Population structure, maturation patterns and fecundity of the squid Loligo vulgaris from southern Portugal

Abstract

This study presents the results of an analysis of data on length, weight maturity stage, and fecundity of the squid Loligo vulgaris. The data are based on monthly sampling, between January 1991 and June 1992, from the landings of a traditional inshore fishery for squid in southern Portugal. Male squid generally have a lower weight than females of equivalent mantle length. The overall ratio of male to female squid is 1.1, with limited periods during autumn and spring when females outnumber males. Mature males occur within the broad size range 115–605 mm, whilst mature females have a more restricted size range within 175–345 mm. Immature stages I–II dominate the population during June and July, and there is progressive maturation of both sexes stage II to mature squid at stage V, between August and the following March and May in the larger males and females, respectively. There is a significant difference between the sizes at which the different sexes achieve maturity ( ML50%), with the male at 245 mm and the female at 227 mm. There is evidence that there are two size modes at which males achieve sexual maturity. It is suggested that maturation of this species takes approximately 8 months in the Algarve. A range of reproductive indices derived from gonad morphometrics in mature squid show a pattern of seasonal development with overall values for gonad maturation indices which are lower during the summer and higher during the autumn to the spring. Fecundity has been estimated by counting the total number of oocytes and ova in the ovary and oviduct of mature (stages IV–V) females. The number of eggs varied between 1441 and 14886 and fecundity was correlated positively with mantle length, body weight, and with length and weight of the nidamental gland.