128 
Fishery Bulletin 107(2) 
Conclusions 
The oyster population in Delaware Bay exhibits popu- 
lation dynamics that are not normally described in 
commercial species. One reason is the presence of 
multiple distinct, dynamically stable states delim- 
ited by temporally rapid regime shifts. Such dynam- 
ics are becoming more widely appreciated in fished 
species as a whole; therefore these unique dynamics 
may be more apparent than real. Oyster popula- 
tions display four unusual biological relationships, 
however, that impute greater peculiarity to their 
population dynamics. First, it seems likely that the 
broodstock-recruitment relationship, at least at low 
abundance, is driven more by the provision of settle- 
ment sites for larvae by the adults than by fecundity. 
Second, the natural mortality rate is temporally 
unstable and bears a nonlinear relationship with 
abundance (Fig. 9). This nonlinearity is driven by 
MSX and Dermo, both acting similarly despite the 
multifarious differences in their life histories, and 
by the environmental gradient of the habitable areas, 
which provide habitats of refuge from disease during 
epizootics. Third, high abundance and low mortal- 
ity, though likely requiring favorable environmental 
conditions, also seem to be self-reinforcing, although 
the specific underpinning dynamics remain unclear. 
As a consequence, an increased probability of high 
mortality occurs over a relatively small range of total 
abundances. The mortality relationship exhibits both 
compensatory and depensatory components. Fourth, 
the geographic distribution of the stock is inter- 
twined with the variables of abundance, recruitment, 
and mortality, such that biological relationships are 
functions both of spatial organization and inherent 
population processes. As a consequence of the imprint 
of geographic distribution on population dynamics, 
epizootic-level mortalities normally occur only when 
the animal has expanded its population beyond the 
refuge sufficiently that a significant fraction of the 
population is exposed to higher mortality. Consolida- 
tion limits mortality. What is equally interesting is 
the parallel influence on recruitment such that the 
consolidated stock has a lower recruitment potential, 
while also minimizing epizootic mortality. 
One is often dismayed by the dispersion of data in 
plots of the relationships of broodstock to recruitment 
and abundance to mortality. This dispersion is nor- 
mally ascribed to stochastic processes, and stochas- 
ticity is certainly a causal element. However, both 
governing regime and geographic distribution of the 
stock influence the dispersion of these data. Of note 
is the influence of stock dispersion, where the ambit of 
the population when the stock is in a contracted state 
is dissimilar from the ambit when the stock is in a 
dispersed state. This dynamic imposes a wider range 
in stock performance for a given stock abundance than 
would be observed for either distributional state alone. 
At least for oysters, a substantive component of ap- 
parent stochasticity observed in the relationships of 
recruitment and mortality to abundance originates 
not from simple year-to-year variation in stock perfor- 
mance, but from different distributions for the stock 
dictated by modifications in the geographic distribu- 
tion of the stock, and these distributional states tend 
to be self-reinforcing, as evidenced by similar changes 
in both recruitment and mortality over half-decadal or 
longer intervals of time. 
Acknowledgments 
We recognize the many people who contributed to 
the collection of survey data during the 54 years sur- 
veyed for this report, with particular recognition of H. 
Haskin, D. Kunkle, and B. Richards for their scientific 
contributions. We appreciate the many suggestions on 
content provided by S. Ford. The study was funded 
by an appropriation from the State of New Jersey to 
the Haskin Shellfish Research Laboratory, Rutgers 
University, and authorized by the Oyster Industry Sci- 
ence Steering Committee, a standing committee of the 
Delaware Bay Section of the Shell Fisheries Council 
of New Jersey. 
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