Thousands of fish have also died in areas of the Latin American river, where the combination of high temperatures and reduced flow is affecting local communities
The Amazon is suffering from a historic drought that is causing unprecedented episodes. More than 120 dolphins have appeared dead in recent days in Lake Tefé, which juts out from the Amazon River. The bodies have been turning up since September 23, with a peak of 70 bodies on September 28, a day when the water temperature rose to 39 degrees Celsius. Biologists are still investigating what exactly caused the mass death of these animals, but the combination of extreme factors that have converged in this catastrophe has a clear link to the climate emergency.
"The waters have dropped very quickly and very drastically in a few days. The flow reached half, and this, added to a temperature as high as 39 ºC, generates a big change in the water conditions, like the concentration of organic matter or the concentration of oxygen, among other parameters", explains the Brazilian ICTA-UAB researcher Leticia Lima to the ARA. One of the hypotheses studied by the group of biologists investigating the event is whether the high water temperature - eight degrees above what is usual in the area - generated some biotoxin that would have weakened the dolphins and prevented them escape the lake "On the 28th the water reached 39 ºC, almost 40 ºC, and the dolphins looked very uncomfortable. It was noticeable in their behavior, they couldn't get down to the bottom, they swam in circles and some died in front of us" , Miriam Marmontel, a biologist at the Mamiraua Institute, who is leading the investigation into the episode, explains by phone from that area.
The dead animals were of two species: the boto or pink dolphin (due to the color of the skin), an endemic river dolphin of the Amazon basin and some of its tributaries that is in danger of extinction, and the tucuxi , another species of river dolphin that inhabits the Amazon and other rivers in eastern South America. The 120 corpses were found in a matter of days in Lake Tefé, a body of water that juts out of the Amazon River right in the center of the Brazilian state of Amazonas, "in the most preserved area of the forest," Lima explains . "In a single week we lost 120 animals between the two species, approximately between 5% and 10% of the population" of dolphins in this area, said Marmontel.
Marmontel's team has performed autopsies on dozens of dead dolphins, from which samples have been taken for analysis in the laboratory, and PCR tests have also been performed on them. "We suspect that there may be biotoxins in the water and that they have been exacerbated by the temperature," explains the researcher, who refuses to believe that the only explanation is the high temperatures: "They are very intelligent animals and they know well the area. Why didn't they go out of the lake to the big river? They seem disoriented, I think there must be something else going on." In this regard, he says that this Tuesday they were able to see a strange bloom of algae in Lake Tefé, which leads them to think that maybe a similar one occurred before the 23rd that could have something to do with the event .
Until this very Tuesday, they have been recovering bodies of pink and tucuxi dolphins. They also look for live dolphins that may show "desperation" behavior to rescue, study them as well and if necessary medicate them. But lethal water conditions in the Amazon haven't just affected dolphins. Thousands of fish have also appeared dead in other areas of the great Latin American river.
In addition, the rural communities that live scattered along the Amazon River, known as ribeirinhos , are also suffering greatly from the consequences of the extreme drought. "These are communities that depend a lot on the river to move from inside the forest to health centers or other services, since they do it in small boats across the river, but with these flows left by the drought they are staying isolated," warns Lima. The supply routes for medicine and food that reach them have also been cut off by the drought, and "they cannot sell their agricultural products or fish because the big ships no longer reach them," reports the researcher, who is a specialist in these traditional Brazilian communities.
The water temperature reached 39 ºC when the flow had been reduced by half
But what was the origin of this intense drought and these extreme temperatures in the Amazon basin? Two key determining factors have come together: the arrival of El Niño , the meteorological phenomenon that causes a warming of the water in the Pacific Ocean that temporarily modifies the climate in many parts of the world, and the high temperatures in the North Atlantic , which have broken records this summer. "There have been major droughts in the Amazon before - in 1997-98, 2005, 2010 and 2014-15 - and scientists have observed that they have all been associated either with El Niño or with the overheating of the Atlantic North , but the worst are those that had a combination of the two factors, as is happening now," explains Lima. The North Atlantic broke its temperature record this summer, while the global ocean temperature also broke records, in addition to many other limits that have been exceeded for the first time due to the climate emergency. But the worst consequences of El Niño are expected for next year, so the situation in the Amazon "could be much worse in 2024", warns the researcher.
In fact, Lima was one of the 72 scientists and academics who signed a letter sent on September 20 to the Brazilian Parliament warning, precisely, of the conditions that could be generated by the conjunction of these two phenomena. "We were late, because the drought happened so quickly that it took the scientists themselves by surprise," reports the researcher, who sees a clear implication of climate change in the mass death of dolphins and fish, an event "that does not had never been seen."
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