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New mercury guidelines for Flathead Lake trout being rolled out

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FLATHEAD LAKE — Montana Fish Wildlife and Parks and the Confederated Salish and Kootenai Tribes are in the process of rolling out new uniform guidelines about how many Flathead Lake trout meals people can safely consume per month. 

“We noticed our fish consumption advisories for Flathead Lake in our handouts, brochures, our state fish guides, weren’t the same between the department and the Tribes,” Fish Wildlife and Parks Biologist Mark Deleray said in a recent Flathead Reservation Fish and Wildlife Board meeting. “There were some subtle differences.” 

Consumption notices are issued for lake trout that accumulate mercury from their prey throughout their lives. Excessive human consumption of mercury-laden fish can lead to nervous system damage. Unborn fetuses, pregnant women, and small children are most at risk for health problems. 

Most of the mercury contaminants are airborne, and affect lakes across western Montana, Deleray said.  

“They have these same types of contaminant issues in Glacier National Park, so it’s not that some of these waters are more accessible than others to humans,” Deleray said. “It’s a problem across the region.” 

According to the National Resource Defense Council the majority of mercury pollution in the United States is generated by coal-fired power plants, of which Montana has five. They include a Colstrip facility that was ranked eighth nationally for overall emissions in 2012, and a Thompson Falls facility that was constructed in 2005. The U.S. Environmental Protection Agency has only regulated mercury emissions since 2011. 

Deleray said although mercury contamination is a regional problem, each set of consumption guidelines must be specific to the body of water and individual fish species in order to protect human health. Perch in St. Mary’s Lake will not have the same amount of mercury present as a lake trout in Flathead Lake, because of differences in the amounts of pollutants and the fish’s place in the food chain. 

To come up with a set of uniform guidelines for lake trout consumption on Flathead Lake, a technical team of state and tribal biologists created a collaborative tissue sample bank for analysis. 

“(Flathead Lake) has the highest number of fish tissue samples and basically the best analysis of this contaminant issue compared to the rest of Montana,” Deleray said. 

The large number of samples allowed more conservative guidelines to be drawn, because authorities were able to see large variances in mercury levels in the fish, Deleray said. 

The more conservative guidelines account for “hot” fish that have higher than expected levels of mercury based on their length, Tribal Fisheries Manager Les Everts said. 

The team decided women and children should avoid all lake trout more than 26 inches long. Adult men should avoid the fishes that are longer than 30 inches. 

The Tribes plan on creating a brochure and pocket guide for the consumption guidelines, Tribal Widlife Information and Education officer Germaine White said. The information will likely be available soon after the start of the spring Mack Days fishing derby, White added. Most of the approximate 50,000 lake trout removed from Flathead Lake during the derby are donated to local food banks, which is another reason the Tribes wanted to update the advisories. 

“Because we’re making these fish available to so many more people through the food banks through things like Mack Days, we wanted something really simple that could be handed out at those facilities,” Everts said. 

Slot limits that only allowed the take of a single 36-inch or longer fish per day were also recently removed for the southern half of the lake, which means bigger fish with more mercury in their systems will be more readily available to the public. 

White told the story of a family in a photograph standing with a large lake trout, as an example of why the guidelines are needed. 

“When asked, they said ‘We ate every bit of it,’” White said. “It’s really important we provide this information. (Eating these large trout is) not a good idea for everyone.” 


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