, r(l) exp (- 10.0 + 0.485 l)/[1 + exp (-10.0 + 0.485 l)]. This equation indi cates that oval squid of a size smaller than the jig is not caught by the j ig. As the squid attacks the jig as a prey, the size selectivity of the squ id jig found here is a type of prey size selectivity.