WorldWide Drilling Resource

Sediment Cores Could Answer Questions About Declining Walleye Population Compiled by Bonnie Love, Editor, WorldWide Drilling Resource ® Minnesota is the Land of 10,000 Lakes , and with more than 11,800 lakes over ten acres in size, it is a fisherman’s dream. The most popular game fish in Minnesota is the walleye with its thick white fillets. In addition to its handsome shape, walleye are very elusive in nature, making them the ultimate prize amongst anglers. When officials noticed a change in the walleye population in Mille Lacs Lake, scientists were cu- rious about what was causing the noticeable decrease. What they noticed was the small walleye weren’t making it past their third autumn in the lake to become big walleye. Drilling core samples from the lake floor is helping to solve the mystery. A group of researchers drilled seven core samples hoping to look back at least 50 years, to determine what was going on then and now, specifically since an invasive species, spiny water flea, was discovered in the lake in 2009. Donn Branstrator, associate professor with the University of Minnesota Duluth partnered with the Minnesota Aquatic Invasive Species Research Center for the project. It's possible spiny water flea made it into Mille Lacs Lake earlier than 2009, and went unnoticed for a while. After all, when core samples were analyzed from Island Lake Reservoir near Duluth, it was discovered the spiny water flea was actually present about ten years before it was noticed. Native to Europe and Asia, the spiny water flea (bythotrephes longimanus) was first noticed in Minnesota in 1987, and has spread to 35-40 Minnesota lakes over the past 30 years. The working theory is the invasive species eat so much native zooplankton, they wipe out the bottom of the food chain, disturbing the whole web. However, in lakes which also have zebra mussels, it can be hard to pinpoint which species is doing the most harm. Project scientists from the Minnesota Aquatic Invasive Species Research Center and Universi ty of Minnesota Duluth plan to analyze the 50 years of sediment pul led from the lake, after extracting about 200 years worth of cores from the icy depths. Once researchers analyze the sediment, which could take at least a year, they will start comparing the new data to the historical data to see what conclusions can be drawn. The basin of the lake provided good samples in and around 30 feet of water. The core samples were taken back to Duluth to be refrigerated and later care- fully sliced a half centimeter at a time and analyzed under a microscope. “By taking cores from around the lake, it will allow us to find remnants, or fossils if you will, of bythotrephes and see where it entered the lake and when. These cores should get us back 250 years,” said Andy Bramburger a research asso- ciate at the Natural Resources Institute at the University of Minnesota Duluth who is in charge of the core samples. Scientists also plan to take core samples from Kabetogama Lake, Leech Lake, and Lake Winnibigoshish. The study of these lakes is set to run through June of 2019. 18 OCTOBER 2017 WorldWide Drilling Resource ®