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Debate is mounting over a study that will see large predator fish culled in an effort to examine whether fewer large fish will lead to lower overall mercury levels in fish.

The study will take place near Jean Marie River.

“As the mercury goes up the food chain from bacteria to plankton to small fish to larger fish, those levels are bio-accumulated and you end up with large old fish having quite high levels of mercury,” said George Low, Dehcho co-ordinator for the Aboriginal Aquatic Resources and Oceans Management project.

Gijs Van Straten, visiting from the Netherlands, holds a large norethern pike caught while fishing a river in the North Slave region. A new study plans to cull large fish in an effort to reduce mercury from fish populations. Not all agree the plan will work.
Mike W. Bryant/NNSL photo

“So what we’re hoping is this will reduce competition after these monsters are fished out of there.”

Since 2012, pike and walleye from Sanguez Lake have been subject to a health advisory – occasional consumption is not a health risk, however two servings per week is considered the maximum.

With Fisheries and Ocean permits to proceed, Jean Marie River chief Stanley Sanguez said reduction in pike and walleye will likely begin next year at Sanguez Lake and the big predator reductions could be expanded to include Kelly Lake, Gargan Lake, McGill Lake and Deep Lake.

“The community basically did a fish study on the five lakes, that was years and years ago. Anyway our community basically wanted to know how long we were eating fish that had mercury,” Sanguez said. “Then we found out levels were too high in Sanguez Lake, then George (Low) says ‘what do we do?’; I say ‘why don’t we do the simple thing, use a net and fish out the big fish.”

However, University of British Columbia professor Marcello Veiga – an expert in mercury pollution on fish – is skeptical of anticipated results from the Sanguez Lake experiment.

“Quite frankly, this is not a solution at all,” Veiga said. “It will not reduce any mercury contamination, except that contained in the extracted fish – the mercury is coming from the air, from the soil, the plants, it’s coming from everywhere.”

Veiga did caution that the best way to avoid ingesting unsafe levels of mercury is to follow the Health Canada guidelines or avoid fish prone to mercury contamination, like tuna or in Jean Marie River’s case, pike and walleye.

“For people who are eating these fish everyday, at 0.5mg/kg or above concentrations, they are going to be contaminated,” he said.

University of Waterloo researcher and project lead Heidi Swanson told News/North that “we are not clearing the lake of large fish predators; we are reducing the density of large fish predators.”

Swanson said the experiment would remove approximately 150 kilograms of contaminated big predators.

“We obviously have to be careful not to remove too many fish. Our target for amount of fish removed is based on data from other studies and we monitor carefully to make sure we’re not removing too many of the non-target fish,” she said. “Also, the lake does not contain lake trout or Arctic grayling, or other species of conservation concern.”

Mercury contamination emanates from two sources; it is both naturally occurring – released due to permafrost decline and lower water levels in rivers and lakes – as well as the product of airborne industrial pollution, which can travel thousands of miles from the source.

Health Canada guidelines prohibit the sale of fish containing more than 0.5 milligrams/kilo of mercury, except tuna.

Low told News/North that the big pike and walleye fished from Sanguez Lake often contain levels of mercury far higher than the Health Canada standard.

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