São Paulo, Brazil, Oct 2 (EFE). – A team of biologists is investigating whether a biotoxin generated by high temperatures in Brazil’s Amazon region caused the death of up to 120 dolphins of two endangered species.

The multiple deaths, recorded over the past week, are the worst event of its kind in at least three decades.

Oceanographer Miriam Marmontel, director of aquatic mammal research at the Mamirauá Institute for Sustainable Development, told EFE that the heat wave that swept through the Amazon raised the water temperature of Lake Tefé eight degrees above the normal maximum.

Handout photo made available by the Mamirauá Institute of one of the 110 threatened river dolphins in the Tefé River, in the Amazon, Brazil. EFE/ Miguel Monteiro/Instituto Mamirauá/ EDITORIAL USE ONLY/ONLY AVAILABLE TO ILLUSTRATE THE ACCOMPANYING NEWS

The warming played a “decisive role” in the dolphins’ deaths, as it could have caused hyperthermia.

However, the specialist said the high temperatures may also have “aggravated” a toxic substance in the water, further weakening the dolphins and preventing them from swimming to the river that feeds the lake to save themselves.

“This is another line of inquiry that could explain why the dolphins did not leave the lake. The combination of high temperatures and biotoxins could have killed them,” she suggested.

To dispel any doubts, the team of biologists coordinated by Marmontel is working to remove the last dolphin bodies from the lake, then carry out necropsies and send samples to laboratories in the south of the country, hoping to have the first results by the end of the week.

Handout photo made available by the Mamirauá Institute and taken on September 23, 2023 of one of the 110 threatened river dolphins that were found dead in the Tefé River, in the Amazon (Brazil). EFE/ André Zumak/Mamirauá Institute/ EDITORIAL USE ONLY/ONLY AVAILABLE TO ILLUSTRATE THE ACCOMPANYING NEWS

The specialist, who cannot recall an event of this magnitude in her 30-year career in the region, estimates that the dead animals, of the pink and tucuxi species, represent just under 10% of the lake’s population.

The Mamirauá Institute for Sustainable Development, which is linked to the federal government, fears that such episodes will be repeated throughout the rest of the Amazon’s dry season, which usually peaks in mid-October but could be prolonged by climate change.

To prevent further deaths, the centre’s team of biologists is considering relocating the dolphins to the Solimões River, as this stretch of the Amazon is known in Brazil.

However, this solution would be complicated if the presence of a toxic substance is detected.

“If the dolphins were exposed to an infectious disease caused by the heat, the problem would be much more serious,” explains Marmontel.EFE

jmc/mcd