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Fishery Bulletin 107(2) 
Some have expressed concerns about managing at 
B msy (e.g., Peterman, 1977; Hilborn, 2002; Mangel et 
al., 2002), but only recently has the possibility been 
raised that carrying capacity may not be the long-term 
constant typically assumed under B MSY management. 
That realization arises ineluctably from the recognition 
that regime shifts profoundly affect the balance between 
population and environment (Rothschild, 2000; Collie et 
al., 2004; Rothschild and Shannon, 2004; Sakuramoto, 
2005). Increasingly, fisheries biologists recognize these 
transitions as an important long-term component of 
population variation (e.g., Botsford, 1981; Steele and 
Henderson, 1984; Ware, 2000; Jackson et al., 2001; 
Choi et al., 2004; Collie et al., 2004; Breitburg and 
Fulford, 2006). Any change in carrying capacity assur- 
edly changes B MSY . 
The acceptance of regime shifts requires an acknowl- 
edgement that populations can exist in alternating sta- 
ble states that are self-reinforcing for protracted periods 
of time. The record of oyster abundance in Delaware 
Bay indicates at least two regime shifts (Powell et al., 
2008), circa 1970 and circa 1985, with intervening and 
succeeding intervals having the attributes of alternate 
stable population states ( sensu Gray, 1977; Peterson, 
1984; Knowlton, 2004). These periods of relative sta- 
bility are multigenerational and demonstrably not of 
anthropogenic origin 4 (see Knowlton, 2004) because 
fishing mortality rates have been far below natural 
mortality rates over much of this time. The periods of 
stability are persistent over a range of climatic condi- 
tions (Soniat et al., in press). The association of unique 
climatic events with each of the regime shifts is consis- 
tent with models that emphasize the unique confluence 
of a set of forcing factors in the initiation of catastrophic 
events (DeAngelis and Waterhouse, 1987; Deakin, 1990; 
Hastings, 1991) and supports the observation of Collie 
et al. (2004) that large-scale changes in the population 
dynamics of species are commonly characterized by 
a poor correlation between the response variable and 
potential forcing factors. 
Evaluation of MSY-style reference points requires an 
understanding of the capacity of a species to expand its 
biomass over a range of biomasses. In fisheries parlance, 
this expansion capacity is related to surplus production. 
Regime shifts change expansion capacity in relation to 
biomass. Surplus production models are well described 
(e.g., Sissenwine and Shepherd, 1987; Maunder, 2003), 
but the influence of range shifts has rarely been con- 
sidered. In the first of two companion contributions, we 
develop relationships supporting a surplus production 
model for a species, the eastern oyster ( Crassostrea 
virginica), and a location, Delaware Bay, characterized 
by distinctive and well described range shifts. We take 
advantage of a 54-yr time series of oyster abundance, 
recruitment, and mortality for this analysis. 
4 We recognize that the introduction of Haplosporidium nelsoni 
(MSX) circa 1957 (Burreson et al., 2000), which subsequently 
played a critical role in the 1985 regime shift, was likely 
anthropogenically driven. 
Table 1 
The bed groups (by location: upbay and downbay) and 
subgroups (by mortality rate) for the eastern oyster 
( Crassostrea virginica ) collected on twenty beds in Dela- 
ware Bay, as shown in Figure 1. Mortality rate divides each 
of the primary groups, themselves being divided by loca- 
tion, a surrogate for up bay-downbay variations in dredge 
efficiency and fishery 
area-management regulations. 
Bed group 
and subgroup 
Bed 
Upbay group 
Low mortality 
Round Island, Upper Arnolds, 
Arnolds 
Medium mortality 
Upper Middle, Middle, 
Sea Breeze, Cohansey, Ship John 
Downbay group 
Medium mortality 
Shell Rock 
High mortality 
Bennies Sand, Bennies, 
New Beds, Nantuxent Point, 
Hog Shoal, Hawk’s Nest, 
Strawberry, Vexton, Beadons, 
Egg Island, Ledge, 
Materials and methods 
The survey time series 
The New Jersey survey began as a response to overfish- 
ing that had reduced stock abundance by the early 1950s. 
By 2006, this 54-yr record covered a number of unique 
periods, including the period of time after the onset of 
MSX, a disease caused by the protozoan Haplosporidium 
nelsoni, circa 1957 (Haskin and Andrews, 1988; Ford, 
1997) and the period after the onset of Dermo, a disease 
caused by the protozoan Perkinsus marinus, circa 1990 
(Ford, 1996; Cook et al., 1998). 
In what follows, we define the population on the twen- 
ty primary oyster beds in Delaware Bay (Fig. 1) as the 
oyster stock in the New Jersey waters of Delaware Bay, 
but for simplicity we refer to it as the Delaware Bay 
oyster stock. 5 The analyses that follow will delineate 
four bed groups based on the long-term average rates of 
natural mortality, productivity, and survey catchability 
(Table 1). Analyses of the Delaware Bay oyster resource 
5 Oysters are also found on the Delaware side of the bay, 
although the total bed area is much less than that in the New 
Jersey waters (Moore, 1911; Maurer et al., 1971; Maurer and 
Watling, 1973), as well as in many of the river mouths; and 
an unknown number (but significant during certain periods 
of history LMacKenzie, 1996; Ford, 1997]) have been present 
on leased grounds, most of which are situated downbay of 
Egg Island (see Fig. 1 of Haskin and Ford, 1982). Inadequate 
survey data exist to include oysters in bay margin habi- 
tats and on leased grounds in the stock analysis. Delaware 
maintains an independent survey, but these data are not 
yet available on a per-m 2 basis. However, abundance and 
recruitment trends typically have been similar on both sides 
of the bay. 
