Maryland Oyster Survival Rates at Highest Levels Since 1997

posted in: Chesapeake Bay News | 0

According to the State’s recently completed fall oyster survey, the number of spat or baby oysters in Maryland waters is at its highest level since 1997, the survival rate for young oysters is also up, and more Marylanders are looking to start up or expand aquaculture businesses.

Since 1939, the Maryland Department of Natural Resources (DNR) and its predecessor agencies have monitored the status of Maryland’s oyster population via annual field surveys. The survey tracks three critical components of the population: Spatfall Intensity, which measures reproduction levels (recruitment) and offers a window into future population levels; disease infection levels; and annual mortality rates of oysters.

The 2-month 2010 fall population assessment, which encompassed 260 oyster bars and 399 samples throughout the Bay and its tributaries, concluded on December 18.  At nearly 80 spat (baby oysters) per bushel, the 2010 spatfall is the highest since 1997, and about 5 times the 25-year average of 16.

Eleven of the 53 oyster bars included in this index had their highest or second highest spat counts since 1985.  The elevated spatfall was a coast-wide phenomenon, with other mid-Atlantic states also reporting better than average numbers.

Equally encouraging was wide distribution of spat throughout the Bay and its tributaries: While the heaviest counts were in the lower Bay’s higher salinity areas, where reproduction is typically more successful, a moderate spatfall also occurred in lower salinity areas that generally receive little to no spat sets at all.  These included the upper Bay as far north as Pooles Island and the upper reaches of the Chester, Choptank and Patuxent River tributaries. Due to reduced disease pressure, oysters historically have good survivorship in these areas, some of which are now protected sanctuaries under the State’s new oyster plan.

Even more encouraging news for the beleaguered oyster is that the frequency and intensity of diseases remains low, based on December’s interim report from the Paul S. Sarbanes Cooperative Oxford Lab.  Of the two diseases that have devastated populations for decades, Dermo, although still widely distributed, remains below the long-term average for the eighth consecutive year, and MSX appears to again be in retreat after an advance in 2009. View chart.

The survey indicates that oyster survivorship — the percentage of oysters found alive in a sample — was at 88 percent, the highest level since 1985, before diseases put a stranglehold on the population; this is more than double 2002 when record disease levels left only 42 percent of Maryland’s population alive. Scientists are hopeful that favorable mortality in recent years may reflect an increase in disease resistance.

Last year, the State of Maryland adopted regulations to implement a new Oyster Restoration and Aquaculture Development Plan. The plan increased Maryland’s network of oyster sanctuaries from 9 percent to 24 percent of remaining quality habitat; increased areas open to leasing for oyster aquaculture, and established a $2.2 million financial assistance program for aquaculture interests; and maintained 76 percent of the Bay’s remaining quality oyster habitat for a more targeted, sustainable, and scientifically managed public oyster fishery.

Since last fall 26 Marylanders have applied for 35 new leases to grow oysters and the State has received 27 applications for more than $2 million in available funding for start up and expansion of aquaculture businesses.  Blue crab disaster funds are being used to support the program.

In a coordinated effort among the Oyster Recovery Partnership, the University of Maryland, the NOAA Chesapeake Bay office and DNR, over 2.5 billion hatchery produced spat have been produced and planted in Maryland’s portion of the Chesapeake Bay since 2000, and thousands of acres of buried shell have been reclaimed from derelict oyster reefs.

Since 1994, the Chesapeake Bay oyster population has languished at 1 percent of historic levels. Over the past 25 years, the amount of suitable oyster habitat has declined by 80 percent — from 200,000 acres to just 36,000 acres.

Maryland’s annual oyster harvest has fallen from an average of 2.5 million bushels in the late 1960s to about 100,000 bushels a year since 2002, while the number of oystermen working Maryland’s portion of the Bay has dwindled from more than 2000 to just 550.

source: MD DNR press release

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