Age and growth of the squid Loligo vulgaris off the south coast of Portugal, using statolith analysis

Age composition and growth rates of the squid Loligo vulgaris (Lamark, 1797) were studied by examination of growth increments within statoliths of 419 specimens (mantle length, ML, ranging from 32 to 400 mm). The squid were obtained by monthly sampling from the catches of commercial trawls off southern Portugal between March and September, 1993. The total number of growth increments in the mounted and ground statoliths was counted using a semi-automatic image analysis system. ML was significantly correlated with both the statolith length, TSL and the number of increments, NI. The female statolith was slightly larger than the male statolith for the same mantle size. Growth rates of individuals showed high variability with an average estimated at 34.6 mm month(-1) for males and 33.5 mm month(-1) for females. Growth in length between 70 and 280 days was best described by a power function for both sexes. The growth index of the statolith (TSL/NI) decreased with individual growth. This result may be related with the onset of sexual maturation. L. vulgaris hatched throughout the year with two distinct peaks, in spring which is the main breeding period, and in autumn. The life cycle of the L. vulgaris population on the south Portuguese shelf was completed in one year.