In the rugged wilds of southeastern Alaska, coastal wolves are making headlines—not for their cunning or beauty, but for what’s showing up in their blood. A newly published study reveals that some of these wolves, especially those feasting on sea otters, have alarmingly high levels of mercury in their systems. And that could spell danger for both the wolves and the delicate coastal ecosystems they call home.
It all started with a mystery in 2020, when a four-year-old female wolf—known as No. 202006—was found dead on Pleasant Island. The wolf had been collared for a study on predator behavior, but her death was unexpected and unexplained.
“We spent quite a bit of time trying to figure out the cause,” said Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game. “What finally came up was really unprecedented concentrations of mercury in her liver and kidneys.”
Sea Otters on the Menu
To crack the case, Roffler teamed up with Dr. Ben Barst, an ecotoxicologist and assistant professor at the University of Calgary. Their research, now published in Science of The Total Environment, shows that wolves that regularly eat sea otters are absorbing dangerous amounts of mercury—a metal that builds up in the food chain over time.
Mercury isn’t new to nature. It’s a naturally occurring element, but when humans burn coal or mine for gold, they send more of it into the atmosphere. Eventually, it lands in water, where it transforms into methyl mercury, a highly toxic form that travels easily through aquatic food webs. Top predators—like sea otters
“The highest concentrations are the wolves from Pleasant Island,” Barst said.
Wolves that are more inland consume more moose and an occasional sea otter, which means they consume significantly less mercury than the coastal dwelling wolves.
Wolves and the Marine Menu
Pleasant Island wolves are unique. With no deer or moose to hunt, they’ve turned to a surprising alternative: sea otters. Decades ago, sea otters were hunted to near extinction in the region, but their recovery has now made them a primary food source for the island’s wolf population.
According to Roffler, 70% of the Pleasant Island wolves’ diet is now sea otters. That shift, while fascinating from a behavioral standpoint, is also what’s leading to mercury overload.
“They’re eating so many sea otters that they’re just getting this higher dose of mercury and it accumulates over time,” Barst said.
Researchers compared wolves from Pleasant Island with others on the mainland and in Alaska’s interior. The verdict? Wolves that eat more sea otters had the highest mercury levels.
A Climate Connection?
The team is also investigating a possible climate change link. As glaciers retreat across Alaska—some of the fastest in the world—they’re releasing ancient bedrock. And some of that rock contains mercury.
“We don’t really know the fate of that mercury. It may just get buried in sediments or it may actually be available for conversion to methyl mercury and get into the food web,” Barst said.
What’s Next for the Wolves?
While it’s unclear if mercury directly caused the death of wolf No. 202006, the findings raise important questions about long-term wolf health and the risks of relying on marine prey. Researchers are now expanding their studies to other regions, including parts of British Columbia, where wolves have also been spotted feeding on sea otters.
As ecosystems shift and climate change reshapes wildlife behavior, one thing’s clear: even the wildest predators aren’t immune to the far-reaching effects of human activity.
