Oysters rescued from VA harvest may return favor
What started last winter as a rescue effort for some of Virginia's largest oysters has brought new hope for the future of the state's oyster population.
Last year, the Virginia Marine Resources Commission agreed to allow oyster harvests in Tangier Sound against the recommendation of its staff and scientists.
The staff had hoped to preserve the large oysters that had survived in that area, despite the onslaught of lethal diseases, during three years of a harvest moratorium.
Several months after the Commission allowed the harvest, it voted to "rescue" the oysters by purchasing 2,300 bushels of the bivalves from watermen and placing them at a manmade reef in the Great Wicomico River.
The result was a huge increase in spat - young oysters - growing on the reef this year.
"We've seen the spat set increase all around that reef, up to six miles from the reef," said James Wesson, who heads VMRC's oyster replenishment efforts. "I don't think there's any doubt that the spat are coming from those oysters that we put there."
The reef averaged 1,000 spat per square meter, Wesson said. Saving the Tangier oysters was important, scientists had argued, because their large size indicated that they had some ability to withstand disease.
The transplanted oysters were 4- to 7-inches long; oyster diseases kill most oysters in Virginia before they reach the market size of 3 inches.
Large oysters are not immune to the diseases, they are just more tolerant of them and can live to a longer age.
Historically, the strategy has been to race to harvest oysters before they died, Wesson said. In retrospect, Wesson said, that was the wrong strategy.
"Every time an oyster got to be 3 inches and had some resistance, we ate him," he said. "We should have been doing exactly the opposite."
By not harvesting oysters and allowing some a chance to survive the disease onslaught and reach a larger size, the hope is that any disease tolerance will be passed on to their offspring. Future generations may then better cope with the parasites that cause MSX and dermo.
Though not harmful to humans, the diseases often kill up to 90 percent of the oysters before they reach market size. The situation is particularly acute in Virginia, where high salinity water means that oysters face intense pressure from both diseases each year, unlike Maryland were periodic flows of fresh water sometimes help to keep disease pressure down.
"These oysters are the first really strong indication that the population of the Bay in some areas is actually concentrating those genetic characteristics that actually allow the oyster to survive longer in the face of disease," said Bill Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation, which provided volunteers to help with the move.
"This is encouragement that the greater population can indeed do that in our lifetime."
Ironically, Wesson said reproduction was probably better than if the oysters had been left alone as originally proposed. Oysters can't move, so they reproduce by releasing eggs and sperm into the water. Moving the oysters to the reef put males and females closer together than was the case for those left in Tangier Sound.
In fact, Wesson said the oysters that remained in Tangier Sound had almost no spatfall this year. "Their spawn is just being wasted out there because they're not close enough to each other to fertilize," he said. "By simply picking them up and putting them closer together on the reef, you get instant results. It's really giving us a good direction for the next few years in how to repopulate some areas, I think."
And therein may lie the secret to managing oysters in Virginia, Wesson said. Establishing concentrated populations of large oysters at manmade reefs could encourage increased natural reproduction. The three-dimensional reefs, which rise up from the bottom, allow males and females to be congregated closer than if they are left on flatter, shell bars.
This winter, Wesson hopes to "rescue" more oysters from Tangier Sound and place them in the Great Wicomico or near another manmade reef in the Piankatank River.
Besides success on the Great Wicomico, Wesson said recently built reefs in the Coan and Yecomico rivers also had good spatfalls this year from large natural oysters that had survived in those Potomac River tributaries for several years.
"We got spat sets on these two new reefs of more than 300 oysters per meter," Wesson said. "That's a very heavy spat set. Other reefs, in other years, we've been really, really excited when we saw 15 or 20 or 30 per meter."
In a state where oyster harvests have decreased from a high of 3 million bushels annually in the 1950s to 15,701 bushels last year, the recent news was the first glimmer of optimism in years.
"The combination of the Great Wicomico and the two reefs in those areas have really perked our hopes up," Wesson said. "That's the best news that we've had in a long time. Our fingers are crossed."
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