The U.S. Army Corps of Engineers is responsible for breakwaters around the country, including the Great Lakes.
The structures calm the waters within them to allow ships and smaller vessels to navigate safely, but take quite a beating, given shifting lake levels and seasonal storms.
The usual "fix" is to install big boulders, 6 to 10-feet in size, to reinforce failing stretches of breakwater.
Upkeep costs a lot, so the Army Corps is looking for ways to get more bang for taxpayer dollars that are set aside for routine repair and maintenance – and is testing one of those strategies here in Milwaukee. By strategically adding smaller rocks to the giant ones along the breakwall structure, the Corps hopes to create habitat for a variety of living creatures.
To test the idea, in April 2014, the Army Corps installed stones along a 500-foot section of the Milwaukee breakwater.
“Engineers went back to the drawing board and redesigned a portion of repair to include two smaller stones - and the smaller 4 to 8 inches wide – on top of that stone to create fish habitat ,” Burton Suedel says. He works out of the Army Corps environmental laboratory in Vicksburg, Mississippi.
The foundation is made up of 6 to 10-ton stones as usual. That's topped with a subbase of stones 8 to 18 inches in size, and finally smaller 4 to 8-inchers.
The Corps needed someone to monitor how the habitat experiment was working. Suedel turned to John Janssen, a fish biologist with UW-Milwaukee’s School of Freshwater Sciences.
Janssen says early monitoring showed those rocks shifted. “Because Lake Michigan can be so violent, particularly in winter. Our first dives were in 2014, a year later it wasn’t the same. Then this year even before we got in the water, we could see that the bigger rocks had moved and then when we got under water, we could see that the smaller rocks had moved.” He adds, “It will reach some sort of a stable point, but that’s information that we keep relaying to the Army Corps, because they need to know something about the stability."
Janssen points to the section of breakwater where the pilot is focused. He says birds gravitate to the wall to feed.
“We see a mix of two kinds of gulls, it’s herring gulls and ring-billed gulls. The birds with the black caps are Caspian terns, which are actually either threatened or endangered species in Wisconsin, but they’re out here fishing,” Janssen says.
Sandpipers feed on tiny flies called midges.
“Midge flies, the babies spend most of their life living on the rocks, scrapping algae off the rocks. Just tiny little things, a quarter of an inch long. The adult phase is only for mating. But that’s one of the things, without these rocks here you wouldn’t have nearly as much food here for the sandpipers,” he says.
Not only birds are finding food in these waters. Janssen and his students have been studying a small shrimp, called Hemimysis, found along the breakwater.
Janssen has learned the shrimp has become a key element in this slice of ecosystem. Until he and his students started digging around the Army Corps rock experiment, Janssen had no idea Hemimysis was so abundant here.
“That little shrimp is showing up in the stomachs of small rock bass, the baby largemouth, rainbow trout that are a foot long or less, brown trout that are that length, smelt, alewives. Everything that comes out of this breakwall, just about, is feeding on these,” he says.
Hemimysis is, by the way, an invasive creature. That’s something, Janssen says, scientists trying to “tend to Lake Michigan” have had to rethink.
“One of the things we’ve learned about invasive species, the best thing is, particularly if you can get something native or desirable that feeds on them. So the basses are native; rainbow trout come from the West Coast, brown trout come from Europe, but people like them and they fit well into this Great Lakes system.” Janssen adds, “It’s a new reality.”
Army Corps’ Burton Suedel sees great promise in the project.
“We expect going forward that they’ll probably begin to start utilizing for spawning. It’s forage mostly as the local populations begin to realize that this is there. Utilization may not be overnight, but what we’re finding out is if that changes over time…That’s why we’re studying it more than a snapshot over one season or one year, but we’re looking at those trends,” he says.
Suedel would love to see Milwaukee harbor’s fish spawning habitat experiment pop up across the Great Lakes.
“Army Corps of Engineers owns over 100 miles of breakwaters alone in the Great Lakes. If we can implement these types of design changes, imagine what we can do over 100 miles over time. We could create an awful lot of habitat,” he says.
But Suedel says that doesn’t mean the Corps will abandon its key mission. “While at the same time actually not actually inhibiting at all the original navigation function of the structure itself,” he says.
Scientist John Janssen has wrapped up the monitoring phase; student Eric Geisthardt is folding the data into his Master’s thesis.
This winter Burton Suedel will hold a final meeting, where he says the path forward will be discussed.
