109 
Multiple stable reference points 
in oyster populations: biological relationships 
for the eastern oyster ( Crassostrea virgin tea) 
in Delaware Bay 
Eric N. Powell (contact author)' 
John M. Klinck 2 
Kathryn A. Ashton-AScox 1 
John N. Kraeuter 1 
Email address for contact author: eric@hsrl.rutgers.edu 
1 Haskin Shellfish Research Laboratory 
Rutgers University 
6959 Miller Avenue 
Port Norris, New Jersey 08349 
2 Center for Coastal Physical Oceanography 
Crittenton Hall 
Old Dominion University 
Norfolk, Virginia 23529 
Abstract — In the first of two com- 
panion papers, a 54-yr time series 
for the oyster population in the 
New Jersey waters of Delaware Bay 
was analyzed to develop biological 
relationships necessary to evaluate 
maximum sustainable yield (MSY) 
reference points and to consider how 
multiple stable points affect refer- 
ence point-based management. The 
time series encompassed two regime 
shifts, one circa 1970 that ushered in 
a 15-yr period of high abundance, and 
a second in 1985 that ushered in a 
20-yr period of low abundance. The 
intervening and succeeding periods 
have the attributes of alternate stable 
states. The biological relationships 
between abundance, recruitment, and 
mortality were unusual in four ways. 
First, the broodstock-recruitment 
relationship at low abundance may 
have been driven more by the provi- 
sion of settlement sites for larvae by 
the adults than by fecundity. Second, 
the natural mortality rate was tem- 
porally unstable and bore a nonlin- 
ear relationship to abundance. Third, 
combined high abundance and low 
mortality, though likely requiring 
favorable environmental conditions, 
seemed also to be a self-reinforcing 
phenomenon. As a consequence, the 
abundance-mortality relationship 
exhibited both compensatory and 
depensatory components. Fourth, the 
geographic distribution of the stock 
was intertwined with abundance and 
mortality, such that interrelation- 
ships were functions both of spatial 
organization and inherent population 
processes. 
Manuscript submitted 29 November 2007. 
Manuscript accepted 9 September 2008. 
Fish. Bull. 107:109-132 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
All federal fisheries, and some state 
fisheries, are managed under biologi- 
cal reference-point guidelines that 
implement a yearly allocation or 
quota, often termed TAC (total allow- 
able catch) or TAL (total allowable 
landing), to constrain fishing mortal- 
ity (e.g., Wallace et al., 1994). The 
biological reference-point approach 
for federal fisheries was mandated 
by the Magnuson-Stevens Fishery 
Conservation and Management Act 
(Anonymous, 1996) which requires 
management at a biomass that pro- 
vides maximum sustainable yield, 
B msy . Under this system, sophisticated 
survey, analytical, and modeling pro- 
cedures are used to identify selected 
biological reference points, such as 
the target biomass, B MSY , and carry- 
ing capacity, K. Fishing mortality is 
then set in relation to these goals. As 
a consequence, much attention has 
been given to the choice and applica- 
tion of biological reference points in 
fisheries management (e.g., Sissen- 
wine and Shepherd, 1987; Hilborn, 
2002; Imeson et al., 2002; Mangel et 
al., 2002). 
Normally, B MSY is defined in rela- 
tion to carrying capacity, the biomass 
present without fishing, where natu- 
ral mortality balances recruitment 
(e.g., May et al., 1978; Johnson, 1994; 
Mangel and Tier, 1994; Rice, 2001). 
This stable point is characterized by 
a population in which most animals 
are adults, where natural mortality 
rates are low, and where recruitment 
is limited by compensatory processes 
such as resource limitation constrain- 
ing fecundity. B MSY is most commonly 
defined as — , based on the well-known 
Schaefer model which stipulates the 
guiding premise that surplus pro- 
duction is highest at ^ (Hilborn and 
Walters [1992]; see Restrepo et al. 
[1998] for more details on the feder- 
al management system; see NEFSC 
[1999 1 , 2000 2 , 2002 3 ] for examples 
of implementation of reference-point 
management). 
1 NEFSC (Northeast Fisheries Science 
Center). 1999. 29 th Northeast re- 
gional stock assessment workshop (29 th 
SAW): Stock Assessment Review Com- 
mittee (SARC) consensus summary of 
assessments. NMFS NEFSC Ref. Doc. 
99-14, 347 p. 
2 2000. 30 th Northeast regional stock 
assessment workshop (30 th SAW): Stock 
Assessment Review Committee ( SARC ) con- 
sensus summary of assessments. NMFS 
NEFSC Ref. Doc. 00-03, 477 p. 
3 2002. 34 th Northeast regional stock 
assessment workshop (34 th SAW): Stock 
Assessment Review Committee (SARC) con- 
sensus summary of assessments. NMFS 
NEFSC Ref. Doc. 02-06, 346 p. 
