The diversity of finfish population in Poonthura estuary, south-west coast of India, Kerala

Quantitative measures of diversity are the ideal tools to reveal the community differences that are due to changes in the relative taxon abundance. The present study is an attempt to investigate the measures of finfish diversity of the Poonthura estuary, located in Thiruvananthapuram district of Kerala, India. Samples were collected using gill nets from three stations. Biodiversity indices such as Margalef’s richness (d), Pielou’s evenness (J’), Shannon diversity (H’) loge(2), Simpson diversity (1-λ), Simpson dominance (λ), average taxonomic distinctness (△+), and variation in taxonomic distinctness (λ+) were worked out for monthly and seasonal data (pre-monsoon, monsoon, and post-monsoon). The ranges of species richness, evenness, Shannon diversity, and Simpson diversity and dominance were 2.30 to 4.51, 0.79 to 0.92, 2.52 to 3.42, 0.76 to 0.91, and 0.11 to 0.23 respectively. Considering the lacuna in information on this estuary, the results of the present study provide reference points for the measures of fish diversity for future studies. Non-metric multidimensional scaling (NMDS) plotted to understand the seasonal and monthly variation of diversity. The clusters showed 40% similarity in the monthly samples, with the post-monsoon season showing the highest number of species. Various physicochemical parameters influenced the temporal fluctuations in diversity including seasons, river runoff, sewage discharge, and intrusion of saline water. Moreover, higher values of chlorophyll a is an indicator of eutrophication. Proper management inputs are necessary to sustain the resources along with pollution abatement measures for improving the livelihood support from this estuary.