The Antarctic fur seal population has grown and shrunk over the past 50,000 years as the climate has changed, a genetic analysis suggests 鈥� and the finding could help us predict where the marine predators will choose to live as the climate continues to warm.
Today, Antarctic fur seals (Arctocephalus gazella) appear loyal to the same islands, . During the annual breeding season, some return to within a few metres of the same spot on the rocky shore year after year.
at the British Antarctic Survey examined the fur seals鈥� history while at the聽University of Agder in Norway. With her colleagues, she sequenced DNA samples from four existing populations on South Georgia, Bouvet Island and the South Shetlands in the south Atlantic and on the Kerguelen Islands in the southern Indian Ocean. They paid special attention to DNA variation, as larger populations carry more genetic diversity.
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They then used software that analyses genetic data and estimates how an animal species鈥� population size has changed through time, and when two or more distinct populations today were last part of a single larger population.
They found that despite seals鈥� tendency not to move to new areas, populations have grown and shrunk over longer periods of time. For example, before the last glacial maximum, which occurred 26,000 to 13,300 years ago, the seals seemed to exist as one global genetic population in which any two animals could interbreed. But then, seal numbers shrank and the population in the southern Indian Ocean became genetically isolated and distinct from the others.
鈥淵ou see that the populations decline when the ice increases, then you see them moving out to new colonies as the ice decreases again,鈥� says Cleary.
Cleary says the seals are likely to need ice-free areas to raise pups 鈥� populations today are all in such areas. During the last glacial maximum, populations probably shrank due to a shortage of ice-free land. 鈥淧resumably they are losing habitat or losing access to prey,鈥� says Cleary.
At the same time, the fur seals feed on species of fish and krill that typically depend on sea ice for their survival, so the marine mammals can鈥檛 stray too far from frozen water.
Cleary says that tracking the way Antarctic fur seal populations have moved around in the past could help conservationists predict where they might move under future climate change scenarios, and enable them to set aside protected areas.
Ecology and Evolution
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