outubro, 17 2023

By WWF-Brazil

Researchers from the Mamirauá Sustainable Development Institute (IDSM, in Portuguese) and members of several other organisations are racing against time to mitigate the impacts of the environmental and health emergency that hit Lake Tefé, in the Middle Solimões River, in the inner state of Amazonas. Since September 23, with the drought spreading strongly across the Amazon and water temperatures rising, 153 river dolphins have been found dead in the region: 130 pink and 23 of the tucuxi species. In one week, the loss was around 10% of the local dolphin population, according to Miriam Marmontel and André Coelho, from IDSM, and Mariana Paschoalini Frias, from WWF-Brazil. Only on the 28th, when the water temperature reached 39,1ºC, 70 river dolphin carcasses were recorded, in addition to hundreds of fish.

The operation was divided into different fronts. One of them, called Alive Operation Sector, monitors groups of pink and tucuxi river dolphins along Lake Tefé, an isolated environment that is home to a large population of these two endangered species. When the team finds an individual with signs of abnormality, they are able to rescue them and take them to the Rehabilitation Float. The Operation Dead Sector, in turn, aims to identify and search for carcasses in the region and perform necropsies to collect samples for laboratory analysis. And the Environmental Operation Sector works to monitor water, fish and phytoplankton, organisms composed of microalgae and photosynthetic bacteria.

Of all the variables analysed so far by experts, the one that has shown discrepant changes is water temperature, reinforcing that river dolphin mortality is related to climate change, the effects of El Niño and extreme drought. The water temperature of Lake Tefé reached close to 40°C, says oceanographer Miriam Marmontel, leader of the Amazon Aquatic Mammals research group at IDSM, when the maximum average over time has been 32 degrees, a fact that certainly generated thermal stress in animals.

Members of the environmental consultancy Aqua Viridi also identified in one of the lake's points an unusual number of alga Euglena sanguinea, which produces a toxin that can cause mortality in fish. The assessment carried out on the river dolphins, however, did not confirm that the animals have been affected by possible toxins produced by these organisms. Other analyses are underway to help understand the algae's possible role in the current environmental and health emergency.

Since the beginning of the crisis, 104 river dolphins have been necropsied and tissue and organ samples have been sent to specialised laboratories. Seventeen individuals have already been assessed and, to date, there is no evidence of an infectious agent as the primary cause of deaths. Molecular diagnostics of 18 individuals also tested negative for infectious agents, such as viruses and bacteria, associated with mass deaths.

“What is happening at Lake Tefé is terrifying. The impact of the loss of these animals is enormous and affects the entire local ecosystem”, warns Mariana Paschoalini Frias, Conservation analyst at WWF-Brazil. “River dolphins are considered ‘sentinels’. In other words: they are indicative of the health of the environment where they live. What happens to them is reflected in the other species that live around them, including humans.”

In Lake Tefé, there is a stretch called Enseada do Papucu, which has been critical for animals due to the water temperature. Even so, many dolphins continue to frequent the area due to the abundance of fish, their basic diet. To prevent further deaths, the area is being isolated with a physical barrier called “pari”, which is made of wooden stakes and is based on traditional riverside knowledge. Subsequently, the species will be moved to deeper, less hot areas.

More than 100 volunteers have already passed through the region and at least 21 organisations from all over Brazil and abroad have supported IDSM in facing the crisis: Aqua Viridi, Aquasis, Fire Department, Brazilian Army, GRAD (Group of Disaster Animal Rescue), Greenpeace Brazil, IBAMA (Brazilian Institute of the Environment and Renewable Natural Resources), ICMBio (Chico Mendes Institute for Biodiversity Conservation), INPA (National Institute for Amazon Research), Aqualie Institute,  Brazilian Humpback Whale Institute, Oswaldo Cruz Institute, LAPCOM USP, Brazilian Navy, Military Police, Tefé City Hall, R3 Animal, Sea Shepherd Brazil, SeaWorld, Tefé Municipal Department of Environment and Conservation, and WWF-Brazil.

What WWF-Brazil is doing

WWF-Brazil has been working in partnership with the Mamirauá Institute for Sustainable Development, which is leading the rescue of dolphins in Lake Tefé, providing fuel, Personal Protective Equipment (PPE), veterinary supplies and logistical support for the movement of volunteers.
We are also in contact with local partners and mobilised to support them in facing the humanitarian crisis caused by the drought in the Amazon region, as the consequences are especially dramatic for the most vulnerable populations, such as indigenous people, quilombolas, extractivists and riverside communities. At this moment, our main area of activity is supplying food to communities impacted by shortages.
"We formed a huge coalition in order to help collect carcasses, to monitor live animals in critical areas of low depth and high temperatures, and to collect and send biological and water samples for analysis. An entire effort to get to the root causes of this unprecedented event", states Mariana, from WWF-Brazil.
"In our studies on Amazonian dolphins, we found that they suffer from several pressures, such as predatory fishing, mercury contamination and the impact of hydroelectric plants. But these events in Tefé show that more research needs to be carried out on how they will be affected by constant climate change ", she says.
The crisis, however, goes far beyond the loss of river dolphins. There is an increase in mortality of fish species in the region which are essential for the food and economy of local populations. Furthermore, for many experts, the unprecedented tragedy in the Amazon could be a preview of what will happen when the biome reaches its tipping point.