Low salinity wallops oysters in Chesapeake Bay

The 2019 fall oyster survey by the Maryland Department of Natural Resources showed that both adult and juvenile oysters were impacted by the heavier-than-normal rains. Here, a researcher measures an oyster.

Aquaculture, restoration efforts and fishery hurt as unrelenting rain earlier in the year made much of Bay water too fresh, causing die-offs and delayed spawning

The rains have finally let up, but they’ve dealt a serious blow to the Chesapeake Bay’s oysters — and to the people who make a living harvesting, cultivating or restoring them.

Oysters need at least a little salt in their environment to live and a bit more to thrive. The record-setting downpours that began last year and continued through the first half of this year flushed so much freshwater into the Chesapeake that salinity sank to abnormally low levels.

In some places in Maryland and on the Potomac River, where the water turned almost completely fresh for months on end, oysters died in droves. Those that survived elsewhere didn’t grow much, and reproduction was spotty.

“What a rough beast of a year that was,” said Martin Gary, executive secretary of the Potomac River Fisheries Commission. “Everybody got hammered by it.”

The condition of the Bay’s oysters matters economically, ecologically and culturally. They’re a money maker for the region’s seafood industry. They’re important water filterers, and the reefs they build provide habitat for fish and other Bay creatures. And, they’re part of the traditional fabric of life around the Bay, a staple at many family, church and community feasts in fall and winter.

Now, with commercial harvests of wild oysters down in both Maryland and Virginia, watermen in the two states face new catch restrictions this fall, imposed at least partly to give the beleaguered bivalves a chance to recover from their freshwater woes.

Oyster farmers, meanwhile, are bracing for another off year, after seeing a dip in production in 2018 — breaking what had been steady growth in each of the two states’ aquaculture industries.

And government agencies and environmental nonprofits had to delay or scale back oyster restoration work, as low salinity disrupted the supply of hatchery-bred oyster larvae for seeding rebuilt reefs.

Hatchery hiccups

Oysters are like Goldilocks when it comes to salt — they don’t like too much, or too little. They’re happiest in brackish to moderately salty water, with salinity ranging from 10 to 28 parts per thousand.

But oysters don’t reproduce well or grow much if salinity drops below that floor. And they can die if it stays under 5 ppt for weeks or months at a time.

At Stingray Point near Deltaville, VA, salinity was 8 ppt in March, half of what’s normal that time of year. Up the Bay, where the water tends to be fresher, salinities dropped to deadly levels late last year and stayed that way well into the spring.

Hatcheries, which draw local water to spawn oysters in captivity for use in aquaculture and ecological restoration, struggled to produce larvae or get them to survive long enough to settle on shells as “spat” or “seed.”

No hatchery had more trouble than the one run by the University of Maryland Center for Environmental Science at its Horn Point laboratory near Cambridge. The facility, one of the largest on the East Coast, produced a record 1.8 billion spat in both 2016 and 2017.

But this year, persistently low salinity in the Choptank River delayed spawning until August, said Stephanie Tobash Alexander, who manages the operation. As a result, Horn Point only managed to produce about 10% of its usual output.

“That’s science for you,” Alexander said. “We made the most of what we could.”

She hopes next year will return to normal. By late September, the salinity had risen to 12 ppt but it was too late to help this year’s class much. The facility spawned its last oysters of the season on Sept. 18.

The hatchery woes at Horn Point and other private facilities around the Bay had a ripple effect for aquaculture, oyster restoration and even the public fishery.

“People didn’t get seed as early as they wanted to get seed. In some cases, they didn’t get as much seed as they wanted to get,” said Mike Oesterling, executive director of the Shellfish Growers of Virginia. “So that puts everyone a little behind.”

Oyster farmers scramble

Oyster farmers in both states felt the impact. In Virginia, the top producer of oysters on the East Coast, the harvest from aquaculture was down by one third, to 248,347 bushels, according to preliminary figures from the Virginia Marine Resources Commission. Growers surveyed by the Virginia Institute of Marine Sciences reported that heavy rains and unusually low salinities were impacting their oyster plantings and sales.

Maryland’s smaller oyster farming industry grappled with even lower salinities. Growers there managed to produce just 57,543 bushels last year, down 22% from 2017, according to the state Department of Natural Resources. That was the first drop in production seen since Maryland revamped its shellfish leasing laws around 2010 to revive aquaculture. Until then, the industry’s output had been growing so steadily that it was on track to overtake the state’s fading wild harvest.

Robert T. Brown, Sr., president of the Maryland Watermen’s Association and an oyster farmer himself, said he lost close to 95 percent of the market-size oysters he had growing on leased bottom in the Potomac, where salinities dropped below 5 ppt in the spring. Closer to the river’s mouth, where salinities were a little higher, mortality was around 35 percent, he said.

The small, young oysters weathered the freshet better, he said, with only about 5 percent dying.

“They didn’t grow, but they didn’t die,” he said. They started growing again in August, he noted, as the salinity levels rebounded. But he doesn’t expect many to reach marketable size until sometime next year.

In Virginia, the Bay’s salinity is generally high enough that oysters reproduce well in the wild. Growers there only have to put down shell before spawning begins in late spring to catch freshly hatched larvae. But in Maryland, conditions are less favorable, and many oyster farmers get their spat from hatcheries, often the one at Horn Point. But its troubles this year forced many growers to approach other, private hatcheries, with limited success.

Some had to do even more. Scott Budden’s Orchard Point Oyster Co. raises bivalves in the Chester River, where salinities aren’t that high even in normal years. Early this year, as rains kept coming down, he saw salt concentrations dropping into the danger zone.

“I’d never seen salinity levels that low in winter,” he recalled.

Some of his oysters in the Chester died, but Budden tried to save as many as he could. He pulled 500 bags of oysters out of the river and hauled them by boat and trailer — 40-plus road miles — to another leased area off Eastern Bay. The slightly higher salinity levels there gave the bivalves “a shot in the arm.”

By late spring, as rains began to ease, salinity started creeping back up, and he and his crew moved the oysters back to the Chester. But Budden continues to use Eastern Bay as a place to grow out oysters just before taking them to market.

Restoration setbacks

The hatchery hiccup also set back oyster restoration efforts in Maryland, which with Virginia has pledged to rebuild the bivalve populations and habitat in five tributaries in each state by 2025. Virginia generally counts on natural reproduction to stock the reefs it has built or expanded, but in Maryland, federal and state agencies depend on Horn Point to for larvae or spat on shell.

Officials had at one point planned to plant spat this year in all five of the Maryland tributaries targeted for large-scale restoration. The Little Choptank and Tred Avon rivers need a final round of seeding to finish up projects that began three to four years ago. Harris Creek, though essentially completed in 2015, was in line for some light overseeding of thin spots. Officials even hoped to begin plantings in the St. Mary’s and Manokin rivers, where restoration plans are still being fleshed out.

Much of that work got scaled back or shelved until next year. So did Marylanders Grow Oysters, the popular program under which about 1,500 waterfront property owners voluntarily raise young oysters in cages from their piers for planting in sanctuaries.

“Most of the sanctuary spat are typically produced in the first half of the hatchery season,” explained Chris Judy, the Maryland Department of Natural Resources shellfish program manager, “but this was when the hatchery had zero production.”

The Chesapeake Bay Foundation had hoped to contribute to the effort by producing 25 million spat on shell, said senior scientist Doug Myers. Four-fifths of that was to go on the Maryland sanctuary reefs, under a $3 million, three-year grant from the National Oceanic and Atmospheric Administration. The other 5 million spat were planned for CBF’s oyster gardening and other initiatives.

CBF normally buys oyster larvae from the Horn Point hatchery and sets them on shell or reef balls at a facility in Southern Maryland. The problems at Horn Point left CBF 13 million spat shy of its goal, Myers said, despite scrambling around to find other sources of larvae.

“It’s been a rough year,” said Stephanie Westby, NOAA’s oyster restoration program manager. “But you know, with climate change, these kind of extreme weather episodes may be the new normal, unfortunately.”

Faltering fisheries

Public fisheries in Maryland and Virginia also suffered.

In Maryland, the DNR works with local watermen’s committees to replenish reefs thinned by harvest. But Horn Point’s problems reduced the amount of hatchery-spawned juvenile bivalves available. Nearly 49 million spat got planted on 48 acres, about a third less than last year, according to the DNR’s Judy.

Meanwhile, salinities north of the Bay Bridge and upriver in major tributaries declined to the point that shellfish in the water grew very little — or died.

In the Potomac River, the extended freshet devastated a promising experiment in rotational harvesting, said Martin Gary of the Potomac River Fisheries Commission. Since 2013, watermen had been planting juvenile oysters annually on reefs or bars above Cobb Island, he said, with plans to harvest them in three years and then every four years afterward.

Virtually all of the bivalves planted there got “crushed,” as Gary put it. The Maryland Department of Natural Resources’ annual survey of oyster reefs in the fall of 2018 found more than 90% of the oysters in that area of the river had died.

Gary said he’s waiting for the DNR survey crew to return in October to find out if any of the oysters there are still alive.

Downriver, near the Potomac’s mouth, low salinity inhibited the oysters’ growth but didn’t kill them.

“We were thankful that we didn’t lose any down there,” Gary said.

Farther south in Virginia, reef surveys found that many oysters didn’t grow much over the last year, either, and some in deeper water had died.

Last season’s wild harvest was the state’s smallest since 2012-13, with just 209,032 bushels landed, according to preliminary data gathered by the Virginia Marine Resources Commission.

Hoping to give Virginia’s oysters a chance to recover, the commission took steps in August to scale back harvests a bit.

The public fishery season traditionally opens Oct. 1, and that’s when watermen using hand or patent tongs can start plucking oysters from the bottom. But the commission delayed until November when watermen can work reefs over with dredges or mechanized hand-scrapes.

The delay gives the oysters more time to reach the 3-inch minimum marketable size, officials explained.

Virginia’s new harvest rules also require that dredge boats stop working by noon on two out of the four months when they’re allowed on the water. Last year’s season allowed them to continue until 2 p.m.

“Generally,” said Andrew Button, who oversees the state agency’s conservation efforts, “it’s a more resource-conservative season.”

Most watermen seemed resigned to the restrictions, but some complained it was unfair to cut back on only certain types of harvest gear.

“If we’re in that bad of shape with the oysters, let’s just shut it all down in October,” said Charles DeMarino, a waterman based out of Cape Charles on the Eastern Shore.

New restrictions took effect this fall in Maryland as well, mainly in response to a study last year that found a long-term decline in the fishery, with most areas being overharvested.

The DNR reduced from five to four the number of weekdays when oysters could be harvested throughout the season, which ends March 31. The agency also scaled back the daily maximum number of bushels that could be harvested by 20 percent to 33 percent, depending on the type of gear used.

The limits were aimed at making the fishery sustainable in eight to 10 years, but the freshwater woes figured explicitly into at least one rule change.

The DNR temporarily barred harvests in several places around the Bay, including much of the area north of the Bay Bridge, where few oysters survived the freshet.

The DNR projected that its package of restrictions could reduce the harvest by as much as 26 percent. Last season’s harvest of 137,000 bushels was already down 25 percent from the 2017-2018 catch.

The Chesapeake Bay Foundation expressed skepticism about the efficacy of the restrictions. The environmental group had urged tighter limits and pointed to the DNR’s own analysis, which found that reducing the harvest by one day a week would have “little conservation value.”

Just one in four watermen harvest oysters five days a week at the start of the season, according to a DNR presentation, while by the end of the season only 5 percent to 10 percent do.

But, watermen say they’re expecting a leaner harvest from the DNR rules, and that the minority who work the water full-time may feel the pinch more than the part-timers.

“The majority recognized some belt tightening was going to be needed,” said Jim Mullin, executive director of the Maryland Oystermen Association, “especially after the tremendous amount of freshwater events of last year that set the Bay and restoration activities back severely.”

Still, Mullin and other watermen say they’re frustrated by the emphasis on curtailing harvests instead of doing what they contend could help sustain or improve the fishery. They have pushed for reopening some of Maryland’s 51 oyster sanctuaries to rotational harvest and for replenishing worn-down harvest reefs with large quantities of old shell dredged from the Bay bottom. Environmentalists have opposed such moves, arguing that by themselves they won’t make the fishery sustainable long-term.

Meanwhile, with oysters still reeling from the prolonged surge of freshwater, the seafood industry in both ends of the Bay is preparing for another gloomy year.

“We’re not going to have as many market oysters this year,” said Tommy Kellum of W. E. Kellum Seafood in Weems, Va. “It’s a Mother Nature event. It’s not like an occurrence we could have prevented or managed for.”

But most say they think that with a little more “normal” — meaning drier — weather, the Bay’s oysters will rebound, along with aquaculture, restoration and perhaps even the fishery.

“Long term, this is just a bump in the road,” said Stephan Abel, executive director of the Oyster Recovery Partnership, a Maryland nonprofit that works on restoration with state and federal agencies and other nonprofits.

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