Seasonal changes in abundance and composition of the fish assemblage in Chiku Lagoon, southwestern Taiwan

Seasonal changes in abundance, species composition, and life-style categories of the fish assemblage in a shallow tropical lagoon of southwestern Taiwan are described. Fish were sampled monthly by fyke nets in Chiku Lagoon for a period of 3 yrs from November 1995 to November 1998. In total, 5713 individuals from 111 species and 46 families were captured. Liza macrolepis, Valamugil cummesius, Pelates quadrilineatus, Leiognathus brevirostris and Gerres abbreviatus were the dominant species and comprised over 50% of the total number. Only eight species (7.2%) in the lagoon were permanent residents, seven species (6.3%) were seasonal visitors, and 96 species (86.5%) might be transient visitors in this lagoon. The fish comprised 85 marine species, of which 47 were marine stragglers and 38 were marine estuarine-opportunists, together with 22 estuarine species and four freshwater species. The index of species richness, Shannon-Wiener diversity, and evenness each showed a consistent seasonal pattern each year. Species richness and diversity were higher in the wet season (from June to October) than in the dry season (from November to May). Classification analysis also showed that in each year, the fish assemblages were distinct between the wet and dry seasons. Ordination analysis demonstrated that the monthly samples consistently followed a seasonal cycle for three successive years. These changes were largely attributable to sequential immigration and emigration of the estuarine-dependent marine species. Correlation analysis indicated that water temperature and precipitation correlated with the seasonal patterns in the fish assemblage.