The Amazon and Orinoco Basins are the home of the largest freshwater turtle in the Western Hemisphere and one of the largest turtles in the world. It also may be unique among turtles in its nesting behavior and communication skills. The Giant South American River Turtle, Podocnemis expansa, is also called the Arrau in Venezuela and Colombia and the Tartaruga-da-amazônia in Brazil. Females can weigh up to 90 kilograms (200 pounds) and be 1.07m (3.5 ft) long. Males are significantly smaller at 0.4m (1.5 ft) and under 45kg (100lbs). The carapace is flattened and without a significant dorsal ridge.
This species is the largest side- necked turtle in the world which means it cannot retract its head under the carapace but rather folds its head to the side under the edge of the carapace when threatened. Adults are almost entirely aquatic and only the females come ashore to bask and lay eggs. As adults these river turtles have few natural predators, but hatchlings are subject to predation by a wide variety of predators including birds at the hatching stage and fish and crocodilians as young turtles. This giant river turtle is almost entirely herbivorous feeding on seeds, fruits and aquatic plants. Young turtles are reported to eat dead fish and carrion. Adults appear to fast during the dry season when access to a flooded forest is not possible.
(30 inch long turtle on the Rio Napo in the Ecuadorean Amazon by Gerard Bertrand)
There is wide disagreement on when females reach sexual maturity, but it is generally believed to be sometime after eight years of age that females begin an annual cycle of laying between 80 and 200 spherical eggs on river sandbars during the time when the river is at its lowest ebb. Depending on the latitude this occurs between September and December each year. Mating occurs in the water and the females bask daily for several weeks thereafter while the eggs develop within her body. Egg laying is at night in a nest up to three feet deep which the female digs high up on the sandbar.
Research in Brazil showed that if the nest reaches an internal nest temperature of 34.5° C (94.1°F) the hatchlings will be 100% females. When the nests are shaded by vegetation or a raised bank and the internal nest temperature is 30.5° C or below (86.9°F), the hatchlings will be 100% males. The timing of egg laying is critical, since rising waters can flood the nest, rot the eggs and result in nest failure. This can happen from a natural disruption of the aquatic cycle or from a premature release of water from upstream reservoirs. After approximately 50 days, the eggs hatch. Unlike any other known aquatic turtle, the female turtle remains nearby and calls the young hatchlings to join her in the water. Although this behavior seems to be unique for an aquatic turtle is a widespread among crocodilians where nests, eggs and hatchlings are guarded and protected for an extended period.
Crocodilians, however, are cannibalistic and hatchlings are readily eaten particularly by males of the same species. This cannibalistic behavior has not been observed in giant river turtles. After gathering the female turtle and young then return to her home territory. As water levels rise they move into the flooded forest to feed. The communication behavior of this river turtle provides new insights to turtle biology. Recent research shows a complex social structure at least among females allowing them to coordinate group breeding activities and post breeding protection for hatchlings. This new information raises more questions for how best to direct species conservation efforts.
Because on the volume of past trade and the massive reduction in the species population and distribution, all Podocnemis species are listed on Appendix II of the Convention on International in Endangered Species (CITES) and are considered by the IUCN Turtle Specialist Group as conservation dependent. Direct human activity and disruption of natural systems through climate change have had and are having major impacts on the status of the South American Giant River Turtle. Although widely protected by legislation, there is still illegal harvesting of adults and eggs. Riverside mining activities for bauxite[i] (the ore from which Aluminum is obtained) and other minerals adversely effects water quality and the noise at known nesting sites may disrupt communications between females and hatchlings. Withholding or releasing water from hydroelectric facilities and reservoirs can disrupt nesting and reduce hatching success. Most recently however the overriding concern is with the unpredictable and extreme changes in water levels in the Amazon basin[ii]. The deep and prolonged drought eliminated or delayed nesting opportunities at some sites during the past year.
On the plus side there is much more awareness by governments and nonprofit conservation organizations of the opportunity to restore this ecologically important species as a viable component of the river ecosystems. Long term study sites have been set up, individual animals tracked, and nesting success studied and recorded. Because this species is slow growing and late to reach maturity, turtle farming does not seem to be a significant option at present, although some individuals are in farms that are raising other aquatic turtle species. Significant efforts are underway to head start young turtles by initially captive rearing hatchlings until they have a greater chance of survival before returning these hatchlings to the wild to augment the populations.
Although not yet documented at Permian’s Guayabero Crocodrilo Reserve in Colombia the species is widespread in Eastern Colombia. The species has been confirmed at Permian’s Rio Cautário project site in the state of Rondônia in Brazil. A nearby conservation initiative on the Rio Guaporé produces 700,000 to 1,000,000 hatchlings annually from a major conservation breeding area. The government, NGOs and the local communities allow the main river-beaches to be protected and monitored, to avoid egg harvesting resulting in more hatchlings reaching the water. This is very important because only a fraction of these hatchlings will achieve breeding age.
Two hundred years ago, the South American giant river turtle was one of the dominant aquatic species throughout the Amazon and Orinoco Basins. With estimated numbers in the tens of millions they ranged from the river basins flowing north and emptying into the Caribbean and to the southernmost parts of the Amazon basin in Brazil and Bolivia. From 1848 to 1859 over 48 million river turtle eggs were gathered annually for commercial export, primarily to Europe. In the past 200 years the species has been greatly reduced in numbers and distribution so that initial basin wide surveys from 2012 to 2014 identified only 147 egg laying females at 89 study sites. Once a major source of protein and oil for local peoples the hope is that conservation action can once again restore the species as a significant ecological component of major river and aquatic systems throughout the Orinoco and Amazon Basins.
[ii] https://brasil.wcs.org/en-us/wildlife/amazonian-turtles.aspx
[ii] “Cannibalism in the American Alligator” Rootes, William L. and Robert H. Chabreck
Herpetologica, pp. 99-107, Herpetologists’ League, Pub.
[ii] “Appendices I, II and III”. CITES Secretariat. CITES. Geneva, Switzerland: Convention on International Trade in Endangered Species of Wild Fauna and Flora. 4 April 2017.
[ii] https://ukgbc.org/our-work/topics/embodied-ecological-impacts/aluminium/
[ii] https://news.mongabay.com/2024/09/extreme-drought-pushes-amazons-main-rivers-to-lowest-ever-levels/
1.Alderton, David Turtles & Tortoises of the World, © UK 1988, Blandford Press, imprint of Cassell Plc, London, UK
2.Ernst, Carl H. and Roger W. Barbour, Turtles of the World, Smithsonian Institution Press, Washington, DC, © 1989
3.Turtles of the World. Annotated Checklist and Atlas of Taxonomy, Synonymy, Distribution and Conservation Status (9th Edition). 2021. Chelonian Research Foundation and Turtle Conservancy Monograph Number 8
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