In the wetlands of Wisconsin’s Great Lakes coasts, a universe of life teems, as key fish species enter the wetlands to forage, feed and spawn before heading out again to the vast waters of lakes Michigan and Superior, where they often end up as an important piece of the Great Lakes network of sports fisheries.
The energy these fish create is critical to the structure of the nearshore food web, just as the food web is critical to their survival.
But the balance is both uneven and precarious. These coastal wetlands comprise less than 3 percent of the Great Lakes, but they provide habitat for a whopping 90 percent of Great Lakes fishes. Here’s another percentage-based statistic to consider: Over the past decade, the amount of healthy coastal wetlands in the Great Lakes have degraded/declined by nearly 50 percent.
Backed by funding from Wisconsin Sea Grant, Patrick Forsythe, an associate professor of biology at the University of Wisconsin-Green Bay, is leading a team that’s trying to chart the nearshore linkages between coastal wetlands and sports fish.
Researchers from Notre Dame, Loyola University and Central Michigan University are also part of the project, studying a similar phenomenon in other coastal wetlands around the Great Lakes.
“We know that these wetlands provide 80-90 percent of the energy that flows into the Great Lakes,” said Forsythe. “We don’t know how fish, especially sports fish, play into this.”
By the time this project is done, they’ll have a much clearer picture. Forsythe and his team spent 2014 tracking fish in seven different wetlands areas around Green Bay. They’ll spend this summer, returning to the same sites to re-sample data and determine possible variances.
What they’re actually doing goes well beyond simple trapping and counting. In Forsythe’s laboratory at UW-Green Bay, they’re using laser ablation to slice and examine the chemical signatures in the otoliths of some of the captured fish—an otolith is a structural membrane in the earbones of vertebrates. Using those “fingerprints,” Forsythe and his team are able to determine where the fish have been within each individual wetland and how long they’ve been there, as well as charting movement patterns. Forsythe likens the otoliths to tree rings.
“When a fish is in a wetland, it’s picking up the chemical signature and incorporating it into its skeletal system,” he explained. “Different wetland areas have very different chemical signatures.”
That’s proved to be the biggest surprise for Chris Houghton, a post-doctoral researcher who’s helped Forsythe collect data in the field.
“It’s amazing how unique and varied these habitats are,” Houghton said. “We’ve sampled from Peshtigo all the way up to Peninsula State Park. I’ve worked in the Milwaukee area, and the tributaries there don’t look anything like the systems up here.”
Forsythe’s team initially set out to sample only key sport fish species like walleye, northern pike and yellow perch, but their time spent tracking the wetlands has shown them that other non-sport fish species—like bowfin and lake sturgeon—are just as dependent on the wetland ecosystem, and just as critical to its continued health and survival.
“This is a unique opportunity to point out these understudied fish and add them to our data set,” said Houghton
As the research teams head out to the wetlands again for a second season of data collection, they’re also beginning the time-consuming process of running the otolith-derived chemical signatures through a machine that can identify the chemical fingerprints. What they’re really looking at is a series of 30-40 stable isotopes, an entirely new area of study for Forsythe.
The upshot of their findings could end up bolstering the case that these Great Lakes coastal wetlands are worth saving from threats like development and industrial pollution.
“If you can tell somebody that these wetlands are critical to fish habitat and then show them the scientific evidence, we’ll be in better position to protect them,” said Forsythe. “Right now we don’t have a quantitative number.”
