Growth strategies in the squid Loligo vulgaris from Portuguese waters

Abstract

The growth of the European squid Loligo vulgaris in northwest Portuguese waters is described and the influences of gender and hatching season analysed, based on statolith readings from individuals of a wide range of sizes. Male and female growth follows different models, males attaining a higher length-at-age than females. Males display increasing growth rates irrespective of the hatching season, but the length-at-age is higher in animals hatched during the warm season. Females may exhibit asymptotic growth or not, depending upon the environmental conditions to which they are exposed through their life cycle. Although growth rates after hatching are lower in females hatched during the cold season, favourable feeding and temperature conditions during the following spring and summer months contribute not only to increase growth rates but also to delay sexual maturation. The higher length-at-age of squid hatching in the warm season, observed in both genders, provides evidence that the temperature close to hatching has a significant impact on the size of juveniles and subadults. However, there is also strong evidence that throughout their life, environmental conditions continue to play an important role in growth rates and in defining the shape of growth.

Keywords:

• Age
• environmental factors
• growth models
• Loligo vulgaris
• squid

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

The authors thank Pedro Mendonça for assistance with the biological sampling and Cristina Castro who helped in statolith processing. Part of this study was carried out under the European Commission-funded projects Eurosquid II (AIR-CT92-0573) and CEPHVAR (FAIR-CT96-1520). Some of the samples were obtained under the PNAB/Data Collection programme. We also thank the anonymous referees for their helpful comments on the draft manuscript.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark