Yield-per-recruit analysis of Eastern King Prawns Penaeus plebejus Hess, in Eastern Australia

Abstract

The eastern king prawn, P. plebejus, has been commercially exploited for over 50 years. Controversy has arisen over the presumed effect of increasing fishing effort on reported declining catch per vessel and the need for further management of the fishery. The present study develops the information necessary to evaluate this presumption by analysing landing statistics, data developed from a log-book programme, commercial catch composition and data from a series of mark-recapture experiments conducted on part of the fishing grounds. Population parameters (growth, mortalities and other losses) were calculated via a series of tagging experiments. Recapture rates of tagged prawns were examined for each point release (local recapture) and for the state as a whole (sequentially applied effort), the difference providing estimates of emigration rate. Weekly values chosen for these parameters allowed calculation of yield-per-recruit estimates. For 1979 and 1980, respectively, fishing mortality estimates ranged between 0.04 and 0.08 per week, depending upon number of vessels per port; emigration was estimated to be 0.13 and 0.18 per week for the two years, tagging mortality (0.08 per week), and all other losses other than by tagging and emigration at 0.06 and 0.08 per week. A compartmented, time-lagged model of the fishery was used to predict changes in yield per recruit as a consequence of changes in management strategy and to describe the relationship between fishing effort and yield per recruit. The analyses suggested that limited benefits in terms of yield per recruit would eventuate from substantial increases in effort but that substantial decreases in catch per effort were likely.