A species of shark uncommon in northern waters may be the culprit behind unusual injuries — like bite marks and flipper amputations — appearing on seals and Steller sea lions in the Bering Strait, Chukchi Sea and Beaufort Sea, researchers say.
Some types of sharks have long been in the waters off western and northern Alaska, but those don't usually go after live mammals. Seals and sea lions now seem to be encountering "a typically uncommon predator in these waters," according to a blog post this week from Alaska Sea Grant, part of the University of Alaska Fairbanks.
Scientists and observers from Alaska Sea Grant, the North Slope Borough Department of Wildlife Management, Kawerak Inc. and Ocean Associates have been recording injuries to or attacks on those marine mammals using stranding and bycatch data, aerial surveys and hunter observations, the blog said. The data collection has been going on for several years.
"They have strong evidence to support it being shark predators," said Cindy Tribuzio, a fisheries research biologist in Juneau with the National Oceanic and Atmospheric Association. "They can't ID exactly what kind it is. It certainly doesn't fit the M.O. for the common species you'd run into up there. … It would not be impossible for something like a great white, but nobody's seen one."
Researchers believe rising ocean temperatures, reduced sea ice coverage and movements of fish and marine mammals related to those changes are "resulting in increased exposure of northern shark species" to prey like northern seals and sea lions, according to Alaska Sea Grant.
"With the warmer climates, it's certainly possible other species are showing up up there," Tribuzio said.
There is one record of a great white shark caught in the central Bering Sea, in 1979, according to Alaska Sea Grant, and it was found to have chunks of Steller sea lion in its stomach.
In some of the injuries researchers look at, the animals' bones have been sliced, Alaska Sea Grant said. People have also reported seals with amputated flippers.
"These are not the marks of a killer whale. Killer whales have pegged teeth," said Gay Sheffield, a marine advisory agent with Alaska Sea Grant in Nome, in the blog post. "The injury pattern would be different, and community members are noting these are novel injuries."
It's unclear whether more injuries on seals and sea lions are happening or whether people are observing them more, according to Alaska Sea Grant, and it's also unclear whether more sharks would have biological implications for those animals.
"Everything needs to be taken with a grain of salt," said Tribuzio. "And we want answers. … But finding the answer is really hard because there's so many things going on."
The researchers hope to eventually gather enough data to publish a study.