Leatherback turtles are making exhausting journeys, in some cases nearly twice as long as usual, from nesting to feeding grounds, because of rising ocean temperatures and changing sea currents.
After nesting, turtles must move to cooler waters to feed, but higher temperatures mean some are having to swim further to reach suitable areas, according to research from Greenpeace and the French Institut Pluridisciplinaire Hubert Curien, part of the Centre National de la Recherche Scientifique.
The researchers tagged 10 nesting female leatherback turtles last year on the Yalimapo and Remire-Montjoly beaches of French Guiana, and then tracked their migration through the north Atlantic. Some of the turtles were found to have swum as far as Nova Scotia in north-east Canada and to France to find new feeding grounds for the jellyfish which form their main diet.
Though small in scale, the research provides an insight into how some marine species are being forced to adapt to the warming oceans. This week scientists warned that ocean temperatures had reached record levels with the last five years, which were the five hottest on record.
Warming oceans pose clear dangers to human life as they lead to more intense storms and rising sea levels, but the impact of the increasing frequency of heatwaves at sea on marine species is much less studied. There is evidence that some species, including commercially important fish such as cod, are migrating towards the poles in search of cooler waters, but more research is needed for a fuller picture.
In another stark example of the dangers to marine life from human actions, one turtle followed was found dead on a beach in Suriname only 120km (74 miles) from the starting point, drowned after having become enmeshed in a discarded fishing net.
Estimates say more than half of all sea turtles have ingested plastic. The animals also face threats from overfishing, though they are mainly bycatch rather than targets.
The beaches of French Guiana were once abundant turtle nesting grounds, but now the eggs laid there are only a small fraction of those laid 30 years ago.
Last year, the complete absence of leatherback turtles from a beach in a nature reserve in Nicaragua also raised alarm.
“Sea turtles survived the extinction of the dinosaurs, but they might not survive us,” said Will McCallum, a campaigner at Greenpeace. “Human activity has put such severe pressure on sea turtle populations around the world that six out of the seven species are threatened with extinction. Without urgent action the situation will only get worse.”
