saildrone

Two Saildrone Explorers, pictured here docked in Macatawa on July 27, 2021, started a 45-day mission in lakes Michigan and Huron Thursday to conduct acoustic surveys. to determine prey fish abundance in the lakes.

HOLLAND — If Great Lakes baitfish scatter at the sound of research vessels, a nearly silent option might get more accurate results.

That’s why two bright orange, robotic sailboats are plying the waters of lakes Michigan and Huron on a 45-day mission to amass important fisheries data — no crew required.

The pair of Explorer drones, as maker Saildrone calls them, left Macatawa near Holland on Thursday and are conducting acoustic surveys for the U.S. Geological Survey, said agency Research Fish Biologist Peter Esselman. It’s not the first time these autonomous boats have been used in fisheries research, with National Oceanic and Atmospheric Administration deploying them in the Pacific Ocean. But they’ve never been used in the Great Lakes.

The boats are 23 feet long with a 15-foot-tall rigid sail like a plane’s wing, according to a release from the USGS. Instruments on board are powered by wind and solar energy, and Esselman said the boats can sail for months at a time.

They’re programmed and monitored to avoid shipping channels and other hazards, Esselman said. Their positions can be monitored, and courses adjusted, from shore, but boaters should steer clear.

Acoustic sensors on board are similar to a more powerful version to what anglers use to find their targets, Esselman said. They’re capable of not only detecting the number of fish in the water, but their size as well.

“So this gives us an ability to understand both the abundance and the size of the fish that are present,” he said.

Each year the USGS partners with the U.S. Fish and Wildlife Service, the Michigan Department of Natural Resources and other agencies to survey the lakes, including to estimate the abundance of prey fish. Crewed boats use the same kind of acoustic sensors, plus nets to conduct midwater and bottom trawls.

Federal, state and tribal governments, plus Ontario’s provincial government, rely on prey fish numbers to manage fisheries throughout the Great Lakes, particularly setting stocking targets for Chinook salmon and lake trout, Esselman said. That data is also key in restoration efforts for fish like ciscoes, the common name for lake herring.

But there are doubts over the accuracy of the results these annual prey fish surveys provide, said Jay Wesley, Michigan DNR’s Lake Michigan Basin Coordinator.

“We’ve been marking less and less baitfish through the decades in Lake Michigan, and we got to a point where the anglers were disagreeing with our findings and saying there’s more baitfish out there than what we’re seeing,” he said.

One theory is that noise from survey vessels could be scaring the fish, Esselman said — USGS’ 78-foot research vessel Arcticus sports two six-cylinder diesel engines displacing 732 cubic inches each, according to boat designer JMS Naval Architects and engine maker Caterpillar.

And Michigan DNR’s boat Steelhead also has twin V-6 diesel engines powering it, according to the department.

“So the idea is that the vessel engines make noise that can cause the fish to flee the vicinity of the vessel, which means that when we either detect fish with sonar or try to catch fish with nets, we’re likely to be catching less fish than is actually present,” Esselman said.

Saildrones, by contrast, are virtually silent, he said.

Wesley said the Steelhead is conducting acoustic surveys in the western half of Lake Michigan, and as of Friday was near Saugatuck after starting near Benton Harbor.

The vessel and its crew are working their way north, he said. As they do, they’ll motor near a Saildrone then move away to see how the survey vessel’s presence affects the results.

As of Friday, one Saildrone was in the middle of the lake between Holland and Racine, Wisconsin, while another was near Benton Harbor, Esselman said. They’re headed to the waters north of Grand Traverse Bay toward the end of August, then they’ll be towed through the Straits of Mackinac — it’s a shipping thoroughfare, he said.

The Saildrones will spend 15 days in Lake Huron, and by year’s end they should log around 2,000 miles in total, Esselman said. They’ll also provide much more data than research vessels alone typically log.

“In a given year we run 25, 10-mile transects in Lake Michigan,” he said. “This year we’ll have probably five times that amount of additional information.”

That’ll give scientists a better estimate of prey fish abundance, Esselman said.

The Saildrone Explorers are set to spend 25 days in Lake Superior in 2022, he said. In 2023, they’re headed to lakes Erie, Huron and Ontario, and potentially headed back to Lake Michigan.

They’re not the only water-going robots USGS is using in the Great Lakes, Esselman said. The agency uses autonomous underwater vehicles to improve estimates of round goby abundance, as the invasive fish has proven to be an important food source for predators. Underwater autonomous vessels also can provide information on invasive mussels and the nuisance algae cladophera.

These devices can provide important data on fish breeding habitats, particularly during times of the year that are dangerous for crewed boats, and even under ice during important development phases for just-hatched fish, Esselman said.

Both Esselman and Wesley said they see an increasing role for autonomous technology in Great Lakes fisheries research.

But research vessels aren’t headed for the scrapyard any time soon.

There still are plenty of tasks biologists can do aboard, like identifying fish marked by acoustic scanners and hauled in from midwater or bottom trawls, Wesley said.

“It’s cool technology but it’s not something we can rely on quite yet for all of our data,” he said.

 

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