The Brazilian Amazon is home to 17 turtle species, all of which are under pressure from overexploitation, the illegal wildlife trade, widespread hydropower dam construction, and mercury contamination. Deforestation, agricultural development and climate change are other looming threats.
The Brazilian government’s Amazon Turtle Program focuses its conservation efforts on the Giant Amazon River Turtle (Podocnemis expansa), plus the Yellow-spotted River Turtle (P. unifilis), and Six-tuberculed River Turtle (P. sextuberculata). The Wildlife Conservation Society works with these same species and is also conserving the Red-headed Amazon River Turtle (P. erythrocephala), and Big-headed Amazon River Turtle (Peltocephalus dumerilianus).
Amazon dams — especially mega-dams like the just built Belo Monte dam and the proposed Luiz do Tapajós dam — alter ecosystems and disrupt the annual flood cycles that inundate lowland Amazon forests, putting turtles and other species at risk.
Mercury contamination of Amazon rivers due to illegal gold mining is a major threat to turtles. Researchers say there is an urgent need for the Brazilian government to develop and implement guidelines for the assessment of mercury toxicity in Amazon reptiles, especially turtles.
For as long as people have lived in the Amazon, turtles have likely been on the menu. But what was once low-impact subsistence hunting escalated dramatically after the arrival of Europeans. From the 1700s onward, demand for turtle eggs and meat skyrocketed. And the eggs weren’t just for eating: estimates suggest that more than 200 million eggs were harvested for both consumption and oil, fuelling lamps across Europe for two centuries.
This overexploitation led to such dramatic population declines that the Brazilian government eventually stepped in, launching the ambitious Amazon Turtle Program in 1979 — an on-going initiative that has so far protected 70 million turtle hatchlings across the Brazilian Amazon, with the intent of conserving vulnerable species.
But while that program continues to work toward a sustainable future for turtle populations —and for the people who still see chelonians as an important source of protein — three more recent threats loom over Amazonian turtle species: the illegal wildlife trade, widespread hydropower dam construction, and mercury contamination.
Turtles at risk
The Brazilian Amazon is home to 17 turtle species that occupy important ecological niches in freshwater habitats ranging from main river channels, to flooded forests and lakes.
The largest neotropical freshwater species, the Giant Amazon River Turtle (Podocnemis expansa), is also at the heart of chelonian conservation efforts. Weighing up to 65 kilograms (143 pounds), P. expansa is a species of side-necked turtle — retracting its neck horizontally as opposed to vertically like other species. It has a large domed shell adapted to swimming in river currents, but it also inhabits lakes and flooded forests during the rainy season. When it’s time to lay eggs, the turtles move en masse to their nesting beaches. Recent research has found that the species uses several vocalizations to communicate during this time, including between mothers and offspring before and after hatching.
Unfortunately for P. expansa, its longevity and late reproductive maturity, coupled with the species’ predictable mass nesting behavior on exposed sandbars and beaches, make it especially vulnerable to hunting and egg-harvesting pressures.
Historical accounts relate how the Amazon’s Madeira River used to became so congested with nesting turtles that boat traffic was impeded, even as many thousands more nesting turtles covered river beaches as far as the eye could see. These turtle tales seem almost unbelievable now; the Giant Amazon River Turtle was listed as Endangered by the IUCN in the 1980s, though it has recovered some since, thanks to persistent conservation efforts.
The greatest threats to Amazonian turtles today are “dams and people collecting them to sell in large cities,” Richard Vogt, of Brazil’s National Institute of Amazonian Research (INPA), told Mongabay. Camila Ferrara, of the Wildlife Conservation Society (WCS) Brazil, cites “uncontrolled consumption of eggs and meat” as the biggest threat, even though prohibited by law, unless authorized by IBAMA, Brazil’s environmental agency.
Ferrara notes that these immediate pressures exist within a broader context of deforestation, increasing agricultural activity, and climate change. “We already know that dams and global warming are threats, but we do not know yet all the consequences,” she said.
From overexploitation to conservation
The Amazon Turtle Program has been a champion of chelonian conservation for nearly forty years. Today, its primary target species for preservation include the Giant Amazon River Turtle, along with several related species within its biological family, including the Yellow-spotted River Turtle (P. unifilis), and Six-tuberculed River Turtle (P. sextuberculata).
The Wildlife Conservation Society (WCS) also works with these species, as well as with the Red-headed Amazon River Turtle (P. erythrocephala), and Big-headed Amazon River Turtle (Peltocephalus dumerilianus). WCS is working in protected areas on the Purus and Negro rivers, where its goal is to reduce overexploitation by finding ways for turtles and people to live together, Ferrara said. Participative programs launched in communities along the Rio Negro — where locals get involved in protecting nests and monitoring populations — are showing promise.
The Amazon Turtle Program’s geographical scope is much broader. It has targeted hundreds of breeding grounds across the Tocantins/Araguaia and Amazon River basins.
“The program tries to protect some of the main nesting areas of [the target species] during the reproductive period,” Roberto Lacava, coordinator of the program at IBAMA, told Mongabay. Some 800,000 females have had their nests protected over the project’s history. “In the last years, we released around 2.5 to 3 million hatchlings [annually],” he reported. Most hatchlings are produced and released on the protected beaches, though in some special cases the nests are relocated to better protect the eggs until they hatch.
Though this may sound like a staggering number of animals to have been released, Vogt, who has been studying turtles in the Amazon for more than 25 years and is an advisor to the Amazon Turtle Program, puts these totals in context: “These are not huge numbers, considering the vast size of the Amazon Basin,” he explained. “Also the survivorship of hatchlings is low, [so] only a small portion of these [young turtles] reach maturity.”
“Releasing hatchlings in some areas has been beneficial, and populations of adults have been increasing,” Vogt noted. Results have been so good, in fact, that the Giant Amazon River Turtle is no longer considered Endangered, and is now classified as low risk but dependent on conservation activities. “We only do headstarting [nest protection and the release of juveniles] with hatchlings in a few places, where the population is in danger,” Lacava revealed. “We don’t consider [it] necessary to continue releasing turtles in most of the areas.”
The Amazon Turtle Program is now focused on regions where the turtle situation has not improved, or is getting worse. In those areas “the adult population keeps going lower because of the continual poaching threat,” Vogt said, a problem that persists due to lack of law enforcement. “Nothing is done to stop poachers; they are captured and released and never pay fines,” he laments.
Larissa Schneider, of the Australian National University, has been studying Amazon turtles for over a decade; she too sees poaching as a serious problem. “The main threat affecting Amazon turtles is still the black market, and uncontrolled smuggling of turtles. The Brazilian government has been ineffective at curtailing this activity,” Schneider declared. Wildlife smuggling is the third largest form of illegal trafficking in Brazil, following drugs and firearms, and it accounts for billions of dollars in illegal trade annually, she said.
Despite these ongoing challenges, Lacava sees Brazil’s turtle conservation efforts so far as a success, “Although,” he adds, “we have a long way to go.”
Dams and turtles don’t mix
Combatting overexploitation is just one part of the turtle conservation challenge. With hundreds of hydroelectric dams already up and running, under construction or planned across the Amazon, numerous aquatic and terrestrial species are seeing their habitats lost or degraded.
Dams disrupt the annual flood cycles that inundate lowland Amazon forests. Reservoirs permanently flood vast areas, and species movements are prevented. Some species are even in danger of extinction as a result.
For turtles, the most obvious impacts of dams are the disruption of migration routes, and the loss of nesting beaches as reservoirs fill with water, and the flow of rivers is altered downstream.
Lacava explained that interrupted migration during reproductive periods “could cause a severe interference in the genetic structure [of turtle populations], especially for P. expansa.” The isolation of populations by dams, as also seen among Amazon river dolphins, can make sub-populations more vulnerable to additional threats.
“Another impact is the change in the river flood regime, causing the disappearance of nesting beaches and the loss of many nests,” due to flooding, Lacava said. But he emphasized that more data is urgently needed to understand these effects, especially species-and-dam-specific studies that could reveal the full implications of Amazon dams before they are built.
Most of what scientists know about the likely impacts of future dams on turtles comes from two of the oldest Amazon mega-dams, Balbina and Tucurui, Schneider said. Balbina dam, built in the late 1980s on the Uatumã River to provide power to the city of Manaus, has an installed capacity of 250 megawatts, and flooded 2,360 square kilometres (910 square miles) of forest. Construction of the 8,370 megawatt Tucurui dam on the Tocantins River began in 1974, and inundated 2,850 square kilometers (1,100 square miles).
Vogt has been involved with turtle mitigation activities at Balbina, a dam that has caused serious problems for turtles. “When the Balbina dam was closed, 65 adult females were [isolated] behind the dam,” Vogt said. “They now nest on the only available beach [there], an island which was too cold [due to shading], so none of their eggs hatched.”
Providing artificial nesting beaches, however, proved to be a partial solution: We built “nesting beaches just below the dam, one of coarse sand for P. expansa and the other of fine sand for P. unifilis. The turtles migrating up to the dam use these nesting beaches. They have been washed out at least once and built up again, [but] they work,” Vogt said.
Further insights regarding Balbina and Tucurui turtle impacts paint a more troubling picture, as Schneider elaborated. “Essential micro-habitats used by turtles are lost in water impoundments including dams, weirs and barrages. Impoundments make juveniles particularly vulnerable due to loss of sheltering sites, loss of important prey/food species, and cooler water temperatures.
“The food chains of turtles are fundamentally different in lakes than in rivers,” Schneider continued. “Amazonian turtles that rely on cloacal respiration [breathing underwater via the single rear opening of the digestive and reproductive tracts] are disadvantaged in the stratified, low-oxygenated, turbid water in impoundments.”
The larger the dam, the greater the impacts, so mega-dams pose the most serious threats. For new mega-dams, such as the just completed Belo Monte dam and the proposed São Luiz do Tapajós dam, “turtles have already been [or will be] detrimentally affected by impoundments due to the loss of riffle habitats [shallow, fast-flowing rapids], and the disappearance of food items such as aquatic plants (macrophytes), the loss of windfall fruits from riparian vegetation as well as some aquatic invertebrates,” Schneider said.
“Changes in water quality is also a straight forward impact faced by turtles right after dams are built. We can anticipate that long-term problems from Balbina and Tucurui will most likely affect the new dams as well,” she concluded.
Concerns are emerging that the Belo Monte dam over the long term may threaten one of the most renowned of annual Amazon natural spectacles — the arrival of 20,000 Giant Amazon River Turtles to lay their eggs at the Tabuleiro do Embaubal, a stretch of sandy beach on the Xingu River. Biologists fear that the dam, located upstream from the nesting area, will prevent the replenishment of sand during the rainy season, eventually causing the beaches to vanish, leaving the turtles no place to deposit their eggs.
Mining and mercury
As if all those obstacles to turtle survival weren’t bad enough, hydropower and the extractive industry are inextricably linked in the Amazon, causing more habitat and species harm. Bauxite, nickel, and copper mines that benefit from the power that dams generate cause habitat destruction and lead to human population migration into remote regions, which results in increased pressures on the natural resources in the vicinity of mining operations.
But an invisible, insidious consequence of mining is of particular concern for turtle species, and to anyone who eats turtle meat and eggs: mercury contamination caused by illegal artisanal gold mining.
“Hg [mercury] causes adverse effects on turtles, such as behavioral and endocrine disruption, and at high concentrations can be lethal,” explained Schneider, who has studied the effects of mercury on the mata mata turtle (Chelus fimbriatus). “Because mercury is a persistent substance, it can build up, or bioaccumulate, in living organisms, inflicting increasing levels of harm on higher order species such as predatory turtles, fish and mammals.”
Gold mining is on the rise in many parts of the Amazon basin. And because the mercury used to extract gold gets into the river system, and then the broader food chain, its effects are felt far beyond the limits of the mines themselves. In southeast Peru, for example, the threat mercury poses to environmental and human health has reached such critical levels that a state of emergency has been declared. It is likewise a serious problem in Brazil and for turtles in the Amazon Basin.
For turtles, “[t]he biggest issue at the present is the fact that there are no mercury guidelines specific for any reptile,” Schneider said. “There is an urgent need to develop and employ appropriate guidelines for the assessment of Hg toxicity in reptiles, including turtles.”
Schneider’s study included the development of “a non-invasive methodology that enables analysis of Hg in turtles and alligators by using samples from their carapace and skin rather than killing animals to collect muscle samples.” Results showed that levels of mercury in the mata mata turtle were high enough to be a health risk for people eating the animals.
The long-term outlook for the Amazon Basin’s turtle species will depend on the effectiveness of a multi-faceted approach to the many threats facing them today. There have already been numerous calls to halt hydropower development in the Amazon in favor of greener options, and for better environmental planning to be put in place for all future infrastructure development. How climate change — especially increased drought — will impact Amazon turtles remains to be seen. But when it comes to one of the biggest problems, combatting overexploitation and trafficking, Lacava sees enforcement as paramount. “I believe that the illegal trade can only be reduced by police supervision and sustainable use initiatives,” he concluded.