Reproductive dynamics of endeavour prawns, Metapenaeus endeavouri and M-ensis, in Albatross Bay, Gulf of Carpentaria, Australia

The spawning patterns of two penaeid prawns, Metapenaeus endeavouri (Schmit t) and M. ensis (De Haan), were examined from data collected at 45 stations between March 1986 and March 1992. An index of population fecundity based on the abundance, proportion and fecundity of sexually mature females was u sed as a measure of spawning output of the prawn stock. The population fecu ndity index for M. ensis was higher than that for M. endeavouri. The monthl y population fecundity index for M. endeavouri varied markedly among years, while that for M. ensis was consistent among years. Spawning of M. endeavo uri occurred year-round, while that of M. ensis was concentrated mainly in spring (September to November). For M. endeavouri, a minor spawning, derive d from a relatively small number of summer spawners, occurred in the 20 to 30 m offshore waters in summer. In early summer (after May), the major spaw ning group consisted of large females from the winter-spawning cohort, and the spawning area shifted to depths of 30 to 60 m. In winter (July), the ma jor spawning, derived from the winter-spawning cohort, occurred at depths o f 20 to 40 m. For M. ensis, the major spawning, derived from the spring-spa wning cohort, was observed in depths < 50 m and was concentrated particular ly in inshore waters (<20 m) in spring. In autumn, the spawning output was mainly from the autumn-spawning cohort, which comprised but a small number of individuals. In winter, the major spawning group again consisted of the large females from the spring-spawning cohort, and spawning increased in th e oceanic waters (> 50 m). These results suggest that mature female M. ende avouri and M. ensis move offshore (>40 m) by May and July, respectively, an d return to shallow waters (<35 m) in July and November, respectively. The monthly reproduction patterns of both species in the "effective spawning" a rea showed that the major spawning season for M. endeavouri is August to Oc tober and that for M. ensis is September to December.