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%.

Juvenile lobsters Panulirus ornatus in the Torres Strait emigrate once a year from the Torres Strait to the Gulf of Papua, several hundred kilometres to the northeast. They mature and spawn during this emigration. After spawning the lobsters disappear. It has been suggested that the combined stress of reproduction and emigration results in mass mortality. To test this hypothesis, lobsters were collected at several stages of the emigration and their condition defined by the water content and composition of the digestive gland and abdominal muscle. A cage experiment, with 2 feeding regimes, was conducted to examine the likelihood of post-reproductive mortality. Compared to lobsters in the Torres Strait, before emigration takes place, lobsters that had con~pleted the breeding emigration were in very poor condition. There were changes in the size and composition of both the digestive gland and abdominal muscle. Three stages of deterioration were recognised; in the final stage the digestive gland tissue was severely atrophied. The physiological characteristics identified in this study provide a quantitative basis for future work on the mortality rates of lobsters that have completed the emigration.

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Aprocedure is presented for incorporating catch totals by both weight and numbers in stock assessment. Their ratio is the weight of an average harvested individual which, in turn, reflects mean mortality rate. The model is age-based and requires, as input, a vector of average age-specific weights in the catch. The model developed for the South Australian rock lobster (Jasus edwardsii) fishery assumes steady state, constant fishing mortality on all age classes and a natural mortality rate equal to 0·1. Also explicit are reduced vulnerability of recruitment-aged lobsters and incidental mortality of lobsters below the legal minimum size. The solution yields estimates of average exploitation rate and yearly recruitment. These give (absolute) age-specific population numbers in the fishable stock. Exploitation rates were estimated for statistical reporting blocks in South Australia using this catch weight–numbers (qR) method and, for comparison, that of Beverton and Holt employing mean length. Each method was also tested with simulated data, the former yielding estimates of lower variance and bias. In practice, counting individuals captured is likely to require less time and to yield lower measurement error than measuring lengths. This method thus offers the possibility for improved precision and accuracy at lower cost.

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