Freshwater megafauna suffer major population decline

freshwater megafauna
© iStock/Jillian Cooper

Concerns have been raised over river biodiversity after the results of a new study, which show that freshwater megafauna populations have declined by 88% between 1970 and 2012.

The study, conducted by scientists at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) and published in the Global Change Biology journal with the title ‘The global decline of freshwater megafauna’, examined distribution data for 126 species around the world. The population loss of freshwater megafauna – comprising all freshwater animals weighing 30kg or higher, including beavers, crocodiles, giant turtles, sturgeons and some river dolphin species – was shown to be most egregious in Europe, Northern Africa and most of Asia; with large species of fish the hardest hit. The decline, which the study attributes primarily to the dual factors of overexploitation of resources and manmade fragmentation of rivers, is more than twice that suffered by vertebrates on land and in the ocean.

Fengzhi He, expert in diversity patterns and conservation of freshwater megafauna at IGB and author of the study, said: “The decline of large fish species is…attributed to the loss of free-flowing rivers as access to spawning and feeding grounds are often blocked by dams. Although the world’s large rivers have already been highly fragmented, another 3700 large dams are planned or under construction – this will exacerbate the river fragmentation even further. More than 800 of these planned dams are located in diversity hotspots of freshwater megafauna, including Amazon, Congo, Mekong and Ganges river basins.”

The study’s senior author Sonja Jähnig, expert in global change effects on river ecosystems at IGB, said: “The results are alarming and confirm the fears of scientists involved in studying and protecting freshwater biodiversity. According to the International Union for Conservation of Nature’s Red List of Threatened Species, over half of all assessed freshwater megafauna species are considered as threatened with extinction. Nonetheless, they receive less research and conservation attention than megafauna in terrestrial or marine ecosystems.”

The study’s authors noted that a number of freshwater megafauna species which had been subject to specific, targeted conservation efforts, including the American beaver and the Irrawaddy river dolphin, experienced stable or growing population levels.

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