Medical News
Life
17 May 2019
Sea otters (Enhydra lutris) are increasingly being bitten by great white sharksArco/Alamy
By Jake BuehlerDecades of conservation work have boosted sea otter populations in many parts of the North Pacific, but the animals are now being killed by great white sharks.
The sharks aren’t actually trying to eat the otters, preferring calorie-dense, blubbery prey like seals and sea lions. The bites are merely investigative, with sharks recoiling with a mouth of fur instead of a fatty meal. But such bites often cause mortal injuries to the otters, and they’re now happening more often off California’s beaches.
After seeing a growing trend in the number of dead, bitten sea otters being washed ashore, Jerry Moxley, at the Monterey Bay Aquarium, and his colleagues set out to investigate where and when these bites were happening.
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The team compiled data on the seasonal movements of sharks and their preferred prey, elephant seals, as well as data on strandings of bitten otters. They used this information to compare the timing of shark bites on prey as well as mistargeted species – otters and humans.
They found that sea otters were being bitten more frequently in the summer, around the time adult sharks come closer to shore before moving on to seal rookeries.
This is also when humans are most often mistakenly targeted. The researchers think the sharks, low on fat reserves after their migration from feeding grounds hundreds of kilometers out into the Pacific, are less discriminating towards any seal-shaped animals they encounter.
Moxley and his team also found that it was mostly intrepid young and male otters that fell victim to sharks.
“The males and younger otters are more pioneering—more likely to venture into new territory beyond the denser kelp cover in the otters’ core range,” says Moxley.
Because pioneering otters are more at risk of fatal shark encounters, this may make it harder for the species to re-establish itself in other areas.
Brent Hughes, of Sonoma State University, thinks otters may start seeking refuge from the sharks in protected estuaries. He has seen something similar happen in Alaska’s Aleutian Islands, where sea otters hide from orca predation in shallow bays.
Moxley says the findings could help guide otter reintroduction efforts. “By documenting when and where otters are most at risk of shark bites,” says Moxley, “we can adjust rehabilitation and release practices to support survival post-release.”
Journal reference: Ecology and Evolution, DOI: 10.1002/ece3.5209
More on these topics:
conservation
marine biology