Past Research: Fish Migration Mysteries

Photo credit: Dave Brenner

One of Dr. Solomon David’s roles at Shedd Aquarium was an aquatic sleuth. He focused on Great Lakes fish migrations — some that have mysteriously reappeared, others that might re-emerge now that obstructing dams have disappeared. In addition to investigating which fishes are doing what and why, his findings were used to inform management strategies for Great Lakes fishes as well as for conservation efforts for migratory fishes around the world.

Return of a lost migration
Solomon was intrigued when lake whitefish recently resumed their spawning migrations from northern Lake Michigan into adjoining Wisconsin rivers and streams. It was a behavior that had disappeared a century ago after deforestation and pollution from North Woods logging operations degraded river habitats. Subsequent generations of whitefish migrated and spawned along the lakeshore. Solomon, working in partnership with the Wisconsin Department of Natural Resources and the University of Wisconsin−Madison (UW−M), wanted to know: What do the re-emerging river migrations mean for the Great Lakes ecosystem?

Lake whitefish are the most commercially valuable native fish in the Great Lakes. Yet we still have many questions about their biology and life history. Historic knowledge on their prelogging migratory patterns is scarce. We don’t know why some whitefish began migrating up rivers again, how these fish differ from the existing lake-migrating population and their importance to the fishery.

To find the answers, Solomon literally put the fish under a microscope. Using tissue samples, he found chemical “signatures” that can be used to tell the river-run fish from the existing lake-run populations as well as reveal what they eat and answer other important ecological questions.

Before runoff, siltation, dams and other manmade impacts made the spawning streams impassable and unlivable for whitefish (and other fishes), this important species provided what are called ecosystem services, helping to renew inland waters each year with nutrients that benefited plants and animals. Thanks to the Clean Water Act of 1972, water quality might have finally improved enough to make spawning possible again in these tributaries. With what Solomon and his research partners discover, critical habitat can be restored and managed to help ensure that these river-run populations thrive.

If you unbuild it, will they come?
Solomon’s second project was a study of the effects of recent dam removals on local fish communities in a Lake Michigan tributary. He was especially looking at migratory northern pike and suckers.

The lowermost dams on Duck Creek, in northern Wisconsin, were removed in 2012. Dam removal can be economically, politically and ecologically controversial. The changes to aquatic ecosystems can be immense as natural water flow is restored after decades.

Working with two years of data on fishes in Duck Creek collected by UW−M partners before the dams were removed, Solomon had a unique before-and-after perspective. He investigated whether migratory fishes will exhibit established patterns of movement or use the newly opened habitat farther upstream for spawning. He also looked at changes in fish biodiversity, habitat and survival rates of the year’s young. In the second season, Solomon included gars and bowfin in his data collection. He was also alert for less welcome fishes. Just as dam removal can benefit native migratory species, it can also be a gateway for invasive migratory species to expand their territories.


The Great Lakes

About the team

Learn more about Dr. David and the conservation research team!


See Solomon's recent work on the National Geographic blog!

You can help!

You can have a hand in keeping lakeshore habitats clean and safe for lake whitefish and other Great Lakes natives by taking part in one of Shedd’s Great Lakes Action Days. By cleaning a beach or restoring native habitat under the guidance of Shedd experts, you’ll be improving the Great Lakes ecosystem for all of its inhabitants—including you!

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