基金Acknowledgments This work was supported by the National Basic Research Program of China (Grant No. 2011 CB409805), the National Science and Technology Planning Project of China (Grant No. 2011BAD13B05), the National Natural Science Foundation of China (Grant No. 41006074) and theSpecial Project of State Oceanic Administration (Grant No. DOMEP (MEA)-02). The authors were grateful to Mr. Zhang Huayue of Xunshan Fishery Group for his cooperation along this work and also to the very constructive comments by several reviewers.