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DNR Releases Preliminary Oyster Mortality Rates For The Upper Bay | Maryland DNR Fisheries Service News

DNR Releases Preliminary Oyster Mortality Rates For The Upper Bay

11/10/2011  |   Posted by jdavidsburg

Tags: Shellfish, Oyster, Commercial, Recreational  

Fall Survey finds concentrated pockets of high oyster mortality

In preliminary findings from the Maryland Department of Natural Resources (DNR) annual Fall Oyster Survey biologists have found concentrated pockets of dead oysters in some areas of the upper Bay, caused by record-high flows of freshwater.

In early November, as part of the Bay-wide survey, biologists collected samples from 15 individual oyster bars north of the Bay Bridge. In the four northernmost bars along the Eastern Shore, oysters suffered a cumulative mortality of 79 percent, with no live oysters on the two northernmost bars. The few live oysters that were found in upper Bay bars were in poor condition — bloated, watery and translucent — and mortalities may continue for some time.

Higher than normal mortality rates were also found along the Western Shore, North of the Bay Bridge. The combined mortality rate for the six bars in the mainstem of the bay between the Magothy River and Man O War shoal at the mouth of the Patapsco Riverwas 74 percent, a 7-fold increase over the 2010 rate of 11 percent. While biologists are still analyzing data from the rest of the Bay, preliminary results indicate low mortality from Sandy Point to points south, and oysters in these areas seemed in prime condition.

Biologists believe the high mortality was caused by the lack of salinity in the upper Bay from March through July, 2011 having set many modern day records for high flow and low salinity. March to May freshwater flows were the highest ever recorded in the Susquehanna River, driving salinity levels to record lows at many Maryland monitoring stations by June. The fact that mortality was highest along the upper western shore, where salinity was lowest, reinforces this hypothesis.

“This is a setback for the upper Bay,” said Mike Naylor, DNR shellfish program director. “This hits a fragile area of the Bay particularly hard. There were very few mature oysters in this area of the Bay to begin with, but it’s very disheartening to see that the remarkable, encouraging 2010 spatset has been lost.”

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