Fish community dynamics of the downstream estuarine zone of Meenachil River, Southern Western Ghats, Kerala, India

Authors :

Letha P Cheriyan, Manu Oommen

 Abstract:

Fish assemblages are one of the most sensitive and reliable indicators of the ecological status of streams and rivers. Fish
composition and abundance pattern of the downstream estuarine zone of Meenachil River were studied from 2015 to 2019, along with assessing water quality parameters. A total of forty-one species of fish belonging to 20 families, 11 orders, and 33 genera were documented from the downstream zone of the Meenachil River during the study period. A continuous and drastic decline of the native species Etroplus suratensis and Dawkinsia filamentosa was seen from 2018 to 2019, along with an unusual abundance of the secondary species Megalops cyprinoides and Gerressetifer. A complete shift in dominance and species re-ordering was noticed in the downstream fish community composition of the river after the extreme flash flood of 2018 occurred in Kerala. Channa diplogramma showed an increasing trend in abundance in the lower stretches of Meenachil River from 2017 to 2019. Higher values for TDS and conductivity, significantly fluctuating values for salinity, and lower values for dissolved oxygen were noticed in the downstream distributaries besides the drastic changes that happened in the community composition. The difference in ranks of the different species reflected a significant change in the community pattern resulting in a re-ordering of species. Re-ordering the position of a dominant species may be a significant driver of community change than species abundance or losses, which cannot be revealed by species richness or dissimilarities alone.