Alaska’s northern fur seal population has been dwindling for decades. But the marine mammals are showing up in growing numbers at an unlikely location—a tiny island at the tip of an active undersea volcano. Scientists hope these rock-loving seals keep coming.
Geographically speaking, Bogoslof Island is a reasonable place for northern fur seals to hang out. God gave these critters thick-coats and large flippers to thrive in the cold, wet conditions. In fact, most of the world’s roughly 1.1 million of the species breed in the eastern Bering Sea. But why they chose explosive, half-square-mile Bogoslof over dozens of other uninhabited islands is a mystery.
“The surface is covered with these big, ballistic [flying] blocks, some as big as [33 feet long] that were exploded out of the vent,” says Chris Waythomas, a U.S. Geological Survey scientist. “It’s pretty wild.”
Vents on Bogoslof Island still spew mud, steam, and gases two years after the last eruption—a huge one that sent ash clouds into the path of jetliners passing over the Bering Sea.
Still, northern fur seal moms find the remote island’s rocky beaches perfect for giving birth and mothering pups. “The population growth of northern fur seals on Bogoslof has been extraordinary,” says Tom Gelatt, head of a group that studies the seals.
Seals are never far from volcanic action on Bogoslof. The center of the island features numerous fumaroles, openings through which hot gases emerge. Some roar “like jet engines” and spurt mud geysers several feet high, Waythomas says.
One reason for Bogoslof’s popularity may be the food supply. Seals dine on squid and deep-water fish right offshore. Bogoslof is also close to the seals’ winter feeding grounds, possibly allowing pups to reach the grounds more easily.
In 2015, biologists estimated about 28,000 pups on the island. The 2019 estimate will likely be more than 36,000 pups. “Barring other future catastrophic eruptions that could dramatically change the geography of the island,” Gelatt says, “there is plenty of room for a lot more seals on Bogoslof.”
(Northern fur seal adults and pups on a beach on Bogoslof Island, Alaska. Maggie Mooney-Seus/NOAA Fisheries via AP)