Seasonal changes bring greater overlap between fisheries and imperiled river dolphins

Nov. 2, 2020


Ganges River Dolphin surfacing
Grant Abel

When the livelihoods of both humans and wildlife depend upon the same resources, human overexploitation of shared resources can threaten wildlife populations. KCRL Ph.D. candidate, Shambhu Paudel, and colleagues recently published some of the results of his dissertation in Nature's Scientific Reports. For the past several years, Paudel has been studying overlap between fisheries and the Ganges River dolphin in Nepal. Shambhu's team document the overlap in preferred fish size and activity times between endangered Ganges River dolphins and fisheries in Nepal. The authors also document the impact of fishing boat proximity on the rate of behavioral changes and foraging behavior in this unique and understudied cetacean. Shambhu and his team found that both humans and river dolphins prefer the same prey size and that the highest overlaps in prey size and activity times occur during the dry season, when there is less riverine habitat available to dolphins. They found significant overlap in harvest preferences, with over 60% of a fishery's catch falling within the Ganges River Dolphin's preferred prey size. Competition for food and space increases during the dry season when water levels are reduced. Not only does this leave little undisturbed habitat for the river dolphin to survive and reproduce successfully, but it also increases the risk of mortality due to bycatch and could negatively affect dolphin behavior.

Proximity to fishing boats also caused dolphins to switch from surface feeding to more long dives, which require more energy. With an estimated ≤ 52 animals in this river system, competition with humans for food and space could be a significant factor contributing to Ganges river dolphin declines and decreased reproduction, while behavioral changes due to human proximity could alter important social structures and increase individual stress levels. Globally, interactions with fisheries is a major threat to small cetaceans and puts them in danger of extinction. Shambhu and colleagues' research highlights important management actions that, if implemented, could reduce dietary and temporal overlap between fisheries and dolphins, allowing for coexistence and persistence of both. 

Read the article here:

Paudel, S., Koprowski, J.L. & Cove, M.V. Seasonal flow dynamics exacerbate overlap between artisanal fisheries and imperiled Ganges River dolphins. Sci Rep 10, 18798 (2020).