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Monday, November 18, 2019
BAJO XINGÚ, Brazil, Dec 6 2011 (IPS) - The more data she gathered for her Master’s thesis, the more alarmed the young Brazilian biologist became. The Amazon turtles born in the dozens of nests examined in 2008 and 2010 were all female. And only eight percent of the hatchlings studied in 2007 had been male.
The sex of chelonians in the Amazon region, of which Amazon turtles (Podocnemis expansa) are the largest species, is determined by the temperature in the nests where their eggs are incubated. And when the temperature rises above 32 degrees Celsius, more females than males are born.
The research conducted by Cristiane Costa revealed that the average temperature of Amazon turtle nests on Juncal beach was 32.6 degrees in 2007, 34.5 in 2008 and 35.9 in 2010. Juncal is an island in Tabuleiro do Embaubal, an archipelago in the Lower Xingú River in the eastern Amazon region of Brazil, and its beaches are the largest known breeding ground of this species.
What will become of the turtles if global warming is even more pronounced in the Amazon region than in other areas, as numerous studies predict? Eventually, their reproduction could be brought to a halt by a scarcity of males and the death of embryos before they hatch due to the excessive heat in the nests.
But these are animals that can live for many decades; exactly how many has not yet been determined. This means that the sex ratio could eventually be rebalanced, as long as the high temperatures do not become permanent or widespread, said Juarez Pezzuti, a professor at the Federal University of Pará who specialises in chelonian species and is Costa’s thesis advisor.
Pezzuti added that it will be necessary to monitor the turtles for many years and assess the various different factors that affect reproduction. An increase in unfertilised eggs would indicate a shortage of males.
Only 230,000 viable hatchlings survived in 2008, 58 percent fewer than in 2007.
However, the sand that was added is much larger-grained than the original sand, and therefore retains more of the sun’s heat. This in turn increased the temperatures in the nests, leading to the death of a large number of embryos and hatchlings. This was probably a factor in the low reproduction rate in 2010, when around 320,000 viable youngsters were counted, as compared to 470,000 in 2009.
These figures are available because of an initiative carried out in Brazil over the last three decades for the protection of Amazon chelonian species. On the beaches monitored as part of the project, baby turtles are gathered and cared for during their first days of life when they are most vulnerable to natural predators, then counted and released into the river.
Costa fears that the environmental authorities will repeat the error of correcting one factor in high mortality rates, flooding, only to create another, the excessive heat in the nests, which additionally leads to the birth of fewer males.
In this context, global warming remains a serious threat for the future.
In the Brazilian Amazon there are at least a hundred other nesting grounds similar to Tabuleiro do Embaubal, although they are not as heavily used, noted Pezzuti. And the turtles migrate a lot, he said.
Pezzuti strives to downplay the alarm over the risks of extinction, which are used to justify a law that prohibits hunting the turtles and that he considers irrational.
A ban on capturing the turtles and gathering their eggs is extremely difficult to enforce, since it goes against the grain of deep-rooted traditions in the communities living along the river. It also makes it hard to promote community participation in the management and conservation of the species when people are asked to give up a source of food with nothing offered in return, and under the threat of punishment, he argued.
Moreover, there are no restrictions on capturing certain species of fish that are almost extinct, he added.
Podocnemis expansa, also known as the Giant South American River Turtle, is currently listed under “least concern” on the International Union for Conservation of Nature (IUCN) endangered species list.
Around three decades ago, however, a steep decline in their population raised fears over their fate. As a result, in 1979, the Brazilian government created the Amazon Turtle Project, aimed at the recovery of reproductive rates and a decrease in the risk of extinction.
For almost three centuries, the meat of these turtles was one of the main sources of protein for the population of the Amazon region. Their fat was also used to preserve other foods as well as for medicinal and other purposes. This earned them the nickname of “the cattle of the Amazon”.
Turtle eggs are mentioned even more frequently in historical records. As well as a source of food, they were also the source of oil that was used as fuel for lighting in Amazon villages and exported to cities across Brazil and abroad.
It is estimated that between 12 million and 48 million eggs were harvested annually between 1700 and 1860, after which these figures declined, according to documentary research conducted by Pezzuti and his colleague George Rebelo, from the National Institute for Amazon Research.
Certain characteristics of Amazon turtles make them more vulnerable than other species to environmental changes and human predation. They can come to weigh more than 60 kilos and can lay more than 100 eggs in a single nest. Adult females gather in massive numbers on the beaches preferred for laying eggs.
Because of their rigid habits they are “more sensitive to changes, since they depend on specific environments,” said Daniely Félix-Silva, a biologist who has conducted research on different species of chelonians in various parts of the Amazon.
For example, she explained, they do not have the same flexibility as the tracajá or yellow-spotted river turtle (Podocnemis unifilis) to adapt to different habitats or change their feeding and reproductive habits.
This “advantage” of tracajás is reflected in their abundance throughout the Brazilian Amazon region, although they are second only to the Amazon turtle among the species most frequently hunted illegally, despite their small size: they weigh only eight kilos at most. Because they also lay their eggs in the midst of vegetation, and not only on open beaches, their eggs are better able to withstand high temperatures.
Amazon turtles were victims of the extractive economy that led to the occupation of the Amazon region, spurred by activities such as rubber tapping. Since the 1960s, the establishment of large industrial complexes and the subsidized expansion of the agricultural frontier have sped up the “human invasion”.
This process led to the growth of the market for the consumption and illegal trade of turtle meat and eggs, but also to an increased supply of beef and chicken, which partly eased the pressure on wild animals.
The new economic cycle in the Amazon has further exacerbated environmental threats, such as deforestation, caused primarily by cattle ranching, monoculture plantations that involve the intensive use of toxic agrochemicals, and large-scale mining.
Turtles are highly vulnerable to interventions in the aquatic environment, such as the hydroelectric dams that are a priority in the government’s energy plans. Dams will be built at numerous points along some of the region’s rivers for the operation of large and small hydropower plants.
The regular cycle of high water and low water periods in the rivers of the Amazon basin is vital to the turtles, which feed on fruits and other vegetation in the flooded forests during the rainy “winter” season, building up reserves for the drier “summer” season, which is also the season for reproduction, explained Pezzuti.
The turtles can also suffer from changes in the sand banks where they lay their eggs. Dams and reservoirs lead to the flooding of river beaches and can retain or modify the sediments carried by the rivers, which in turn will lead to alterations in the sand banks.
In the case of the Xingú River, the Belo Monte hydroelectric dam project, on which construction is now beginning, will reduce the water level during high water periods along the 100 km of the Volta Grande section, through the diversion of part of its flow. Along this stretch, the tracajás that are the most abundant species in the area will suffer the worst effects.
But in Tucuruí, also in the eastern Amazon, it was the tracajás that most successfully withstood the environmental shock of the construction of a hydroelectric plant in 1984, and today there are large numbers of them living in the plant’s enormous reservoir, said Félix-Silva.
*The writer is an IPS correspondent. This story was originally published by Latin American newspapers that are part of the Tierramérica network. Tierramérica is a specialised news service produced by IPS with the backing of the United Nations Development Programme, United Nations Environment Programme and the World Bank.
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