MAZINA’IGAN PAGE 4 SUMMER 2017 Mille Lacs (a shallow, well-mixed lake, with moderate amounts of dissolved nutrients“mesotrophic”)isafamouswalleye(ogaa)fisheryinMinnesotaharvested by both tribes and state anglers. Walleye are harvested by the Mille Lacs, Fond du Lac, Bad River, Mole Lake, St. Croix, Red Cliff, Lac du Flambeau, and Lac Courte Oreilles tribes located in the 1837 Ceded Territory. Tribal members traditionally harvest walleye during the spring spawning period with gill nets and spears, with minimal harvest occurring with rod and reel throughout the year. Mille Lacs Lake is also a prominent walleye fishery among recreational anglers, who target walleyes with hook and line year-round, except duringearlyspring.Asaresult,tourismassociatedwiththewalleyefisherysupports the local economy. Overall, walleye have been the centerpiece for both subsistence and recreational fishing in Mille Lacs Lake. Cooperative walleye research The Minnesota Department of Natural Resources (MNDNR) with support from the Great Lakes Indian Fish and Wildlife Commission (GLIFWC) and Mille Lacs Band of Ojibwe conduct gill net surveys throughout the lake each fall. These surveys allow biologists to estimate the number of mature adult walleye in the lake. These yearly estimates of adult walleye abundance are supported by a more laborious mark-recapture population estimate, approximately every five years. In 1999, Mille Lacs Lake had over 2 million pounds of adult walleye but declined to approximately 1.5 million pounds in 2005, a low adult walleye biomass for this lake but within the range of natural variation. Unfortunately, adult walleye stocks continued to decline, reaching an all-time low of approximately 0.7 million pounds in 2013. Luckily, a relatively large year-class (i.e., lots of young walleye) was produced in 2013, and most survived to become adults, resulting in a moder- ate increase to 0.89 million pounds of adult fish in 2017. Even with this moderate increase, the pounds of adult walleye are still well below historical levels (Figure 1; Figure 2). The production of more large year-classes (i.e., lots of babies) and subsequent survival to adulthood is required to recover walleye stocks to near historical levels. Monitoring the harvest MNDNR, GLIFWC, Mille Lacs, and Fond du Lac are responsible for moni- toring harvest of walleye from Mille Lacs Lake throughout the year. Creel surveys conductedbytheMNDNRcollectinformationfromindividualanglersaboutspecies, fishsize,baittype,numberofhoursfished,numberoffishcaught,numberofboats, and number of ice shanties. From this information, MNDNR estimates the number of walleye harvested by anglers every year, including the number of fish that die after being released. GLIFWC counts and weighs every fish captured by netting or spearing, thus providing an exact number of walleye that tribal members harvest by these methods every year. Combined, these numbers equal the total walleye fishing mortality every year. In 1999, total fishing mortality was approximately 625,000 lbs but was reduced by more than half in 2005 (~275,000 lbs) because of a lower adult population size. Total fishing mortality decreased again to 160,000 lbs in 2013 when pounds of adult fish was at its lowest (~0.7 million pounds). Corrective management actions were taken by the State of Minnesota and Ojibwe Bands to limit harvest to relatively low levels so that adult walleye stocks would not continue to decline, with a low total fishing mortality of approximately 46,000 lbs in 2016 (Figure 1; Figure 3). The invasive species wildcard A potential complicating factor in understanding the decline of walleye in Mille Lacs Lake was the introduction of invasive species. In 2005, zebra mussels were found in Mille Lacs Lake, which were most likely introduced by hitchhiking on boats and trailers or in bilge water. Similarly, spiny waterflea was introduced in 2009 and again, these organisms were most likely transported by unknowing boaters (see invasive species article this issue for more info and this website (http://stopaquatichitchhikers.org). These invasive species can compete with and consume native zooplankton (microscopic organisms that age-0 fish eat), which can negatively affect their population size. In fact, by 2012, the native zooplank- ton population decreased from ~60/liter to less than 20/liter, directly correlating with the increasing number of spiny waterfleas and zebra mussels in the lake. The effect these exotic species have on top predators (walleye, northern pike) remains unclear, but research efforts are underway that will attempt to understand how productivity and food web connections (who is eating whom) might have changed since these invasions. Althoughmoreresearchisneededtounderstandrecentchangesinthewalleye fishery, it is clear that continued implementation of a conservative management strategy will help promote recovery. The good news is that the State of Minnesota and Ojibwe Bands have agreed to a small increase in the total fishing mortality to 64,000 lbs in 2017. This approach will result in a moderate increase in the mature adult population in 2017, an outcome that should assist with the recovery of this fishery. GLIFWC and MNDNR will need to monitor this fishery closely over the coming years to ensure management strategies (e.g., habitat protection, harvest limits) are achieving mutually agreed upon recovery goals. Please contact Dr. Aaron Shultz, Mark Luering, Ben Michaels, Carl Klimah, Dr. Adam Ray, or Joe Dan Rose for more information. Total Fishing Mortality Figure 1. A closer look at Lake Mille Lacs management By GLIFWC Inland Fisheries Section Figure 2. Adult walleye biomass (pounds of adult fish) in Mille Lacs Lake from 1998 to 2016. Solid line represents a best fit curve. Figure 3. Walleye fishing mortality in Mille Lacs Lake from 1998 to 2016. Mortality estimates include fish that die after being released by anglers. Zebra Mussels. (National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory photo) Changes in the Ecosystem • LAKE MILLE LACS •