On a tiny, remote island in Southeast Alaska, scientists recently made a surprising discovery: Wolves are eating sea otters.
And not just one every so often. For this pack, it’s the wolves’ main source of food. The study is making waves in the scientific community.
Pleasant Island is located about a mile south of the mainland near the town of Gustavus. Historically, wolves would occasionally swim over but had never colonized the island until about a decade ago.
“This pack of wolves really defied all of our predictions,” said Gretchen Roffler, who has studied wolves in Southeast for eight years.
Roffler is the lead author of a study published in January in a journal of the National Academy of Sciences on the island’s wolves. This new pack killed all the black-tailed deer on the island — a favorite meal for Southeast wolves. They’re a territorial species and an established pack was back on the mainland preventing a return. Roffler and other scientists assumed they would die off from starvation.
“Instead, what we found was that the wolves stayed on the island, and they continued to reproduce annually,” Roffler said.
But how? The island is small, just over 20 square miles. What were the wolves eating?
Nearby residents in Gustavus noticed new wolf activity on the island where they would hunt deer and pick berries. Greg Streveler is one of them and his first thought was, “Uh-oh.”
Streveler is a retired ecologist with the National Park Service and has studied the area’s land and animals for over 50 years.
“The ‘Uh-oh’ was, you can see what’s coming,” he said. “Having the pack discover the place. And [then] there was two wolves instead of one. You could kind of read the tea leaves.”
Within a few years, Streveler and other residents saw the island’s deer disappear. So the scientists stepped in and began to gather data. In 2015, they counted three wolves. A year later there were 10. By the year 2017, there were 13 wolves.
“The wolf densities on this island at this time were some of the highest ever recorded,” Roffler said.
Roffler’s team collected scat and studied it in a lab to see what the wolves were eating. And it showed something surprising: sea otter.
“At first, I thought, well, this is maybe just a blip,” said Roffler. “Maybe this is just an occasional thing that wolves are able to do.”
They decided to collect wolf hair. While scat shows what wolves have eaten recently, hair gives scientists a longer-term look. And tests on the hair proved it wasn’t a blip. The wolves were eating lots of sea otters and had been for a while. Roffler said it underscores how adaptable wolves are.
“Something that we assume about wolves is that they really can’t live without ungulate prey,” she said. “They very quickly switched to a diet that primarily consists of sea otters. It really just took a couple of years for that to happen.”
Starting in 2020, Roffler’s team GPS-collared some of the wolves so they could study so-called “kill sites” where the wolves likely feasted for a while. They noticed the wolves were traveling around the circular island, along the tideline.
“When we look at all the wolf GPS location data, if we just splashed onto a map, it sort of looks like a doughnut,” Roffler said.
Sea otters might look cute — maybe you’ve seen photos of them floating on their backs and holding hands — but they aren’t small or defenseless. They have sharp teeth for cracking shellfish to eat and males can grow to 100 pounds. Based on the kill sites, the scientists believe the wolves are targeting otters at low tide when they’re on land or in the shallows and they’re more vulnerable.
Roffler hasn’t witnessed the pack hunt and is hesitant to speculate about it. But Streveler has a theory.
“The wolves are not dealing with a healthy group of otters,” he said. “So I don’t think it’s a big deal for wolves to find some.”
He says the otters in the area might be weak and are hauling out on land more than normal. Sea otters were introduced to the region in the 1960s after being hunted to near extinction. Streveler said it’s possible that there are more otters in the area than the habitat can support.
“Before, nobody here ever saw an otter haul out. Ever,” Streveler said. “And so, to find a naive group of very easy-to-catch, very, very delicious critters. Oh, my God, you know, it’s like discovering the Garden of Eden.”
Scientists don’t know how this unusual diet might affect wolves in the long term. Roffler said that’s their next big question – how contaminants accumulate in the food web.
“Wolves are apex predators, and sea otters are apex nearshore predators,” she said. “So any sort of contaminants in the environment, if they’re being consumed by sea otters, or by sea otter prey, they would bioaccumulate in wolves. So this is something we’re trying to study more.”
They also don’t know how long the food source will be around. But Streveler thinks it’s temporary.
“The sea otter-wolf thing is probably a flash in the pan,” he said. “It’s not likely there’s going to be both a lot of sea otters and a lot of weak sea otters available very long. It’s a very, very brief, I think, opportunistic window.”
Besides the future of this wolf pack, the implications of the study are turning some corners of the science world upside down. In a commentary, Princeton University Ecology professor Robert Pringle says the conclusions “challenge dogma.” New ways of gathering data are debunking “grand theoretical generalizations.” He writes, “One thing it needs now is a rejuvenated commitment to figuring out what is what in the real world.”
