The following report is a description of the two FIR TA projects (85/85 & 89/13) which examined recruitment processes in penaeids at Albatross Bay in the northeastern Gulf of Carpentaria over the years 1985 to 1992. The aim of the first of the two projects was to identify the main factors which control the recruitment of prawns, while the aim of the second project was to build on the results on the first to provide managers with explanations for declines in commercial catches that had been experienced in the fishery.

The work was focused in three main areas: measuring year-to-year variation in numbers of the main life history stages (eggs, larvae, juveniles and adults in the Albatross Bay region) and correlating the abundances with changes in the environment; measuring the year-to-year variation in the extent of predation by fish on juvenile and adult prawns; and examining relationships between commercial fishery catches throughout the Northern Prawn Fishery and meteorological data.

The results of the projects have enabled us to better define the life history dynamics of the banana prawn Penaeus merguiensis and, to a lesser extent, the grooved tiger prawn Penaeus semisulcatus. Life cycles of both species were found to be based on two cohorts per year. Comparison with P. merguiensis life cycles throughout the Indo-West Pacific region has shown that two cohorts per year was the common pattern, and that the relative contribution to offshore commercial fisheries of each cohort in the various regions wa􀁴 governed to a large extent by the local pattern of rainfall. In the case of P. merguiensis in Albatross Bay, differential mortality results in only one of these cohorts contributing significantly to the commercial fishery.