Amazon’s giant South American river turtle holding its own, but risks abound

In Venezuela it is called arrau; in Peru and Ecuador, charapa; in Brazil, tartaruga-da-Amazônia. Regardless of name, the Podocnemis expansa, or giant South American river turtle, as dubbed in English, has inhabited the vastness of the Amazon and Orinoco basins for centuries. To this day, the arrau as it is most commonly called, is the largest freshwater turtle in the region and one of the most consumed species — its meat is said to be delicious.

Not surprisingly as a result, its population has been drastically reduced since the 19th century, when the species numbered in the tens of millions, according to historical estimates. Foreign naturalists from that time reported that it was virtually impossible to navigate the Tefé River, in Amazonas state, without a boat often hitting turtles swimming along the way. In recent decades, faced with imminent extinction in parts of South America, conservation initiatives were launched, especially in Brazil.

However, neither those national, regional nor local efforts have had the capacity to survey populations across the species’ entire range — a vital process, biologists say, that gathers species baseline data and assesses threats in order to devise the best protection strategies.

So in 2014 a group of researchers and conservationists from six Amazonian countries (Peru, Ecuador, Brazil, Ecuador, Colombia and Bolivia) came together in Balbina, in the Brazilian state of Amazonas, with the purpose of carrying out a range-wide survey.

The meeting served as launch point for a sweeping study presented in the Oryx journal. The recently published results, The Future of the Giant South American River Turtle, Podocnemis expansa, highlighted conservation successes, registering more than 147,000 females protected or monitored by 89 conservation initiatives and programs between 2012 and 2014. Out of that total, two thirds are in Brazil (109,400), followed by Bolivia (30,000), Peru (4,100), Colombia (2,400), Venezuela (1,000) and Ecuador (6).

Those current arrau statistics are cause for celebration, even though recent numbers fall far below the 1848-1859 accounting period, when 48 million eggs produced by 400,000 females were gathered annually from the upper Amazon, Solimões and Madeira rivers, primarily for export to Europe, said Germán Forero, the science director at Wildlife Conservation Society (WCS) Colombia and lead author of the recent arrau study.

“It is good news that there are still large numbers of turtles in the Amazon and Orinoco basins, and that there is a large group of people and communities concerned with and investing in their conservation,” said Forero. “This represents a great opportunity for the species. Many communities want to preserve it for its use over time, as the [arrau] represents part of their diets and culture.”

Still, he felt the need to temper that good news: “The figures cannot be interpreted without context. Those are the numbers of protected or managed females, [and] there are many more females in the basin [who are not well protected or managed]. Also, [as] the numbers used to be much higher, it does not mean the species is recovering. Some populations seem to be [doing] so, while others seem to be going down. That is why the effort to gather information for long-term monitoring is so important.”

With the study complete, the research team’s next goal is to develop an observatory that could monitor specimens and understand trends across the region, while also serving as a repository for all data gathered, and technical information and lessons learned, across the six Amazon countries. All of that information would be available for public access.

Arrau life

There are some nights when 300 females come out together from the water to spawn,” recalls Camila Ferrara, study co-author and a WCS Brazil researcher. She’s referring to the time of year when the animals leave igapós, lakes and rivers and migrate to nesting beaches, sometimes traveling up to hundreds of kilometers to lay eggs. The Guaporé River, which begins in Mato Grosso state, hosts one of the longest journeys the arrau makes, travelling to the Bolivian department of Beni, where the stream name changes to the Iténez River, in a region that shelters the largest protected P. expansa population outside Brazil.

After nesting on river beaches, the females don’t leave, as with other turtle species; instead, they await the hatchlings for months so that mother and off springs can return together to their home aquatic habitat. It is the only species known to have such a behavior.

Unfortunately, this natural sociability makes the species and its eggs more vulnerable to human predation. And visible these animals certainly are: an adult female reaches up to 1.09 meter (3.5 feet) in length and 90 kilograms (198 pounds) in weight. Adult males measure between 0.4 meters (1.3 feet) and 0.5 meters (1.6 feet).

Arrau threats: traffickers, dams, mining companies

The IUCN Red List currently places the arrau in its “Unspecified” category, noting that the species’ population is extremely fragmented with “continuing decline of mature individuals,” and requiring more research and conservation action. Though not classified as endangered on the Red List, it is listed on CITES Appendix II: “Not necessarily now threatened with extinction, but that may become so unless trade is closely controlled.”

Among the 89 P. expansa program study sites, the new research found wide variations in population trends, even within the same nation. In Brazil, for example, the Amazon Chelonian Program run by IBAMA (the country’s environmental agency), learned that monitored areas (including the Tapajós, Guaporés, Foz do Amazonas and Purus river systems) experienced an increase in nesting females between 1980 and 2014, while in generally less monitored river systems (including the Javaés and Baixo Rio Branco, but not the Trombetas which was fairly well monitored, numbers fell).

“The Baixo Rio Branco [in Roraima state] is considered one of the most dangerous areas to work [with conservation]. It is called the ‘pirate river’ because it attracts many turtle traffickers and an IBAMA official was murdered in the region a few years ago,” Ferrara told Mongabay.

According to the biologist, threats to the species include the predatory hunting of females and eggs, the flooding of beaches caused by hydroelectric dams, and mining operations near turtle habitat. A case in point is the Trombetas River Biological Reserve which is adjacent to the Mineração Rio do Norte — the nation’s largest bauxite producer located on the banks of the Trombetas River, in Pará state. Bauxite is utilized to make aluminum.

“For maritime transportation, the mining company had the river dredged, and those interferences likely disrupt turtle communication,” explained Ferrara. In the 1960s and ‘70s, the Trombetas River Reserve was one of the most important arrau spawning areas in Brazil, boasting 6,500 adult females. Today they are less than 600.

“The number of born hatchlings also depends on [having sufficient] resources for oversight and monitoring, but under the current [Jair Bolsonaro] government resources have decreased significantly,” added Ferrara.

Managing arrau threats is also complicated by the species’ behavior. For example, during her doctoral work, the researcher learned that P. expansa females and their offspring communicate in and out of the water. “Sounds were emitted by hatchlings in the egg, in open nests, in the river, and in captive conditions. Adult females were recorded producing sounds in the river, while basking, while nesting, and in captivity. Females were recorded in the river approaching and responding to hatchling sounds,” notes the study. Researchers believe that noisy mining operations could disrupt those communication patterns.

In a recent study Ferrara concludes: “Noise pollution from human activities, once thought to be irrelevant in turtle conservation, may now generate some concern. Noise produced by ships, boats, jet skis, and other motorized watercrafts may affect the reception of sound by turtles and potentially interfere with their communication, to such a degree that it has a negative effect on hatchling survivorship and adult communication.”

Currently Ferrara is utilizing satellite imagery and vocalized sound recording to investigate how and when turtles communicate with each other, with an eye toward how that knowledge might be utilized to enhance conservation efforts.

Turtle lives in flux

Another human influence impacting the arrau: climate change is altering temperatures, rainfall patterns and hydrology in Brazil’s 11 large nesting areas and, as a consequence, impacting the reproductive capacity and success of P. expansa, as well as other species.

“There has always been a certain annual variation in the number of turtle births due to climate and human pressure. Climate change may be impacting those populations more broadly, though,” Roberto Lacava told Mongabay. He is IBAMA’s environmental analyst and the national coordinator for the Amazon Chelonian Program.

Climate change alters the rainfall regime, Lacava explains, which in turn alters river water levels, with extreme precipitation events causing the flooding of nests before hatching. Freshwater turtle females depend on decreasing river levels so that nesting beaches are exposed and nests can be built. When river levels rise rapidly, flooding the nests before the hatchlings are born, the eggs rot and the number of births decline.

“That happened on the Monte Cristo tabuleiro [turtle nesting beach, in Pará] in the 2018/2019 season, when 78 percent of the nests were lost due to atypical flooding,” said the analyst. Extreme weather isn’t the only cause of such events: large water releases from hydroelectric dams can similarly flood downstream nest sites, unless dam operators control releases during nesting times.

Arrau reproductive productivity can also be affected by the climate crisis through a complex sequence of events. The giant South American turtle is predominantly herbivorous and depends on the rising of river levels to create forest floods (called Igapós) during which fruits and leaves fall into the rivers, offering up easily accessible food for the chelonians. But during climate change-intensified drought, when river levels don’t rise sufficiently to flood, the turtles’ feeding is compromised and the animals have less energy to reproduce. Again, dams that withhold water releases at the wrong times can have a similar effect.

“The future of the Amazonian turtles in the face of climate change is worrisome,” said Lacava. “For an animal that has evolved so synchronously with the water regime of the Amazon basin — so that both its reproduction and food are directly affected — it is difficult to trace any prognosis that is not catastrophic.”

“Some measures can mitigate those impacts, such as raising artificially the level of the beaches, but they have controversial results and high costs to be implemented,” concludes Lacava. So it is that the long-term survival of the arrau not only hinges on Amazon region conservation, but also on international action to curb climate change.

Citations:

Forero-Medina, G., Ferrara, C., Vogt, R., Fagundes, C., Balestra, R., Andrade, P., . . . Horne, B. (n.d.). On the future of the giant South American river turtle Podocnemis expansa. Oryx, 1-8. doi:10.1017/S0030605318001370.

Bates, H.W. (1892) The Naturalist on the River Amazon. John Murray, London, UK.

Zwink, W. & Young, P.S. (1990) Desova e eclosão de Podocnemis expansa (Schweigger, 1812) (Chelonia: Pelomedusidae) no Rio Trombetas, Pará, Brasil. Forest, 90, 34–35.

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