World’s turtles getting such a hard time
Writing in the journal BioScience, Jeffrey Lovich of the US Geological Survey claims that 61% of the world’s turtle species are threatened with extinction. Some have already disappeared. These reptiles, he and his co-authors conclude, are now among the world’s most threatened vertebrates.
That turtles should be in trouble is particularly poignant, considering the enormous difficulties they overcame in the past. These armoured-personnel-carriers, carrying their homes on their backs, first appeared during the Age of Reptiles, around 220 million years ago, when dinosaurs roamed the land. Their slow laid-back lifestyle should have been a recipe for disaster but, ironically, it protected the turtles during the global catastrophe of 66 million years ago. While three quarters of the world’s plant and animal species perished in a ‘nuclear winter’ following the giant meteorite impact, the turtles, able to go without food for long periods, retreated into their shells and bided their time until the danger passed.
According to Lovich and his co-authors, turtles became very numerous after the demise of the dinosaurs. Ever since, they have played a vital role in soil and sea-bottom regeneration, significantly altering marine and land eco-systems. Their numbers began to fall when humans arrived on the scene, but whether our ancestors were a major factor in turtle decline back then is an open question. Some 356 species survive today.
The causes of their current troubles, however, aren’t hard to find. Vital habitats are being destroyed, turtles are exploited for food and the pet trade, and global warming is creating relentless pressures. The decline affects many other organisms. Some plants, for example, need these vegetarians to disperse their seeds, which pass undamaged through the turtle’s digestive tract.
Are there Irish turtles? It’s often claimed that the viviparous lizard is Ireland’s only reptile, but this isn’t strictly true. According to the National Biodiversity Data Centre, five sea turtle species visit our waters.
Three years ago, Coastwatch volunteer Aoife Flynn found a Kemp’s ridley turtle on Rossnowlagh beach in County Donegal. Deemed to be ‘critically endangered’ by the International Union for Conservation of Nature (IUCN), the tiny Kemp’s ridleys lay their eggs in the sand of just one beach in Mexico. Only about 1,000 breeding females remain. Over 40 ripleys have been found in Irish waters since recording began in the late 18th Century.
The hawksbill is also on the ‘critical’ list, while the green turtle is classified as ‘endangered’. A loggerhead, driven to our shores by Storm Eva, was rehabilitated by Galway Atlantica. Aer Lingus flew it to Gran Canaria. Like the ripleys hawksbills and greens, it’s an accidental ‘vagrant’ here. Another visitor, however, deserves full citizenship status. ‘Leatherback sea turtles are part of our natural heritage, and have probably been visiting Irish waters for millennia’ wrote UCC’s Dr Tom Doyle. The leatherback is one of the world’s largest reptiles; only the salt water crocodile is heavier. One stranded in Wales in 1989 weighted 916kg. The species, which diverged from the other turtles over 100 million years ago, has a tractor-tyre rubbery shell rather than a bony one. It’s also able to generate its own body heat, a great advantage to a creature venturing into colder waters. The main Atlantic nesting locations are on the north coast of South America.
Plastic objects in the sea are a major threat. Mistaking them for jellyfish, the leatherbacks swallow them. Their digestive tracts become blocked and they starve to death.
Jeffrey Lovich et al. Where have all the turtles gone, and why does it matter. BioScience 2018.
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