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%.
Population structure in marine teleosts is often investigated to aid conservation and fisheries management (e.g. to assess population structure to inform restocking programs). We assessed genetic population structure of the important estuary-associated marine fish, mulloway (Argyrosomus japonicus), within Australian waters and between Australia and South Africa. Genetic variation was investigated at 13 polymorphic microsatellite markers. FST values and Bayesian estimates in STRUCTURE suggested population differentiation of mulloway within Australia and confirm strong differentiation between South Africa and Australia. The 12 Australian sample sets fell into one of four spatially separated genetic clusters. Initially, a significant signal of isolation-by-distance (IBD) was evident among Australian populations. However, further investigation by decomposed-pairwise-regression (DPR) suggested five sample sets were influenced more by genetic-drift, rather than gene-flow and drift equilibrium, as expected in strong IBD cases. Cryptic oceanographic and topographical influences may isolate mulloway populations from south-western Australia. The results demonstrate that DPR is suitable to assess population structure of coastal marine species where barriers to gene flow may be less obvious than in freshwater systems. Information on the relative strengths of gene flow and genetic drift facilitates a more comprehensive understanding of the evolutionary forces that lead to population structure, which in turn informs fisheries and assists conservation management. Large-bodied predatory scale-fish may be under increasing pressure on a global scale, owing to a variety of anthropogenic reasons. In southern Australia, the iconic sciaenid A. japonicus (mulloway, jewfish or kob) is no exception. Despite the species supporting important fisheries, much of its ecology is poorly understood. It is possible that a greater understanding of their genetic population structure can help ensure a sustainable future for the only southern Australian sciaenid.
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