By Howard Meyerson
Grand Rapids, MI – Efforts this summer to improve lake trout, whitefish and cisco populations in Grand Traverse Bay, by building a stone reef near Elk Rapids, produced some good results during the fall spawning season. Lake trout spawned there and deposited more eggs than last year, but that wasn’t the case with ciscoes and whitefish.
“We don’t know why,” said Randy Clarmunt, fisheries research biologist for the Michigan DNR, who has been studying the area and knows they have spawned there. “Ciscoes (lake herring) are finicky. Their egg deposition there isn’t promising. It’s safe to conclude that they didn’t spawn there in any great numbers, but this is the first year.
“With lake trout we went from less than one egg per square meter (last year) to an average of six per square meter – and as high as 10 per square meter,” Clarmunt said. “If you multiply that by entire surface area (of the reef) we estimate having 10,000 native fish eggs there this first year. We’ll go back in spring and look at the emerging larvae to see if we have a tenfold increase. That would be exciting.”
The reef project was completed in August. It required placing 450 tons of limestone on top of what researchers thought was a degraded natural reef. Stone was piled up to provide protective nooks and crannies for eggs and protective nursery areas for young larval fish. Both were susceptible to predation by rusty crayfish and gobies that are plentiful there, and being swept out of the old reef by strong wave actions.
Egg sampling devices placed in the reef confirmed the results, according to Clarmunt. That new reef and two others nearby, where spawning success historically has been higher, all have been studied by Clarmunt for a decade.
The $181,000 project is collaboration between The Nature Conservancy, Michigan DNR and Central Michigan University. It was funded by the Meijer Foundation, Great Lakes Basin Fish Habitat Partnership and Dole Family Foundation.
Matt Herbert, an aquatic ecologist for The Nature Conservancy said the work in August turned out to be a reef rehabilitation rather than reef restoration. The site, about 300 yards off shore, was thought to be a degraded natural reef that had been altered by construction of an old iron ore dock in the 1800’s. But researchers have since changed their assessment.
“In all likelihood it isn’t a natural reef,” Herbert said. “It is rock put in as part of the dock that fish were using. But we knew that egg deposition and survival of those eggs has been much higher on two other reefs (nearby). We will be monitoring this site in the future. There is (naturally) a lot of variation in spawning success from year to year.”
Clarmunt began researching Lake Michigan reefs in the early 2,000s using scuba gear in an effort to better understand why lake trout were not doing well. He found the Elk Rapids reef site and determined all three species were spawning there. It was the only known cisco-spawning site in the lake. Since then, however, he has heard many reports about ciscoes being caught elsewhere and surmises there are other spawning areas though none have been identified.
Ciscoes were once highly abundant in Lake Michigan. That population crashed in the 1950’s and 1960’s, Herbert said. Their demise is attributed to over-fishing by commercial netters, habitat degradation and predation by alewives, smelt, gobies and rusty crayfish.
“Cisco is what brought us here,” Herbert said. “Randy knew where they were spawning. For years they had been reported around Grand Traverse Bay, but no one knew where. A hundred years ago they were the top fishery in Lake Michigan. They were an important prey fish and a major component of the lake trout diet. So now we are trying to boost their population.”
Surveys of a nearby reef used as a control zone showed increased lake trout egg deposition as well, according to Clarmunt, who said those findings suggest there are more lake trout in the bay this year.
“We’re probably not done,” Clarmunt said. “We’ll wait and see how the reef winters. It’s going to settle and we’ll map it in the spring. But I anticipate we will be going back next summer and adding another 100 tons of rock.
“We need 100 eggs per square meter to produce a sustainable population. To approach carrying capacity we need more like 1,000 eggs per square meter. We’ve just gone from one egg to 10 eggs.”
© 2016 Howard Meyerson
Appears in Michigan Outdoor News.