Sea otters are innovative, charming and apex predators in their ecosystem—until now. On Pleasant Island, an uninhabited 20-square-mile island off Alaska, deer populations have likely declined due to wolf predation. With the decrease in available prey, it appears that sea otters are now on the wolves’ menu.
According to a a new study from Oregon State University and the Alaska Department of Fish and Game, this may be the first time that sea otters have become a predominant food source for terrestrial predators such as wolves.
(Credit: Laura Hedien/Shutterstock)
Researchers analyzed wolf feces and tracked them with GPS collars, finding that in 2015 their diet was 75 percent deer and only 25 percent sea otters. However, by 2017, sea otters made up 57 percent of the wolves’ diet, while deer made up only 7 percent. This remained the same until 2020, when the study ended.
“Sea otters are that famous predator in the coastal ecosystem, and wolves are one of the most famous apex predators in terrestrial systems,” says Taal LevyAssociate Professor at Oregon State, in a press release. “So it’s quite surprising that sea otters have become the most important food resource for wolves. You have top predators feeding on top predator.”
A history of wolves and sea otters
While this may be the first recorded case of sea otters falling prey to land animals, it may have happened in the past. According to the study, wolves and sea otters may have once lived together on Pleasant Island before fur traders decimated sea otters in the area in the 19th and 20th centuries.
The wolf population in the area remains relatively healthy compared to wolves in lower 48 states. According to the study, this pack of wolves arrived on the island in 2013 after swimming over from the mainland.
After passing the Marine Mammal Protection Act in 1972rehabilitation efforts have helped establish a healthy sea otter population in Alaska, allowing wolves and sea otters to interact in the same environment.
Researchers analyzed the Pleasant Island wolf pack and adjacent shoreline from 2015 to 2021. Wildlife biologists such as Gretchen Roffler of the Alaska Department of Fish and Game collected nearly 700 samples of wolf feces, much of which was coastlines. They analyzed the samples in Levy’s lab using molecular tools such as genotyping and DNA Metabarcoding to identify certain wolves and break down their diet.
(Credit: Shawn Neilson) Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, collects wolf droppings in Alaska’s Gustavus Forelands.
Roffler also tagged four Pleasant Island wolves and nine mainland wolves with GPS collars to track if mainland wolves come to the island to hunt. A 2014 study published in BMC Ecology found that gray wolves (Canis lupus) can swim up to 13 km (about 8 miles) between land masses. However, evidence from GPS collars and droppings proved that wolves from the mainland did not come to the island to hunt. This shows that the island’s wolf population is stable.
The GPS collars also helped determine where and when wolves killed sea otters—mostly when the otters were in shallow water or resting on rocks at low tide. According to the press release, Roffler and her team analyzed GPS collars during three 30-day field seasons since 2021, finding evidence of 28 sea otters killed by wolves.
“The thing that really surprised me is that sea otters have become the main prey of wolves on this island,” Roffler said in a press release. “Occasionally eating a sea otter that’s washed up on the beach because it’s died, that’s not unusual. But the fact that wolves eat so many of them shows that this has become a widespread pattern of behavior in this pack and something they learned to do very quickly. According to Roffler, wolves actively hunt and kill sea otters – they don’t just look for the old or die.
(Credit: Bjorn Dihle) A wolf traveling and foraging in the intertidal zone of Pleasant Island, Alaska.
With the island’s deer population depleted, Levy thought the wolves would either die out or leave the island. Instead, according to Levy, the wolf pack appears to have grown to a density not seen before in wolf populations. He believes that wolves, which consume sea otters, have a central role in this.
Currently, Ellen Dimmitt, a PhD student in Levy’s lab, and Roffler, along with their teams, are studying interactions between wolves and sea otters in Katmai National Park and Reserve, about 700 miles from Pleasant Island. Early research suggests that wolves also eat sea otters there.
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