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How Zebra Mussels Were Removed from Lake Winnipeg - Almost

IJC staff
October 28, 2014
Zebra mussels in a container

This story starts with a single zebra mussel found on a boat moored at a Lake Winnipeg harbor in Manitoba.

It ends with boat washing stations, billboards and lessons for other watersheds on dealing with the threat of invasive species.

In October 2013, the solitary mollusk was reported by the public, after it was found attached to the hull of the boat. Authorities had been monitoring the Red River - one of the lake’s main inflows - at the Canadian-U.S. border for years, and never detected any evidence of the mussels.

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Zebra mussels are a concern for multiple reasons, from fouling beaches with sharp shells that can cut swimmers’ feet to creating circumstances that enhance nuisance algae and curbing native species. Zebra mussels also cling to surfaces, and can clog water supply pipes at power plants and other water supply infrastructure. Lake Winnipeg drains via the Nelson River, which flows to Hudson Bay, home to several hydropower stations.

So the lone mussel triggered a rapid response protocol to attack the threat, from the Department of Conservation and Water Stewardship in Manitoba and other agencies.

They only had a few weeks before the water would be frozen, and the mussels would be difficult to detect and ready to reproduce in the spring.

“We had a small group of people in and out of the water physically searching the human infrastructure such as docks, beaches and the hulls of vessels, trying to figure out where these things were,” said Jeff Long, manager of Fisheries Science and Fish Culture at the Department of Conservation and Water Stewardship.

Crews found about 500 mussels at four harbors on the lake: Winnipeg Beach, Gimli, Arnes and Balsam Bay. The mussels were found on the underside of docks, and on boats pulled from the water for the winter. Initial samples, analyzed by the University of Guelph, suggested the mussels had been in the water – but gone undetected – for more than a year, based on their size.

However, given that the samples were taken from infrastructure that could not support mussels through the winter, it became apparent that the mussels were from the 2013 open water season and exhibited a high growth rate.

Zebra mussels in a container. Credit: Manitoba Department of Conservation and Stewardship.
Zebra mussels in a container. Credit: Manitoba Department of Conservation and Stewardship.

But what about the open waters? Lake Winnipeg, the world’s 10th largest lake, was too vast to search, especially in such a short period of time. So the department looked at samples collected from a research vessel that’s been plying the lake for the last decade. They found no trace of zebra mussels.

“By all appearances, we were in an early stage of an infestation,” Long said.

In the midst of the search, those involved had formed a scientific advisory team of experts to come up with recommendations on how to fight the mussels. The team found a company that had eradicated zebra mussels from a quarry in Virginia, and decided to use a similar method in Lake Winnipeg, closing off the four infected harbors with a construction-type silt curtain.

The treatment began in May 2014, using potassium chloride, also known as potash, a chemical fertilizer. The dosage was targeted at 100 parts per million, so as not to harm finfish, but kill the zebra mussels.

By June, the work was finished.

Following the potash treatment, departmental staff undertook monitoring of the treated harbors. “There was no evidence of juveniles in the spring sampling done inside and outside of the treated harbors,” Long said.

Not finding any evidence of zebra mussels in the treated harbors was important, since a single zebra mussel can produce up to 1 million eggs, and that amount of spawn could quite easily re-colonize the harbors.

“Following up the harbor monitoring, the department undertook specific zebra mussel sampling from the research vessel, the Namao, since it was reasonable to expect that any substantial population of zebra mussels in the lake would reveal itself through veligers (early life-stage zebra mussels) in the open water,” Long added.

In the summer, hearts were broken. In the southern basin, toward the end of July, nine tiny mussels were found in samples collected by staff aboard the research vessel. Subsequent sampling found adult mussels on the outer breakwater wall at Balsam Bay and juvenile mussels at the harbors and on flotsam in the open water.

Back to the rapid response plan: “We enhanced our containment program, which had always been aimed to prevent the spread out of the lake and into other water bodies in Manitoba,” Long recalled.

This enhancement has resulted in a significant increase in a Watercraft Inspection Program, with more teams and boat decontamination units present than the department has ever operated in Manitoba.

A decontamination unit being used on Lake Winnipeg. Credit: Manitoba Department of Conservation and Stewardship.
A decontamination unit being used on Lake Winnipeg. Credit: Manitoba Department of Conservation and Stewardship.

“We still think it’s in everyone’s interest to prevent the spread up slope,” Long said. “Zebra mussels don’t swim upstream, but human vectors seem to manage to do that very well,” allowing the mollusks to travel on the hull or in the live wells of a boat that’s moved from one lake to another, for instance.

More inspectors are being trained as containment efforts ramp up. The focus is on the south basin, where mussels have been found most recently.

Stationary and mobile units are hitting high-boat traffic areas. Boats are cleaned with high-temperature, high-pressure washers before they leave on trailers.

There’s also been a media campaign of billboards and other materials to educate the public about ways to prevent the spread of mussels.

An example from the ‘Don’t Move a Mussel!’ campaign.
An example from the ‘Don’t Move a Mussel!’ campaign.

So far, reaction from the public has been mostly positive, Long says. Meanwhile, the department has been contacted by others interested in Lake Winnipeg’s fight against the invasive mussel, including Spain, and Texas and California in the U.S.

“We’ve learned some things about the difficulty of eradication, the rate of infestation, and the value of prevention,” Long said.

IJC staff

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