sea otters are innovative, lovely and apex predators in its ecosystem, until now. On Pleasant Island, a 20-square-mile uninhabited island off Alaska, the deer population has likely declined due to predation by wolves. With available prey dwindling, it appears sea otters are now on the wolves’ menu.
according to 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 the predominant food source for a terrestrial predator like a wolf.
(Credit: Laura Hedien/Shutterstock)
The researchers analyzed wolf scat and tracked the wolves with GPS collars, finding that in 2015 their diet was 75 percent deer and just 25 percent sea otter. However, in 2017, sea otters made up 57% of the wolves’ diet, while deer made up just 7%. This stayed the same until 2020, when the study ended.
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“Sea otters are this famous predator in the nearshore ecosystem, and sea lions are one of the most famous top predators in terrestrial systems,” he says. Taal Leviassociate professor at Oregon State, in a Press release. “So it is quite surprising that sea otters have become the most important resource for feeding sea lions. You have top predators feeding on a top predator.”
A story of sea wolves and sea otters
While this may be the first recorded case of sea otters becoming prey for terrestrial animals, it may have happened in the past as well. According to the study, sea lions and sea otters may have lived together on Pleasant Island before fur traders wiped out sea otters in this area during the 19th and 20th centuries.
The wolf population in the area remained relatively healthy compared to wolves in the lower 48 states. According to the study, this pack of wolves arrived on the island in 2013 after swimming from the mainland.
After passing the Law for the Protection of Marine Mammals in 1972rehabilitation efforts helped establish a healthy population of sea otters in Alaska, which has led sea lions and sea otters to interact in the same environment.
The researchers analyzed the wolf pack on Pleasant Island and the adjacent shoreline from 2015 through 2021. Wildlife biologists such as Gretchen Roffler of the Alaska Department of Fish and Game collected nearly 700 wolf scat samples, many of which were which were found along the coasts. They analyzed the samples in Levi’s lab using molecular tools such as genotyping and DNA metabarcode to identify certain wolves and break down their diets.
(Credit: Sean Neilson) Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, collects wolf scat in the Gustavus Forelands in Alaska.
Roffler also tagged four Pleasant Island wolves and nine mainland wolves with GPS collars to track whether mainland wolves came 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 the GPS collars and scat showed that wolves from the mainland did not come to the island to hunt. This indicated that the wolf population on the island was stable.
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The GPS collars also helped identify where and when sea otters were being killed by sea lions, primarily when the otters were in shallow water or resting on rocks at low tide. According to the news release, Roffler and her team analyzed the GPS collars over three 30-day field seasons from 2021 and found evidence of 28 sea otters killed by sea lions.
“What really surprised me is that sea otters became the main prey for sea lions on this island,” Roffler says in a news release. “Once in a while eating a sea otter that has washed up on the beach because it died, that’s not unusual. But the fact that the wolves are eating so many of them indicates that it has become a pervasive behavior pattern throughout this pack and something they learned to do very quickly. According to Roffler, wolves are actively hunting and killing sea otters, not just scavenging for old or dying ones.
(Credit: Bjorn Dihle) A wolf traveling and feeding in the intertidal zone off Pleasant Island in Alaska.
The wolves are adapting
With the deer population on the island depleted, Levi thought that the wolves would have either died out or left the island. Instead, according to Levi, the wolf pack seems to have grown to a density never seen before in wolf populations. He believes sea otters consuming sea lions play a central role in this.
Currently, Ellen Dymit, a doctoral student in the Levi’s lab, and Roffler, along with their teams, are studying interactions between sea lions and sea otters in Katmai National Park and Preserve, about 700 miles from Pleasant Island. Early research indicates sea otters are also eaten there by sea lions.
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