Midwest Fish & Wildlife Conference 2016

AUTHORS: Catherine Riseng*, University of Michigan, School of Natural Resources and Environment; Kevin Wehrly, Michigan Department of Natural Resources; James McKenna, USGS, Great Lakes Science Center; Chris Castiglione, U.S. Fish and Wildlife Service; Lizhu Wang, International Joint Commission; Edward Rutherford, NOAA, Great Lakes Environmental Laboratory; Lacey Mason, University of Michigan, School of Natural Resources and Environment; Lucinda Johnson, University of Minnesota, Natural Resources Research Institute

ABSTRACT: We used variables describing depth, thermal regime, and mechanical energy to develop an aquatic ecological classification for waters of the Great Lakes. The classification is developed across aquatic zones including coastal (0-3 meters), nearshore (3-30 meters), and offshore (>30 meters) areas for all five lakes. The nearshore and offshore zones were divided into shallow and deep categories. We calculated cumulative degree-days above zero in the coastal zone using surface temperatures, and in the nearshore and offshore zones using the mean water column temperature of the upper 20 meters. Mechanical energy was described using relative exposure index in the nearshore and coastal areas and dominate spring circulation patterns in the offshore zone. We developed classification thresholds for each of these variables using information from the literature and from a team of Great Lakes’ experts. Our resultant classification contains ~50 unique aquatic ecological units (AEUs) across the entire Great Lakes. Lake Superior and Lake Erie were relatively homogeneous whereas Lakes Michigan, Huron, and Ontario were more complex and contained many more ecological units. Our classification describes the major environmental gradients structuring chemical, physical, and biological factors, and provides a means to simplify and describe the complex array of habitats found throughout the Great Lakes. Because our classification was developed for both U.S. and Canadian waters using the Great Lakes Aquatic Habitat Framework, it provides a common spatial and classification framework for assessing and managing the Great Lakes at the basin scale.