Drought-threatened Amazon dolphins studied for climate change impact

By Bruno Kelly

A team of biologists, vets and fishermen temporarily captured rare freshwater dolphins in the Amazon this week to study their health in hopes of avoiding a repeat of the deaths of hundreds of the mammals last year due to a severe drought.

The dolphins, that are in danger of extinction, were brought ashore for blood tests and other examinations and returned to Lake Tefé in the Amazon basin as soon as the researchers had finished their work.

Fishermen were careful not to injure an adult female dolphin during capture and kept her close to her young offspring to avoid stressing the animals.

“She relaxed and we could do all the tests. She appeared in good health,” said project leader Miriam Marmontel of the Mamirauá Institute for Sustainable Development, which planned the expedition to temporarily capture up to 20 dolphins.

The work included removing a sample for a biopsy to see whether there were contaminants in her blubber, and the placing of a microchip for future identification. Satellite tags to follow the behaviour the dolphins, the depth they swims at and check water temperatures remotely had not been attached yet.

In a grim fallout from the longest drought in the Amazon rainforest’s recorded history last year, induced in part by climate change, the carcasses of more than 200 river dolphins were found floating on Lake Tefé, which is formed by a tributary of the Amazon River.

Low river levels during the drought heated the water to temperatures that were intolerable for the dolphins, researchers say. Thousands of fish also died in Amazon waterways due to a lack of oxygen in the water.

The Amazon river dolphins, many of a striking pink colour, are a unique freshwater species found only in the rivers of South America and are one of a handful of freshwater dolphin species left in the world. Slow reproductive cycles make their populations especially vulnerable to threats.

Marmontel said they hope to establish what caused last year’s deaths before this season’s drought set in as the Amazon dry season begins, so that researchers can react faster.

“We aim to learn more about the health of the dolphins at a time when water levels begin to go down and temperatures start to rise, so we can identify the changes and know whether they are due to higher temperatures or a toxin or pollutant in the water,” she told Reuters.

Marmontel said most of the dolphins that perished last year were in Lake Tefé, a 45-km-wide expanse of water where the dolphins like to be located, just off the Solimoes River.

The lake’s waters reached 40.9 degrees Celsius during the 2023 drought, more than 10 degrees higher than the average for that time of the year. The water is now at 30 degrees Celsius, said Ayan Fleischmann, a geosciences researcher at the Mamirauá Institute.

Environmental activists have blamed the unusual conditions on climate change, which makes droughts and heat waves more likely and severe. The role of global warming in last year’s Amazon drought is unclear, with other factors such as the El Niño weather phenomenon also seen as a factor.