Impact of Hydroelectric Projects on Bivalve Clams in the Sharavathi Estuary of Indian West Coast

The impact of freshwater discharges from upstream hydroelectric projects on estuarine ecology, particularly on commercial bivalves was seldom ever studied, despite the fact that they contribute substantially to local livelihoods. Such projects have been executed in many rivers of Indian Western Ghats unmindful of their ecological consequences. Through a period of the past five decades, two hydroelectric projects were commissioned in the river Sharavathi of central west coast, in the district of Uttara Kannada, Karnataka. Obvious consequences were on mangrove vegetation and fishery, and the livelihoods of fisher-folks were also badly affected. This study in the Sharavathi estuary is with the special objective of assessing the impact on commercial clams of incessant releases of freshwater after power production. For comparison, the study was also carried out in the undammed Gangavali River estuary in the same district. The study covers the diversity and distribution of commercial bivalves in relation to salinity, the key factor that expectedly gets altered due to freshwater releases from dams. The status of bivalves was collected through primary observations, interviews with local fisher-folks, and based on earlier studies. Whereas clam fishery involving Paphia malabarica, Meretrix meretrix, M. casta, Tegillarca granosa, Polymesoda erosa and Villorita cyprinoides goes on rather unchanged in Gangavali estuary, Sharavathi witnessed collapse of clam fishery, following salinity decline, indicative collapse of estuarine ecosystems itself. All clams gathered earlier, barring a lone species Polymesoda erosa, tolerant of low salinity remained here.