WEST GLACIER – A “first-of-its-kind” study released last week discovered mercury in fish in some of the most remote and pristine lakes and streams in national parks across the western United States and Alaska – but it wasn’t a surprise to Glacier National Park fisheries biologist Chris Downs.
Glacier is updating information for a brochure it already puts out regarding guidelines for fish consumption from waters inside the park because of contaminants such as mercury, which is harmful to both human and wildlife health.
“The national study continues to demonstrate that contaminants are reaching places we think of as isolated or protected,” Downs said. “Because of airborne transport, it’s a global issue.”
National parks can serve as something of a canary in a coal mine, given their protected status and the way they are managed, when it comes to mercury levels, Downs suggested.
That’s exactly why the new study focused on mercury levels in fish in 21 national parks located in 10 Western states. Even though the study area accounts for less than one-third of national park units, it contains 89 percent of the land area managed by the National Park Service.
“Although fish mercury concentrations were elevated in some sites, the majority of fish across the region had concentrations that were below most benchmarks associated with impaired health of fish, wildlife and humans,” Collin Eagles-Smith, lead author of the 54-page report, said.
Eagles-Smith added that the wide range of mercury concentrations that were found in fish in national parks’ suggest “that complex processes are involved in driving mercury accumulation in these environments.” He said more research is needed to better assess the risks.
Co-author Colleen Flanagan Pritz, a National Park Service ecologist, called the report “a wake-up call.”
“We need to see fewer contaminants in park ecosystems,” Pritz said, “especially contaminants like mercury where concentrations in fish challenge the very mission of the national parks to leave wildlife unimpaired for future generations.”
The U.S. Geological Survey, where Eagles-Smith works as an ecologist, and National Park Service published the scientific report. It showed mercury levels in some of the fish tested in national parks exceeded U.S. Environmental Protection Agency health thresholds for potential impacts to fish, birds and humans.
While researchers tested fish from multiple lakes and streams to compare numbers within a specific park, Glacier was not one of them.
Only lake whitefish and bull trout were sampled from Lake McDonald in Glacier for the study.
Still, Downs said being able to offer the researchers frozen samples of bull trout, a threatened species, was an important contribution to the study.
Both Glacier’s whitefish and bull trout had high mercury concentrations relative to the mean across all fish in the study, the report said, and after accounting for the effects of size and species, fish from Glacier Park “were some of the highest in the large-size class. Mercury concentrations in Glacier NP fish approached or exceeded the EPA criterion for protection of human health and the level at which reproductive impairment to piscivorous (fish-eating) birds could occur.”
The mercury concentrations in many individual fish from Glacier exceeded the level at which tissue-based toxicity to a fish is a concern.
“This is particularly important, considering bull trout is federally listed as threatened under the Endangered Species Act,” the report stated.
Because only fish from Lake McDonald were sampled, “we cannot assess whether these data are representative of other lakes in the park” the report said.
It goes on to note that a different 2008 study found that fish from two other lakes in Glacier had the lowest mercury concentrations among 14 lakes measured in national parks in the West.
“These contrasting results suggest that substantial variation in (mercury) concentrations exists among water bodies within Glacier NP,” the study went on.
Downs said the risk to birds and wildlife in Glacier appears to be fairly low right now, “although increases in mercury concentrations would likely cause us to re-examine that.”
Eagles, osprey, loons and kingfishers all feed on fish in Glacier, Downs said, as do mink and otters. Glacier’s bear population focuses on berries, forbs and grasses, not fish.
Downs said in 2010 Glacier biologists tested fish “from a whole bunch of lakes, and a lot of different species.”
“We’ve been doing it for quite a few years,” Downs said. “Depending on the species and size of fish, the results ranged widely.”
Cutthroat trout, he explained are “low on the food chain” and don’t live particularly long lives, so they don’t accumulate as much mercury as predacious lake trout, which eat other mercury-contaminated fish and have considerably longer life spans in which to accumulate higher levels.
“You have to pay attention to what size fish you’re eating,” Downs said. “Smaller lake trout are probably not a concern, but when they get larger, they do start to exceed” recommended levels.
Mercury concentrations in fish are of particular concern to children, and to women of child-bearing age. Mercury is distributed on a global scale from natural sources, such as volcanic eruptions, and human sources, such as burning fossil fuels in power plants. It is also distributed on local scales as a result of mining activities.
The human-caused mercury distribution has increased the levels of atmospheric mercury between three and five times in the past 150 years, according to the report.
Fish in Montana’s other national park, Yellowstone, had total mercury concentrations above the study-wide mean value from all parks. The concentrations for 200 millimeter standard-length fish were among the highest found in any park, although the report noted natural geothermal mercury sources occur throughout Yellowstone.
“It is unclear if those sources play a role in fish bioaccumulation,” the report said.
Next door at Grand Teton National Park, meantime, mercury concentrations in fish from two lakes and one stream sampled were consistently among the lowest measured in the study.
You didn’t have to go from one park to another to find starkly contrasting patterns.
In Yosemite National Park in California, mercury concentrations in fish from Spillway Lake were uniformly low – half the study-wide mean from all 21 parks.
Yet a brook trout from Mildred Lake in Yosemite had the highest total mercury concentration of any of the nearly 1,500 fish measured in the study, and overall, fish from Mildred had more than twice the study-wide mean levels – yet their individual concentrations had a 15-fold range within the lake.
In all, the fish sampled came from 86 lakes and rivers within the 21 national parks and included 16 species, with a focus on commonly consumed sport fish. Smaller prey fish consumed by birds and wildlife were also tested.
National park resource managers collected the fish between 2008 and 2012. USGS scientists measured the mercury concentrations in fish muscle tissue.
The scientific report’s official title is “Mercury in Fishes from 21 National Parks in the Western United States – Inter- and Intra-Park Variation in Concentrations and Ecological Risk.”