Artificial reef under construction in Lake Erie near Lorrain, Ohio. Image: Ohio Sea Grant
Artificial reefs in all five Great Lakes and some of their tributaries are intended to improve sport-fishing, enhance fish habitats and reduce the impact of current and waves.
But it’s uncertain whether they’ve been as successful as hoped in achieving those goals, according to a new study by scientists at the U.S. Geological Service’s Great Lakes Science Center in Ann Arbor, Mich.
The problem is a shortage of long-term monitoring data on the region’s expanding number of artificial reefs.
“Artificial reefs have been proven to attract fish and increase catch rates in recreational fisheries, but the ability of reefs to increase fish abundance is not well documented in freshwater and marine systems,” according to the study. “Artificial Reefs and Reef Restoration in the Laurentian Great Lakes” appeared in the Journal of Great Lakes Research.
Some research shows increased spawning and fish feeding success, the study said, and sometimes the deposition of fish eggs has been greater on artificial than natural reefs.
However, “from an ecological perspective, whether artificial reefs can function as well as natural reefs remains unclear. Some artificial reefs have produced fish communities that are different in composition from those in natural habitats,” the study said. “We found no studies that directly linked artificial reef projects to increased fish abundance at the population level.”
Matthew McLean, a co-author of the study, said, “What has been done shows a lot of promise. Monitoring them is very important” to provide “solid evidence they are doing good.”
McLean, formerly with the Great Lakes Science Center, is now a technician with the U.S. Fish & Wildlife Service.
Co-author Edward Roseman, a research fishery scientist at the center, said, “We don’t know what we’d learn by monitoring these things for a long time.”
According to Roseman, long-term monitoring data could help scientists decide where to site future artificial reefs.
“What are the physical conditions at the bottom, and the current systems?” he said. That includes the river systems’ depth, flow and suitability for species. And it would be useful to know how the reefs mature over time, including whether they silt in from sediment and whether vegetation grows on them.
Almost 40 reefs were built in the Great Lakes basin between the late 1800s and 2013, according to the study, with the most in Lake Michigan and the fewest in Lake Superior.
They’ve been used for fishery management for more than four decades. Those designed to improve recreational fishing of species such as smallmouth bass and walleye were most frequently placed near cities, including Chicago and Cleveland.
Other artificial reefs are newer than 2013, such as ones at Harts Light in the St. Clair River and at Pointe aux Chenes near Algonac in Michigan. Another recent project in the Milwaukee River was built for sturgeon, walleye redhorse and other rock-spawning species.
And this summer, construction is scheduled for an artificial reef at Grassy Island north of Grosse Ile in the Detroit River, Roseman said. Michigan Sea Grant is coordinating that project with federal funding from the Great Lakes Restoration Initiative.
He said the initiative has paid for the majority of such projects during the past five years, with other support from local and state governments, nonprofit organizations and the Ontario Ministry of Natural Resources and Forestry.
While most were intentionally constructed for fish habitat, the earliest ones were unintentional, such as a 19th-century reef in the North Channel of the St. Clair River formed when ships dumped coal cinders while moored at the site near Detroit.
Their size, design and construction materials–including limestone, granite cement and rubble from an old sports stadium–varied.
Monitoring of projects in the Detroit and St. Clair rivers already has shown that “we can get away with cheaper material, such as broken limestone which is a native geological form” in the Great Lakes Basin “and less expensive than fieldstone,” Roseman said.
The newly published study examined prior research about eight artificial reefs in Lake Michigan, six in Lake Erie, three each in lakes Ontario and Huron, two in Lake Superior, nine in connecting channels and six in tributaries.
“Although artificial reefs have been successful in attracting fish for feeding and spawning purpose, the long-term effects on fishes remain unclear,” it said.
The scientists found that most monitoring programs are too short and on too small a scale to effectively evaluate long-term effects. Biological monitoring in the Great Lakes generally lasts only two to seven years after construction, for example, and McLean said there’s even less monitoring of the physical structures for erosion, sedimentation and vegetation.
The study calls for development of better standards to monitor the reefs’ biological and physical attributes. That would include water quality parameters, fish use and invertebrates.
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