novembro, 03 2023

By Solange Azevedo, WWF-Brasil, from Tefé (Amazonas state) 

Less than 200 kilometres separate lakes Tefé and Coari, inner state of Amazonas. These two bodies of water that flow into the Solimões, one of the rivers that has suffered most from the drought that has spread across the Amazon in recent months, are so similar that it is possible to mistake one for the other. “The only difference is that the Coari has a much shorter channel until it reaches the Middle Solimões river”, highlights oceanographer Miriam Marmontel, leader of the Research Group on Amazonian Aquatic Mammals at the Mamirauá Institute for Sustainable Development (IDSM, in Portuguese).

The similarities are so many that the drama experienced in the first was repeated, albeit on a smaller scale, in the second. “Since September 23, we have recorded 155 carcasses of pink and tucuxi river dolphins in Lake Tefé and 23 in the neighbouring municipality. But I'm sure there were deaths in other places because there are more than 50 lakes in the region”, warns the researcher. “This is the first time in the world that heat, the climate crisis, has killed aquatic mammals in this way. What is happening in the Amazon is comparable to what is happening in the Arctic with walruses and polar bears.”

If in the Arctic animals are dying due to the melting of glaciers, in the Amazon one of the most serious consequences of climate change for aquatic fauna is the increase in the temperature of water bodies, which in 2023 was aggravated by a very warm North Tropical Atlantic Ocean and an El Niño phenomenon, resulting in an unprecedented drought in the biome. Out of the 62 municipalities in Amazonas, for example, 60 are in a state of emergency, according to Civil Defence. More than 600 thousand people were impacted.

“Extreme droughts and floods will happen with increasing frequency and intensity. And the tendency is for the situation in the Amazon region to worsen, as the expectation is that next year El Niño will be even stronger”, highlights Miriam. “River dolphins are perfectly adaptable to the movement of water during floods, they move with tremendous flexibility in the flooded forest to feed. But they are not adapted to drought. Reversing this scenario does not depend on us, researchers, it depends on all of humanity mobilising.”

Around 10% of Lake Tefé's river dolphin population was lost in just one week, while the average number of carcasses was found was one or two per month, highlights Miriam, one of the country's leading experts on the subject. She and other researchers are still investigating the reason for the discrepancy between the dead species. Of the 155 carcasses recorded at the site, 84.5% are pink (Inia geoffrensis) and 15.5% are tucuxi (Sotalia fluviatilis), generally the most vulnerable.

Miriam points out, however, that the respiratory system of pink river dolphins is more fragile. “I have been doing this work since 1993 and in field activities I have witnessed many of them making noises when breathing. Histological and ultrasound analyses also confirmed many cases of pneumonia and parasites in the lungs,” she reports. “So, other climate-related factors may have interfered in on the current context. On September 28, the day the water temperature reached almost 40°C in Papucu Cove and we documented 70 deaths, the air quality was terrible due to the intense fires and the humidity was at 50%, when it usually ranges around 80% and 90% during this period of year”.

Thermal stress

Ayan Fleischmann, leader of the Research Group on Geosciences and Environmental Dynamics in the Amazon at IDSM, adds that the most likely hypothesis is that, as a result of thermal stress, the animals stopped eating and, therefore, lost the ability to regulate body temperature. “In situations like this, blood pressure rises and there may be a brain collapse, such as congestion or stroke. But we are still waiting for the histopathology analyses to define this for sure,” he says.

This would explain the fact that individuals, mainly of the pink species, were seen disoriented in Lake Tefé, making circular movements, as if they did not know where to go moments before losing their lives. “If the increase in blood pressure is confirmed in the tests, we will have discovered in the worst possible way the temperature limit that the dolphins can withstand. Therefore, the next few years terrify us”, adds the researcher.

After repeated temperature measurements at different times, depths and locations, IDSM concluded that Papucu Cove, one of the region's river dolphins' favourite spots due to its abundance of fish, drains water from a very shallow area of Lake Tefé, a vast water sheet that is only measuring between 20 and 30 centimetres depth and has the potential to get very hot under the scorching sun.

A true cauldron that exceeded 40°C on September 28, the deadliest day for animals, when the water temperature reached 39.1°C in the Cove. “Above Papucu we measured almost 41°C, but the temperature dropped along its course until it reached 33°C or 32°C into the Solimões River. We saw that the flow of water was dissipating the heat”, says Fleischmann.

Based on the drama that began in Tefé, IDSM created a network of partners to monitor other lakes in the Amazon and already has researchers in municipalities such as Manaus and Iranduba, in Amazonas, and Santarém, in Pará state. In Coari, for example, the team from UFAM (Federal University of Amazonas), led by professor Waleska Gravena, has been monitoring the lake three times a week. In addition, automatic sensors are being installed to measure water temperature and samples have been collected for physical-chemical analysis in the laboratory.

“Just as the air temperature breaks records, the hypothesis is that now the water temperature has also broken. From the measurements we have available, we had never reached the current level in the Amazon”, comments Fleischmann.
 

No infectious agents

Among the results documented so far are 124 necropsied animals and tissue and organ samples sent to specialised laboratories distributed throughout Brazil. Seventeen were evaluated with histological analyses and there is no evidence of related infectious agents as the primary cause of mortality. The molecular diagnostics of 18 individuals were also negative for the infectious agents Morbillivirus, Toxoplasma, Clostridium, Mycobacterium and Pan-fungal, associated with mass deaths of cetaceans.

Several institutions have been involved in the operation with the dolphins, including: Aiuká Environmental Solutions Consulting, Aqua Viridi, Aquasis, Tefé Fire Department, Regional Council of Veterinary Medicine of Amazonas, European Association for Aquatic Mammals, Brazilian Army, Friends of Nuremberg Zoo Association, Aquatic Mammals Foundation, Fundación Mundo Marino, GRAD - Disaster Animal Rescue Group, Greenpeace, IBAMA (Brazilian Institute for the Environment and Renewable Natural Resources), INPA (National Institute for Amazon Research), Aqualie Institute, Humpback Whale Institute, Oswaldo Cruz Institute (IOC/Fiocruz), International Fund for Animal Welfare, IPAAM (Amazonas Environmental Protection Institute), Lapcom-USP, Loro Parque Fundación, Brazilian Navy, National Marine Mammal Foundation, Nuremberg Zoo, Oceanogràfic València, Planète Sauvage, Amazonas Military Police, Tefé City Hall, R3 Animal, Rancho Texas, Sea Shepherd Brasil, Sea Shepherd France, SeaWorld & Busch Gardens Conservation Fund, SEMMAC (Tefé Municipal Secretariat for the Environment and Conservation), Universidad de Las Palmas de Gran Canaria, WWF-Germany, WWF-Brazil, YAQU PACHA and Zoomarine Portugal.
 

What WWF-Brazil is doing

WWF-Brazil has worked in partnership with IDSM providing fuel, Personal Protective Equipment (PPE), veterinary supplies and logistical support for the movement of volunteers. It is 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 dwellers. At this moment, our main area of activity is supplying food to communities impacted by shortages.

“In the Amazon, we are experiencing a historic drought, with forest fires and high temperatures, caused by increased deforestation and intensified by El Niño. The consequences of this drought are serious for local populations and biodiversity, so much so that we have already recorded the death of 178 dolphins in the region”, says Mariana Paschoalini Frias, Conservation analyst at WWF-Brazil and coordinator of SARDI (South American River Dolphins Initiative). “This tragedy shows the urgency of adopting joint measures in order to conserve the Amazon, a key biome for climate dynamics around the world, and river dolphins, species that are fundamental to ecological balance and that allow us to assess the health status of ecosystems where they live.”