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  • Writer's pictureScience & Environment

Biodiversity Crisis Meets Climate Crisis

At least 125 Amazonian river dolphins die in heat wave

By Anastasia Goelitz 


Pink River Dolphin by Boto Vermelho via Flickr


Local scientists got a firsthand taste of climate change's direct consequences for ecosystems when a rare winter heat wave surged through Brazil at the end of September. Water levels of the Amazon were dropping 30cm daily, making the waterway impassable and cutting off important food supply routes; Lake Tefé, connected to the Amazon, reached record temperatures of 39°C. On the 29th of September, the Mamirauá Institute for Sustainable Development (IDSM) informed the public of an unusual die-off; thousands of dead fish were floating on the lake's surface, and more than a hundred freshwater dolphins had been washed ashore.


Two species were identified from the carcasses: pink river dolphins (Inia geoffrensis) and tucuxi river dolphins (Sotalia fluviatilis), which are IUCN red-listed as endangered. Although local researchers have considered both disease and contamination of the water as possible causes, they strongly suspect that the extreme heat, a consequence of the combination of El Niño (a period where natural sea level temperatures are increased) and human-made global warming, has caused water temperatures beyond the animal’s tolerance threshold. Extreme temperatures are weakening the dolphins and causing disorientation, which can lead them to suffocate. A declining population of the two species of endangered dolphin, which are slow to reproduce, live in Tefe Lake. It is thought that 1,400 of the two species of endangered dolphins live in Tefe Lake, although the population was decreasing due to their slow reproduction. Dr. Miriam Marmontel, the emergency response coordinator, has explained, “In one week, we have already lost around 120 animals between the two of them, which could represent 5% to 10% of the population.” Percentages this large could have unknown effects on the local ecosystems and the species' survival. 


Scientists from the Mamirauá Institute, along with numerous conservation groups and support from national authorities, are trying to exert as much damage control as possible. Steps are being taken to monitor the live animals, search for and collect carcasses, collect samples for disease and water analysis, and monitor the waters of Lake Tefé. By examining the deceased animals, the team hopes to gain total clarity about the causes of death.


With external support from several institutions and NGOs, an emergency dolphin rescue mobilisation is taking place, searching for live animals in the shallow areas close to shore and moving them to deeper water, where their survival chances are higher. Additionally, artificial ponds have been set up to aid in observing and rehabilitating sick dolphins. Still, relocating animals is always risky; stress and pathogens in these new habitats can increase mortality. There is also concern that even if we can prevent the worst outcome this time unless we start fighting climate change, another heat wave will definitely come. 


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