Temporal population dynamics in arrow squid Nototodarus gouldi in southern Australian waters

Nine monthly samples of arrow squid Nototodarus gouldi were obtained off Portland, Australia, during 2001. Statolith age analysis was used to determine growth rates and cohort structure during the study period. The results of statolith increment periodicity experiments were inconclusive due to difficulties in discerning increments in the cultured squids, although the region of the statolith in the maintained squids did increase over time. The maximum age obtained was 360 days, which is consistent with a 1-year life cycle in this species. Squid obtained were >150 days old and usually >200 mm mantle length. While there was often a mix of maturity stages for females, the majority of males were mature. Monthly length frequency distributions suggested that there was a complex mixture of cohorts in the samples obtained. Fitting a Normal mixture model to the age frequency distribution suggested that at least four cohorts were present during the period of the study. Growth was modelled with an exponential function with individuals grouped according to hatch season. The rate of growth for seasonal groups of squid was considerably different between males and females. There was no evidence of seasonal differences in growth rates of males. In contrast, the summer hatched females had significantly greater growth rates than winter and spring at P=0.05, and the growth rates of autumn hatched females were found to be significantly different to the winter hatched females at the 0.1 level. © Springer-Verlag 2005.