Virginia Institute of Marine Science
Journal Of Shellfish Research
We describe oyster population trends in the Great Wicomico River, VA, from 2000 through 2009 using quantitative fishery independent survey data collected using a stratified random design. The seven public reefs examined cover a total of 2.8 X 10(5) m(2) and vary in individual size from 1.36 X 10(4) to 7.16 X 10(4) m(2). The river is functionally divided by a sand spit into upriver and downriver regions. Oyster densities on the upriver reefs were typically an order of magnitude higher than densities on the downriver reefs within the same time period. Throughout the system, the highest observed densities were coincident with high annual recruitment events (2002, 2006). Recruitment events were usually followed by high mortality, with small percentages of the population reaching >= 3 y of age. A predictive stock recruit relationship is absent; rather, population demographics appear to be dominated by periodic high recruitment events. In the absence of seed removal, biomass maxima follow 1-2 y after recruitment maxima. Standing stock for the system varied between 1.56 X 10(6) g and 3.63 X 10(7) g in 2005 and 2006. Year-specific age-at-length relationships were estimated from demographics data. Length demographics were recast as age demographics to estimate mortality. Observed proportional mortality between young of the year and age 2 oysters was approximately 0.88 for the 2006-y class, which is slightly higher than the 0.62-0.71 observed for the 2007-y class. The ability to estimate age specific mortality accurately allows the construction of shell (habitat) budgets for the individual reef systems. The Great Wicomico oyster population appears to be maintained by episodic and extraordinary recruitment in the face of high mortality the latter driven by disease (predominantly Perkinsus marinus) epizootics. The shell resource is modest, equivalent to little more than a monolayer several centimeters thick. Over short timescales (years), the available shell resource oscillates in concert with mortality. The shell accretion rate on upriver reefs is consistently 4-5 times greater than that observed on downriver reefs. Periodic modest shell planting has maintained the habitat base (the shell resource) throughout the system over decadal scales.
Eastern Oyster; Crassostrea Virginica; Population Demographics; Mortality; Recruitment; Shell Budgets; Great Wicomico River
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Commonwealth of Virginia; Virginia Marine Resources Commission; National Oceanic and Atmospheric Administration [NA06NMF4570312, NA07NMF4570335]
Southworth, Melissa; Harding, Juliana M.; Wesson, James A.; and Mann, Roger L., Oyster (Crassostrea Virginica, Gmelin 1791) Population Dynamics On Public Reefs In The Great Wicomico River, Virginia, USA (2010). Journal Of Shellfish Research, 29(2), 271-290.