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In Tampa Bay, boat propellers have killed seagrass. A new mapping project may help.

Scientists at two universities are using artificial intelligence to map boat damage in the bay. They’ve already uncovered thousands of propeller scars.
Quenton Tuckett, a UF research assistant scientist, displays a handful of Syringodium, or “manatee grass” that he plucked from the water Monday, Dec. 5, 2022.
Published Dec. 7, 2022|Updated Dec. 7, 2022

ON TAMPA BAY — Quenton Tuckett hopes he doesn’t find them. But he knows they’re here.

His boat is a few hundred feet from the enchanting mangrove islands of Cockroach Bay, on the southeast shoreline of Tampa Bay near Ruskin. On this cool Monday morning, it’s clear how Cockroach Bay earned its name: A baby horseshoe crab, which closely resembles its insect cousin, scurries across the bottom of the bay. The day is hovering around 70 degrees, and the shallow water is clear with a slight green tint.

Tuckett kills the engine. And then, suddenly, he finds what he feared.

He spots them one by one: Barren lines etched into the seafloor. Moonscapes stretching for hundreds of feet, void of life-sustaining seagrass. The irrefutable damage left by humans.

Soon, the scars are seemingly everywhere in the shallow waters beneath the boat. Tuckett points out the scarring, caused when a boat propeller slices across the shallow bottom, as fast as he can.

“There’s one! Right here!”

“Here’s another one!”

“Look how far that one goes! It just keeps going. That’s a long one.”

“This one’s cut too deep. It won’t be able to fix itself.”

Quenton Tuckett, a research scientist at the University of Florida, points out the propeller scars in the seagrass while off the shore of Ruskin in Tampa Bay on Monday.
Quenton Tuckett, a research scientist at the University of Florida, points out the propeller scars in the seagrass while off the shore of Ruskin in Tampa Bay on Monday. [ DIRK SHADD | Times ]

Tuckett, a research scientist at the University of Florida’s Institute of Food and Agricultural Sciences, is out on the bay to identify boat propeller scarring “hot spots” where years of boating mishaps have decimated seagrass at several popular recreational areas. He’s joined by Josh Patterson, an associate professor of restoration aquaculture at the university.

Together, they make up two-thirds of the research team that just completed the first phase of an ambitious new mapping project using artificial intelligence to pinpoint propeller scarring throughout the entire 400-square-mile estuary. So far, they’ve found nearly 24,000 scars — about one for every four registered boats in Hillsborough and Pinellas counties.

The crux of the project rests at the intersection of science, public outreach and recreation. Working with the Tampa Bay Estuary Program, the team will now take what they’ve learned from mapping the hot spots and use that information to enhance boater education and outreach at the areas where seagrass is suffering the most. Final results from the study, which officially became public Wednesday, are not expected until 2023.

“The vast majority of people that are causing seagrass scars are doing it by accident,” Patterson said from the bow of the 22-foot Bayliner Trophy. “And that’s why we think an educational project like this is something that could actually help.”

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Evidence on the seafloor

Boat propellers can strike the seafloor while moving as fast as 3,800 revolutions per minute. At that speed, a boat’s transom, hull and metal propeller blades buzzsaw anything in their path — especially the fragile manatee grass, turtle grass and shoal grass species. Once the damage is done, the sloped angle of the scars makes it nearly impossible for seagrass to take hold and regrow.

Repeated waves and erosion, often called scouring, can increase the width of propeller scars. It can cost as much as $20 per linear foot to restore scarred seagrass beds, according to Patterson.

As more people move to Florida, more boats are out on the water. Across the bay, there were more than 117,000 recreational boats registered in Pinellas, Hillsborough and Manatee counties as of 2021. That’s nearly 12,000 more registered boats — or roughly a 10% rise in the Tampa Bay region — compared to just a decade ago, according to the latest data provided by the Florida Fish and Wildlife Conservation Commission.

That added human impact can, over time, increase the stress put on an ecosystem already fighting to fend off the effects of nutrient pollution, a warming climate and the encroaching footprints of urban development. That’s why raising boater awareness on the environmental impacts of propeller scars is such an important step, Tuckett argues. If scarring decreases, it’s one less thing we would have to worry about the bay (and ultimately the life that depends on it.)

“This is something that we can all do something about,” Tuckett said. “What’s your average person going to do about Red Tides? With this, it’s just so concrete: If you scrape up a scar, you know you did it. It’s right there.”

The discolored lines seen here off the shore of Ruskin in Tampa Bay are caused by propeller scars in the seagrass.
The discolored lines seen here off the shore of Ruskin in Tampa Bay are caused by propeller scars in the seagrass. [ DIRK SHADD | Times ]

If Patterson and Tuckett are the brawn behind the project, then Katelyn Lawson of Auburn University is the brains. As a geographic information systems analyst, Lawson used cutting-edge artificial intelligence technology to pinpoint where the bay is struggling the most from propeller scarring.

For 16 days straight, Lawson’s computer analyzed aerial images of Tampa Bay. She taught the computer to uncover the linear propeller scars like a virtual scavenger hunt, picking out their predictable patterns across Florida’s largest open-water estuary. The results weren’t guaranteed, so on day 16, when the program finally finished chugging through its survey and the findings appeared, Lawson let out a suppressed sigh of relief.

“I was over the moon,” she said with excitement. The final product: A comprehensive map of the bay’s “hot spots,” where years of boat propellers have carved scars into once-luscious seagrass beds.

Scientists with the University of Florida and Auburn University used artificial intelligence to map where seagrass in Tampa Bay is experiencing the worst propeller scarring from boats.
Scientists with the University of Florida and Auburn University used artificial intelligence to map where seagrass in Tampa Bay is experiencing the worst propeller scarring from boats. [ Courtesy of the University of Florida ]

The Fort De Soto area, nestled between the Pinellas National Wildlife Refuge and the Sunshine Skyway Bridge, saw the most dense grouping of propeller scars, according to the universities’ findings. To Patterson, that’s not entirely surprising. It has all the ingredients for a heavy human impact: The area is popular among boaters, tides move in and out quickly and the water is shallow.

But other areas around the bay’s perimeter — where shallow water near the shoreline stretches for miles — also saw severe propeller scarring. Robinson Preserve in Manatee County, for instance, contains hundreds of propeller scars. And here in Cockroach Bay, south of Ruskin, scars stretch for hundreds of feet, zigging and zagging in each direction. Just as the map predicted.

“One benefit of this new process is that it can be applied year after year with new imagery, and we apply this same model and get results as quickly as the computer will run the program,” Lawson told the Times. “We can now compare seagrass scarring every year in a transparent, repeatable way — and detect differences in imagery.”

The benefits of that are two-fold: It saves both time and money, and helps better target where responsible boating education and outreach needs to increase.

Take, for instance, a similar propeller scarring research project Patterson helped to lead in 2017. The research team hired a contractor to analyze images of the waters offshore of Citrus and Hernando counties, highlighting each propeller scar by hand. It took several months to get the final product, Patterson said.

“We can now do that in a fraction of the time,” he said.

The team has already surveyed more than 2,000 registered boaters for the project. The next step is to better inform boaters on how to minimize scarring in the bay. Among other tips, they advise boaters to use navigational beacons to avoid shallow water, know the tides, slow the boat and lift the propeller when in shallower water, and wear polarized sunglasses to better spot seagrass beds.

Boater education is the next step

At a time when correcting some of the bay’s largest environmental issues seems out of reach at the individual level — nitrogen pollution from urban runoff, human encroachment and climate change — being smart when out on the water is one tangible thing every person can do to help, Tuckett said.

“Seagrass is a critical habitat in Tampa Bay and is considered an indicator of a healthy estuary,” Sheila Scolaro, the community programs scientist with the Tampa Bay Estuary Program, said in a statement. “It stabilizes sediment, reduces shoreline erosion, sequesters carbon and provides food and habitat for a variety of fish and wildlife at important times during their lives.”

Between 2018 and 2020, seagrass acreage in the bay declined by 16%, Scolaro said. Now knowing where the problem is at its worst, Patterson and Tuckett plan to target hot spots and flood them with their advice. Educational signs, billboards and an outreach campaign are all on tap.

“We think we’ve created the recipe book for how to address this,” Tuckett said. “Even some of the most experienced boaters can still run aground. It’s an accident. But this is just another way to help the bay.”

Patterson chimed in: “We don’t want to cut down on boating. We’re both boaters, we both fish. We’re not saying, ‘Don’t boat.’ There are just a few pretty simple things we can do to solve this problem.”

Josh Patterson, left, University of Florida associate professor, and Quenton Tuckett, UF research scientist, discuss their research while anchored off the shore of Ruskin in Tampa Bay on Monday.
Josh Patterson, left, University of Florida associate professor, and Quenton Tuckett, UF research scientist, discuss their research while anchored off the shore of Ruskin in Tampa Bay on Monday. [ DIRK SHADD | Times ]