White suckers in a tributary of Lake MichiganWhite suckers in a tributary of Lake Michigan (©Shedd Aquarium/Karen Murchie)

By Dr. Karen Murchie, Research Biologist, Shedd Aquarium

Mighty fish migrations are among the greatest marvels of nature. On April 21, 2018, people around the globe will celebrate World Fish Migration Day, building awareness of just how critical moving between habitats is for many species. Why spend the energy to migrate? These fish are on a quest to find suitable sites to spawn and then move back to productive habitats to feed for the rest of the year.

Culverts are installed to allow road crossings over streams, but can be a barrier to fish migrationCulverts are installed to allow road crossings over streams, but can be a barrier to fish migration (©Shedd Aquarium/Karen Murchie)

Migratory fishes come in all sorts of sizes, from wee minnows to giant catfish that weigh three times as much as a refrigerator! Regardless of size, many challenges arise during these marathon swims. For example, man-made barriers such as dams can stop fish in their tracks. Rivers around the world now have at least some dams, but few of them include passages to allow fish to migrate around or over them. Not even the Olympic athletes of the fish world, salmon, can overcome such obstacles.

While dams are numerous, their numbers pale in comparison to road crossings. Culvert pipes are installed where our roads pass over streams and rivers. If poorly designed or maintained, these road crossings create major challenges for navigation. In the Laurentian Great Lakes region alone, there are over 257, 000 obstacles (culverts and dams) that fish encounter in their migratory quests. When fish can’t reach ideal locations for spawning or feeding, the consequences for their population size can quickly become noticeable.

Dr. Murchie installs a monitoring station where citizen scientists will record their observations of sucker migrations and collect key environmental dataDr. Murchie installs a monitoring station where citizen scientists will record their observations of sucker migrations and collect key environmental data (©Shedd Aquarium/Heidi Zeiger)

World Fish Migration Day is an opportunity to raise awareness about the threats that migratory fishes face, but I think about these challenges year-round. As a research biologist at Shedd Aquarium, I’m currently working with Dr. Pete McIntyre and other scientists from the University of Wisconsin-Madison’s Center for Limnology to discover the effects of culverts on the greatest of the spring migrations from the Great Lakes: white suckers (Catostomus commersonii) and longnose suckers (Catostomus catostomus)! Along with understanding which barriers block fish, I’m also concerned with how the timing of migrations is shifting as our climate warms. Why would it matter if the suckers show up in the streams earlier than usual? Because they fertilize the streams, boosting the growth of plants in much the same way that a gardener does by adding fertilizer to young plants. These nutrients kick-start the food web each year, boosting the growth of the bugs that become prey for stream fish, birds and bats. If the suckers show up before the algae and invertebrates are ready for their growth spurt, the productivity of the whole ecosystem could be affected.

Citizen scientists Julie Knox, Matt Peter, and Jane Whitney assist in the installation of equipment as part of the sucker migration monitoring programCitizen scientists Julie Knox, Matt Peter, and Jane Whitney assist in the installation of equipment as part of the sucker migration monitoring program (©Shedd Aquarium/Karen Murchie)

With the help of citizen scientists who volunteer their time to record the arrival of the fish in Illinois, Wisconsin and Michigan, we are creating a first-description of the timing of the enormous sucker migrations from Lake Michigan and Lake Superior. Last year alone, our team documented the migrations of more than 26,000 fish.

We are not alone; many other scientists worldwide are investigating other aspects of fish migrations and how to help reduce the obstacles that block these spectacular animals from fulfilling their quest. Through public assistance and collaborative efforts, we can all help migratory fish get where they need to go.

To learn more about World Fish Migration Day and find a celebration near you, visit www.worldfishmigrationday.com. And, to learn more about our research on sucker migrations, visit Shedd Aquarium’s website.

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