How a Finnish Lake’s Peculiar Shape Has Been a Boon to Endangered Seals

A Saimaa ringed seal.

A Saimaa ringed seal. AKI MYKKÄNEN VIA FLICKR

The Saimaa ringed seal of southern Finland is among the most endangered seals on Earth. But despite its small numbers, this population boasts a surprising degree of genetic diversity, thanks to the labyrinthine shape of its home along Lake Saimaa, a new study finds.

Southern Finland was once trapped beneath a massive ice sheet, which melted around 10,000 years ago. As the ice retreated, the land beneath rebounded. The ringed seals in that region, which had once lived among ice and sea, soon found themselves landlocked, confined to the newly formed Lake Saimaa and its surroundings. These seals, the Saimaa ringed seals, are today one of the world’s only freshwater seals.

Once numbering in the thousands, the population of Saimaa ringed seals dropped to less than 200 in the 1980s. Through conservation efforts, the seals have bounced back slightly, totaling around 400 today.

Finland's Lake Saimaa.

Finland's Lake Saimaa. GOOGLE MAPS

Scientists had feared that this small population would bear little genetic diversity, making it unlikely that at least some of the seals could adapt to rising temperatures. To investigate the matter, researchers studied the genomes of 145 seals, working from samples preserved in a tissue bank. Their study revealed a surprising degree of genetic diversity.

Living on the intricately shaped Lake Saimaa — with its many coves, straits, and islands — the Saimaa ringed seals had divided into three distinct groups. “This means that the population as a whole has retained much of its original genetic variation,” Ari Löytynoja, a researcher the University of Helsinki and lead author of the study, said in a statement. The findings were published in the journal Current Biology.

“Despite recent growth, the population remains highly vulnerable, and especially, warmer winters and shorter periods of ice and snow cover, crucial for the formation of birth lairs, pose a serious risk to the reproduction and early life of the pups,” the authors wrote. However, the high degree of genetic diversity in the population “gives hope for its future revival.”

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