DEH CHO
Researchers are continuing to build on data looking at the levels of mercury in whitefish, pike and walleye in a series of lakes throughout the Deh Cho.

This sign appears at the entrance of the road to Ekali Lake near Jean Marie River, bearing suggested serving guidelines for walleye and pike. - April Hudson/NNSL photo

Heidi Swanson, a professor of biology at the University of Waterloo, is looking ahead to an upcoming March meeting with the Dehcho Aboriginal Aquatic Resource and Oceans Management (AAROM) program, which will determine plans for the coming summer.

Swanson said she will be sampling Ekali Lake near Jean Marie River and Big Island Lake on the Horne Plateau for the fifth year in a row.

"It's been amazing work, really fun," she said, adding much of the project's success comes from the efforts of AAROM program co-ordinator George Low.

Swanson first started her research in 2013. One of the goals she is working toward is discovering why mercury levels in fish vary depending on the lake - and then helping people to choose the safest food sources.

"What we've found so far is that whitefish everywhere are really good to eat. Every lake we've looked at, whitefish are well below guidelines, which is great news," she said.

"We've also found the mercury levels in walleye and pike vary among lakes."

That could reflect water chemistry differences, such as how much algae is present in a lake or how far the water flows over a watershed before coming into the lake.

Swanson's study includes four lakes around Jean Marie River, two near Kakisa and two by Fort Providence.

"For every community we've gone to, we've looked at all the lakes and showed them how mercury changes with the size of the fish," she said, referring to how mercury levels increase as fish get bigger.

"We're giving recommendations on, if you want to eat walleye and pike, these are the lakes where mercury is lowest - for example, Kakisa has very low mercury in walleye."

Over the years, Swanson has aimed to increase awareness of the fish that are safe to eat in the Deh Cho region.

"I think what I've been encouraged by is people do seem to be getting the message . that fish can be part of a food security strategy," she said.

"I also find it really encouraging that we're starting to find ways we can manage it."

Swanson has been researching mercury in fish for nearly 15 years. Part of her passion for her research comes from her career as an ecologist, she said.

"I love thinking about the whole ecosystem - the catchment, the lake, how it all works together and fits together, and then how humans fit into that," she said.

"The amount we fish and harvest from a lake influences the mercury - it's like this double feedback."

As an example, Swanson points to Lake Sanguez near Jean Marie River, which has high mercury levels. There used to be an elder who lived at the end of the lake and fished it frequently.

"When we take pressure off a fishery, obviously there's more fish in the lake. Those fish are all competing - especially in Northern lakes - for limited resources," she explained.

"That means there's more fish, and they grow more slowly . (which means) they get more mercury."

Much of the mercury Swanson has found in Deh Cho lakes comes from southern sources, she said.

That includes coal-fired power plants and other industry, which send mercury into the air.

But once mercury falls out through rain or snow into lakes, it's possible to have high levels in water but low levels in fish - and vice versa. Mercury goes up through the bottom of the food chain, and its trek through the food chain can depend on the depth of the lake, warmth and how much oxygen there is. Each of those factors vary depending on the lake.

However, fish that feed near the top of the food chain have higher mercury levels, which is why walleye and pike have higher levels than whitefish.

"That's called biomagnification - every time something eats something else, more mercury gets concentrated," Swanson said.

"We burn calories faster than we burn mercury, basically, and that's why it builds up."

Swanson said some areas of the world use intensive fishing as a way to help lower mercury levels.

That could come as a pilot project this summer for lakes around Jean Marie River.

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