The Alaskan island of St Paul was on of the final outposts of the woolly mammoth 5,600 years ago. However, as its lakes shrunk, the giant species gradually vanished from existence.
The ultimate fate of woolly mammoths has been studied for years, with the likes of climate change, humankind and other predators all thought to have played a role.
However, a new study suggests that a safe population of the animals, living on an island in the Bering Sea, were finally undone by water – a reduction in fresh lakes causing their demise.
After studying layers of dated sediment from St Paul Island lakes, a gradual decline in water quality and volume left the last woolly mammoths doomed, with no way off the island after the sea swallowed up the Bering Sea land bridge.
“It paints a dire picture of the situation for these mammoths,” said Matthew Wooller, director of the Alaska Stable Isotope Facility at the University of Alaska Fairbanks and a co-author of the study.
“Freshwater resources look like the smoking gun for what pushed them into this untenable situation.”
Rising sea levels – the Bering Sea Bridge is almost inconceivable now – saw St Paul Island gradually shrink to its current size of just 110sq km, offering fewer drinking outlets for its megafauna.
Some woolly mammoths survived on the nearby Wrangel Island – far larger than St Paul Island – for another millennium. Mainland woolly mammoths had died off around 5,000 years earlier following bouts of temperature changes towards the end of the Pleistocene age. As their populations declined, humans turned up to hunt down the remaining mammoths.
“The abrupt warming of the climate caused massive changes to the environment that set the extinction events in motion, but the rise of humans applied the coup de grâce to a population that was already under stress,” said Prof Chris Turney from the University of New South Wales, author of a previous paper.
However, St Paul Island shows no evidence of humans for the subsequent 5,000 years, meaning it was water that played the role of killer.
A little over one year ago, permafrost-preserved mammoths allowed scientists to discover 14 specific genes that separate woolly mammoths from today’s elephants – Asian elephants are the closest relations.
Some scientists hope this brings the cloning of the species closer to reality.