These wolves in Alaska ate all the deer. Then, they did something unexpected

Wolves on an Alaskan island are showing a remarkable adaptation.

Pleasant Island in Alaska is not exactly befitting of its name. The frigid, 20-square-mile island is uninhabited by humans, but it hosts a remarkably large and rich ecosystem that features deer, otters, red squirrels, and even brown bears. But in 2013, the island got a new addition: wolves.

When wolves colonized the island in 2013, it set up a natural experiment.

“This provided a great opportunity to study predator-prey dynamics of wolves and deer,” says Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game. “We were interested in seeing how the newly colonizing wolf population would impact the deer population and predicted that the wolves might eat all the deer, and then leave the island as it is only separated from the mainland by 1.5 km.”

The first part of the prediction came true. The deer population of around 120-200 deer plummeted. The island’s deer had already been hit hard by an exceptionally severe winter in 2006–2007, but researchers concluded that sustained wolf predation after 2013 was ultimately responsible for their disappearance.

But instead of moving to greener pastures, the wolves remained on an island and shifted their diet to unexpected prey: sea otters.

A marine predator becomes prey

Sea otters are themselves a top predator in the near-shore ecosystem, while wolves are an apex predator in the terrestrial area. — so it’s pretty surprising that you end up with a dynamic where one eats the other, says Taal Levi, an associate professor at Oregon State. “You have top predators feeding on a top predator,” Levi says.

Gretchen, Levi, and colleagues were studying wolf diets throughout southeast Alaska. The work also has an important conservation-management dimension. Alexander Archipelago wolves have been petitioned for federal protection several times, but in August 2023 the U.S. Fish and Wildlife Service concluded that listing the subspecies under the Endangered Species Act was not warranted.

They tracked some of the wolves with GPS collars and analyzed their scat. They found that in 2015, deer were the primary food of wolves, representing 75% of their diet. By 2017, wolves transitioned to eating primarily sea otters (57% of their diet), while deer only made up 7% of their diet. The pattern held through to 2020, when the study ended.

×

Get smarter every day...

Stay ahead with ZME Science and subscribe.

Daily Newsletter
The science you need to know, every weekday.

Weekly Newsletter
A week in science, all in one place. Sends every Sunday.
No spam, ever. Unsubscribe anytime. Review our Privacy Policy.

Thank you! One more thing...

Please check your inbox and confirm your subscription.

Otters themselves have had a rough history in the area. During the 19th and 20th centuries, sea otters in the region were hunted by fur traders and basically wiped out from the region. Local wolves were not hunted to extinction, unlike wolves in other parts of the US. But it was only in recent decades, thanks to the legal protection granted to sea otters, that the two populations overlapped.

But researchers weren’t expecting wolves, a terrestrial species, to become so proficient at eating sea otters — which, as the name implies, spend most of their time at sea.

“They are both scavenging otters and hunting them when the sea otters haul on land. Sea otters are very unlikely to be vulnerable to wolves in the ocean,” notes Levi.

Wolves were often seen patrolling the shoreline of Pleasant Island and investigating rocky outcrops. The GPS data confirmed that they spent a lot of time in the intertidal zone as if looking for something — and indeed they were: they were looking for otters to ambush.

RelatedPosts

Measles Doesn’t Just Make You Sick. It Resets Your Immune System
Inside the World’s Oldest Medical Text Where Science and Sorcery Were One
China covered all its new energy demand with renewables in 2015 — and there was still plenty left to spare
Roald Dahl Lost His Daughter to Measles. His Heartbreaking Letter on Vaccination Is Very Relevant Today

Sea otters haul out on rocks to conserve energy, says Roffler. But this makes them more vulnerable to predation as they are slow and awkward on land — and wolves are quick to take their chance. “We have collected evidence of wolves killing sea otters by ambush when they haul out on land or are in shallow water,” Gretchen adds.

This new twist to the ecosystem makes for a very interesting case study, Gretchen continues.

“Previously there have been investigations into the effects of marine predators on sea otter populations, but until now very little attention has been paid to the impact of terrestrial predators on sea otters, or how sea otters may be an abundant marine prey to terrestrial predators. This interaction was unexpected, but has had profound effects, at least on Pleasant Island.”

For now, it’s not clear how the otters are adapting to this (or if they are adapting at all). The biggest effect might be a behavioral change that forces them to spend more time at sea, even when it would be beneficial to them to conserve energy on land — the effects of this could be stressful in the long term, but this is something that warrants future research, Levi says.

But overall, the researchers don’t expect that wolves will have a big effect on the sea otter population. The more important ecosystem implication is that wolf population dynamics can be decoupled from the large mammals that make up their typical prey.

“This allows wolves to remain abundant even as they cause large herbivore populations to decline. That is, sea otters may allow wolves to maintain large herbivores at lower densities, which has implications for vegetation and the animals that depend on it (bees, birds, bears for floral and berry resources, for example), across a huge coastline that will be eventually occupied by sea otters as their recovery continues,” Levi adds.

This surprising finding of wolf diets definitely warrants more studies to better understand the interactions in this ecosystem — and Levi says they’re working exactly on that.

“We are now increasingly following up on the wolf-sea otter story with additional field studies, including one by PhD student Ellen Dymit, comparing mainland study areas with and without sea otters along the colonizing front of sea otter population expansion.”

Turns out, the behavior isn’t even limited to Pleasant Island. Researchers have now documented wolves eating sea otters at several sites along Alaska’s coast. Near Gustavus, a nine-wolf pack killed 31 sea otters during eight month-long study periods between 2019 and 2024 — including 26 in just one month in 2022 — even though moose were still available.

The same pattern showed up elsewhere: wolves ate more sea otters in places where otters were abundant, including Glacier Bay and coastal Katmai, and very few where otters were scarce, such as Lake Clark. That suggests sea otters may be becoming a regular food source for coastal wolves, rather than an unusual fallback on one island. These broader results are still preliminary and have not yet been published in a peer-reviewed study.

A toxic trade-off

But there may be a cost to relying so heavily on marine prey: contaminant exposure.. A 2025 study reports that switching to marine prey leads to unprecedented mercury concentrations. The otter-eating wolves on Pleasant Island pack had mercury concentrations nearly 8 times as high as reported in Arctic wolf hair.

Methylmercury is produced in aquatic ecosystems, primarily by microbes in sediments and water bodies. The aquatic food chain magnifies mercury concentrations, meaning predators at the top, like sea otters, accumulate high levels of it. When wolves consume marine mammals such as sea otters, they absorb the mercury that has built up along the food chain.

Pleasant Island wolves had an average total-mercury concentration of 17.59 ppm in their livers. That was seven times the comparison level in other coastal Alaska wolves and 278 times that in Interior Alaska wolves; the authors also reported that Pleasant Island wolf hair contained nearly eight times as much mercury as had been reported in Arctic wolf hair.

So while adapting to the otters has offered wolves a lifeline, it also raises unexpected problems the wolves now have to deal with.

“The ability of wolves to switch their diets from terrestrial prey to marine prey, just shows how resilient they can be. But we now know that their reliance on marine prey can also lead to the risk of toxicity,” Roffler said.

“We can assume that as sea otters continue to recolonize parts of their former range and grow in numbers, that wolves and other terrestrial predators will start using them as prey.”

The study was published in the Proceedings of the National Academy of Sciences.

A separate peer-reviewed study published later in 2025 added another piece to the contaminant story. Researchers compared stable isotopes and trace elements in wolf hair from Pleasant Island, Gustavus, Juneau and Douglas Island. Populations making greater use of marine food showed distinctive isotope signatures and elevated concentrations of several trace elements. The result reinforces the link between marine foraging and contaminant exposure, although it likewise does not establish a population-level health effect.

This article originally appeared in January 2023 and was re-edited to include additional information and the mercury contamination study.

It was updated again in September 2026 with longer-term Pleasant Island observations, evidence from other coastal Alaska wolf packs, additional contaminant research and corrected Endangered Species Act context.