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Gretchen Roffler recalls looking down the boardwalk in Alaska’s Katmai National Park and Preserve when three wolves came into view and then disappeared behind some rocks. When the predators returned, all three held the same limp sea otter between their jaws. Together the wolves tore the otter to pieces. “It was like a tug of war,” says Roffler, a wildlife biologist with the Alaska Department of Fish and Game.
Roffler and her colleagues paid close attention to this; They had to document the event in June 2021 in detail. After all, according to Roffler, this is “one of the first observations that wolves kill sea otters”.
Sea otters were extirpated in Alaska in 1830, but their reintroduction in recent decades has been very successful. The resurgence of marine mammals means that in Alaska, sea otters and wolves inhabit the same environments for the first time in the modern scientific record. This coincidence of historic predator and prey has important ramifications — particularly for the region’s deer.
Scientists tend to believe that the size of a wolf population is determined by the availability of ungulates such as deer and elk. But on the Alaskan coast, scientists like Roffler are increasingly documenting cases of coastal wolves eating marine mammals. Indeed, on Pleasant Island, near Glacier Bay National Park and Preserve, Roffler and her colleagues analyzed wolf droppings and showed that local wolves have almost entirely switched their diet from deer to sea otters.
Rather than the wolves leaving the deer alone, Roffler says this new nutrient source has kept the wolf population so healthy that it has wiped out the region’s deer.
By attaching GPS collars to wolves on the Alaskan coast to see where they traveled and hunting, and analyzing wolf droppings and hair samples collected between 2015 and 2021, Roffler and her colleagues have the changes that have taken place are tracked.
Her research shows that sea otters first recolonized the area around Pleasant Island in the early 2000s, while wolves landed on the island in 2013. The deer population collapsed in 2015, and in 2016 the wolves mainly ate sea otters.
While wolves occasionally eating sea otters may not be unexpected, Roffler says it’s surprising that one pack was able to completely transform its diet and continue to maintain a healthy population on a small island devoid of deer. “We assumed that the wolves would eat a lot of deer and possibly decimate the population, and then the wolves would either die or leave,” she says.
The scientists are curious how common this type of prey switching is in other areas along the coast where sea otters have also recovered. They’re also interested in how wolves learn to hunt sea otters — and whether this behavior might become common among wolf packs.
So far, Roffler says, it’s too early to predict whether wolf populations fattening up on sea otters could mean problems for deer elsewhere, as is happening on Pleasant Island, but they suspect it will only do so on other relatively isolated ones small islands where wolves live would have a similar impact and would have easy access to sea otters.
Chris Darimont, a conservation biologist with the Raincoast Conservation Foundation who wasn’t involved in the study, says this type of work not only helps us understand how the ecosystem is changing, but also provides a glimpse of history — before the sea otters were exterminated by hunters. “In a way, we’re looking into the past by studying something that’s just recovering.”