Minnesota’s resident expert on Red Lake said zebra mussels recently confirmed in the North Woods walleye fishery will face a couple of unique growth obstacles and won’t destroy the lake’s trademark hue.
The invasive mollusks are expected to spread and attach en masse to offshore rocks and other substrate, but the coming and going of bottom-scraping ice could keep the mussels out of critical walleye spawning grounds near shore, said Tony Kennedy, the large lake specialist in Bemidji for the Department of Natural Resources.
Red Lake also is home to a large population of freshwater drum — fish that will feed on the mussels, he said. The change in diet isn’t expected to cause the drum to overpopulate.
“It’s not all doom and gloom,’’ said Kennedy, who has assisted in the DNR’s ongoing study of the state’s 10 largest walleye lakes.
Red Lake, a resource that Minnesota shares with the Red Lake Band of Chippewa Indians, is now the last of those sporting destinations to be breached by a significant invasive species. Most of the lake is off limits to state anglers, but Minnesota’s slice of so-called Upper Red Lake draws huge crowds of ice anglers each December and January. In May and June, the oval-shaped lake hosts thousands of fishing boats per week. Two-thirds of the annual walleye harvest happens during winter.
Kennedy said last week’s declaration that the state’s largest inland lake is infested with zebra mussels was an obvious disappointment. In Mille Lacs, Cass Lake and other naturally reproducing walleye haunts, zebra mussel populations have exploded and altered aquatic food webs. The nutrient-sucking mussels also boost water clarity, allowing for deeper penetration of light that can alter plant life and invite unwanted algae. In addition, too much light is viewed as a detriment to daytime walleye fishing.
But Red Lake gets its root beer-colored water from surrounding bogs. Kennedy said zebra mussels won’t wash away the stained runoff even as they constantly filter gallon after gallon. The fingernail-sized mollusks also won’t stop the lake’s west winds from frequently whipping up powerful waves — a key to Red’s walleye-friendly turbidity.
Yes, it’s disappointing that zebra mussels have been introduced to Red Lake, Kennedy said. But the DNR is taking a wait-and-see approach before sounding alarms about the chance that Red Lake walleyes will become less productive.
“Let’s not freak out,’’ he said.
DNR Fisheries prepared for the possibility of a zebra mussel infestation in Red Lake by studying the lake’s food web and measuring baseline levels of zooplankton and other nutrients. State and tribal biologists also have a good handle on the lake’s fish populations.
The pre-infestation data and standardized surveys will allow managers of the lake to recognize changes.
“It has to change things, but is the lake going to be less productive?’’ Kennedy said. “We’ll be able to see ... and we’ll make adjustments.’’
For now, the undeniable presence of breeding zebra mussels in Red Lake won’t stop the DNR from liberalizing the local fishing regulation. For more than a decade, Red Lake has been supporting a surplus of spawning-age walleyes even as officials have eased constraints on the annual harvest.
Kennedy said the agency is again on the brink of easing Red Lake’s special restrictions. The current bag limit is four walleyes, but only one of the fish can be longer than 17 inches. A new proposed regulation will be announced soon, probably changing the parameters around the four-walleye limit.