Role of larval distribution and abundance in overall life-history dynamics: a study of the prawn Penaeus semisulcatus in Albatross Bay, Gulf of Carpentaria, Australia

The distribution and abundance of Penaeus semisulcatus de Haan larvae in Al batross Bay was studied during the 6 yr from March 1986 to April 1992. The study is a component of an investigation into the causes of interannual rec ruitment variation. Protozoeae were found in a wide range of temperatures a nd salinities and in both the presence and absence of thermoclines and halo clines, although density of larvae was low in water warmer than 30"C. Two d istinct peaks of larval abundance were evident: from January to March (summ er), and from August to November (spring). First-stage protozoeae were rare ly found during summer, although later stages were common, which suggests e ither that they were less catchable in summer or that most summer spawning was outside the study area. Three extended cruises during 1987 found high d ensities of larvae as far as 120 km offshore; these larvae represent wasted reproductive output since they are beyond the zone of effective spawning. The annual variations in abundance of larvae were compared with the results of parallel CSIRO studies of other P, semisulcatus life-history stages in Albatross Bay. There is poor agreement between larval numbers and the popul ation fecundity index (a measure of egg production), but a stronger match w ith densities of postlarvae in the Albatross Bay estuaries, particularly in summer. This indicates that variable rates of egg hatching and early larva l survival may be important determinants of successful recruitment to the P . semisulcatus fishery.