Diagram of spawning reefs in the Detroit and St. Clair rivers. Image: Michigan Sea Grant
By Katie Amann
LANSING — Whitefish, lake sturgeon and walleye will soon have a new place to breed.
A team from Michigan Sea Grant and its research and industry partners is currently laying rock for a new spawning habitat at Harts Light in the St. Clair River.
This new habitat will span four acres, which is about three times larger than the spawning reef built earlier this year at Pointe aux Chenes near Algonac.
Another reef will be built in the Detroit River next year.
Bruce Manny, a fish biologist with the U.S. Geological Survey (USGS) Great Lakes Science Center in Ann Arbor, said the Harts Light location is an experiment because there is no evidence that fish are already using the area for spawning. However, it’s positioned in the main channel of the St. Clair River, which puts it directly in the path of the movements of whitefish, walleye and lake sturgeon.
“They can’t help but stumble upon it,” Manny said.
Lake sturgeon, walleye and whitefish typically spawn in deep, rocky areas with fast-flowing water.
That type of habitat is important because “it provides a great safe place for fish to deposit their eggs,” said Lynn Vaccaro, a coastal research specialist at Sea Grant. “If they don’t have that kind of rocky habitat, then their reproduction is a lot less successful,” she said.
Manny and fellow USGS scientist David Bennion developed a model to select sites for future restoration efforts in the St. Clair—Detroit river systems. That model was used to pick the Harts Light location which is 60 feet deep with fast-flowing water, about 2.9 mph.
Vaccaro said the goal is to choose locations that “will remain clean and free of silt and free of invasive species and algae and other organisms that degrade the habitat structure over time.”
Placement of rocks at Harts Light will take eight to 12 weeks to complete. Once finished, the new spawning habitat will consist of an interlocking bed of four- to eight-inch pieces of limestone about two feet deep.
Based on results from the construction of previous spawning habitats, the Sea Grant team determined that this size limestone discourages invasive species, such as sea lamprey, from building nests. However, it’s still conducive to whitefish, lake sturgeon and walleye spawning.
According to Vaccaro, the Detroit and St. Clair rivers are important restoration locations because they are “the heart of the Great Lakes.” Other rivers are dammed or have other obstacles that keep fish from migrating upstream, but these two rivers are still free flowing.
“It’s degradation we’re hoping to reverse, but there’s also this stronghold of biodiversity that makes us feel really optimistic about restoring populations here,” Vaccaro said.
Restoration efforts focus on increasing populations of sturgeon because it’s a threatened or endangered species in both the U.S. and Canada.
Manny said, “Whitefish and walleye are the so-called ‘money fish’ of the Great Lakes.”
According to Vaccaro, those two species are caught commercially and are also popular for recreational fishing.
“The hope is that if we boost populations here, then those fish can spread out and repopulate the rest of the Great Lakes,” she said.
During the late 1800s and early 1900s, the Detroit and St. Clair river systems underwent significant changes and their bottoms were dredged to create deep shipping channels.
According to a study by Manny and Bennion, 430 million cubic yards of material were removed from the bottom of the Detroit River alone. In both rivers, 800 to 1,000 acres of prime fish spawning habitat were removed.
The Harts Light project is the sixth spawning habitat built by the Michigan Sea Grant team in U.S. and Canadian waters of the two rivers. Through ongoing restoration efforts, the team plans to construct a total of 15 acres of spawning habitat.
Vaccaro said, “This is a realistic goal given the resources and given the overall remediation plan of the river.”
Sea Grant received $2.3 million in grants to build three spawning habitats in 2014. In addition, the Great Lakes Restoration Initiative provided $2 million for physical and biological assessments of the projects.
Richard Drouin, a lead management biologist at the Ontario Ministry of Natural Resources and Forestry, said the reefs seem to be getting “some positive results in terms of production off the reef. Time will only tell what those reefs are doing in terms of contributions to the local fisheries.”
The Sea Grant team plans to finish the Harts Light spawning reef this year and to begin construction on the Grassy Island spawning reef in the Detroit River next spring.