We found that maintaining ecological flows in sync with sustainable fishery regulations is key to averting river dolphin declines in even not-dammed rivers like Karnali in Nepal.
Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability.
River flow regulation and fragmentation is a global threat to freshwater biodiversity, ecosystem processes, and associated human activities. Large dams in the Ganges river basin of the Indian subcontinent have severely altered natural flow regimes, particularly in the low-flow dry season. Altered flows could have negative impacts on endangered species such as the Ganges river dolphin Platanista gangetica.
Habitat fragmentation of freshwater ecosystems is increasing rapidly, however the understanding of extinction debt and species decline in riverine habitat fragments lags behind that in other ecosystems. The mighty rivers that drain the Himalaya – the Ganges, Brahmaputra, Indus, Mekong and Yangtze – are amongst the world’s most biodiverse freshwater ecosystems. Many hundreds of dams have been constructed, are under construction, or are planned on these rivers and large hydrological changes and losses of biodiversity have occurred and are expected to continue.
The Ganga River sustains diverse group of flora and fauna including the endangered Ganges river dolphin (Platanista gangetica gangetica) and critically endangered gharial (Gavialis gangeticus). Because, of the highest productivity and most populous regions on earth there is a strong demand and competition for natural resources, which threatened the survival of indicator species such as gharial and dolphin in river Ganga.