Powell et at: Multiple stable reference points in oyster populations: Crassostrea virgmica in Delaware Bay 
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75° 30' 
75° 20' 
75° 10' 
39° 25' 
39° 20' 
39° 15' 
39° 10' 
39° 25' 
39° 20' 
39° 15' 
39° 10' 
75° 30' 
75° 20' 
75° 1 0' 
Figure 1 
The twenty natural oyster beds of the eastern oyster ( Crassostrea virginica ) in the New Jersey waters of 
Delaware Bay may be characterized in terms of high-quality (dark shade) and medium-quality (light shade) 
grids, the term quality referring to a relative differential in long-term average oyster abundance (Powell et 
al, 2008). The footprints for the Middle bed (upper portion of figure) and the beds downbay from it, excepting 
New Beds, Egg Island, and Ledge, were updated with data from surveys in 2005 and 2006. The footprints 
for the remaining beds were based on historical definitions. 
of New Jersey routinely reveal a division between an 
upbay group of eight beds (Round Island, Upper Ar- 
nolds, Arnolds, Upper Middle, Middle, Sea Breeze, Co- 
hansey, and Ship John) and a downbay group of twelve 
beds (Shell Rock, Bennies Sand, Bennies, New Beds, 
Nantuxent Point, Hog Shoal, Hawk’s Nest, Strawberry, 
Vexton, Beadons, Egg Island, and Ledge) (Fig.l). Salin- 
ity, natural mortality rate, and growth rate are higher 
downbay. Dredge efficiencies are significantly higher 
downbay (Powell et al., 2002a, 2007). Both regions can 
be subdivided by natural mortality rate and productiv- 
ity. In the upbay group, natural mortality rates and 
growth rates are significantly lower for the upper three 
beds, Round Island, Upper Arnolds, and Arnolds, than 
for the remaining beds. Henceforth these two groups 
will be termed “the low-mortality” and “medium-mor- 
tality” beds, respectively (Table 1). In the downbay 
group, growth rates and mortality rates are lower for 
