ABSTRACT
Based on the four seasonal oceanographic cruises investigation data in the Yangtze Estuary (122 degrees 00'-123 degrees 30' E, 29 degrees 00'-32 degrees 00' N) in 2002-2003, the diversity and abundance dynamics of pelagic mysids as well as their relationships with fishing ground were studied. A total of 14 species were identified, among which, 10 species occurred in autumn, 8 species in spring and summer, and 2 species in winter. Clear seasonal alterations were observed, among which the highest alteration ratio (90.9%) occurred from autumn to winter. Shannon diversity index (H') in spring, summer and autumn was above 2, and that in winter was 1. Mean abundance was the highest in summer [234.70 ind x (100 m3)(-1)], followed by in autumn [103.34 ind x (100 m3)(-1)], spring [80.36 ind x (100 m3)(-1)], and winter [12.40 ind x (100 m3)(-1)]. The changes in mean abundance were in accordance with the fluctuation of seasonal temperature. Due to the adaptation to a wide range of temperature and salinity, Gastrosaccus pelagicus was dominant in spring, autumn and winter. Acanthomysis brevirostris was dominant in summer and autumn, and A. longirostrisas in winter. The dominant species in each season all made a significant contribution to total abundance. A. brevirostris was observed in large agglomerates in summer. As a kind of fish diet, mysids were of importance in the formation of fishing grounds in the Yangtze Estuary and Zhoushan Islands.
