RIDDLE · Dams and Dolphins: Linking cutting-edge science with endangered species conservation

Dams and Dolphins: Linking cutting-edge science with endangered species conservation

The exceptional loss of biodiversity over the last few centuries has been described as a sixth mass extinction. Vertebrate species are disappearing at 100 times background extinction rates. The planet is changing faster than scientists can document that change, let alone be effective on the scale and speed required to try to prevent it. Freshwater habitats occupy only 1% of the Earth’s surface yet are biodiversity hotspots that support 10% of all known species, and a third of vertebrate species, however, they are intensely used, modified and degraded by humans. As a result, there are severe declines in the range and abundance of many freshwater species, so that they are now even more imperilled than their marine or terrestrial counterparts. Only 37 per cent of rivers longer than 1,000 kilometres remain free flowing over their entire length; dams and their downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity and biodiversity. The number of dams is increasing globally, and climate change will likely accelerate the associated environmental impacts. Freshwater megafauna species (e.g. predatory fish, otters, crocodiles, turtles, gharial, manatees, caimans, dolphins etc.) are amongst the most vulnerable species, and as the top predators in many systems their extirpation often leads to large changes in aquatic community structure through trophic cascades which also impact human communities that rely on those resources. Among these aquatic top predators are freshwater dolphins and porpoises, little known animals that occur in 15 countries, and 9 river systems in two continents (Asia and South America). There are river dolphins in some of the largest freshwater systems: the Yangtze, Amazon, Orinoco, Mekong, Irrawaddy, Brahmaputra, Ganges and Indus, and they are one of the most threatened animal groups; listed as endangered or critically endangered on the IUCN Red List in all places they occur. One of the major causes of this endangerment is the construction and presence of dams. These are in the form of run-of-the-river hydropower schemes, high storage dams, weirs or gated diversion dams (hereafter all termed ‘dams’) each of which fragment populations and deplete and degrade habitat in differing ways. The speed with which river dolphin species can go extinct was exemplified by plummeting population and subsequent extinction in 2006 of the Yangtze River dolphin; the first vertebrate extinction in the last 50 years. In July 2019 the International Whaling Commission convened a River Dolphin Task Team which made a number of high priority recommendations regarding river dolphins and dams that were then endorsed by the Scientific Committee meeting and circulated to Contracting Parties and Member States. Key recommendations were: 1. that, as a priority, studies be conducted to fully understand movements of dolphins across barrages in all countries and quantify the extent of population connectivity and impacts on dolphin populations in fragmented riverine habitats; and 2. that possible tools be evaluated and trialled to reduce the number of dolphins becoming trapped in canals. The overall goal of this Fellowship was to bring together the cross-disciplinary expertise and cutting-edge technology to tackle these complex issues to help solve the challenge of sustaining river dolphin populations in dammed and regulated rivers.

Data: CORDIS, © European Union