Climate change threatens population of Earth’s largest sea turtle

By: Jessica Shugart, special to mongabay.com
November 19, 2012



A female leatherback surveys the ocean at Playa Grande, Costa Rica. While her hatchlings will be affected by rising beach temperatures, she faces threats at sea. Photo by: The Leatherback Trust.
A female leatherback surveys the ocean at Playa Grande, Costa Rica. While her hatchlings will be affected by rising beach temperatures, she faces threats at sea. Photo by: The Leatherback Trust.

A drier, hotter climate in Central America could wipe out the population of leatherback sea turtles from the eastern Pacific Ocean by the year 2100, according to a grim projection published on July 1 in Nature Climate Change. Already critically endangered from fisheries by-catch and historic egg poaching, leatherbacks can hardly accommodate another human-related threat. Yet scientists still hold out hope for interventions that could save the turtles.

Leatherbacks (Dermochelys coriacea)—the largest turtles on Earth—spend most of their lives at sea, only hauling their rubbery bodies onto the beach every three to four years to lay eggs in deep holes they dig in the sand. This is no small feat, as the turtles can weigh up to a ton. The number of hatchlings that emerge from each clutch depends greatly upon the temperature and moisture of the sand. Fewer baby turtles survive in hot, dry conditions, whereas cooler, wetter conditions provide more fertile ground. The most recent projections from the Intergovernmental Panel on Climate Change (IPCC) concur that Central America will become hotter and drier during the 21st century, a scenario that does not bode well for the region’s leatherbacks.

Scientists from Princeton University, Drexel University, Indiana-Purdue University, and the National Oceanic and Atmospheric Administration (NOAA) assessed how these trends might affect a well-studied population of leatherbacks at Playa Grande beach in northwestern Costa Rica. One of four nesting sites in the eastern Pacific, the beach is protected within the boundaries of Las Baulas National Park. The team merged seven leading climate models with a leatherback population model based on data gathered at the nesting beach for more than 20 years.

Cooling nests to counter climate change. Researchers at Playa Grande hope to counter the effects of climate change by watering and shading leatherback nests. Photo by: The Leatherback Trust.
Cooling nests to counter climate change. Researchers at Playa Grande hope to counter the effects of climate change by watering and shading leatherback nests. Photo by: The Leatherback Trust.
They found that by the year 2100, rising beach temperatures could cut the leatherback population at Playa Grande by three-quarters. This is a daunting projection, as leatherback numbers there already have dropped from nearly 1,500 nesting females in 1991 to about 40 in 2011 due to egg poaching and fisheries by-catch. Egg poaching was put to a halt in 1990 with the founding of Las Baulas National Park, but fisheries remain an imminent threat.

"My main concern is not climate change right now; it’s what’s happening in the ocean," said first author and NOAA fisheries biologist Vincent Saba in an interview with mongabay.com. "Lots of countries have laws, but the problem comes with enforcing them," he said, noting that enforcement costs are too high for many poor countries. Grassroots organizations like Pro Delphinus in Peru are working closely with fishermen to promote changes in fisheries practices that will save turtles.

To address the threat posed by climate change, coauthor Pilar Santidrian Tomillo, a field ecologist from Drexel University, is experimenting with shading and watering leatherback nests at Playa Grande to cool them down. "We're doing an experiment to see how the effects of shading and watering would change temperature and humidity in the sand," explained Tomillo in an interview from Costa Rica. If the work succeeds, it could help the turtle population cope with rising beach temperatures.

George Meehl, a climate scientist at the U.S. National Center for Atmospheric Research who was not involved in the study, told mongabay.com that the research is a good example of climate data being put into action. "You’re taking climate change information and trying to actually do something with it," Meehl said. "This is a sequence we like to see."



Leathery hatchlings emerge from a sandy nest. Rising beach temperatures threaten hatchling survival in the sand. Photo by: The Leatherback Trust.
Leathery hatchlings emerge from a sandy nest. Rising beach temperatures threaten hatchling survival in the sand. Photo by: The Leatherback Trust.






Jessica Shugart is a graduate student in the Science Communication Program at the University of California, Santa Cruz.



CITATION: Saba, V.S., Stock, C.A., Spotila, J.R., Paladino, F.P., Santidrián-Tomillo, P. 2012. Projected response of an endangered marine turtle population to climate change. Nature Climate Change, 2, 814-820. DOI: 10.1038/nclimate1582













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CITATION:
By: Jessica Shugart, special to mongabay.com (November 19, 2012).

Climate change threatens population of Earth’s largest sea turtle.

http://news.mongabay.com/2012/1119-ucsc-shugart-leatherbacks.html