Wolves eliminate deer on Alaskan Island then quickly shift to eating sea otters, research finds (College: 2015, how much)

[AKStafford]

https://phys.org/news/2023-01-wolves...d-quickly.html

Wolves on an Alaskan island caused a deer population to plumet and switched to primarily eating sea otters in just a few years, a finding scientists at Oregon State University and the Alaska Department of Fish and Game believe is the first case of sea otters becoming the primary food source for a land-based predator.

Using methods such as tracking the wolves with GPS collars and analyzing their scat, the researchers found that in 2015 deer were the primary food of the wolves, representing 75% of their diet, while sea otters comprised 25%. By 2017, wolves transitioned to primarily consuming sea otters (57% of their diet) while the frequency of deer declined to 7%. That pattern held through 2020, the end of the study period.

"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. "So, it's pretty surprising that sea otters have become the most important resource feeding wolves. You have top predators feeding on a top predator."

The finding were published today in PNAS.

Historically, wolves and sea otters likely lived in the study area, Pleasant Island, which is located in an island landscape adjacent to Glacier Bay about 40 miles west of Juneau. The island is about 20 square miles, uninhabited and accessible only by boat or float plane.

During the 1800s and much of the 1900s, populations of sea otters in this region were wiped out from fur trade hunting. Unlike wolves in the continental U.S., Southeast Alaskan wolves were not hunted to local extinction. Only in recent decades, particularly with the reintroduction and legal protection of sea otters, have the populations of both species recovered and once again overlapped, providing new opportunities for predator-prey interactions between the two species.

The researchers studied the wolf pack on Pleasant Island and the adjacent mainland from 2015 to 2021. Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, and others from the department collected 689 wolf scats, many along the island's shoreline.

Once the scat is collected, members of Levi's lab in Oregon used molecular tools, such as DNA metabarcoding and genotyping of the scat, to identify individual wolves and determine their diets.

Roffler also captured and placed GPS collars on four wolves on the island and nine on the mainland. The researchers were curious whether wolves were traveling between the mainland and island, considering other scientists have found they are capable of swimming up to eight miles between land masses. Both the GPS collar data and genotypes of the scats confirmed they were not, indicating that the island wolf pack is stable and that the island is not a hunting ground for mainland wolves.

Locations from the GPS-collared wolves also provide evidence that the wolves are killing sea otters when they are in shallow water or are resting on rocks near shore exposed at low tide. Roffler and her crew have investigated wolf GPS clusters on Pleasant Island for three, 30-day field seasons since 2021 and found evidence of 28 sea otters killed by wolves.

"The thing that really surprised me is that sea otters became the main prey of wolves on this island," Roffler said. "Occasionally eating a sea otter that has washed up on the beach because it died, that 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.

"And 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."

Shortly after wolves colonized Pleasant Island in 2013, the deer population on the island plummeted. With the wolves having consumed most of the deer, their main food source, Levi said he would have expected the wolves to leave the island or die off. Instead, the wolves remained and the pack grew to a density not previously seen with wolf populations, Levi said. The main reason, he believes, is the availability of sea otters as a food source.

The findings outlined in the PNAS paper build on research findings published in 2021 by the same researchers. In that paper they showed—in what they believe is a first—that wolves were eating sea otters. This was documented throughout the Alexander Archipelago, a group of Southeastern Alaskan islands which includes Pleasant Island.

The research has now expanded to study wolves and sea otters in Katmai National Park & Preserve, which is in southwest Alaska, about 700 miles from Pleasant Island. Early research by Ellen Dymit, a doctoral student in Levi's lab, and Roffler indicates that wolves are also eating sea otters there. In fact, at that location Roffler and Dymit observed three wolves killing a sea otter near the shore

In addition to Levi and Roffler, co-authors of the PNAS paper are Charlotte Eriksson, a post-doctoral scholar in Levi's lab, and Jennifer Allen, the environmental genetics lab manager in Levi's lab. Levi is in the Department of Fisheries, Wildlife, and Conservation Sciences in the College of Agricultural Sciences.

[Parnassia]

Interesting, but it doesn't really surprise me. The whole area was buried in glacial ice relatively recently (Little Ice Age) which precluded many terrestrial animals that would normally make up a lot of a wolf pack's diet from colonizing from the AK mainland to the east. The land was also devoid of vegetation (ie food for herbivores) for a long time after the ice retreated.

On top of that, there are significant mountain barriers for them to cross and only one major river corridor through them: the Alsek River almost 100 miles farther north. The river formed the only relatively easy migratory route into this lower elevation coastal area (glacial outwash plains that make up Gustavus, coastlines of lower Glacier Bay, Pleasant Island, etc) that became exposed once Grand Pacific Glacier retreated.

Moose only reached the area around Gustavus about 40-50 years ago. Not sure when deer reached it but even now it is still pretty rare to spot one around town. Wolves followed the moose and deer, so deer retreated to the islands to get away from them. But all three of those species swim, and the swim over from Gustavus is protected and short. Even today there are no rabbits, few small mammals, few if any beaver, no gophers around Gustavus. There are squirrels, voles, and an occasional deer mouse but those wouldn't support much of a wolf population. If I was a wolf, a clumsy, slow moving sea otter hauled out on a beach would make a great meal. They don't have a blubber layer so not a very fat meal like a seal, but there would be a lot more of them to make up for that.

Pleasant Island isn't very big and large areas of it wouldn't support much of a deer population anyway. A lot of the interior is muskeg bog, the outer fringes are decadent spruce forest that established itself after the ice retreated, surrounded by a narrow fringe of deciduous shrubs, forbs, and other browse. The vegetative communities are naturally evolving beyond what deer would thrive in. Its marginal at best, even for the small Sitka blacktails. On top of wolf predation, humans also hunt them, though how much is somewhat controlled by state game regulation (for those people who respect such laws...there's no local law enforcement presence in Gustavus, the state troopers make patrols over from Juneau periodically).

[Northrick]

I've been around a lot of sea otters. It's hard to wrap my head around one being killed by a wolf. I don't know that I've ever seen one on shore. Sleeping on ice bergs, rocks sticking out of the water, etc. but never on shore. I can't imagine a wolf out swimming an otter either.


I would love to see a video on how these wolves are hunting sea otters.

[Metlakatla]

I was in my living room one evening and heard something on the deck. Looked outside and there were maybe 5 or 6 young deer just standing there. Tried to shoo them away and they wouldn't budge; dog was barking and everything. Then I realized why they wouldn't leave the deck.

[Metlakatla]

Originally Posted by Northrick

I would love to see a video on how these wolves are hunting sea otters.

I was interested too and found this:


https://www.youtube.com/watch?v=cSeQKiDU8xk

[Parnassia]

Originally Posted by Northrick

I've been around a lot of sea otters. It's hard to wrap my head around one being killed by a wolf. I don't know that I've ever seen one on shore. Sleeping on ice bergs, rocks sticking out of the water, etc. but never on shore. I can't imagine a wolf out swimming an otter either.

They definitely do come on shore occasionally. There are smaller islands in Glacier Bay where they're spotted hauled out regularly, more so as the local population re-establishes itself farther and farther up the Bay.

[RayinAK]

Originally Posted by Metlakatla

I was interested too and found this:


https://www.youtube.com/watch?v=cSeQKiDU8xk

Very good Met

[Northrick]

Originally Posted by Metlakatla

I was interested too and found this:


https://www.youtube.com/watch?v=cSeQKiDU8xk

Originally Posted by Parnassia

They definitely do come on shore occasionally. There are smaller islands in Glacier Bay where they're spotted hauled out regularly, more so as the local population re-establishes itself farther and farther up the Bay.

Cool video.


Most of my experience with sea otters is in Prince William Sound. Not saying they don't haul out on shore, just never saw them do that. We have seen them sleeping while floating in cove or small bay. With a sea kayak you can sometimes get pretty close to them before they wake up and dive. Maybe a clever wolf can sneak up on them too.

[RayinAK]

If you happen to subscribe to Netflix, there is a documentary of the sea wolves in Vancouver Island. I haven't watched the documentary, but have it in my watchlist.

[Igor Blevin]

Intelligent species.

It is interesting to learn that wolves can catch otters.