The squid Loligo vulgaris has an extended spawning season within the upwelling system off north-west Portugal, and its paralarvae may thus develop under a wide range of environmental conditions. Both temperature and salinity are expected to affect the metabolism of young squid and we tested their effects on growth during the embryonic and post-hatching phase, based on measurements of growth increments in statoliths of juveniles and adults, using generalized additive models. There was no evidence that statolith increments representing early growth become unreadable in adult statoliths. Variability in the statolith size at hatching was weakly but significantly related to the variables in the model. On the other hand, the effects on statolith growth of both sea surface temperature and of sea bottom temperature were significant during early post-hatching life. Thicker increments are deposited in the statoliths of squid living under higher temperatures, which results in summer hatchers having larger statoliths at the age of 90 days. Inspection of the statolith accretion pattern, using a piecewise linear regression method, revealed an ontogenetic shift in increment width, which may be an indication of the age of transition from paralarva to juvenile. On this basis, it is suggested that the planktonic stage lasts 60 or 90 days, depending on whether the paralarvae lived at higher (>15°C) or lower (<15°C) sea surface temperatures. The life strategy under warmer conditions potentially favours survival by reducing the duration of the vulnerable planktonic phase.

Age and size-at-maturity of Loligo vulgaris from Portuguese waters were evaluated in order to explain its complex population structure, which is strongly influenced by continuous spawning. Age was obtained by increment counting in statoliths. Maturity ogives by age group indicated that males mature one month earlier (at 277 days) than females (at 298 days). Females mature at a ML50% of 17.6 cm, while males mature at smaller sizes. The later, however, showed a high degree of complexity in the size at maturity with evidence of two size at maturity groups. In both sexes, maturity was ultimately found to be primarily dependent on size rather than age. The effect of hatching season on age-at-maturity, size-at-maturity and reproductive investment was analysed by comparing two groups of squid hatched under distinct environmental conditions, namely the temperature during the first 3 months of life, the cold cohort (CC), hatching between December and March and the warm cohort (WC), hatching between May and September. Significant differences were found between cohorts on age-at-maturity, size-at-maturity and reproductive investment, giving indication of the environmental influences on sexual maturity. CC squid mature ca. 2 months later in life than WC squid and at a significantly larger size. The reproductive investment as measured by GSI was higher in the WC squid. Much of the variability in age and size-at-maturity of females in the population was due to differences between cohorts but this was not the case for males.