Modeling the effect of the seasonal fishing moratorium on the Pearl River Estuary using ecosystem simulation

The coastal ecosystem of the Pearl River Estuary (PRE) has been overfished and has received a high level of combined pollution in recent decades. Fisheries’ stock assessments have shown a declining population and have led to the implementation of a number of management measures, including a fishing moratorium. This study evaluated the effect of a fishing moratorium on the sustainability of PRE fisheries through an ecosystem approach. Two Ecopath models of the PRE coastal ecosystem in 1998 and 2008 were applied to obtain snapshots of the ecosystem in different periods. An dynamic simulation of the period from 1998 to 2008 was developed using Ecosim based on the assumption that the seasonal moratorium was never applied to the PRE fisheries from 1999 onward, which resulted in the predicted ecosystem of 2008* (the so-called 2008* ecosystem). Then, the attribute indices of the 2008* ecosystem were compared with those of the actual 2008 ecosystem to investigate the effect of the fishing moratorium. Finally, a series of 100 years dynamics simulations was examined according to five scenarios based on the 1998 Ecopath model to explore better strategies for the fishing moratorium. The results show that the 2008* ecosystem was not supposed to feature a seasonal moratorium, as the system in 1999 was more deteriorated, immature and fragile than the actual ecosystem in 2008. The seasonal fishing moratorium did benefit ecosystem protection, although its effect on ecosystem recovery was limited. A comparative analysis of different scenarios indicates that most functional groups will decrease without executing a fishing moratorium (S1). The prolonged moratorium (S2) seemed to be slightly more beneficial to stocks recovery than S0, during which fishing operations were carried out following the present fishing moratorium policy. However, banning all fishing operations during the moratorium season (S3) has little effect on the recovery of fishing stocks from overexploitation. Moreover, reducing the fishing effort by 50% (S4) led to the largest increase in both fish stocks (28.0%) and total landings (43%).