On a small island near Gustavus, Alaska, a dramatic shift in the local wolf pack’s diet has emerged, raising concerns about the health of these apex predators.
Historically, wolves in the region have relied on the local deer population for sustenance. However, as the deer numbers dwindled due to excessive predation, wolves have turned their attention to sea otters.
This adaptability showcases the coastal wolves’ resilience in reorienting their diets, but it comes with unforeseen health risks.
Researchers were startled when they discovered one wolf carcass, which had lost about a third of her body weight, emaciated and found under a tree.
Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, detailed the findings from the wolf’s liver, muscle, brain, and kidney samples sent to a wildlife veterinarian for testing.
While diseases and common toxicities were ruled out, the alarming discovery was elevated mercury levels in its tissues.
Roffler noted, “They were many orders of magnitude higher than other wolf liver tissues analyzed in other parts of the world.”
This initial finding initiated a broader research project focused on how the dietary shift toward marine prey impacts the wolf populations’ mercury levels and overall health.
In a recent study published in the journal Science of the Total Environment, researchers concluded that two wolf populations near Gustavus increasingly rely on marine prey, particularly sea otters, for food.
This transition is correlated with significant mercury exposure, as seen in the unfortunate case of the deceased wolf.
“The ability of wolves to switch their diets from terrestrial prey to marine prey just shows how resilient they can be,” Roffler stated.
“However, we now know that their reliance on marine prey can also lead to the risk of toxicity.”
The study focused on several areas, including Pleasant Island, where wolves are primarily consuming sea otters instead of deer.
In contrast, wolves on the Gustavus mainland maintain a more traditional diet of terrestrial animals such as moose but have begun incorporating more marine species.
Using archived hair and muscle tissue samples collected over the past two decades, the research team drew connections between marine-heavy diets and adverse health outcomes, particularly marked against wolves in other locations.
Wolves from Douglas Island near Juneau and the Interior, whose diets are predominantly terrestrial, showed significantly lower mercury levels.
Roffler explained that while some mercury presence is common among marine predators such as foxes and polar bears, the exceptional concentration levels in these wolves present cause for concern.
The implications of this study extend beyond just the wolf populations around Gustavus, as the dynamics between sea otters and other terrestrial predators may shift across Alaska’s coastal regions.
Sea otters, historically hunted to local extinction during the fur trade in the 1800s, were reintroduced in the 1960s and have since reclaimed several territories, including areas around Glacier Bay National Park.
Roffler indicated that as sea otters continue to regain and grow in numbers, it is likely that wolves and other terrestrial predators will increasingly target them as a food source.
But this raises a critical question: why is mercury present in marine environments?
According to report co-author Ben Barst, an assistant professor at the University of Calgary specializing in ecotoxicology, mercury pollution stems largely from human activities such as coal combustion and gold mining.
Mercury can be released into the atmosphere as vapor, traveling long distances before being deposited as precipitation, including rain and snow.
In Southeast Alaska, an additional source of mercury may stem from glacial runoff, which contains mercury and is exacerbated by climate change.
Once mercury infiltrates aquatic ecosystems, microbes transform it into a more toxic form that can easily enter living organisms like mussels, clams, and sea urchins.
As noted by Chilkat Valley local and marine mammal hunter Tim Ackerman, the marine food web allows elevated mercury levels to accumulate: “The sea otters are going to dig those up and consume them.”
Thus, by the time a sea otter becomes prey for a wolf, the potential for significant mercury transfer increases.
“We see this in other instances with fish,” Barst explained. “Smaller fish are eaten by larger fish, leading to higher concentrations of mercury in the biggest fish.”
Initially, researchers suspected the problematic mercury concentrations in wolves might be confined to the Gustavus and Pleasant Island area.
However, Barst emphasizes the need for further research to clarify whether this issue is widespread, especially concerning glaciers’ contributions and the fluctuations in wolf diets.
As the sea otter population grows and continues to expand its range, the trend of terrestrial predators consuming marine species raises critical environmental health questions for the ecosystem at large.
image source from：https://alaskapublic.org/2025-06-11/some-southeast-alaska-wolves-are-eating-sea-otters-it-could-be-toxic
