758 



Abstract— Culture of a non-native 

 species, such as the Suminoe oyster 

 iCrassostrea ariakensis). could offset 

 the harvest of the declining native 

 eastern oyster (Crassostrea virginica) 

 fishery in Chesapeake Bay. Because of 

 possible ecological impacts from intro- 

 ducing a fertile non-native species, 

 introduction of sterile triploid oysters 

 has been proposed. However, recent 

 data show that a small percentage 

 of triploid individuals progressively 

 revert toward diploidy, introducing the 

 possibility that Suminoe oysters might 

 establish self-sustaining populations. 

 To assess the risk of Suminoe oyster 

 populations becoming established in 

 Chesapeake Bay, a demographic popu- 

 lation model was developed. Parameters 

 modeled were salinity, stocking density, 

 reversion rate, reproductive potential, 

 natural and harvest-induced mortal- 

 ity, growth rates, and effects of vari- 

 ous management strategies, including 

 har\'est strategies. The probability of a 

 Suminoe oyster population becoming 

 self-sustaining decreased in the model 

 when oysters are grown at low salinity 

 sites, certainty of harvest is high, mini- 

 mum shell length-at-harvest is small, 

 and stocking density is low. From the 

 results of the model, we suggest adopt- 

 ing the proposed management strate- 

 gies shown by the model to decrease 

 the probability of a Suminoe oyster 

 population becoming self-sustaining. 

 Policy makers and fishery managers 

 can use the model to predict potential 

 outcomes of policy decisions, supporting 

 the ability to make science-based policy 

 decisions about the proposed introduc- 

 tion of triploid Suminoe oysters into 

 the Chesapeake Bay. 



A model for assessing the likelihood of 

 self-sustaining populations resulting from 

 commercial production of triploid Suminoe oysters 

 iCrassostrea ariakensis) in Chesapeake Bay 



Jodi R. Dew 



Jim Berkson 



Eric M. Hallerman 



Department of Fisheries and Wildlife Sciences 



106 Cheatham Hall 



Virginia Polytechnic Institute and State University 



Blacksburg, Virginia 24061-0321 



E-mail address (for J. Berkson, conlaci auttior). |berkson(gvt.edu 



Standish K. Allen Jr. 



School of Manne Science 



Virginia Institute of Manne Sciences 



Gloucester Point, Virginia 23062 



Manuscript approved for publication 

 16 June 2003 by Scientific Editor. 



Manuscript received 26 June 2003 at 

 NMFS Scientific Publications Office. 



Fish. Bull. lOhT.'JS-TeS (2003). 



The native eastern oyster (Crassostrea 

 virginica) population in Chesapeake 

 Bay has declineti because of habitat 

 degradation, over-harvest, and dis- 

 ease- and parasite-mediated mortahty. 

 Efforts to restore the eastern oyster pop- 

 ulation in Maryland and Virginia have 

 been hindered by persistent diseases 

 and habitat degradation (Mann et al., 

 1991; Gottlieb and Schweighofer, 1996). 

 Recent restoration efforts have included 

 intensified reef building programs. In 

 addition to restoring the native oyster, 

 discussions about introducing non- 

 native disease- and parasite-resistant 

 oyster species into the Chesapeake 

 Bay have gone forward since the early 

 1990s (Mann et al., 1991; Lipton et al., 

 1992; Gottlieb and Schweighofer, 1996; 

 Hallerman etal., 2002). 



In 1997, in-water testing of non-na- 

 tive oyster species (sterile triploids) 

 began in Virginia, first with the Pa- 

 cific oyster (Crassostrea gigas), then 

 with the Suminoe oyster (Crassostrea 

 ariakensis) (Calvo et al., 1999; Calvo 

 et al., 2001). Field studies with Pacific 

 oysters showed poor performance under 

 Chesapeake Bay conditions (Calvo et 

 al., 1999). However, field studies with 

 Suminoe oysters demonstrated disease 

 resistance and rapid growth, and indi- 



viduals reached minimum harvest shell 

 length of about 77 mm in approximately 

 one year (Calvo et al., 2001). These re- 

 sults, and subsequent small-scale trials 

 by industry, evoked strong interest in 

 the commercial culture of Suminoe oys- 

 ters to supplement the eastern oyster 

 fishery. 



Ideally, aquaculture with 100% tri" 

 ploid oysters would pose no risk of es- 

 tablishment of a self-sustaining oyster 

 population (Guo and Allen, 1994a). 

 However, a number of factors make the 

 use of triploids imperfect. For example, 

 recent data have shown that a small 

 percentage of triploid oysters progres- 

 sively revert toward diploidy with age 

 (Calvo et al., 2001; Zhou. 2002). Rever- 

 sion of triploids leads to mosaicism in 

 which individuals comprise both dip- 

 loid and triploid cells. Mosaics them- 

 selves are innocuous unless the re-es- 

 tablishment of diploid cells leads to re- 

 covered reproductive capability, which 

 could in turn lead to the establishment 

 of a self-sustaining Suminoe oyster 

 population. We define this hazard, 

 "reproductively effective reversion," as 

 the process of yielding mosaics with re- 

 covered reproductive capability. Repro- 

 ductively effective reversion introduces 

 the possibility that triploid Suminoe 



