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The Mystery of the Migrating Fishes: Investigating Clues for Great Lakes Conservation Efforts

The Great Lakes are the largest supply of freshwater in the world, and more than 36 million people depend on them for drinking water. As a result, monitoring and maintaining the health of the Great Lakes ecosystem is an urgent priority. Of the diverse organisms inhabiting freshwater systems, fishes are familiar to scientists and laypeople...

The Great Lakes are the largest supply of freshwater in the world, and more than 36 million people depend on them for drinking water. As a result, monitoring and maintaining the health of the Great Lakes ecosystem is an urgent priority. Of the diverse organisms inhabiting freshwater systems, fishes are familiar to scientists and laypeople alike. They can also serve as effective indicators of ecosystem health.  The Great Lakes are home to over 200 fish species; many of these, such as salmon and lake sturgeon, make impressive migrations to spawn and feed.  These migrations connect lake and river ecosystems, providing valuable nutrient inputs through their waste and carcasses, as well as influencing energy flow in these systems as they eat and forage; they also support vibrant sport and commercial fisheries.

Dr. Solomon David in the field
Dr. Solomon David in the field with a spotted gar, Lepisosteus oculatus (Solomon David/Shedd Aquarium)

Hello everyone, this is Dr. Solomon David and I am a postdoctoral research associate in the Daniel P. Haerther Center for Conservation and Research at the John G. Shedd Aquarium in Chicago, IL. Shedd is committed to protecting the Great Lakes by conducting science and research with our partners, offering immersive learning programs and outreach for all ages, and facilitating work between Great Lakes leaders to develop solutions for conservation challenges. Our research helps advance understanding of Great Lakes aquatic wildlife and habitats in order to develop effective management strategies. As part of Shedd’s work in local waters, I am studying the importance of migratory fishes in the Great Lakes, and how these species and the Great Lakes ecosystem may have been affected by human-related impacts such as habitat loss, invasive species, overfishing, and pollution.

Shedd Aquarium has partnered with several institutions in the Great Lakes region, including the University of Wisconsin-Madison (where I am co-supervised by the Center for Limnology), University of Wisconsin-Green Bay, Wisconsin Department of Natural Resources (WDNR), The Nature Conservancy, and United States Geological Survey Great Lakes Science Center, to investigate two important migrations: the reemergence of lake whitefish (Coregonus clupeaformis) migrations in northern Lake Michigan, and habitat use by migratory northern pike (Esox lucius) after dam removal in Duck Creek, a tributary of Green Bay, Wisconsin.  Our field seasons are just getting started, so I would like to tell you a bit about each project.

Dr. Solomon David with a lake whitefish during field research in Green Bay, Wis. (Solomon David/Shedd Aquarium)

Follow that Fish

Lake whitefish is the largest commercial fishery in Lake Michigan, and it’s an economically and ecologically important species throughout the Great Lakes. In addition to its financial significance for fisheries, the lake whitefish also provides living evidence that helps us investigate the impacts of anthropogenic activity in Lake Michigan and associated tributaries. Habitat degradation via sawmill pollution and deforestation wiped out lake whitefish migrations in the early 20th century, causing lake whitefish migrations to vanish. Yet, recently, we’ve seen some of those migrations reappear. This may be due to the 1972 Clean Water Act, which possibly improved water quality enough to make spawning possible in some of the lake’s river habitats.  If we can understand why certain migrations have reemerged among Lake Michigan populations, we can inform conservation and management strategies for lake whitefish populations and migratory species in and beyond the Great Lakes.

With Shedd and the University of Wisconsin, my team will study the ecological characteristics of river- and nearshore-spawning lake whitefish populations in northern Lake Michigan to understand what might be contributing to these re-emerging migrations and to inform species conservation efforts.  In late fall 2012, I traveled to the area and joined WDNR researchers in sampling two lake whitefish populations: one population that spawns in rivers and one that spawns in lakes. This spring, we will analyze the chemical signatures of those samples and look at morphological differences between populations.  We will continue our fieldwork and lab analyses during the next two years.

Up the Creek

Dam Removal
Standing on the frozen river at the site of the Duck Creek dam removal (Solomon David/Shedd Aquarium)


Beginning this spring, we will start our second major project to study a recent dam removal and the associated fish community in Duck Creek, a Lake Michigan tributary in northern Wisconsin.  Dam removal is an economically, politically, and ecologically charged issue that can have profound impacts on aquatic ecosystems.  In 2012, the lowermost dams on Duck Creek were removed, opening the so-called floodgates for species to begin using the newly available waterway. This situation offers a unique opportunity to study potential reemergence and improved recruitment of Great Lakes Migratory fishes in the system.  Will they use the new habitat further up the waterway? Will they stick with established patterns from the past decades when the dams were present? We hope to answer these questions and more.

Northern pike sign
Signs alert visitors that this area is prime spawning habitat for northern pike (Solomon David/Shedd Aquarium)

Building upon a recent University of Wisconsin-Madison study, we have two years of pre-dam removal data on fishes and habitat in this system. We will focus on northern pike, as well as migratory patterns of other species such as suckers (family Catostomidae), as well as the resident fish community. Through our work, we will learn about how Great Lakes migratory species respond to habitat restoration efforts, information that we hope to share with restoration professionals and wildlife managers considering dam removals in their regions.

Stay tuned for updates from the field!


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Meet the Author

Shedd Aquarium
The John G. Shedd Aquarium in Chicago sparks compassion, curiosity and conservation for the aquatic animal world. Home to 32,000 aquatic animals representing 1,500 species of fishes, reptiles, amphibians, invertebrates, birds and mammals from waters around the globe, Shedd is a recognized leader in animal care, conservation education and research. An accredited member of the Association of Zoos & Aquariums (AZA) and the first U.S. aquarium to be awarded the Humane Conservation™ certification mark for the care and welfare of its animals by American Humane, the organization is an affiliate of the Smithsonian Institute, and is supported by the people of Chicago, the State of Illinois and the Chicago Park District.