In a wild area of Alaska, home to a population of only about 200 deer, wolves began to appear. Many predictions suggested that they would quickly leave after hunting the deer. However, the reality turned out to be quite the opposite; the wolves remained, seeking alternative food sources.
Pleasant Island in Alaska is a place that contradicts its name. This island is extremely cold, measuring just over 30 square kilometers with human inhabitants. Yet, it boasts a remarkably rich and diverse ecosystem with species such as deer, otters, red squirrels, and even brown bears. In 2013, this island welcomed a new inhabitant: wolves.
When wolves invaded the island in 2013, they inadvertently created a perfect ecological observation environment for scientists.
Instead of leaving, the wolves here continue to stay in search of other food sources.
Roffler Gretchen, one of the study’s authors, stated: “This provides a fantastic opportunity to study the predation dynamics of wolves. We are interested in how the newly settled wolf population will impact the deer population and predicted that the wolf pack might eat all the deer on the island and then move to another area just 1.5 km away.”
The first part of this prediction came true. The deer population, which numbered around 120-200, significantly declined. However, instead of moving to greener pastures, the wolves remained on this island and shifted their focus to an unexpected prey: sea otters.
Sea otters became the next target for wolves after the deer population declined.
Sea otters are themselves top predators in the nearshore ecosystem, while wolves are top predators on land on this island. Therefore, scientists were extremely surprised by this phenomenon. Taal Levi, an associate professor in Oregon, commented: “It’s surprising that one top predator is preying on another top predator.”
Gretchen, Levi, and their colleagues tracked several wolves using GPS collars and analyzed their behavior. They found that in 2015, deer constituted the main food source for wolves, making up 75% of their diet. By 2017, wolves had shifted to eating sea otters, which accounted for 57% of their diet, while deer only made up 7%. This pattern persisted until 2020 when the study concluded.
Wolves switched to eating sea otters (57% of their diet) starting in 2017.
Sea otters have had a challenging existence in the region. In the 19th and 20th centuries, they were hunted by fur traders and were essentially on the brink of extinction in the area.
However, only in recent decades, thanks to legal protections for sea otters, their population has gradually begun to recover.
Yet researchers did not expect that wolves—a terrestrial species—would become adept at preying on sea otters, which, true to their name, spend most of their time at sea.
“Wolves will eat the carcasses of sea otters, but they also actively hunt sea otters when they swim close to shore. Sea otters are rarely attacked by wolves when they are swimming in the ocean,” Levi noted.
Wolves are often seen patrolling the beaches and rocky outcrops of Pleasant Island. GPS data confirms that in recent years, they have spent considerable time moving around the intertidal zones, as if searching for something—and indeed, they are looking for sea otters to ambush.
Wolves spend much of their time at sea searching for food.
Sea otters often cling to rocks to conserve energy, Roffler mentioned. But this inadvertently makes them more vulnerable to predation as they are quite slow and clumsy on land—and at this moment, wolves quickly seize the opportunity to turn sea otters into prey.
Gretchen added: “We have gathered evidence of wolves killing sea otters by ambushing them when they move onto land or in shallow waters.”
Gretchen continued: “This new twist in the ecosystem creates a fascinating case study.”
“There have been previous studies on the impact of marine predators on sea otter populations, but until now, there has been little attention paid to the impact of terrestrial predators on sea otters. This interaction is relatively rare, but it has profound effects, at least on Pleasant Island.”
Currently, it is still unclear how sea otters are adapting to this (or if they are adapting at all). The most noticeable impact may be a change in behavior that forces sea otters to spend more time at sea—the long-term effects of this could lead to stress.
The diet of wolves is gradually changing.
Overall, researchers do not expect that wolves will have a significant impact on the sea otter population. This surprising discovery about the wolves’ diet certainly requires further research to better understand the interactions in this ecosystem. Levi stated that they are currently investigating this issue.
“We are increasingly following the story of sea otters and wolves with additional field studies, including research by graduate student Dr. Ellen Dymit, comparing study areas on land with and without sea otters along the region where the sea otter population is expanding.”
