Wolves on Alaskan Island Shift to Hunting Sea Otters After Decimating Deer Population
Researchers say it's the first instance of a land-based predator adapting its diet to feed primarily on sea otters
Wolves are highly adaptable predators. A recent study by Oregon State University and Alaska Department of Fish and Game scientists illustrates the impressive extent of their adaptability. The researchers discovered evidence of wolves making sea otters their primary food source after killing off the local deer population. It’s not only the first time wolves have been documented feeding primarily on river otters but the first time any species of land-based predator was found doing so.
The study took place on Pleasant Island, which is adjacent to Glacier Bay. It’s a 20-square-mile island that is uninhabited by people. Researchers studied a wolf pack on the island between 2015 and 2021. During that time frame, they collected and analyzed 689 wolf scats from the island’s shoreline. They also used GPS collars to monitor several of the wolves. In 2015, deer made up 75 percent of the wolves’ diets. But the wolves caused the deer population to plummet and by 2017, sea otters began to comprise a majority of their diets. In 2017, deer only made up 7 percent of the wolves’ diets.
“Occasionally eating a sea otter that has washed up on the beach because it died is not unusual. But the fact that wolves are eating so many of them indicates it has become a widespread behavior pattern throughout this pack and something that they learned how to do very quickly,” said Alaska Department of Fish and Game biologist Gretchen Roffler. “From the work we are doing investigating kill sites, we are learning that wolves are actively killing the sea otters. So, they aren’t just scavenging sea otters that are dead or dying, they are stalking them and hunting them and killing them and dragging them up onto the land above the high tide line to consume them.”
The researchers say that such a shift in predation patterns could not have been possible without conservation efforts. The sea otter population in Alaska was decimated in the 1800s and 1900s due to commercial fur trapping. In recent decades, legal protections and reintroduction efforts have helped the species recover.
“Sea otters are this famous predator in the near-shore ecosystem and wolves are one of the most famous apex predators in terrestrial systems,” said Taal Levi, an associate professor at Oregon State. “It’s pretty surprising that sea otters have become the most important resource feeding wolves. You have top predators feeding on a top predator.”
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The researchers have now begun studying wolves and sea otters in the Katmai National Park & Preserve, which is 700 miles from Pleasant Island. Early research indicates that wolves are successfully hunting and eating sea otters there, too.