Whether it is by land or by sea, the coastal wolf population of southeastern Alaska has become increasingly exposed to high levels of mercury, and the prime suspects among researchers right now are sea otters.

The emerging theory dates back to 2020, when a female coastal wolf collared for a study on predation patterns unexpectedly died in southeastern Alaska. At just four years old, the cause of the wolf’s death for a long time eluded scientists.

After a deep analysis of different tissue types from the individual, Gretchen Roffler, a wildlife research biologist with the Alaska Department of Fish and Game, finally landed on the conclusion that cause of death was due to “unprecedented concentrations of mercury in the wolf’s liver, kidneys, and other tissues.”

According to new research now published in the journal Science of the Total Environment, the root cause of this mercury could be a diet of sea otters. 

Pulled together with Dr Ben Barst, an assistant professor in the Faculty of Science at the University of Calgary, alongside an extended team of scientists, Roffler’s research shows that wolves eating sea otters have much higher concentrations of mercury than those eating other prey, such as deer and moose.

Mercury is a naturally occurring element that, once released into the atmosphere in its elemental form, can travel huge distances. Once it gets into marine environments, it is converted into methyl mercury – an organic form of mercury that moves “quite efficiently through the food web.”

“It can reach high concentrations in predators that are trapped into aquatic food webs,” said Dr Barst. “So, we see higher concentrations in wolves that are tapped into a marine system.”

The research compares wolves from Pleasant Island – located on the Alaska Panhandle region, west of Juneau – with the population on the mainland adjacent to the island, as well as wolves from interior Alaska.

“The highest concentrations are the wolves from Pleasant Island,” said Barst, noting that the mainland population mostly feeds on moose and only the occasional sea otter. According to Barst, there could be a number of factors driving the higher concentrations of mercury, all of which are still being investigated.

Years of data collected by Roffler, however, shows that 70% of Pleasant Island’s wolves’ diet is in fact sea otters.  So high, in fact, that the higher dose of mercury from the marine food web is “accumulating over time.”

According to Roffler, there are other populations of wolves in Alaska – as well as in British Columbia – that appear to be eating sea otters.

“It turns out that this might be a more widespread phenomenon than we thought originally,” she said. “At first, I was surprised it was happening at all.”

Links have also been made, however, to climate change and the warming temperatures that are currently shrinking Alaska’s glaciers. 

“We know that glaciers can release tremendous amounts of mercury,” said Barst. “In coastal Alaska, glaciers are retreating at some of the most rapid rates in the world. 

“And with that melting of glaciers, you get the release of the particulate bedrock and some of that bedrock contains mercury – so 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. That’s the part we’re looking into now.”

The paper – Switching to marine prey leads to unprecedented mercury concentrations in a population of coastal Alaska wolves – has been published in the journal Science of the Total Environment.

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