The life history of Loligo vulgaris and Loligo forbesi

The population biology of Loligo vulgaris and Loligo forbesi in Galician waters is described based on monthly samples from the fishery obtained during the period February 1991-June 1992. Maturity was assessed using a maturity scale and indices. The estimated number of oocytes in mature females varied from 782 to 21 885 in L. vulgaris and from 1317 to 14 956 in L. forbesi, and showed a slight positive correlation with the length of the mantle (ML) for both species. Oocytes in the ovaries fall into three discrete size classes, which suggests that L. vulgaris and L. forbesi are intermittent or multiple spawning species. In L. vulgaris males mature at two different modal sizes, hence perhaps at two different ages, while in L. forbesi this occurs in both males and females. Males mature earlier in the season than females in both species. The maximum number of spermatophores found was 1010 and 1000 in two L. vulgaris males with 119 mm and 400 mm ML respectively, and 1035 in a L. forbesi male with 150 mm ML. In both species, spermatophore length increases with ML. Loligo forbesi males maturing at a larger size produce fewer but larger spermatophores than those maturing at a small size. Loligo vulgaris spawn throughout the year, but the period of more intensive spawning extends from December to April. The breeding season of L. forbesi extends from December to May, the more intensive spawning extending from December to February. Sex ratios were variable for both species. Age and growth for both species and sexes were estimated by examining growth increments in the statoliths. Like-sized individuals had different ages in both species. The life span of L. vulgaris was estimated at about l year while L. forbesi seems to reach an age of 15-16 months. A list of prey species found in gastric contents of both species is given. The diet of L. vulgaris comprises fish (86.8%), cephalopods (6.0%), crustaceans (3.0%) and polychaetes (1.8%), and the diet of L. forbesi includes fish (75.6%), crustaceans (18.5%) and cephalopods (4.4%).