Rebuilding a Lost Reef in Saginaw Bay

Picture of Kevin Bunch
Kevin Bunch
October 14, 2019
crane saginaw bay reef

As the last pieces of limestone and glacial cobble splashed into the waters of Lake Huron’s Saginaw Bay in late August, an experiment got underway to see how the ecosystem responds, and if the restoration of a degraded lake system reef might be repeatable elsewhere in the basin.

The project to restore 2 acres of Coreyon Reef in the bay is the culmination of more than a decade of studies, assessments, planning and on-the-water construction work. It hopefully will provide spawning habitat for vital species such as walleye, lake whitefish, lake trout and cisco, said Dr. David Fielder, fisheries research biologist with the Michigan Department of Natural Resources.

The next step will be observing the site in the spring and fall spawning seasons of 2020 and 2021, said Dr. Tomas Hook, researcher with Purdue University. Biologically, these assessments will primarily focus on walleye and lake whitefish (and record any other fish using these sites). A physical assessment also will take place over that time frame to learn more about dissolved oxygen, temperature, water quality and sedimentation at the sites, as well as watching for algal growth and mussel colonization on the rocks, according to Fielder.

Coreyon Reef was a natural, rocky reef that extended from the southeastern inner bay out to the Charity Islands. This site is largely degraded and covered with sediment today due to human-induced erosion, but the project aims to restore the southeastern end of the reef.

The project came out of a Saginaw Bay walleye recovery plan put together by Fielder back in 2004, shortly before the invasive alewife population in Lake Huron collapsed and walleyes started to bounce back. The plan found that reef restoration would be a great avenue to fully recover the fishery, said Bretton Joldersma, Lake Huron coordinator with the Michigan Department of Environment, Great Lakes, and Energy’s Water Resources Division.

construction crew gps saginaw
The construction crew uses GPS and mapping to ensure they drop the rocks in the precise spot. Credit: Michigan DNR

About four years ago, a pre-assessment was carried out looking at Coreyon Reef and several other sites in the bay to see which fish were still using them and in what numbers, as well as any indications of how sediments might be moving around on them. Hook said they found that a small number of walleye and Lake Whitefish have continued to lay eggs but the predominantly sandy remnants provide poor protection from egg predators, including channel catfish and white suckers.

“We think the reef restoration will make it harder for those fish to get at those eggs,” Hook said.

The project initially called for 1 acre of Coreyon Reef to be restored, along with a nearshore reef by the mouths of the Saginaw and Kawkawlin rivers to see how wave action would impact eggs laid in that area, Fielder said. Navigational concerns cropped up late in the process, however, so the nearshore component had to be pushed back for now, with that money going toward a second acre at Coreyon.

The experiment will use limestone on both acres, but one acre also will see a top layer of (more expensive) glacial cobble that more closely mimics natural reefs. Joldersma explained that this will allow researchers to see if the cobble is more attractive to fish than the limestone, and thus worth the extra cost for restoration projects. The total project cost (minus the assessments) came out to about $1.36 million from a number of sources, including the US Great Lakes Restoration Initiative and Saginaw Bay Watershed Initiative Network. Meanwhile, he said the project team is looking into alternative nearshore sites that might work for other restoration projects and secure local backing to fulfill the other part of their research near the Saginaw River mouth that was pushed off.

While there have been reef restoration projects in the St. Clair and Detroit rivers, Joldersma said this project, being done in a relatively shallow, productive part of the lake, has some fundamental differences that may prove informative for helping fisheries throughout the Great Lakes.

“Hopefully this will be a success story that we can learn from and apply to other reef restoration projects in Saginaw Bay, and around the Great Lakes,” Joldersma said.

Hook said other routes toward restoring reefs also are being explored, including experiments to see if blowing sediment off of buried reefs is a viable approach.

Picture of Kevin Bunch
Kevin Bunch

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.