Identification of ontogenetic growth models for squid

Abstract

Several ontogenetic growth models were fitted to size-at-age data of twelve species of squid from the recent suborders Myopsina and Oegopsina. These squid represent different habitats of the world ocean – from shelf to meso- and bathypelagic waters and from tropical to polar regions. Two main criteria were used in selecting the squid: large sample size (>150 individuals) and wide range of ontogenetic coverage (>2/3 of the whole ontogenesis). The growth models used were the exponential, Gompertz, Schnute and ad hoc two-stage models. They were fitted to size-at-age data using maximum likelihood for estimation and Akaike weights for identification. In all species, the 4-parameter Schnute or the 3-parameter Gompertz models provided the best fit. Size at the inflection point of the growth curve for most squid was smaller than size at 50% maturity, suggesting that maturation is not a major cause of the change in growth rate for these species. Mathematical and statistical procedures to calculate standard measures of growth, such as the instantaneous relative rate of growth, G, which are valid for all continuous growth models, are also presented.