AIS Research on Mille Lacs Lake may explain walleye woes

Duluth News Tribune 2/19/17

Researchers hope to get to the bottom of the challenges that face Mille Lacs Lake walleyes by digging deep into the lake's past.

A group of researchers drilled seven core samples from the lake floor this past week, hoping to look back at least 50 years at what was going on then and now, specifically since the invasive species, spiny waterflea, was discovered there in 2009.

The group of scientists from the Minnesota Aquatic Invasive Species Research Center and University of Minnesota Duluth plan to analyze that 50 years’ worth of sediment pulled from the lake, after extracting about 200 years’ worth from the icy depths. Researchers hope to learn more about the role that spiny waterfleas have had in disrupting the food web and contributing to the decrease in walleye numbers.

Researchers will analyze the data to identify potential ecosystem impacts that could be felt by game fish like walleye. This study could also help researchers learn more about the long-term threat to fish posed by spiny waterflea, and how Minnesotans will be affected, according to Christine Lee, communications specialist with Minnesota Aquatic Invasive Species Research Center.

Donn Branstrator, associate professor with the University of Minnesota Duluth, partnered with the Minnesota Aquatic Invasive Species Research Center for this project. He was out hopping from hole to hole this week gathering samples from three main sites throughout the basin of the lake.

In his initial assessment of the sampling, there was not much to be surprised about except for the high volume of people on the lake.

"There are a ton of fish houses out here," he noted shortly after pulling the last sample from the lake.

It's possible spiny waterflea made it into Mille Lacs Lake earlier than 2009 and went unnoticed for a while, Lee said. They were first discovered in Minnesota in 1987 in Lake Superior and are now in about 40 waterbodies in Minnesota. They are native to Asia and Europe.

The hypothesis with spiny waterflea is that they eat so much native zooplankton, they wipe out the bottom of the food chain and disturb the whole web, Lee said. However, in lakes that also have zebra mussels, it can be hard to pinpoint which species is doing what.

"There is a lot that is still unknown regarding their ecological impacts; we do know that in addition to these ecological impacts, they also clog the eyelets of fishing rods and cause problems for recreationalists," Lee said in an email.

As a way to better understand what effect spiny waterflea and zebra mussels have on a fishery, the researchers are not only looking at Mille Lacs, which has both invasive species, they also plan to take samples from Lake Winnibigoshish and Leech Lake (which have zebra mussels, but no spiny waterflea) and Kabetogama Lake (which has spiny waterflea, but no zebra mussel.)

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