Miami - One of the world's last surviving groups of woolly mammoths likely died of thirst as the salty seas rose around these iconic Ice Age creatures 5 600 years ago, researchers say.The study also warns that a similar scenario could imperil island people and animals in the coming years as the climate warms and sea level rises, making fresh water harder to access.The research took place on St Paul Island, a remote area of Alaska that was once part of the Bering Land Bridge that joined the Americas to Asia.The island became isolated between 14 700 and 13 500 years ago due to sea level rise during the last deglaciation, and the land area shrank significantly. Its current size is 110km².No humans were known to live in the area at the time, said the report in the August 1 edition of the Proceedings of the National Academy of Sciences, a peer-reviewed US journal.To find out what happened to the woolly mammoths, researchers collected a sediment core from one of the few freshwater lake beds on St Paul Island.By analysing the core for signs of fungi that grow on animal dung and using radiocarbon dating, they were able to tell when mammoths disappeared. The sediment DNA "showed the presence of mammoth DNA until 5 650 years ago, plus or minus 80 years", said the study, which described the finding as the most precise dating yet of a major extinction event."After that time, there is no mammoth DNA and so no mammoths on the island."So what happened?Researchers think that these large beasts, similar to modern day elephants, somehow persisted for about 5 000 years after mainland populations disappeared - likely from a combination of hunting and climate change - but were done in by the continual shortage of fresh water.Much like elephants, which drink about 200 litres per day, woolly mammoths would have struggled during what researchers found to be an extended period of dry conditions and declining water quality.Over the course of 2 000 years, the area grew progressively smaller and drier.Lakes became shallower, and water holes more crowded.When scientists analysed mammoth bones and teeth as well as the remains of other aquatic creatures, they found signs of progressively drier conditions leading up to the extinction event. "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."The Alaskan mammoths were outlived only by a population of mammoths on Wrangel Island, off the coast of Siberia, which survived until about 4 700 years ago."Freshwater availability may be an underappreciated driver of island extinction," said the report in PNAS."This study reinforces 21st-century concerns about the vulnerability of island populations, including humans, to future warming, freshwater availability, and sea level rise."