- In December, researchers gathered extensive data on a population of Amazon river dolphins in the Amanã Sustainable Development Reserve in the Brazilian state of Amazonas.
- They fitted some of the dolphins with radio transmitters to help map their preferred zones and identify priority regions for species protection.
- At the top of the food chain, the river dolphins play important roles as regulators of Amazonian river life and as environmental indicators for potential zoonoses.
- Hydroelectric dams, fishing, and contamination from mining pose the greatest threats to the species across its range.
It took several days of observation before researchers and local fishermen found the best way to catch the Amazon river dolphins they were studying in the largest lake in the Amanã Sustainable Development Reserve, deep in the Brazilian Amazon.
The lake, part of this 2.35-million-hectare (5.8-million-acre) conservation unit in the state of Amazonas, is fed by small blackwater streams, or igarapés, that branch off from the Rio Negro, mixed with the sediment-rich whitewater from the Rio Japurá. It’s home to a robust fish stock and, therefore, a large dolphin population. What the fishermen learned through observations at the start of the study was that the cetaceans enter and leave the lake through a narrow channel, so it was this passageway that they chose to close with a net.
“First we surrounded them, placed a net in the water and then slowly pulled it over to the edge. We removed them from the water one by one, so they wouldn’t get hurt,” says Antônio de Oliveira, a fisherman from Vila Alencar in the neighboring Mamirauá Sustainable Development Reserve. “We lifted them onto the land and put them on a stretcher. Then we put a tape around their mouth so they couldn’t bite and carried them to the scales where the researchers took down their data.”
But this wasn’t predatory fishing — one of the factors that has placed the Amazon river dolphin (Inia geoffrensis) at risk of extinction, according to the Chico Mendes Institute for Biodiversity Conservation and the IUCN, the global wildlife conservation authority. The fishermen are residents of the Amanã reserve and were there to help with a broad study on the health and behavior of this freshwater species, commonly called the pink dolphin or boto-cor-de-rosa in Portuguese.
The expedition to Amanã last December was organized by the Mamirauá Sustainable Development Institute (IDSM) and WWF-Brasil. Over the course of eight days, the team captured 20 river dolphins and collected data to better understand their state of health. They fitted radio transmitters on five of the animals to monitor their movements through Amazonian waters, with the aim of filling scientific gaps, detailed in a 2022 study.
Each dolphin caught during the research was pulled ashore and placed on a large stretcher. Measuring up to 2.5 meters (8 feet) in length and weighing up to 200 kilograms (440 pounds), the animals were carried to a tent where the scientists prepared to run a series of tests, take measurements and carry out exams — all in the space of around 20 minutes.
“We worked as quickly as possible so the animal wouldn’t be under stress for too long,” says expedition coordinator Miriam Marmontel, who heads the Amazonian aquatic mammals research group at the Mamirauá Institute. “Once they were out of the water, we were fully prepared. The animal was held still and constantly hydrated so its skin wouldn’t dry out. The whole team was working at the same time.”
While the fishermen immobilized the dolphins, researchers would draw blood for tests, including hematology, biochemistry, mercury and selenium levels, and virology tests to detect illnesses like leptospirosis, toxoplasmosis and brucellosis. Others collected nasal, genital and anal swabs as well checked for any apparent injuries. Then they measured the animal’s length, circumferences and weight. Breathing rates and body temperatures — taken from the face, flippers and dorsal fin — were monitored throughout the exam to detect any abnormalities. Before releasing some of the dolphins, the team installed a radio transmitter resembling a clothespin to the animal’s dorsal fin.
Mysterious injuries
Pink dolphins inhabit Amazonian rivers in seven countries: Brazil, Bolivia, Colombia, Peru, Venezuela, Ecuador and Guyana. In Brazil, they’re found in the Amazon, Branco, Negro, Madeira, Tapajós and Xingu river basins. Like all large aquatic mammals, they’re the first to be affected by environmental problems, Marmontel says. Signs of weakness or illness in the dolphins can be warnings to humans of risk of zoonoses, for example.
“As they are at the top of the food chain and are piscivorous, the pink dolphin basically controls fish populations, as they eat the weakest fish. In a way, they clean up the environment for the rest of the biota,” Marmontel says. “We are trying to get ahead of the game by learning about their health so that, in the case of a tragedy, we will be ready to intervene.”
In the Amanã reserve, the dolphins live in a region with little human presence and are therefore unaffected by the impacts the species commonly faces in other parts of the Brazilian Amazon, like hydroelectric dams and mining. Still, this protected area isn’t immune to disturbances from surrounding areas, like water pollution, deforestation, and mercury contamination.
Even though the reserve is ostensibly a protected environment, the researchers found something they weren’t expecting here.
“Most of the dolphins had some sort of injury on their skin. We found one with lesions on its eyes; it was blind and had a broken jaw,” Marmontel says. “It was shocking to find this number of lesions in a population from such a pristine environment. We expected them to be healthier.”
The researchers attributed the injuries to possible encounters with other animals, like crocodiles, or with local fishermen — some injuries seemed like they could have been caused by spears — as well as to fungal infections.
Antônio de Oliveira, known in the region as Peixe-Boi, or manatee, is 58 years old and has worked as Marmontel’s assistant for decades, accompanying the scientist on expeditions on rivers throughout the Amazon Basin in Brazil, Peru and Ecuador. He says he was also struck by the number of injured animals, “all covered in ugly scars.”
“The one that was blind even had some growths on its eye that looked like tumors. We’d never seen dolphins like that, no,” Oliveira says.
The samples that the researchers collected from the dolphins are currently being analyzed. Full results should be ready in about six months, but there have been some preliminary findings. Blood tests and biochemical exams identified normal parameters for the pink dolphins. Swab test analyses showed neither Brucella nor Campylobacter bacteria — which cause brucellosis, or undulant fever, and acute gastroenteritis, respectively, that can also affect humans — but PCR tests should provide more precise results. One feces sample showed a parasite and an oocyst, an infectious agent that causes toxoplasmosis, which is also under further analysis.
Mercury isn’t commonly found in the Amanã reserve, unlike in the Rio Tapajós, where the researchers found the element local in dolphin populations. But samples were collected to evaluate mercury levels in the blood and skin of the animals captured in December. According to Marmontel, it’s still not known at what levels mercury concentrations in Amazonian dolphins could affect their health.
“Aquatic mammals have selenium in their bodies. This is a substance that counterbalances the effects of mercury,” Marmontel says. “We are beginning to do studies at the subcellular level to see what may be happening within the systems, if there are any alterations. I am hoping this will be the big payoff of this expedition.”
Radio monitoring of the dolphins could go on for up to six months, depending on how long the batteries in the transmitters last. When the animals surface, a signal is sent to a satellite, allowing researchers to identify the types of environments they visit, their preferred habitats, and the fish resources in certain areas. Understanding the species’ preferences for locations will help in formulating protection strategies, especially in the case of new offspring and calf maintenance.
“They still inhabit their traditional spot — where the waters meet, when the whitewater [carrying sediment] runs in at times of the year, fertilizing the region, resulting in many fish,” Marmontel says. “As the water rises, we will see if they head, for example, toward the Rio Japurá or the Mamirauá reserve.”
“One of the dolphins is emitting nearly twice as many signals as the others,” says Marcelo Oliveira, a WWF-Brasil conservation expert and coordinator of SARDI, the South American River Dolphin Initiative. “We are going to check its data to know if this was the animal with respiratory problems, because it needs to come up for air to breathe more often.”
Another expedition to the Amanã reserve is scheduled for the second half of 2023.
“It’s productive to capture the animals, do the satellite monitoring and then repeat the study to better understand their ecology and the mechanisms we can use to reduce conflict between dolphins and people, especially fishermen,” Olivera says.
Combating accidental capture
The Amanã expedition included researchers representing SARDI, which was created in 2017 by WWF and partner institutions like the Mamirauá Institute and the Omacha Foundation in Colombia. The project brings together researchers from countries across the region and helps strengthen conservation projects for the various species of South American river dolphins, including the pink river dolphin and the tucuxi (Sotalia fluviatilis), both symbolic cetaceans for the Brazilian Amazon.
“We started out wanting to consolidate the regional conservation strategy developed in Colombia, which needed redefining,” says Oliveira, who has coordinated SARDI since its founding. “We began gathering researchers, holding meetings and understanding what our priorities would be.”
The SARDI researchers adopt the same research protocols, for example, for fitting radio transmitters and monitoring, carrying out dolphin counts, and using drones. The group has captured dolphins in Brazil, Bolivia, Peru and Colombia, and the information collected is consolidated in an online platform. The near-term plan is to analyze the data together and check for patterns relating to health, behavior and movement.
SARDI is also investing in conservation projects aimed at reducing conflicts between dolphins and humans. In the Amanã reserve, accidental capture is the biggest problem for the pink dolphins.
“This is a very productive region, with whitewater that is rich in nutrients,” Marmontel says. “The human population is growing and everyone wants to throw out fishing nets. The problem is that the dolphins also get caught, oftentimes because they are trying to pull fish out of the nets. They don’t even necessarily get caught in the nets, but the fisherman is right there, sees what is happening, and gets angry because the dolphin tears his net when it pulls the fish out. Or it scares away fish that may be approaching.”
Marmontel says the exchange of scientific knowledge and traditional knowledge in the region is helping reduce this conflict as a cause of dolphin death in the region, thanks to the participation of community members in decision-making and research expeditions.
Banner image: Researchers examine an Amazon river dolphin in the Amanã Sustainable Development Reserve. Image by Adriano Gambarini.
This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on May 29, 2023.
Citation:
Campbell, E., Alfaro-Shigueto, J., Aliaga-Rossel, E., Beasley, I., Briceño, Y., Caballero, S., … Godley, B. J. (2022). Challenges and priorities for river cetacean conservation. Endangered Species Research, 49, 13-42. doi:10.3354/esr01201
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