Developing indicators of recruitment and effective spawner stock levels in eastern king prawns (Penaeus plebejus)

Abstract

The eastern king prawn Penaeus plebejus is the basis of a major commercial trawl fishery in New South Wales and south-east Queensland. Logbook data indicate that a total of about 2700 tonnes are landed annually. The majority of the catch, about 1900 tonnes, is landed in Queensland waters. At a conservative wholesale price of $15 per kilogram, annual total landings are valued at $40.5 million. P. plebejus is the largest and most oceanic of Australia’s endemic commercial penaeid prawns. It is trawled on the continental shelf to depths of about 300 m and is the most migratory of Australia’s commercially important prawns. Tagging studies have shown that individuals can migrate over 1000 km, generally northward along the coast and usually from shallow to deep water.

In order to assess the stock annual recruitment must be accurately measured, monitored and assessed. In Queensland, a mandatory logbook system is used to record catch and fishing effort. However, in shallow areas such as Moreton Bay where recruitment occurs, the logbook data are of limited value because there are several species of prawns that are caught and fishers do not differentiate between them. Groups of species are retained and collectively recorded and marketed as ‘bay prawns’. Clearly, a more precise method of monitoring recruitment is required and the project addressed this need by examining factors affecting recruit catch rates and by developing a fishery-independent index of recruitment.