Method for Analyzing Fish Assemblage Distribution with Application to Fishery Landings of Tropical Shallow Lake as Songkhla Lake, Thailand

Fish community structure can provide potentially powerful tools for assessing aquatic environmental health. Monthly catch weights in Songkhla Lake were recorded over the period January 2003 to December 2006 inclusive for each of 127 species- 72 were marine vertebrate; 22 freshwater vertebrate; 21 marine invertebrate; 10 diadromous, and 2 catadromous. Linear regression model base on the log-transformed catch weights classified species and months, using these factors as multiplicative determinants based on principal components were performed, enabling assessment of clustering of species. The model has four such components which correspond to predominant seasonal time series patterns, giving an r-squared value of 87.6%. Purely seasonal patterns were identified for the first two components- estuarine and marine vertebrates showed considerable seasonal fluctuations but otherwise appeared to be steady over the four year period. Trends, mainly confined to the most recent year (2006) were identified for the third and fourth components- freshwater and estuarine fish had increasing catch weights, while the catch weights of marine invertebrates decreased. This model can provide practical lake information and reinforces that migratory fish species in tropical shallow lake need to be managed for sustaining their diversities.