Survey dredges up good oyster news
Maryland spat index is 2nd best since ‘39
As John Hess stuck the long, metal pole into the water, he could feel the oyster bar under the boat. The crunching of shells could be heard through the water.
"There they are," Hess called out. "Eighteen feet."
A metal and rope dredge was lowered by cable from the boat as it drifted along the bar. Hess, a supervisor with the Maryland Department of Natural Resources, stuck the pole in the water again. "There they are - 17 feet."
The dredge was now scraping across the oyster bar. Hess stuck the pole in the water again. "There they are - 14 feet."
Soon, the dredge was pulled from the water, dumping its load of oysters and shells into the boat - one of about 350 samples scraped off oyster bars around the state during the DNR's annual fall oyster survey.
The survey crew pulled a half-bushel sample of oysters from the pile and began sorting through them. As they did, they called out what they were finding: "Three market." "Two smalls." "Box." "Two market."
Those designations indicated whether the oysters had made it to the 3-inch market size, whether they were smaller than that, or whether they were dead. A record keeper made careful notes of what was being found.
Occasionally, someone would call out, "spat."
A spat is an oyster that was spawned this year. And in the 1997 survey, there have been a lot of them. In fact, this fall's survey has recorded the second highest spat index since the survey began in 1939.
The index is the average number of spat counted in half-bushel samples collected at 53 sites around the Bay. This year, the average count was 277 spat per site.
Last year, the index was 2. The highest index on record was 331, in 1965.
Of course, good "spatfall" is no guarantee of future harvest potential: The oysters still have to survive the diseases that have decimated oyster populations in recent years.
In the late 1980s, with the arrival of the oyster disease MSX, Maryland oyster harvests dropped from more than 1 million bushels annually to fewer than 400,000 bushels. In the early 1990s, a second disease, dermo, arrived and harvests fell further, to about 100,000 bushels a year.
This year's survey found hopeful signs on the disease front as well. Only about 10 percent of the oysters counted this year were "boxes" - dead oysters.
"We're seeing nowhere near the mortality we were seeing four to five years ago," said Roy Scott, a DNR biologist overseeing the survey. In the bad years, he said, it was not unusual to find 70 percent to 80 percent - sometimes 90 percent - of the market-size oysters dead.
This year, by contrast, the oysters also looked healthy. A handful of each sample were pried open to examine the amount of fat and the color of the meat. "The appearance of the oysters is a pretty good indicator of whether you have a disease problem," Scott said.
In years of intense disease pressure, the insides of the oysters are runny and their shells can have deep recesses. That's not the case this year.
To some degree, the lack of disease is to be expected. The single-cell parasites that spread MSX and dermo require high salinities to survive. A series of wetter than normal years has driven MSX, which requires higher salinities than dermo, almost entirely out of Maryland's portion of the Bay. And last year's record-high freshwater flow into the Chesapeake suppressed dermo levels in Maryland waters.
But even as salinities increased with this year's unusually low flow into the Bay, survey samples sent to the lab for analysis have shown lower concentrations of the disease in oysters than anticipated.
"We're seeing better survival than we might have expected based on our history of disease over the last several years," said Steve Jordan, director of the Cooperative Oxford Laboratory, a joint operation of the DNR and the National Marine Fisheries Service. "We've kind of got our fingers crossed here, but we may be seeing some tolerance of these parasites that's developing in the populations."
Bill Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation, cautioned against reading too much into the near-record index, noting that good spatfalls in dry years that follow wet years are not unusual. "From my way of thinking, this is not at all a surprise for this year," he said.
Still, he added, "every time we get a good spat set, we move forward with regard to the population overcoming the disease problem."
Though this year's index is high, the success has not been evenly distributed.
Almost all of the highest spat counts were in the Eastern Bay. Some of the bars in that area recorded huge spat sets: Parson's Island had 3,375; Turtleback 3,368; Ash Craft 2,248.
At those sites, oysters were completely covered with spat seeking solid surfaces on which to take hold. Bottles and cans were covered with spat.
"People we talked to who had been around there for a long time had never seen anything like it," said Mark Homer, a member of the survey crew. "It's just spectacular."
The survey crew kept one of the Eastern Bay oysters on the boat. It was about 5 inches long, and covered with dozens of tiny spat that completely obscured the oyster underneath. "That's what it looked like on the Eastern Shore," Scott said. "Every one was like that."
But on Western Shore bars, spat counts were often in single digits, and sometimes zero. One exception was a bar in the middle of the St. Mary's River which had a spat set of 1,390.
The reason, Jordan suggested, could be that some of the Eastern Bay tributaries may act as "larval traps."
After eggs are fertilized, free-swimming larvae develop. In some areas, and under some circulation patterns, the larvae may drift or be flushed far from the oyster beds, perhaps never finding a suitable solid surface on which to perch.
But in larval traps, the circulation patterns help to keep the larvae confined over areas of oyster shells which provide better habitat. Once the larvae attaches to a surface, it becomes a spat.
The decline of the oysters has sparked a variety of efforts to plant hatchery-raised oysters in the Bay. But this year's survey, which focused on natural oyster production in the Chesapeake, offers hope that after nearly a decade of disease, some natural recovery may be taking place.
"We're pleased not just because we had a good spat set, but because we think the overall patterns we're seeing are very encouraging," Jordan said.
That doesn't necessarily mean that the oysters are immune to the disease; although they may be developing enough tolerance to survive longer amid the infestations.
Jordan cautioned that the findings of this year's survey, though optimistic, are at best only a "crude" indicator of potential future harvests. Conditions conducive to major infestations of parasites could still overwhelm the oysters and offset much of this year's gain.
"The worst case is that we get a real dry year next year, and then we see MSX all over the place," he said. "Then, I don't think we are going to see the survival that we would like to see at all."
"But," he added, "if nature cooperates a little bit, we may do really well."
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