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You can’t see them to count them, but Amazonian manatees seem to be recovering

  • Following intense commercial hunting from the 1930s to the 1950s, scientists and community members are seeing signs that the manatee population in the Amazon is growing.
  • A study carried out in the Piagaçu-Purus Sustainable Development Reserve in the state of Amazonas shows large manatee populations nearby human communities, apparently co-existing in peace.
  • Threats still remain in the form of poaching and accidental capture; calves that are orphaned or injured in these incidents are taken to rehabilitation centers, but these are low on funding and overcrowded.
  • Monitoring of manatees returned to nature from these rehabilitation centers shows their work is paying off: one female being tracked since her return was later found to be pregnant.

Diogo de Souza used to wake up at 3 a.m., stop by the house of a community member who knew about manatees, and the two began work among the carapanãs, the large Amazonian mosquitoes, as the sun came up. Sitting still in their wooden canoe under the scorching sun typical of the dry season, they watched for signs of the presence of Brazil’s largest freshwater mammal, which can grow to 3 meters (10 feet) in length and weigh 500 kilograms (1,100 pounds). How could an animal so large be so hard to see?

Amazonian manatees (Trichechus inunguis) are so elusive that some call them a “ghost animal.” Fishermen say they can’t even let cigarette ash fall into the water because the manatee will quickly disappear, blending into the murky colors of the Amazonian waters. People also say that manatees learned to hide from humans, leaving only their nose sticking out of the water to breathe, during the period of uncontrolled hunting from the 1930s to the 1950s. That was the time manatee leather was in high demand abroad for industrial applications such as hoses, transmission belts, pulleys and loom parts.

To make studying them easier, de Souza, a biologist and vice president of the Manatee Friends Association (AMPA), led a study evaluating several methodologies for estimating the distribution range of the manatee in the central Amazon. The researchers undertook a 44-day survey of 33 lakes in the Piagaçu-Purus Sustainable Development Reserve, created in 2003 and located just over 200 kilometers (120 miles) from Manaus, the capital of Amazonas state.

In the course of their studies, they found several encouraging indications that the manatee population is rebounding in the Purus River region. Even without an estimate of the population — manatees are impossible to count the way one would count, for example, porpoises — clues such as feces, the plants they feed on, and also sightings of the animals themselves suggest a recovery. Members of local communities also agree the population is returning.

Community members monitor radio-tracked manatees in the Purus River. Image by Diogo de Souza.

“Creating the reserve seems to have had a positive effect. It is possible that the populations are recovering in the area we studied,” de Souza says. “We did interviews with community members and fishermen and they say they see more traces of manatees.”

Although these indications can’t be extrapolated to other areas or reserves in the Amazon Basin, a 2004 genetic study carried out throughout the Brazilian Amazon found evidence of the manatees’ demographic expansion.

“As they are protected and it has been made illegal to sell them, the species has had room to grow and the expectation is that [the population] is increasing,” says Vera da Silva, a researcher at the National Institute of Amazonian Research (INPA) and a co-author of the two studies. “We don’t know how much it is increasing, though. We don’t have these numbers.”

De Souza says he sighted groups of up to 12 animals during the field research. “We even saw them mating … males trying to mate with females in groups,” he says. “There we were, hiding in silence, getting very close to seeing … without being able to yell with joy.”

To the surprise of the researchers, the Piagaçu-Purus study revealed that many manatees live near human settlements. The best habitat for the animal is also the best place for people to settle in, and within the reserve, they co-exist in harmony. Areas like floodplains, fertilized by nutrients washing down from the Andes, areas with rich springs, and also places connected to other water bodies are prime spots for both species.

“The people who live here are knowledgeable about the forest, they protect these animals, actively participating in the reserve by monitoring the lakes and protecting the pirarucu and other fish,” de Souza says. “This local ecological knowledge is extremely important for the Amazonian manatee and serves as important information when we want to collaborate to carry out management plans and decision-making for the reserve.”

An AMPA researcher feeds a manatee at the INPA rehabilitation center in Manaus. Image by Jonne Roriz/AMPA.

Historic release

The Amazonian manatee belongs to the same genus as the West Indian and West African manatees (Trichechus manatus and T. senegalensis), but unlike those better-known species, lives only in freshwater, specifically in the Amazon Basin. It’s categorized as vulnerable on the IUCN Red List.

Manatees are a slow-breeding animal, whose gestation lasts 12 months, at the end of which they produce just one calf. The calf breastfeeds for the first two years of its life, following its mother through a survival course where it learns about Amazonian waters, migratory routes, and how to avoid predators, including humans.

In Brazil, a ban on hunting manatees was enacted in 1967. By then, commercial exploitation had led to a drastic drop in the population of Amazonian manatees in the Purus River.

Today, orphaned manatee calves are brought to one of three rehabilitation centers that care for the animals and prepare them for eventual release back into the wild. The center in Manaus is run by INPA, a government agency.

When she arrived at the INPA center, Gigi refused to eat. She had salmonella and chronic diarrhea, but eventually pulled through. When her condition stabilized, she was placed in a tank along with another manatee, friendly and always eating. But after sharing the same waters for 10 days, the two orphans didn’t become friends. Gigi continued to refuse to be fed from a bottle, until she was finally separated from her tankmate. All in all, her keepers say, she’s responding well.

“The animals arrive as calves, normally rescued by environmental agencies and the environmental police squads after someone reports a situation,” says INPA’s da Silva. “They are brought to INPA and here we start the rehabilitation process.”

Before Gigi arrived at the INPA rehabilitation center, she had been found and cared for by residents in the town of Almeirim, in the neighboring state of Pará. Today, she shares her tank at INPA with 61 other manatees also undergoing recovery; the center’s staff anticipate releasing all of them back into the wild eventually. At least 12 of the manatees are very young and still bottle-feeding every five hours. “We will soon have to transfer a group of animals to semicaptivity, not only to reduce the number of animals in our tanks, but also with a view to future release,” da Silva says.

From July 20-23 this year, staff carried out a historic release of 13 manatees into the Piagaçu-Purus Sustainable Development Reserve. Five of the animals were fitted with transmitter belts for monitoring. “Usually we took eight to 10 animals because of the difficulty in transporting them. It’s a 24-hour trip on a regional boat with fiberglass tanks on the boat’s deck,” says da Silva, who led the AMPA expedition in partnership with INPA. “We fill them with water and then place the animals inside. There are 24 hours of monitoring.”

Release of a manatee in the Piagaçu-Purus reserve in July 2021. Image courtesy of AMPA.

Caring for orphaned manatee calves is expensive, and it can take three to six years before the animals are ready for reintroduction into the wild. And that’s if it’s logistically and financially feasible to release them at that time. Da Silva says the five-day trip this past July to get to the reserve, release the animals and return cost 30,000 reais ($5,400), outside the logistical expenses of loading the animals onto the boat from the tanks and so on.

In addition to full-time monitoring, the researchers say they need to be careful with reintroduction. “We carry out a series of medical exams so as to ensure that we are not introducing any disease from captivity to natural populations,” da Silva says.

Due to lack of funding and infrastructure, most rehabilitation centers aren’t currently taking in new animals. Miriam Marmontel, a researcher at the government-funded Mamirauá Institute for Sustainable Development, there are currently three official rehabilitation centers for Amazonian manatees, all of which are at maximum capacity, with 50 animals or more, including the INPA facility.

“Keeping manatees in captivity is costly in financial, logistical and personnel terms,” Marmontel says. “We are in this situation because many calves are rescued each year, either because they ran aground, got tangled in nets or were harpooned to attract their mother.”

Despite the decades-old hunting ban, manatees continue to be targeted for food and illegal trade in local markets in the Amazon. Many of the calves rescued and taken to rehabilitation centers are victims of fishing activity.

Fishermen deliberately target them by stringing nets near the banks of the whitewater rivers that feed the floodplains, an area where manatees tend to swim. Adult manatees can usually break free of the nets when they become entangled, but the younger animals aren’t strong enough and can become trapped. Unable to surface to breathe, they can die. The mother manatee, unwilling to leave her calf behind, becomes easy prey for hunters.

Researcher Miriam Marmontel from the Mamirauá Institute of Sustainable Development, with a month-old female manatee, rescued in Acre state in 2014. Image by Danielle S. Lima.

The rehabilitation centers face many difficulties, but the tracking of the animals after their release shows their efforts are paying off. “We managed to recapture four individuals 18 months after they were released and one of them, a female, was pregnant,” da Silva says.

“When a released animal reproduces in nature, it means the reintroduction worked,” she adds. “For us, it confirms that the methods we are using — the readaptation period in the seminatural lake, in semicaptivity, the age group separation we have been doing — are working.”

Citations:

de Souza, D. A., Gonçalves, A. L., von Muhlen, E. M., & da Silva, V. M. (2021). Estimating occupancy and detection probability of the Amazonian manatee (Trichechus inunguis), in Central Amazon, Brazil. Perspectives in Ecology and Conservation19(3), 354-361. doi:10.1016/j.pecon.2021.03.009

Cantanhede, A., da Silva, V. F., Farias, I. P., Hrbek, T., Lazzarini, S., & Alves-Gomes, J. (2004). Phylogeography and population genetics of the endangered Amazonian manatee, Trichechus inunguis Natterer, 1883 (Mammalia, Sirenia). Molecular Ecology14(2), 401-413. doi:10.1111/j.1365-294x.2004.02413.x

 
Banner image of manatees in an INPA tank by Anselmo d’Affonseca.

This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Nov. 2, 2021.