Spatial variation in mean growth rates at size of southern rock lobster, Jasus edwardsii, in South Australian waters

Abstract

Size-specific growth rates of Jasus edwardsii were estimated from 16 000 recaptures of tagged lobsters during a 3-year mark–recapture study. The von Bertalanffy growth model was fitted to observed increases in carapace length. A normal likelihood of predicted length increment as a function of starting length and time-at-large was maximized. Estimated standard deviation of the likelihood, taken as an allometric function of predicted length increment, quantified individual growth variation. The distributions of residuals indicated satisfactory fits. von Bertalanffy parameters of growth were estimated at three levels of spatial resolution: 18 statistical reporting blocks, 6 growth subregions, and 2 fishery management zones. Among blocks, the mean annual growth of lobsters of 100 mm carapace length was 7–20 mm for males and 5–15 mm for females. Females grew more slowly after reaching sexual maturity. Growth rates declined by approximately 1 mm year –1 per 20 m increase in depth of habitat, at depths of 20 m and deeper. Density-dependent growth was indicated by spatial anti-correlation between male growth rates at 100 mm and fishery catches by number per unit effort. Regression implied that a 10% decrease in catch rate corresponded to increased growth by weight of 2–5%.