Plebejus

Abstract: The geographic differentiation of Metapenaeus bennettue. M. macleuyi and Penueus plebejus has been examined by electrophoretic techniques. Differences between localities were detected in M. bennettae and M. macleayi. but not in P.plebejus. The observations for M. bennettae and P. plebejus are consistent with what has previously been revealed by ecological investigations. Despite the existence of detectable genetic heterogeneity in M. bennettae and M. macleayi, the differences in gene frequency are in almost all cases of a minor order, and the overall degree of divergence between populations is quite small. The comparative measures of geographic differentiation for the three species M. bennettae. M. macleuyi and P. plebejus are Φ* = 0.051. 0.014, and 0.007 respectively.

Abstract: Juvenile prawns were captured with a beam trawl from two intertidal seagrass sites (one sparsely and one densely vegetated) in Tin Can Bay, a subtropical estuary in south-eastern Queensland. The abundance and recruitment patterns of two commercial prawn species (Penaeus plebejus and Metapenaeus bennettae) were investigated. P. plebejus was the dominant species at both the sparse and dense seagrass sites. Die-back of the above-ground vegetation in the sparsely vegetated site coincided with a significant increase in the abundance of both P. plebejus and M. bennettae at this site. Natural loss of intertidal vegetation may cause an immediate reduction in the total fisheries value of an area because of fewer herbivorous commercial fish entering the area. In the longer term, this reduction in the fisheries value of the area may be compensated by an increase in value as a nursery ground for juvenile P. plebejus, thereby providing the potential for higher adult P. plebejus recruitment to local commercial fisheries and maintaining the overall value of the area.

Abstract: The mechanisms that drive density dependence are rarely studied in the applied context of population management. We examined the potential for competition for food and shelter and the resulting demographic density dependence to influence how well populations of the eastern king prawn Penaeus plebejus Hess can recover following marine stock enhancement programmes in which captive-bred juveniles are released into the wild. Specifically, manipulative laboratory experiments were used to quantify the differential effects of competition for food and competition for shelter on survival of wild and captive-bred P. plebejus as densities were increased and as each category of P. plebejus (wild or captive-bred) was supplemented with the alternate category. Increasing population densities when food and shelter were limited lowered survival for both categories. When food was limited, survival of both categories was unaffected by addition of the alternative category. Adding wild P. plebejus to their captive-bred counterparts when shelter was limited under laboratory conditions resulted in significantly higher mortality in captive-bred individuals. In contrast, adding captive-bred P. plebejus to wild individuals under these conditions did not affect wild P. plebejus. We conclude that if the current results can be extended to wild conditions, competition for shelter may lead to the loss of captive-bred P. plebejus, thereby reducing the intended outcomes of stock enhancement. This highlights the importance of investigating interactions between wild and captive-bred animals prior to stock enhancement to predict long-term outcomes and identify situations where stock enhancement could be an effective response to the loss of populations or recruitment limitation.