Changes in the distribution and abundance of Todarodes pacificus (Cephalopoda, Ommastrephidae) paralarvae in the southwest Sea of Japan with changing stock levels

Abstract

Larval distribution is one of the most basic topics of the study on early life history. In order to determine the paralarval distribution and abundance of the ommastrephid squid Todarodes pacificus, annual surveys during October-November have been conducted from the southwest Sea of Japan to the northern part of the East China Sea since 1973. Paralarvae were collected by 80cm diameter ring nets towed obliquely from a depth of 75m to the surface. The results indicate that the paralarvae were abundantly distributed all over the survey area when stock levels were high in the early 1970 s and after the late 1980 s, and that when stock levels were low, the range of paralarval distribution contracted northeasterly. We conclude that these changes of paralarval distribution may be a direct cause of stock fluctuation.