Indications of long term changes in the species composition and catch rates of postlarval and juvenile prawns in Moreton Bay

Abstract

Long term changes in the species composition and catch rates of the postlarval and juvenile stages of three commercially important species of prawn (Metapenaeus bennettae, Penaeus plebejus and Penaeus esculentus) in Moreton Bay (27_20'S, 153_15'E), were examined by comparing data from two research studies conducted twenty years apart. Data for the later (1991-1993) study were collected using the same techniques and locations that were used in the earlier (1972-1973) study. Results suggest that the species compositions have changed, particularly at two of the three areas studied, with a relative increase in M. bennettae at these locations. Changes in catch rates varied between species and areas. Catch rates of all three species differed significantly between the two study periods at Deception Bay and Pelican Banks whilst at Bramble Bay the catch rate of M. bennettae and P. plebejus did not differ significantly. No P. esculentus were caught at Bramble Bay during either study. Changes in species composition and catch rates are discussed in relation to environmental variables, nursery habitat alterations and spawning stock sizes.