Population Structure of the Squid, Loligo japnica, Distributed in Sendai Bay

Abstract

The population structure of the squid, L. japonica, caught by set nets and small trawlers in Sendai Bay during May 1975-July 1976 and Oct. 1978-Dec. 1979 was studied based on the relationship between mantle length and maturity of the female. Three groups with different breeding seasons are distributed in Sendai Bay. Group I becomes mature and copulates in the offshore region. When this group approaches the coastal region, most have completed maturation and copulation. Spawning in this group occurs between May-July. Group II becomes mature and copulates on the way to the coast from offshore. When this group appears in the coastal region, most have completed maturation and copulation. This group stays in the coastal region from May-July while in the pre-spawning stage. Group III is found in the coastal region from June-Aug where it becomes mature and copulates. Judging from growth patterns, the estimated life span of all 3 groups is 1 yr. From mantle length composition in the offshore region, the mean mantle length of the adult was estimated.