Fishery policy exploration in the Pearl River Estuary based on an Ecosim model

The Pearl River Estuary (PRE) is a tropical estuary that was an important fishery ground in the South China Sea, where many other fisheries have also experienced substantial declines in productivity. In this study, we develop an ecological model constructed by Ecopath with Ecosim (EwE) software to explore the consequences of different fishing policies on the management of the PRE ecosystem. Scenarios are examined that maximise the net profits from the fishing activities, the jobs provided by the fisheries and the measures of ecosystem status. Then the trade-offs due to the ecosystem-scale optimisation of fishery management policies are analysed. The results indicate that optimising short-term economic and social (employment) goals in the PRE creates a depletion of the top predators and losses of biodiversity. Alternatively, focusing on the structure of the ecosystem leads to a reduction in fishing effort for almost all fleets and a corresponding increase in the biomass of most fishes at the expense of reduced profits and jobs provided by the fisheries. An ideal policy compromise is found when equal weight placed on profits, jobs and ecosystem structure, which leads to an overall increase in profits, jobs/catch value, ecosystem maturity and biodiversity. The effects of changing weights placed on profits, jobs/catch value and ecosystem maturity on ecosystem indices are examined and the parameters of vulnerabilities and discount rates are also analysed in this paper.