Mapping a future for sturgeon in Milwaukee River
THIENSVILLE – Northern roughwinged swallows swooped past the bows of our paddle boats and performed aerial acrobatics the envy of any barnstormer.
The banks right and left were shaded by towering black willow and silver maple trees.
And taken as a whole, this largely undeveloped stretch of the Milwaukee River was captivating in its beauty.
But at the moment, Ryan Miller of the Ozaukee County Fish Passage Program was interested only in what lay beneath the river’s surface.
It’s there, and only there, data will be found to answer a compelling question in the continuing restoration of Wisconsin’s most urban river: Do lake sturgeon have sufficient habitat to once again spawn in the Milwaukee?
“Nice bunch of cobble there,” said Miller, describing the sonar image of the river bottom in a stretch south of Thiensville. “That looks promising.”
On June 19, I joined Miller and Andrew Struck, director of the Ozaukee County Planning and Parks Department, and Beth Wentzel, civil engineer with the department, on a paddle and float to collect data on about 10 miles of the Milwaukee.
Miller and Wentzel used a canoe and formed the brains and brawn of the operation.
Wentzel paddled from the bow at a prescribed 4 mph down the waterway while Miller monitored a side-scan sonar device. A digital display was affixed in the middle of the craft; the unit’s transducer hung from the stern.
The technology produces a two-dimensional image of the bottom. It can gather data about 60 feet out from the transducer on both sides, Miller said.
While the rest of us watched the bucolic Ozaukee County landscape drift past, Miller called out highlights from the watery world below.
“That pool has a big downed tree it in,” Miller said. “And now the bottom is getting really soft and silty.”
Such information, when added to water depth, river gradient and stream flow, will be used to rank areas as potential sturgeon spawning sites.
Sturgeon are native to many Wisconsin waters, including the Milwaukee River. But they likely haven’t spawned in our city’s river since was it was blocked by a dam in 1835.
For certain, no living person can bear witness to sturgeon reproducing in the Milwaukee. Efforts underway for more than a decade intend to change that.
Since 2006, Riveredge Nature Center in Saukville, in partnership with the DNR, has reared and released approximately 11,000 juvenile sturgeon into the Milwaukee River.
The fish are slow to mature, with males requiring about 15 years and females 20 to reach sexual maturity. However, some adult sturgeon were also transferred to the Milwaukee river and harbor, so the sight of the state’s largest fish reproducing in southeastern Wisconsin may not be far off.
Biologists, however, don’t know whether the fish have adequate spawning sites. To find out, Ozaukee County officials made a plan. Field work started this summer to map the river bottom.
The project is funded through grants from: Fund for Lake Michigan; Wisconsin DNR River Protection Planning; Wisconsin DNR Office of Great Waters; and National Fish and Wildlife Bring Back the Natives. Riveredge Nature Center is a partner in the work.
The habitat assessment is based in part on side-scan sonar, a valuable technology for remotely sensing underwater features. First developed in the 1960s, it has traditionally been used to locate sunken vessels and for charting navigational channels.
Locally in 2016, Brennan Dow, then a UW-Milwaukee graduate student and now a DNR employee, used side-scan sonar to chart the lower Milwaukee River and Milwaukee harbor.
The Ozaukee County team decided to apply side-scan to its sturgeon project. It’s one of the latest chapters in the growing story of the county’s exemplary efforts to improve and restore local waters and habitat.
From 2006-18, the Ozaukee County Planning and Parks Department was awarded $11.6 million in federal, state, local and private funding for its fish passage program. The work seeks to restore natural stream functions and reconnect and enhance habitat for native fish, birds and wildlife through dam removals, fishway construction, culvert replacements and stream and habitat restoration. It has already removed the Lime Kiln Dam and Newburg Dam, for example, and installed a fish passage at the Mequon-Thiensville Dam.
The side-scan work will collect sonar imagery of 14.5 river miles of the Milwaukee River and 3.5 miles of Cedar Creek.
Miller hopes to have all the data by the end of this summer. He then expects to spend the winter classifying the imagery and adding other information to rank sites for sturgeon spawning suitability.
Sturgeon spawn most successfully in rocky substrate where the stream flow is about 2 feet per second and higher. The key is to keep eggs oxygenated and free of silt.
Also, it’s best if the rocks have gaps into which the eggs can fall and tumble. Eggs on the surface of rocks are often eaten by fish, including suckers, and also sturgeon.
Limestone rocks from 6 to 18 inches in diameter are very good, said Ron Bruch, retired DNR sturgeon biologist who helped restore spawning sites on the Wolf River. Bruch said adult sturgeon also require a staging area of deeper water relatively close to the spawning site.
Miller has already determined several sites on the Milwaukee with good rocky substrate, including one just downstream of the Thiensville dam. Also, the river gradient and stream flow is suitable is several stretches, including as it runs through Lime Kiln Park.
To assist with upstream movement of sturgeon, Ozaukee County also plans to modify the fish passage at the Thiensville Dam to accommodate larger fish. That work is slated for 2020.
Miller is scheduled to produce a final report on sturgeon spawning habitat in June 2020. That could well set the stage for the next chapter.
“If we feel it’s necessary, we’ll certainly pursue habitat improvement projects such as adding cobble to sites in the river,” said Struck, department director.
For a native species that hasn’t spawned in the Milwaukee in more than a century due to human interference and neglect, adding a few “just right” places to spawn seems like the least we can do.
Bruch, one of the world’s most knowledgeable sturgeon biologists, thinks the odds are high of successful sturgeon spawning in the Milwaukee. The ancient species is tougher and more adaptable than many people realize, Bruch said. They just need adequate protections from over-harvest and access to good spawning sites.
“They’re going to do it here,” Bruch said. “It’s only a matter of time.”