Recruitment of postlarval penaeid prawns to nursery areas in Morton Bay, Queensland

Abstract

The recruitment of postlarval Penaeus plebejus Hess to nursery areas in Moreton Bay, Qld, was examined in detail. The distribution and annual recruitment of postlarval immigrants of this species and that of P. esculentus Haswell and Metapenaeus bennettae Racek & Dall in Moreton Bay were also studied.

Pelagic postlarval P. plebejus entering the Nerang River mouth showed no regular significant difference in vertical or horizontal stratification. Entry occurred substantially at night, was completed within the first 3 h of the flood tide, and the number decreased as the water velocity reached a maximum. Epibenthic P. plebejus immigrants settled upon the substrate in inverse proportion to their distance from the river mouth, their numbers decreased as the salinity decreased, and more settled in shallow than in deep areas. Water temperature showed no significant effect on their distribution, and similar numbers settled on seagrasses as on bare substrate.

The annual recruitment pattern showed a seasonal cycle for P. esculentus and M. bennettae with maxima in January-February and March-May respectively. P. plebejus showed at least two peaks in the annual cycle with a maximum usually from July to September, suggesting that when the three species coexist in a habitat a temporal partitioning may occur. Generally, differences in the form of recruitment were seen between geographic areas, but not on different habitats within the areas.

P. plebejus recruits were no more abundant on seagrassed than on bare substrates, but there were fewer at stations with a freshwater influence. In contrast, consistently greater numbers of P. esculentus recruits were obtained from seagrass meadows and most occurred adjacent to river mouths near the ocean. M. bennettae occurred over the whole study area but more were present at stations with a greater freshwater influence. When present in large numbers more were found on seagrassed areas.

These differences in recruitment were considered to be a result of the reproductive biology of the species concerned, tidal currents, and distance between the spawning areas and each study site.