Stock-recruitment relationships of the tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in the Australian northern prawn fishery

Abstract

This paper investigates the stock-recruitment and equilibrium yield dynamics for the two species of tiger prawns (Penaeus esculentus and Penaeus semisulcatus) in Australia's most productive prawn fishery: the Northern Prawn Fishery. Commercial trawl logbooks for 1970-93 and research surveys are used to develop population models for these prawns. A population model that incorporates continuous recruitment is developed. Annual spawning stock and recruitment indices are then estimated from the population model. Spawning stock indices represent the abundance of female prawns that are likely to spawn; recruitment indices represent the abundance of all prawns less than a certain size. The relationships between spawning stock and subsequent recruitment (SRR), between recruitment and subsequent spawning stock (RSR), and between recruitment and commercial catch were estimated through maximum-likelihood models that incorporated autoregressive terms. Yield as a function of fishing effort was estimated by constraining to equilibrium the SRR and RSR. The resulting production model was then used to determine maximum sustainable yield (MSY) and its corresponding fishing effort (fMSY). Long-term yield estimates for the two tiger prawn species range between 3700 and 5300 t. The fishing effort at present is close to the level that should produce MSY for both species of tiger prawns. However, current landings, recruitment and spawning stock are below the equilibrium values predicted by the models. This may be because of uncertainty in the spawning stock-recruitment relationships, a change in carrying capacity, biased estimates of fishing effort, unreliable catch statistics, or simplistic assumptions about stock structure. Although our predictions of tiger prawn yields are uncertain, management will soon have to consider new measures to counteract the effects of future increases in fishing effort.

Modelling the recruitment of tiger prawns Penaeus esculentus and P. semisulcatus to nursery grounds in the Gulf of Carpentaria, northern Australia:implications for assessing stock-recruitment relationships

“…The main evidence against effective spawning being concentrated within untrawlable or shallow waters is that in the past fishing has strongly affected the recruitment of tiger prawns to the fishery (Wang & Die 1996). While this does not preclude unfished areas from contributing significantly to the effective spawning population, ~t means either that the fishing grounds contribute to a large portion of the effective spawning or that fishing impacts spawning populations outside the trawling grounds.…”

“…The results of this study provide one means of identifying stock boundaries for tiger prawns within the NPF, hence enabling the stock-recruitment approach of Wang & Die (1996) to be extended from the whole of the NPF to individual regional stocks.…”

“…In considering the relationship between spawning stock and recruitment for this fishery, both species of tiger prawns have been assumed to come from unit stocks, despite the fact that this fishery extends across about 6000 km of coastline in northern Australia. Excessive fishing on tiger prawns by the NPF fleet in the 1980s caused a significant decline in the abundance of spawners and recruits (Wang & Die 1996). The protection of spawning tiger prawns has therefore become a crltical issue for the managers of the NPF.…”

“…Penaeus setiferus (Gracia 1996), brown tiger prawns P, esculentus and grooved tiger prawns P. semisulcatus (Penn & Caputi 1986, Penn et al 1995, Wang & Die 1996. The last 2 species comprise about 40% of the total catch from Australia's most valuable commonwealth fishery, the Northern Prawn Fishery (NPF).…”

Growth Models and Analysis of Crustacean Growth Data

“…In fisheries research, modelling the growth of animals is fundamental in stock assessment to assure sustainable fisheries and optimal management (Wang & Die, 1996;Somers & Wang, 1997).…”