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DNR officials confirm established zebra mussel population in Cass Lake

BY Pat Miller/Bemidji Pioneer

It probably was only a matter of time before an invasive species would find its way to one of the major fishing lakes in the Bemidji area.

A little more than a year ago zebra mussels were discovered in Lake Winnie and on Friday Minnesota Department of Natural Resources officials confirmed that zebra mussels now have infiltrated the waters of Cass Lake.

A citizen discovered three hollow zebra mussels shells earlier this week while collecting shells on the beach on the southeast corner of Cedar Island. According to DNR officials, that portion of Cedar Island is a popular beach and swimming area where people park their watercraft to swim and fish.

The shells were brought to a DNR creel clerk who submitted them to the fisheries staff at the Bemidji Area DNR office and the staff verified them as zebra mussels.

On Tuesday and Wednesday, DNR Aquatic Invasive Species officials conducted a search of the waters surrounding Cedar Island and inspected more than 200 items along 565 feet of shoreline and 2,500 square feet of lake habitat. The search revealed zebra mussels in a variety of sizes.

“We can’t date when the zebra mussels first came to Cass Lake but it appears that they have been in the lake for years,” said DNR Northwest Region Fisheries Supervisor Henry Drewes, who is based in Bemidji. “It is very disappointing to find zebra mussels in Cass Lake but it is not a surprise. Fishing boats now come from such a wide area and Cass Lake receives a great deal of pressure.”

Evidence of that pressure can be found this weekend as the Cass Lake Chain is home to a Master’s Walleye Circuit tournament. Last year the tourney attracted 76 boats and the anglers represented every corner of the country.

“The zebra mussels that were found in Cass Lake did not likely come from Winnie,” said Gary Bernard, the DNR Bemidji Area Fisheries supervisor, referring to the discovery of zebra mussel veligers in Winnie last summer. “Zebra mussels tend to spread downstream so I doubt these came from Winnie. I think they would have had to have been transported somehow by a boat, a dock or a lift.”

Once established, there is nothing that can be done to eliminate the zebra mussels. And the mussels in Cass Lake are established.

“In rare instances where you find them early (such as on a boatlift that just was placed in the water), you can treat small areas,” Barnard said. “But in a lake like Cass, there is little we can do.”

Further testing will indicate if the zebra mussels are also present in the other lakes of the Cass Lake Chain, including Buck, Andrusia, Wolf, Pike Bay, Pug Hole, Kitchi, Little Rice and Big Rice. The assumption is that they are or, at least, will be soon so all of those connecting waters have also been designated as infested.

The impact the zebra mussels will have on the lakes and on the fishing isn’t fully known and DNR officials will learn on the go.

“We understand the recreational impact (zebra mussels have very sharp shells and will pose a problem to swimmers and waders) but the effect on the ecology is less certain,” Drewes said. “We know that in lakes with zebra mussels the water is clearer. The (density) of the zooplankton will change and we will learn how that will affect the fish populations.”

Zebra mussels are efficient filters and as they strain the water they consume the nutrients. Those nutrients are also what sustains the zooplankton and the zooplankton is among the favorite food sources of young fish.

“Zebra mussels aren’t eating the zooplankton but they filter the nutrients in the water that the zooplankton feed on,” Barnard said. “Larval walleyes and perch need zooplankton to feed so you need a healthy zooplankton population to grow and raise fish.”

DNR officials have been monitoring the zooplankton population in many of the state’s premiere fishing waters for the past few years in an effort to establish baseline data. Among those lakes are Cass, Bemidji, Winnie, Leech and Red.

“We have that pre-date information and we will be able to track what changes occur in Cass Lake,” Drewes said.

“If there is a response in the zooplankton because of the zebra mussels, we will know,” Barnard said. “We have the data to compare any changes to.”

Zebra mussels are in Cass Lake and there isn’t anything anybody can do to remove them. What can be done, however, is continue the vigilant fight to prevent zebra mussels from spreading further and do everything possible to keep other invasive species out of Cass Lake’s waters.

“Even users of Cass Lake have to step up their vigilance,” Drewes said. “Zebra mussels are in Cass Lake but we can’t write off the lake. We need to work even harder to prevent other invasive species such as spiny water flea from reaching Cass.”

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