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Zebra mussels' effect on local fisheries

Alexandria's Shawn Olson (left) and Terry Crosgrove of Carlos hold up four smallmouth bass that helped them take fourth place with an eight-fish total weight of 23.48 pounds on a Lake Minnewaska tournament during the summer of 2017. Smallmouth fishing on many area lakes has taken off in the ability to catch fish of both size and numbers in recent years. (Eric Morken / Echo Press)1 / 2
This graphic shows the drop in zooplankton levels on Lake Carlos since the infestation of zebra mussels in 2009. Carlos is one of 25 lakes across Minnesota that is part of the Sentinel Lakes Program that does intensive surveying to look at the overall health of the lakes in the program. (Graphic provided by the Minnesota DNR)2 / 2

This is part two of a two-part series on zebra mussels and how the invasive species have impacted fishing and the fish communities on area lakes since they were first discovered in Douglas County on the Alexandria Chain of Lakes in 2009.

When zebra mussels were first found in the Alexandria Chain of Lakes in 2009, one of the questions asked was how this would eventually affect game fish in infested waters.

Fisheries biologists are looking closely at the data, and how things will look 10, 20 years down the road is yet to be determined. As it stands now, many serious anglers in the area talk of populations that are doing well, at least when it comes to targeting certain species.

Where to find those fish—especially walleyes—has changed in many of the infested lakes. That alone can lead to frustrating days on the water for those who do not have the resources, both in time or equipment, to relearn these systems all the time.

"Everything is changing and every year is different," Alexandria's Gene Sullivan said. "I am concerned if some of these outlying lakes start getting zebras in them and they get enough of a population to clean the lake up. Then I'd say we're going to have some problems, and we're really going to have to start learning something new all over again."

Zebra mussels feed on plankton, taking the nutrients from the lower levels of the water's food chain. One zebra mussel can filter one quart of water per day.

Along with their threats to the food chain, zebra mussels attach themselves to and kill native mussels. They can clog water intakes and encrust equipment. They also excrete waste that can fertilize the growth of mats of algae.

Zebra mussels in 42 Douglas County bodies of water have meant expanded weed growth in many of those waters. Anglers have had to adjust their fishing tactics, but there has been nothing concrete to suggest yet that the overall population numbers of game fish in these lakes has dropped directly because of the mussels.

"We've had two surveys since zebra mussels were found (on the Alexandria Chain of Lakes)," Glenwood Area DNR Fisheries Manager Dean Beck said. "I went through for the whole chain, and there's some inconsistencies. It's hard to suggest that those two samples are a function of zebra mussels or not. There's just not consistency among the lakes to suggest there is a cause and effect type of response."

Beck has heard from anglers and lakeshore owners on a lake like Minnewaska who say the overall numbers of zebra mussels seem to have declined from the early introduction period.

"There's some natural population fluctuation going on, but they're generally abundant," Beck said. "Typically, with any invasive species in that introduction you'll get that exponential population growth phase and they'll plateau at a point where their new environment can no longer support that many and they'll drop down to a lower level."

A booming bass bite

Minnesota is known for having some great bass fisheries, and the Douglas County area holds its own among destinations for anglers in the state.

In 2015, Bassmaster Magazine ranked the Alexandria Chain of Lakes No. 35 on its list of 100 best bass lakes in the country. That list was based on three sets of criteria: trophy potential, numbers potential and aesthetics.

In the three years since then, bass anglers continue to talk of local fisheries that are booming. The Reel Team Bass Circuit, which features many top amateur bass anglers in the area, set more record weight numbers during a tournament on Lake Ida this past June, a lake that was infested with the mussels in 2013. Much of that has to do with the growing number of smallmouth bass available in both numbers and size.

"We've had fish up to a 24-incher. We had a 23.5, a 23 and couple 22.5s last year. Those are all smallies, monster smallmouth," area fishing guide Joe Scegura said. "I'd say going out on Miltona or Ida or Minnewaska right now and getting a fish over 20 inches is not a problem at all. That used to be considered quite a trophy."

Scegura also says many of the panfish are doing well in both size and numbers when he fishes them. Expanded habitat for these fish as a result of the zebra mussels could have a role in that.

"You'd expect to see an expansion of aquatic plants," Beck said. "That has occured. It's reasonable to assume then that you're creating an environment more conducive to those fish who are oriented to that. The bass, bluegill, northern pike. They'll be there, but growth rates might slow."

Becks' greatest concern with that weed growth pertains to some of the more popular shallow lakes in his work area.

"Osakis, Mary, Minnewaska—are they just going to come in solid with vegetation?" Beck asked. "Osakis, there is so much shallow-water habitat there. It's a big lake, but is that going to come in with vegetation? There's a lot of 15-foot or less area there."

What does it mean for walleyes?

What more vegetation ultimately means for walleyes is what many anglers are interested in.

Minnesota's state fish relies on rock and sandy bottoms to successfully reproduce. Most of the lakes in this area already have limited natural reproduction, meaning stocking efforts are an important part of the population.

The DNR has their own stocking program. Outdoor groups in the county like the Viking Sportsmen have also invested thousands of dollars over the years to help put walleye fingerlings into these waters.

Local fishing guide Mike Frisch has lived on Elbow Lake for 30 years. He says he had to travel to Otter Tail County to get the best walleye fishing in his early years of guiding. He credited the additional stocking efforts for changing that.

"I think overall fish populations, walleyes are as good as I've seen them," Frisch said. "We have, in my mind, better fishing here or as good as that part of the state."

How sustainable that is on some of the infested waters remains to be seen. Beck, for his part, is at least concerned.

"From a fish management standpoint and wanting to sustain very popular fisheries, a lot of that interest is on walleye," he said. "I see that as a bit of a struggle. We can look at water quality and tell you what species will be most abundant. At a higher trophic level with poorer water quality, walleye and crappie tend to do well. They will persist, but I think bass, pike and bluegill will be benefactors."

A local study and concern level for the future

DNR netting surveys have not yet shown a discernable difference in game fish populations since zebra mussels arrived in Douglas County, but the same cannot be said at the lower levels of the system on Lake Carlos.

The Sentinel Lakes Program, which began in 2008, is a collaborative effort between the DNR and the Minnesota Pollution Control Agency focused on assessing lake water quality data. The program looks at 25 lakes spread out across Minnesota's four major land types every year.

Lake Carlos, a part of the Alexandria Chain, is one of the lakes in the program and the only one that is infested with zebra mussels.

"It gave us a unique window into the impacts of zebra mussels," said Casey Schoenebeck, a Sentinel Lakes Coordinator with the DNR. "The zebras got into Carlos in 2009, and we have seen the phytoplankton decrease and the zooplankton decrease. It was fairly dramatic after zebra mussels came in. Then after the decrease, it's been fairly constant at that lower level."

The Sentinel program looks at every aspect of a lake's health: nutrients and transparency, water levels, temperature, available oxygen, algae levels and aquatic plans. They are studying several facets of the entire fish community such as cisco and lake shiners—popular bait fish for the game species anglers want to target.

"Cisco are a cold-water fish, so we're concerned by the amount of habitat they have," Schoenebeck said. "What we're seeing in Carlos is cisco are moving deeper in the water column over time. That's interesting."

The intensive sampling on Carlos should lead to more answers as to how zebra mussels are affecting that body of water as the years go on.

As for anglers, the current level of concern for the future of fisheries around Douglas County remains mixed. Scegura lives on Lake Mary and said he does not see the same number of lake shiners on the lake as he used to.

"I'm a little concerned about that. Not sure if that has to do with zebra mussels taking away their bait as fry," he said. "You'd think that would go down the whole ecosystem, but it seems like the sunfish and crappies and perch are doing just fine in that aspect."

Alexandria's Drake Herd, who fishes the AIM Pro Walleye Series, says he is not as concerned about zebra mussels as he is about other invasives like Asian carp and rusty crayfish. He points to a lake like Erie that has had zebra mussels since the late 1980s but is still a popular walleye fishery as reason to believe fish populations can survive infestations.

Lake Erie is a huge body of water with almost 870 miles of shoreline. How exactly some of the smaller, shallow waters in the area might be affected 20 years down the road remains to be seen if treatment options to eliminate the mussels are not found.

"I'm kind of an optimist by nature, but I would say I'm concerned," Frisch said. "I'm nervous because we don't know where it's headed. Clear water and a lot of weed growth, I don't care what you're fishing, I think it makes it tougher for the most part. It's not as enjoyable."

There are still thousands of lakes in Minnesota and many in Douglas County that do not have zebra mussels. Those lakes, too, need to be of primary concern, Frisch said.

"I'll see as a guide quite a bit how a local lake property owner will say we have zebra mussels in our lake, or my lake. They're concerned about their particular lake," Frisch said. "My thing there is we have to worry about every lake. This my-lake mentality I think is shortsighted. If my lake ends up in a bad situation, odds are pretty good that every lake is going to end up in a bad situation. We have to look at taking care of all lakes."

Part one of this series can be seen in the Aug. 10 Outdoor section of the Echo Press.

Eric Morken

Eric Morken is the sports and outdoor editor at the Echo Press and Osakis Review newspapers in Douglas County, MN. Follow him on Twitter at echo_sports.

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