Long-Term (1939 to 2008) Spatial Patterns in Juvenile Eastern Oyster (Crassostrea virginica, Gmelin 1791) Abundance in the Maryland Portion of Chesapeake Bay

Stocks of eastern oysters (Crassostrea virginica, Gmelin 1791) have undergone dramatic declines in the Chesapeake Bay since the mid 1800s. As a result, substantial efforts have been made to try and reverse this decline to provide support for a commercially and socially important fishery and, more recently, to restore the oyster's important ecological role. Since 1939, juvenile oyster abundance has been measured at sentinel oyster bars in the northern portion of Chesapeake Bay, Maryland. We conducted a cluster analysis on these data and detected 4 distinct spatial patterns. These patterns were related to juvenile oyster abundance (i.e., bars that experienced high overall juvenile abundance grouped together) and salinity. Of the sentinel bars sampled since the mid 1980s, our analysis identified 13 bars that were characterized by high juvenile oyster abundance and low variation among years, which makes them prime candidate bars for protection to aid in restoration. A comparison with bars already protected within oyster sanctuaries revealed some overlap (4 total bars in common); however, the 13 bars we identified were found over broader geographical and salinity ranges. Juvenile oyster abundance on this group of 13 prime bars was intercorrelated significantly, suggesting that interannual variability in juvenile oyster abundance affects each region similarly. Significant correlations between the juvenile oyster abundance time series and the Palmer hydrological drought index suggest that variations in wet/dry cycles are the cause of this interannual variability. Our analysis also indicates that the entire oyster population of the northern Chesapeake Bay may respond in similar manner to climate change effects.