Spotty oyster mortality appears in Bay
Special from the Star Democrat
— Oysters in waters from Tilghman Island south are turning up dead, and there could be any number or a combination of several reasons why.
The mortality is spotty, said Maryland Department of Natural Resources Shellfish Division Director Chris Judy, but still something watermen should keep an eye on and inform the department when they pull up dead oysters.
DNR is conducting its fall oyster survey. Meanwhile, it has been getting reports from watermen about this oyster season being a worse harvest year than last season.
The mortality levels depend on the bar, Judy said. A lot of areas have similar mortality rates compared to last year, he said.
“We’ve been to oyster bars were the mortality is well over 30 percent, which is high,” he said. “But in the very next bar, it looks fine.”
There are a few theories about the causes of the mortality.
The most obvious of which, Judy said, is it has been very dry and salinity levels are up, and have been for more than a year. High salinity levels can cause a spike in disease, and when disease increases, mortality can follow, he said.
Another theory points to low dissolved oxygen in the water, which can suffocate the oysters.
Another theory is they are dying be-
cause it has been warmer than usual lately, and because of that, oysters have been spawning longer and are weakened for an extended period of time.
“Here it is November, and it feels like October or even September,” Judy said. “We actually see some oysters at the tail end of spawning, and it’s midNovember already.”
When oysters spawn, they become weak, “so if you have a situation where the temperatures are increased late into the season, they’re in a weakened condition,” and if they’re infected with disease, “you’ve got an oyster that is highly stressed,” he said.
They’re all complicating factors, but still only theories, Judy said. It won’t be known for sure what exactly is happening until the fall survey is finished and results are released in mid-December and laboratory disease test results come in, which Judy said should happen shortly after the survey results are released.
“The pieces of the puzzle fit together, but the problem is you cannot predict this is going to happen,” Judy said.
It’s not the first time Maryland’s oysters have been confronted with potential disease. The last drastic drop in the state’s oyster population came after disease hit it hard in 1999.
A bad spat set that year led to less oysters to harvest a few years down the road, and landings were at their worst in Maryland history during the 2003-04 oyster season, when Maryland watermen caught a little more than 25,800 bushels, compared to about 413,000 bushels in the 1998-99 season and about 370,800 the season after that, according to DNR figures.
The last strong spat sets were in 2010 and 2012, Judy said. Strong spat sets will yield more harvestable oyster later on when they grow to market size in a few years, which is why Maryland recently had several good years of harvest.
Since 2010, harvest peaked during the 2013-14 season, when Maryland watermen landed more than 431,000 bushels.
But since 2012, spat set has been low. As a result, harvest is now in decline, Judy said.
“The Maryland oyster fishery is highly dependent on the level of spat set,” he said. “Favorable set rates will increase the harvest and low set rates will depress the harvest.”
Landings dipped back into the 300,000s in the 2014-15 season, and Maryland watermen landed more than 374,000 bushels last year.
Landings are expected to decline again this year, Judy said, which is something DNR has been hearing from watermen throughout the season so far.
Judy said if any watermen are seeing dead oysters in the water, they should mark down the name of the bar and the tributary. He asked watermen to provide that information to DNR, so scientists can get a clearer picture of what’s happening and where it’s happening. Any information can be relayed to DNR by calling 410-260-8259.