100s Of Confirmed Deaths Among Freshwater Dolphins In Ongoing Amazon Basin Drought; Species' Prospects Uncertain
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The historic drought in the Solimões River has drastically reduced the water level of Lake Tefé, which reached just 4.5 meters (14.9 ft) in October. Image courtesy of ICMBio/Tefé.
“In recent decades, we have observed extreme hydrological events intensifying, with record floods and droughts year after year,” says Ayan Fleischmann, a senior researcher at the Mamirauá Institute’s Research Group on Geosciences and Environmental Dynamics in the Amazon. Monitoring is also carried out by a platform developed by the World Wildlife Fund Brazil (WWF-Brazil) and MapBiomas, which monitors 23 of the more than 60 lakes in the Amazon Basin. It revealed that the waters of lakes connected to rivers have also reached higher temperatures since August. In 2024, 12 of these lakes already have seen temperatures above those recorded in 2023. The data also show that these lakes have had average temperatures above those of the previous year for 5-9 months, which points to physiological stress experienced by living beings repeatedly exposed to high temperatures and low water levels. That is the case of dolphins.
In Lake Tefé, in September and October 2023, 209 carcasses of pink river dolphins (Inia geoffrensis) and grey river dolphins locally known as tucuxi (Sotalia fluviatilis) were collected, according to researchers from the Mamirauá Institute. On Sept. 28 alone, 70 carcasses were found in the area, an unprecedented mortality event for these species. That year, most of the deaths were related to the overheating of the waters, which reached temperatures above 40ºC. According to estimates made by the Mamirauá Institute, Lake Tefé is home to approximately 900 pink dolphins and 500 tucuxis. With an annual replacement rate of only 5%, the loss of more than 200 animals in 2023 represented a significant impact on these populations. About 80% of the animals killed that year were pink dolphins.
Bodies of pink dolphins and tucuxis rescued by Sea Shepherd Brazil from Lake Coari, in the Amazon. Image courtesy of Sea Shepherd Brazil.
Both species of Amazonian freshwater dolphins are on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The pink dolphin and the tucuxi are considered “endangered,” meaning the species will likely become extinct in the near future. This is the second most serious level of threat on the IUCN list. In 2024, the Chico Mendes Institute for Biodiversity Conservation (ICMBio) and the Mamirauá Institute decided to anticipate the tragedy. “The drought was so intense last year that the river never recovered its level. We already started with water shortage. The expectation was that the tragedy would repeat itself,” says Miriam Marmontel, leader of the Mamirauá Institute’s Amazonian Aquatic Mammals Research Group. “We were prepared for a new emergency, with more intense monitoring, team training and acquisition of specific equipment.”
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Given the high number of dead animals, ICMBio established the Tefé Dolphin Emergency in 2023, an operation to investigate the situation, with technical support from the Mamirauá Institute and in partnership with several institutions. The agency also launched the 2024 Aquatic Fauna Emergency in September, in order to strengthen monitoring of animals in the area and prevent new deaths. More than 50 professionals were in charge of monitoring water conditions and animal behavior twice a day. However, the dolphin mortality rate was not as expected. “This year was drier; it was very hot, and we didn’t see any dolphins dying. We didn’t understand,” says Magno, who, in 2023, helped collect and transport carcasses that often ended up in his backyard.
Valdinei Lemos Lopes, who has worked with dolphins for more than 20 years and has collaborated with the National Institute for Amazonian Research and the Mamirauá Institute, says he believes the animals anticipated an even more severe drought and moved to safer places. “The animals know more than we do; after all, they live there. Last year, the drought came suddenly, and they didn’t have time to leave the lake. This year, they made sure to leave it earlier,” he explains. According to Fleischmann, what prevented the 2023 tragedy from being repeated was the lower incidence of solar radiation. This year, there were fewer consecutive days of intense sunlight as well as more rainfall and clouds, which prevented the lake from remaining at 40ºC for long periods. “The water temperature in Lake Tefé varies a lot. It can go from 27ºC [81°F] in the morning to 40ºC in the afternoon in a single day. This affects all beings in the aquatic environment but does not result in extreme overheating of its waters,” Fleischmann says.
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https://news.mongabay.com/2024/12/the-uncertain-future-of-amazon-river-dolphins-amid-historic-drought/