Patterns in Community Structure of Trawl Catches along Coastal Area of the South China Sea

Community structure of trawl catches including fishes and macro-invertebrates was assessed in relation to depth zone, time of year, and the influence of selected environmental factors. A total of 151,799 fishes, representing 59 families and 157 species were collected by bottom trawls during daylight hours between November 2005 and July 2007 from 16 sites along coastal waters off Pattani and Narathiwat provinces, Thailand. Of these, the ten most dominant species accounted for 90.7% of the catch. A great dominance of Leiognathidae, principally Leiognathus splendens (51.5%) and Leiognathus brevirostris (16.5%) was recorded. Families with the greatest number of species were Leiognathidae (10 species) and Carangidae (8 species). A highly significant difference (P<0.001) between fish density collected at different zones indicates that depth is a major factor structuring the community. Highly significant differences (P<0.001) between months on fish species richness and biomass were found (P<0.05). Cluster analysis indicated further that the difference was based mainly on seasonal and annual effects. Temperature had an impact on fish species richness and density, whilst dissolved oxygen influenced only on fish biomass. For macro-invertebrates, 5,574 individuals belonging to three main groups including Decapoda, Mollusca, Echinodermata and other phyla were recorded. Analysis of variance indicated site differences for macroinvertebrate density (P<0.05) and biomass (P<0.005) and monthly difference for species number (P<0.0005). Molluscs and crabs were the largest group together with shrimps and other organisms and could be divided by cluster into two different depth communities.