Spat low, diseases up in bay oysters

Wednesday, Feb. 4, 2009

The preliminary results of the annual study, released in January, performed by the Maryland Department of Natural Resources, show low oyster reproduction throughout the bay, with the exception of some parts of the lower Eastern Shore, according to a press release. A comprehensive report is likely to take several months because of the depth of analysis required, according to a DNR spokeswoman.

Prevalence of dermo and MSX, two oyster diseases that have decimated bay populations for 50 years, increased in 2007, the release said. That year also bucked a trend, however, in that the disease tends to upsurge in drier years because it thrives in saltier water, but disease levels remained below normal despite that summer's severe drought.

Also, despite increases in disease abundance, mortality has dropped, with 2007 being the fifth straight year overall mortality remained low.

"Oyster mortality in 2006 and 2007 were the two lowest years since the 1980s. It's too early to know if this is a trend, but this is a very positive development that we will be monitoring carefully," said Mike Naylor, director of DNR's shellfish program, in the release.

The survey, which has occurred annually since 1939, reviews the health and abundance of bay oysters by dredging oyster bars at spots through the estuary and assessing their condition. In 2008, scientists collected more than 1,800 oysters from 282 bars.

Larry Simns, president of the Maryland Watermen's Association, said the lower disease rates along parts of the Eastern Shore can be attributed to the use of power dredging in Tangier Sound and other places.

"What we're saying is, [there were] a lot of oysters down in the Tangier Sound area that live, but there's a couple reasons we think they lived," Simns said. "That's an area we power dredge, which cleans shells up and takes old, diseased oysters away so [young oysters] have no oysters there to give them disease. … If we don't take all the diseased oysters up, that means there's more diseased oysters out there to give it to new ones coming along. You're better off harvesting them than having them hang around and spreading the disease."

Simns said additional regulation is not required because it is diseases, not overharvesting, that is harming oyster survival.

"Regulation is not going to help the oyster industry," Simns said. "We've got disease — that's what killing oysters. It's not catching them — it's dying off from the disease. We don't think that should make any more restrictions, because you can stop oystering tomorrow and they're still going to die from disease."

DNR also announced Wednesday the release of full results from the 2007 dredge survey, which were compiled last September. That document suggests a dismal year, with a very low setting rate for spat, or baby oysters. This was followed by a substantial increase in disease levels following four years of decline, with Dermo found on 93 percent of oyster bars tested, and MSX spreading throughout the lower bay and its tributaries.

Despite these changes, however, mortality continued to decline, possibly a consequence of large volumes of water entering the bay in late 2006 and early 2007, the report suggested. Of three ‘sanctuaries' tested, where power dredging is forbidden, two suffered death rates above the bay average.

emitrano@somdnews.com