Significance of Dam Altered Vis-À-Vis Free Flowing Stretches of a Himalayan River, Teesta with Special Reference to Icthyofaunal Diversity: Importance Towards Riverine Fisheries Sustainability

Abstract

River Teesta rises from the Eastern Himalayas and known as a transboundary river between India and Bangladesh. In India, the river crosses through two states viz. Sikkim and West Bengal before entering into Bangladesh. The study was undertaken in the 47.6 km stretch, from Triveni to Teesta barrage of the Teesta River. The selected study stretch has two major dams, Teesta Low Dam Project (TLDP)-III and TLDP IV and a barrage Teesta barrage, with a combined reservoir length of 17 and 9 km of combined water deprived downstream of dam/barrage representing altered river stretches. Therefore, allowing 21.6 km free flowing river stretches. The study aimed at assessing the fish diversity, distribution, and abundance in the selected study stretch of the river representing reservoir, water deprived downstream, and free flowing stretches of the river Teesta. Fish samples were collected seasonally from five sites representing free flowing (1 sites), reservoir (2 site), and just downstream of dam/barrage (2 sites) using different gears between May 2018 and October 2019. Total 41 fish species under 6 orders and 9 families were recorded. Cyprinidae represented the maximum (26) number among all the families. Critically endangered (Schistura spiloptera), vulnerable (Cyprinion semiplotum, Schizothorax richardsonii, and Garra arupi), and near threatened (Botia lohachata and Neolissochilus hexagonolepis) fishes were recorded. Migratory fish species, viz. Schizothorax richardsonii (Snow trout) and Neolissochilus hexagonolepis (Chocolate Mahseer) were dominated in the free flowing stretches of the river. The Simpson’s diversity index (D) ranged from 0.3 to 0.8, the Shannon index (H) varied from 0.5 to 2.61, and the evenness index varied from 0.5 to 0.9 across the stations and seasons. Cluster analysis indicated formation of two major groups with 90% dissimilarity and 3 sub-groups with similarity varying from 20 to 50%. All the diversity indices showed that the lowest icthyofaunal diversity was in the water deprived downstream of dam stretch as compared to free flowing and reservoir stretch. The study documented for the first time the icthyofaunal diversity in the different river ecosystems representing reservoir, free flowing, and dam obstructed water deprived downstream stretch of river Teesta and recorded the lowest fish diversity in the water deprived downstream of dam stretch. The study highlights for future studies on ecological flows release from the dams for sustainable fisheries particularly in the downstream of the dam stretch, through proper scientific fish based habitat suitability study.KeywordsTeesta RiverDam alterationFish diversityMigratory fish