CAMBRIDGE — After the field crew loaded 320,000 baby oysters on board the Robert Lee, Capt. Doug West steered his 72-foot, oyster-planting barge away from the dock and toward the mouth of Choptank River.

On an early August morning, West drove the weathered boat out of the Choptank, past Trippe Bay, around the peninsula and into the Little Choptank River.

The Little Choptank, Harris Creek and the Tred Avon River — all part of the Choptank River system — are some of the large-scale oyster restoration sites mandated by the 10 Tributaries by 2025 federal order signed by President Barack Obama in 2009. The goal is to restore 10 Chesapeake Bay tributaries: five in Maryland and five in Virginia.

After two hours of cruising, the Robert Lee hovered over the planting site marked by red shapes on one of West’s navigation devices. Beneath the surface, 165 acres of artificial hardbottom had been covered by more than 562 million spat on shell — baby oysters attached to recycled shell — through 2016.

West flung a large black hose over the port side of the vessel, turned on a pump, pulled up his Wrangler jeans and hurried back to the cabin. Now the machine was sucking up river water through the hose and pumping it to a nozzle attached to a crane on the bow. Flanked on his left by Megan Munkacsy, oyster restoration field specialist, and on his right by black metal levers labeled “hoist,” “boom,” “crowd” and “swing,” West spun the wheel to position the boat.

Munkacsy used her laptop, equipped with custom GPS software, to ensure West was planting the correct part of the reef. The oysters werepiledin front of the cabin in a three-sided plywood corral and the crane aimed back toward the cabin.

While the day’s work went on, potential changes to oyster sanctuary policy in Maryland loom.

In Annapolis, politicians, scientists, environmentalists and watermen debate the effectiveness of what has been called the largest oyster restoration project on Earth. State and federal governments and nonprofits have invested almost $50 million in the three Choptank tributaries through 2016, yielding 3.1 billion oyster seed planted, according to the 2016 Maryland Oyster Restoration Update — a report on the project’s progress produced by the National Oceanic and Atmospheric Administration Chesapeake Bay Office in Annapolis.

Driving the debate are Maryland’s watermen, professional fishermen who are the living legacy of generations who have worked the Chesapeake Bay. Backed by Gov. Larry Hogan, they are questioning the validity of sanctuaries and want them opened to harvesting that would support their businesses and families.

Robert Brown, president of the Annapolis-based Maryland Watermen’s Association, said the policy that created the sanctuaries is failing. They haven’t achieved their goal of replenishing oysters across the bay and boosting harvests.

“They said they would have all this recruitment, and larvae would replenish the bay,” said Brown, a Coltons Point resident. “We still have problems with water quality, though it’s a little better than it was.”

Scientists and environmentalists, on the other hand, maintain the oyster sanctuaries are yielding promising results, and that a change in strategy could negate progress.

“From the scientific community, it is considered to be really successful so far,” said Allison Colden, a fisheries scientist at the Chesapeake Bay Foundation in Annapolis. “All signs point to yes, though it’s still early.”

The foundation and other scientists define success differently. They say it is determined by measuring reef elevation, reproduction, oyster density and biomass per square meter.

Of the Harris Creek restoration reefs planted in 2013, 97 percent met the minimum threshold for oyster growth, 80 percent grew at the optimal rate, and 100 percent had multiple year classes present — a sign that some oysters are reproducing naturally — according to the NOAA Chesapeake Bay Office’s 2016 Oyster Reef Monitoring Report.

Water quality measures have also shown promise, said Jeffrey Cornwell, a research professor at University of Maryland Center for Environmental Science’s Horn Point Laboratory near Cambridge. Cornwell studies water quality, specifically denitrification — a process that reduces nitrogen.

Increased nitrogen levels, common with nonpoint source pollution such as fertilizer runoff from farms, produce more algae and can cause dead zones in the water. Areas with oyster reefs can help reduce five to 10 times more nitrogen, Cornwell said.

Unconvinced, watermen are adamant about opening sanctuaries for rotational harvest.

Sanctuary oyster bottom is “not being used to its potential,” Brown said. “We’ve only asked to take part” of the sanctuaries.

On the Little Choptank, it was time to plant.

With a flick of a switch, West opened the corral door nearest the far-right oyster pile — the doors are rigged with hydraulics to open like floodgates. He turned his attention to the levers, rotating the crane to blast water on the pile of spat-loaded shells.

As he sprayed the pile, the mountain eroded in an avalanche of cascading water and brownish oysters. West’s eyes were locked on the oyster pile and crane. He leaned over the dashboard, nearly pressing his wire-framed glasses against the window overlooking the bivalves.

His beige, short-sleeve, button-down shirt revealed his tanned muscular forearms, a sign of his years working on the water. He operated the levers effortlessly, maneuvering the crane about until the first pile was gone.

The crane pulley and chain clanked as the arm moved right to left and up and down.

This planting session was tough, he said. At almost one-third of an acre, he thinks it’s the smallest site he’s planted. A lifelong waterman, West has planted oysters with the Oyster Recovery Partnership for more than 20 years.

“It’s such a little spot I need to keep starting and stopping,” West said.

After site one, West pushed the throttle forward. The engine — housed below the cabin — roared like a tractor-trailer as the green-hulled barge labored on: three more sites to go.

As the Robert Lee approached site two, Munkacsy and Emily French, ORP marine scientist and project manager, left the cabin and climbed down to the stern to collect water samples with a sonde. The sonde is used to measure water salinity, dissolved oxygen, temperature and pH — all useful data because levels of each are associated with degrees of oyster productivity.

French held the control panel while Munkacsy dangled the cylindrical, water-collecting end into the murky river water.

“Any sanctuary that’s Annapolis or north are low salinity,” said Chris Judy, shellfish division manager at the Maryland Department of Natural Resources in Annapolis.

These sanctuaries have low spat set and good survival because the water conditions offer greater protection from diseases that have ravaged the oyster population in the past, MSX and Dermo.

In the southern reaches of the bay, Judy said, there is higher salinity and spat set. Oysters are surviving well there now but could be devastated by disease outbreak, as “diseases are highly responsive to salinity.”

DNR is part of a network of organizations that contribute to oyster restoration efforts. The department is responsible for managing 51 state sanctuaries —including three in Anne Arundel County’s Severn, Magothy and South rivers.

Oysters have long been a staple of Chesapeake Bay culture and ecology.

Watermen count on oystering (Nov. 1 through March 31) to sustain themselves when crabbing and rock-fishing seasons close. Nature counts on oysters to filter water and to create habitat for crabs and fish by developing reefs.

“For our industry to work right we need oystering, we need crabbing, (fishing and clamming),” Brown said. “So we don’t hit one asset real hard.”

The bivalves population is estimated to be 1 percent of historic levels after years of overfishing, pollution and diseases, according to the NOAA Chesapeake Bay Office.

Watermen disagree overfishing contributed to the diminished population, Brown said.

“We did not get in the situation we’re in because of overfishing, it was because of disease.”

Maryland’s efforts to rejuvenate the bay’s oyster population date to the turn of the century and the Chesapeake 2000 commitment, which called for tenfold increase of oysters through small, scattered restorations.

The small restorations showed promise, but “the challenge is to expand these projects to a larger scale,” read the 2004 Chesapeake Bay Oyster Management Plan.

In 2009, the federal government got involved with an executive order that paved the way for the 10 Tributaries by 2025 project.

Watermen and scientists are struggling to find common ground on sanctuaries, including the federally mandated ones.

“Rotational harvest is far better than sanctuary,” Brown said. “You harvest, then you plant it and leave it alone for four years.”

Once the oysters grow to market size, watermen return to harvest the oysters and start the cycle again.

Watermen argue tilling the bottom with dredges and tongs is better for oysters, otherwise they would sink into sediment and die.

But scientists say dredging the bottom busts up reefs, Colden said. “The idea that you have to turn up the bottom has no scientific basis.”

She added: “As oysters grow larger than market size they provide proportionally more benefits,” like filtration and reproduction, which increase with the size of the oyster.

Also, reefs maximize oysters’ ecological benefits, Cornwell said. “We definitely see oysters are more efficient, with all they do, in a reef.”

Both sides agree nobody has a clear picture of how many oysters are in the bay or how many can be harvested safely each year.

The Maryland General Assembly authorized in April 2016 an oyster stock assessment to establish a more precise count of oysters, determine their rate of reproduction, how quickly they are growing and how well they are coping with disease.

This is the first oyster stock assessment in Maryland, though similar studies paved the way for blue crab and rockfish policy, two other cornerstone species of the bay.

“You can’t manage something if you don’t know how many there are,” said Tom Horton, an environmental writer and Chesapeake Bay expert.

The assessment should have been done years ago, Brown said. Though he’s concerned about how the study is being conducted.

Legislation mandating the stock assessment passed in 2016. It prevented the DNR from opening any of the 48 state sanctuaries to harvest until the study is completed in December 2018. At that point, the Oyster Advisory Commission — watermen, seafood industry representatives, scientists and politicians tasked with shaping oyster management policy — will weigh the results and determine appropriate measures.

The three federally sponsored sanctuaries are exempt from any policy changes resulting from the stock assessment.

“The administration will review and consider the commission’s recommendations once they are finalized,” said Amelia Chasse, Gov. Larry Hogan’s deputy communications director.

Brown said he and other watermen are skeptical about how the study is conducted, though Brown admitted “DNR does a pretty good job on all that.”

Regardless, they won’t be satisfied “until we see the data and how it’s done,” Brown said. “We want a fair shake.”

Brown, who was raised in a family of watermen, has been a waterman since he graduated high school in 1968. He said his peers have already had their season shortened and catch cut.

“We’re trying to stay in business,” Brown said. “We’re up against it right now.”

Near the mouth of the Little Choptank at the last site, West slowed the Robert Lee before flipping the last floodgate open and clearing the remaining oysters from the deck like a seasoned landscaper leaf-blowing fall leaves off a lawn.

Once the last bivalves were cleared, West scampered to the bow, retrieved the black hose and turned the pump off.

At around 2 p.m., the sky was blue and waters calm, the shoreline a faint, dark line on the horizon. It would be another hour or so before the Robert Lee approached the dock, so the 20-year oyster industry veteran leaned back in his leather captains chair, steadied the large brass steering wheel with the heel of his boot and took a swig of the iced coffee he’d put in a recycled soda bottle.

The tired captain could relax with his chilled coffee — until the next time baby oysters find their shelled sanctuaries.