Simulating fisheries management options for the Beibu Gulf by means of an ecological modelling optimization routine

The Beibu Gulf is a semi-enclosed sea surrounded by land territories of China, Vietnam and China's Hainan Island. Historically, the Beibu Gulf supported various commercial, recreational, and artisanal fisheries. Many fisheries are now depleted or had experienced substantial decline in productivity. In this paper, we developed a mass balance model using Ecopath with Ecosim (EwE), to evaluate how the ecosystem may respond to changes in fisheries activities over a period of 20 years. Input data were mainly from the information collected in trawl surveys from October 1998 to September 1999. Four fishery management scenarios, which maximized three independent (fishery profits, employment, and ecosystem) and the combination of the above three objectives were simulated with different vulnerability settings. Results suggested that socioeconomically driven policy caused the ecosystem to be vulnerable whereas maximized ecological stability and the compromise scenarios were generally consistent with different vulnerability settings. To maximize social and economical criteria, the ecosystem structure was shifted to a simplified state where the high trophic level species became depleted and the low trophic level species gained dominance. Therefore, the optimal state (social strategy) had the lowest trophic level, 2.78. When an ecological stability criterion was considered, the model predicted effort should decrease more than 70% for all fishing sectors. A trade-off analysis indicated that 'Big compromise' strategy would be optimal to balance fishery and conservation. These results indicate that developing multispecies harvesting strategies is a complex task, and goal functions may be conflicting, while initial model conditions can affect the results. (c) 2007 Elsevier B.V. All rights reserved.