SPAWNING STOCK DYNAMICS OF 2 PENAEID PRAWNS, METAPENAEUS-BENNETTAE AND PENAEUS-ESCULENTUS, IN MORETON-BAY, QUEENSLAND, AUSTRALIA

Spawning stock dynamics of 2 commercially important penaeid prawns, Me tapenaeus bennettae and Penaeus esculentus, from 9 stations in Moreton Bay (27 degrees 15' S, 153 degrees 15'E), southeast Queensland, Austr alia, were examined. An egg production index (EPI), based on the relat ive abundance, proportion that were mature or ripe, and size of adult females, was used as a measure of egg production in the 2 populations. Egg production by M. bennettae was 20 to 30 higher than that by P. es culentus, extended over 7 to 8 mo each year and peaked from February t o March (late summer to early autumn). Monthly patterns in egg product ion by M. bennettae varied between years. In contrast, P. esculentus p roduced most of its eggs in a single, clearly defined peak in October (spring), although production continued to March (early autumn) each y ear. The seasonal onset and subsequent decline in maturation in P. esc ulentus were rapid. Egg production by M. bennettae was several times h igher al the 5 northern stations than at the 4 southern stations and n egatively correlated with salinity during the main spawning period. Eg g production by P. esculentus was less varied among stations and posit ively correlated with depth. FI esculentus appeared more likely than M . bennettae to experience recruitment overfishing because (1) the peak spawning period for P. esculentus was dependent on relatively few adu lt females spawning over a short period, and (2) the selectivity of tr awl nets used in the bay was much higher for P. esculentus spawners th an for those of M. bennettae. Compared with more northern populations, P. esculentus in Moreton Bay matured at a larger size, had lower inci dences of insemination and mature or ripe females, and had a shorter s pawning period. These results suggest the likelihood of recruitment ov erfishing in P. esculentus increases with increasing latitude.