- The Amazonian Chelonian Program counted 120,000 Arrau turtle hatchlings (Podocnemis expansa) in Cantão State Park in Brazil’s Tocantins state last year, a 300% increase from just four years earlier.
- But researchers also noticed changes in nesting behavior, including the choice of a new nesting beach, and eggs buried deeper in the sand.
- They suspect nearby fires forced the turtles to find a new nesting site, and warn of a potential gender imbalance in the population if the turtles continue to bury their eggs deeper.
- Other threats to the species include plans to widen the Araguaia and Tocantins rivers for freight ships, and the main problem that has plagued the species for centuries: hunting for human consumption.
Countless of them were massacred over centuries, and their eggs pilfered by the hundreds of millions. Today, the Arrau turtle is a rare species conservation success story in the Brazilian Amazon — but one that could be derailed by a wide range of threats.
In 2020, 120,000 Arrau turtle hatchlings (Podocnemis expansa) swam into the waters of the Araguaia River, marking a steady increase from 40,000 in 2017, 76,000 in 2018, and 96,000 in 2019.
There are 18 different species of chelonians, the order of turtles and tortoises, in the Amazon, from aquatic to semiaquatic to land-dwelling species. Experts say there are at least five more still being described. Brazil’s Tocantins state is home to 11 of these species, the most populous of which are the Arrau turtle, the yellow-spotted Amazon river turtle (Podocnemis unifilis), and the yellow- and red-footed tortoises (Chelonoidis denticulatus and C. carbonarius).
Because it’s the largest of these species (its shell can measure more than a meter, or 3 feet, across), the Arrau turtle is the one most people living in the region are familiar with. It was also historically one of the most sought out by hunters for its meat and fat, which was used for lamp oil.
Historians tell of Arrau turtles being massacred in huge numbers in past centuries. Between 1700 and 1903, an estimated 214 million of their eggs were shipped to Europe as food. The species is an easy target for capture as it lays its eggs on beaches, leaving both turtles and eggs exposed and vulnerable.
In recent years, the government-run Amazonian Chelonian Program (PQA by its Portuguese acronym) has had tremendous success helping the species rebound.
“The PQA is Brazil’s strongest animal conservation program,” says program coordinator Wilson Rufino Dias Júnior. “It is 40 years old and active in a number of northern states. In Tocantins, the project is at work on the Araguaia River near to the municipality of Caseara inside Cantão State Park, which is a permanently preserved area.”
The PQA begins its work of monitoring the turtle nests in mid-September, when the females start to lay their eggs. The species spawns once a year, depositing an average of 100 eggs in each nest. It takes 60 days of incubation before the tiny turtles hatch, in late November or early December. During this time, PQA teams monitor the nesting beaches and mark the nests with numbered sticks. When the eggs hatch, they help the baby turtles get to the river.
Impact of forest fires
Praia da Onça, or Jaguar Beach, in Cantão State Park was an area that Arrau turtles had nested in since 2018. Last year, however, they passed it by, heading instead to a different beach, called Abrãaozinho.
“The hypothesis is that they changed locations because of the fire,” says Thiago Portelinha, an environmental engineer at Tocantins Federal University, one of the institutions with which the PQA partners.
“There was a large burn near to Jaguar Beach and this could have altered their reproductive pattern. The turtles sought out a place where they felt safer,” he adds, noting that Arrau turtles prefer to lay their eggs on high beaches with white sand and little human interference.
The Amazon suffered extensive burning last year, as it did in 2019. According to the Institute of People and the Environment of the Amazon (IMAZON), 6,920 square kilometers (2,670 square miles) of green space were destroyed by fire between January and October 2020, 23% more than during the same period in 2019.
“Turtles prefer to lay their eggs at night because they are more well-hidden. The nearby fire most likely caused the change,” says Maria Augusta Agostini, an environmental engineer at the Amazonian Chelonian Research Center (CEQUA), another partner institution of the PQA.
“Perhaps the brightness of the fire made the females feel exposed to predators and they sought out another place to lay their eggs,” she says.
Another recent change that researchers noted among the turtles in Tocantins was the depth of the nests, which were deeper at the new site — so much so that the project staff had difficulty finding them at the time of hatching. The reason for the change is still unknown, but researchers say it may happen again.
“Deeper nests mean the hatchlings take longer to get out, leaving them exposed to predator attacks for a longer period of time,” Agostini says.
Being buried deeper could also raise the average temperature in the nests. “Higher temperatures produce a higher ratio of females in the population,” says the PQA’s Dias. “So if this behavior continues, over the years the turtle population on the Araguaia River may come to have more females and affect the genetic variability in the region.”
He adds there’s also the risk of flash floods along the banks of the Araguaia. “This is when heavy rains at the headwaters and its tributaries cause the river to rise suddenly, flooding the nests. It compacts the sand and makes it harder for the hatchlings to get out.”
Monitoring the species
Another notable observation from the 2020 hatching season was the occurrence of albino babies. This rare genetic condition occurs when related individuals interbreed. While the odds of a chelonian being born albino is one in 2 million, the Arrau turtle’s reproductive behavior favors the condition, making albinism more common in the species.
“Albino hatchlings have been seen in other years in Tocantins, but the frequency needs to be monitored. An increase in albino young could signify a decrease in population, causing related individuals to cross,” Dias says.
Constant monitoring of the species is important in ensuring the Arrau turtle continues to play its role in the Amazonian ecosystem. Besides being prey for species like jaguars and alligators, the Arrau turtle also serves to disperse seeds in the forest through its feces and maintain water quality.
“In addition, this species holds great social and economic importance for traditional populations, especially Indigenous and river-dwelling communities, as they can be their main source of animal protein,” Portelinha says.
Another threat to the turtle’s survival is a federal government project to widen the Araguaia and Tocantins rivers to facilitate shipment of soybeans and mineral ores for export to China and Europe. The plan involves dredging millions of cubic meters of riverbank, potentially allowing other species to move in that could compete with the Arrau turtle.
“Any change made to nature must be carried out with great caution,” Dias says. “There are genetic studies on turtles and tortoises in the Araguaia-Tocantins basin proving that the characteristics of the rivers, which we call natural barriers, impede or diminish the migration of animals. This makes it possible for different populations of chelonians of the same species to exist. If these barriers change the dynamic of the population, if animals used to living in one place are forced to cohabitate with animals adapted to another space, we don’t know how nature will respond.”
But the main threat, he says, is the same one that decimated the species’ population centuries ago. “It’s nearly certain that there will be a drop in the chelonian population because of changes in their habitat or because of human consumption for food — the greatest impact on turtle species,” Dias says.
Banner image of an Arrau turtle hatching from its egg on a beach in Cantão State Park, courtesy of Luiz Baptista/IBAMA.
This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on March 4, 2021.