Nonnative Oysters in the Chesapeake Bay (2004) / Chapter Skim
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9. Elements of Risk Assessment for the Introduction of Crassostrea Ariakensis in the Chesapeake Bay
9. Elements of Risk Assessment for the Introduction of Crassostrea Ariakensis in the Chesapeake Bay
Pages 187-231
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From page 187... ...
In these studies, risk management is defined as a decision-making process that takes into account the probability distribution of harms given exposure to the hazard and the associated conditional costs and benefits. That is, risk assessment and risk management are reduced to characterizing the branches and conditional probabilities of a decision tree and selecting a strategy based on preferences regarding the conditional net benefits.
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From page 188... ...
(1995) , we define risk assessment as a decision-making technique that incorporates objective and subjective estimates of the probability of uncertain factors and identifies preferred actions with respect to multiple objectives (see Box 9.1~.
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From page 189... ...
. For example, stakeholders who favor the establishment of nonnative oysters might prefer management actions that increase the likelihood of reproduction, while those who oppose establishment of nonnative oysters might prefer management actions that decrease the likelihood of reproduction, decrease the likelihood of reproduction by reverted oysters, or decrease the likelihood of successful establishment of nonnative populations.
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From page 190... ...
Development of a risk assessment framework for the decision would involve characterizing and developing probability distribution functions for the various risks, evaluating those risks according to the diverse objectives, and balancing those objectives in a multiple criteria decision analysis. At this stage there is insufficient information for a formal risk assessment of management options concerning the introduction of a nonnative oyster into the bay.
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From page 191... ...
(2003) provides a useful example of a simple model of the likelihood of self-sustaining populations resulting from commercial production of supposed triploid nonnative oysters.
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From page 192... ...
Adherence to the International Council for the Exploration of the Sea protocols, discussed in more detail below, would significantly reduce the risk of bringing in a new disease-causing organism as a consequence of introducing a nonnative oyster. Some of the linkages are more robust than others, and some researchers are more confident of a causal relationship than others.
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From page 193... ...
Mortalities of the scale caused by the parasite in Delaware Bay and later in Chesapeake Bay had never before been recorded in those estuaries, and it was assumed that the parasite was new to the region (Ford and Tripp, 1996~. Later, two separate investigations (Katkansky and Warner, 1970; Kern, 1976)
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From page 194... ...
Further, this parasite was identified in tissues of oysters in the southeastern United States, including the Virginia portion of Chesapeake Bay, as soon as investigators looked in the late 1940s and early 1950s. It was not detected in the northeastern United States, however, and numerous studies documented that the parasite multiplied and killed most readily at elevated water temperatures.
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From page 195... ...
as a cautionary example of a disease agent brought with an introduced host. Others are less sure of the connection (Grizel and Heral, 1991~.
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From page 196... ...
Vibrio tapetis (Brown Ring Disease) Brown Ring Disease is a disease that has caused mortalities of the Manila clam, Ruditapes philippinarum, in Western Europe (Paillard et al., 1994~.
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From page 197... ...
Considerations for Disease Risk Assessment Implications of Detecting Pathogens in Disease Surveys One of the questions raised about the potential introduction of C ariakensis is the lack of knowledge of parasites and diseases of the species in its native range.
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From page 198... ...
The International Council for the Exploration of the Sea Code of Practice The greatest risk of C ariakensis introducing a disease agent would occur if seed or adult oysters were to be placed in Chesapeake Bay directly from another location (e.g., "rogue" introductions from China or
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From page 199... ...
The guidelines direct that the exotic oysters would be used only as brood stock in a quarantined hatchery and would be destroyed after spawning. Only the offspring, produced in the hatchery, would be placed in Chesapeake Bay and strictly monitored for evidence of disease.
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From page 200... ...
The Risk of Disease C ariakensis has performed extraordinarily well in field trials conducted in the lower bay (salvo et al., 1999~.
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From page 201... ...
What are the chances of the nonnative oyster dispersing to regions out
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From page 202... ...
The primary ecological risk associated with deploying triploid oysters in the bay is the probability that a self-sustaining population of nonnative oysters will be established there, because of the direct introduction of a small percentage of diploid individuals among mated triploids or the reversion of triploids to diploids. If this should happen, the ecological risks would be similar to those of introducing reproductively viable oysters into the ecosystem.
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From page 203... ...
Bayne (2002) , for example, demonstrated that the competitive advantage the nonnative Pacific oyster, C
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From page 204... ...
In situations of intense aquaculture grow-out with high concentrations of oysters, one should see positive benefits on water clarity. However, aquaculture of triploid nonnative oysters is likely to be limited in spatial extent initially, owing to high production and biosecurity costs, and thus unlikely to contribute substantially to total oyster filtration capacity of the
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From page 205... ...
ariakensis proves successful and more grow-out areas in the bay are established, presumably the ecosystem services provided by biofiltration would increase proportionately (e.g., Bayne and Warwick, 1998~. Water clarity could be magnified locally if intensive aquaculture operations are located in some of the smaller "trap" or retentive estuaries and tributaries within the bay that have more restricted water movement.
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From page 206... ...
The extent and time frame of this possible event are also highly dependent on how well C ariakensis could adapt to the bay's environmental conditions and how quickly wild populations of oysters would become established and proliferate into sufficiently dense reefs to have an effect like that of the historical native oyster population.
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From page 207... ...
Many of the attributes that make C ariakensis an attractive species for the establishment of a fishery in Chesapeake Bay are the same characteristics that have been attributed to aquatic nuisance species.
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From page 208... ...
may be positively affected (see Baird and Ulanowicz, 1989~. Rapid population expansion of the nonnative species may also displace native oysters and other fouling species.
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From page 209... ...
Risk to Social, Economic, and Cultural Systems Human Health Assuming that monitoring of water quality and shellfish sanitation practices are followed, there is no known reason to expect the human health risks of consuming triploid or diploid C ariakensis harvested from the Chesapeake Bay to be any different from those of consuming C
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From page 210... ...
This is because restoration activities associated with the noaction option are not expected to result in significant near-term increases in the stock of native oysters, and nonnative triploid-based aquaculture is not expected to result in sufficient production to affect regional and national oyster prices. It is possible that introduction of diploid nonnative oysters could result in rapid colonization of the Chesapeake Bay and provide a basis for a public-bottom fishery, but even if nonnative oyster populations expanded rapidly, it would take several years for significant numbers of adult oysters to recruit to the fishery.
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From page 211... ...
Any increase in the bay's supply, whether native or nonnative, is likely to have a positive effect on this sector as long as the price of the Chesapeake oysters is competitive with oysters from other regions. Recreational and Amenity Services Interdiction of nonnative oyster culture, inception of open-water aquaculture of triploid oysters, or outplanting of nonnative diploids could be expected to generate differing arrays of risk to recreational and amenity services.
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From page 212... ...
The least complex challenge may involve changes in management strategies within the same agency in response to such functions as permitting, compliance monitoring, and law enforcement as an agency shifts from managing a wild fishery to managing aquaculture-based production. A more complex challenge (i.e., in response to the managed introduction of nonnative oysters)
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From page 213... ...
However, in an era of governmental budget constraints and mandates for increased efficiency, institutional risks are often magnified as agencies compete for funding. Additionally, the likelihood is that the institutional risk is high as agencies develop management structures and practices to deal with the introduction of nonnative oysters, because the overall challenge of managing the Chesapeake Bay's natural resources is a high-profile activity.
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From page 214... ...
In addition, both in the case of intentional diploid introductions and the case of triploid-based aquaculture, monitoring and enforcement costs will increase to cover measures to reduce the risk of accidental cointroductions of exotic disease organisms and nuisance species. Measures that might be taken to reduce these risks include, for example, review and regulation of aquaculture operations plans; mandatory bonding of aquaculture facilities; random sampling of aquaculture oysters during the growing period to determine reversion rates, maturation, and the cause of unusual mortalities; genotyping of aquaculture brood stock; and sampling of adjacent grounds to detect the establishment of escaped nonnative oysters.
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From page 215... ...
The prospect of augmentation of current and future oyster harvests is a critical factor in watermen's support for the common management plan. The introduction of nonnative oysters, on the other hand, brings a risk of differential economic returns to watermen, depending on their state of residence and on whether the introduction is based on triploids used in aquaculture or reproductively competent diploids for wild harvest.
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From page 216... ...
If Maryland watermen are not able to compete effectively, many of the same risks and benefits associated with interdiction of nonnative oysters may occur. Moreover, there may be decreasing support for current restoration efforts with the increasing economic success of triploid aquaculture in Virginia.
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From page 217... ...
While these challenges must be addressed, restoration of the native oyster fishery fits well within broader environmental ethics and values throughout the Chesapeake Bay area, values that emphasize restoration based on native species. The use of native species in restoration efforts can be an important environmental platform for innovative alliances among stakeholders that redefine traditional social roles and relationships toward resource management, including fisheries.
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From page 218... ...
Implementation Risk Risk of Political Objection Inception of triploid nonnative aquaculture or the sanctioned introduction of diploid nonnative oysters could be obstructed through objections raised in the regulatory approval process or through legal challenges brought by concerned parties. Several potential avenues for challenge were explored in Chapter 8.
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From page 219... ...
They may similarly be unlikely to object to the introduction of diploid nonnative oysters if such introduction is represented as accelerating water quality improvements. They may object to aquaculture of triploid nonnative oysters because they do not anticipate aquaculture being sufficiently extensive to result in large-scale water quality improvements and because they may perceive aquaculture as a competitive claimant on funds presently allocated to restoration efforts.
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From page 220... ...
Objections could be mounted as well to certain restoration activities, such as those employing selectively bred, diseaseresistant stocks to artificially supplement natural populations, based on the perceived risks to natural diversity. Risk of Rogue Introductions A rogue introduction would be a nonsanctioned direct release of diploid reproductive Suminoe oysters into the Chesapeake Bay, likely executed without benefit of adherence to the ICES protocols.
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From page 221... ...
. Rogue introductions of the Pacific oyster have occurred previously in the Chesapeake Bay and elsewhere on the East Coast.
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From page 222... ...
MANAGEMENT OPTIONS The biological and social factors likely to be impacted by each of the three management options for introducing the Asian oyster, C ariakensis into the Chesapeake Bay are listed in Table 9.2.
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From page 223... ...
223 o c be V)
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From page 224... ...
224 u ¢ Em =o ~ so ou .
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From page 225... ...
The chief benefits of maintaining the status quo would be: · avoidance of risks identified with either of the alternative options for introducing a nonnative oyster; · increased emphasis on aquaculture of native oysters selectively bred for resistance to MSX and Dermo diseases; · increased employment in the native oyster aquaculture sector, especially with new strains of disease-tolerant C virginica; and · affirmation of cultural value on conserving native species and natural habitats. Simply banning the introduction of nonnative oysters into the Chesapeake Bay, however, will not necessarily maintain the status quo.
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From page 226... ...
Finally, under this option, management would presumably be burdened with monitoring for rogue introductions and with eradication of diploid nonnative oysters were they detected. Eradication of introduced marine species is extremely difficult or impossible, as recent experiences with the invasive seaweed Caulerpa in the Mediterranean Sea attest (Thibaut et al., 2001~.
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From page 227... ...
· . maxlmlzecl; · economic hardships for watermen communities, unless they switch from fishing to aquaculture; · no marked improvement in bay water quality in the near term, owing to only a marginal increase in oyster filtration capacity from triploid aquaculture; · continued threat of rogue introductions of diploid nonnative oysters; · potential introduction of pathogens that may not be excluded by adherence to ICES protocols; · potential introduction of other pathogens owing to inadvertent breaches of ICES protocols; · susceptibility of nonnative oysters to endemic pathogens or parasites; · conflicts with cultural value placed on conservation of native species and habitats;
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From page 228... ...
Genetic markers could be profiled in all tetraploid and diploid stocks used to make triploids, so that the provenance of any diploids that might subsequently be detected or become established could be determined. Some short- and long-term benefits of this option, aside from those attending the establishment of a diploid population, are: · management control over most aspects of the authorized introduction; · viability of aquaculture; · aquaculture employment; · possible retention of tourism, recreational, and sports fishery benefits associated with Chesapeake Bay oysters, even though nonnative; and · increased incentive for restoring the native oyster, if it serves to rally the political constituents of restoration.
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From page 229... ...
However, introductions are not always successful. Initial trials with triploid Pacific oysters in the Chesapeake Bay showed, for example, that this nonnative oyster, though resistant to the diseases that kill native oysters, was susceptible to infestation with the shell-boring polychaete worm Polydora, which made them unacceptable in the market.
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From page 230... ...
ariakensis, and even by lack of sufficiently detailed ecological information for the native oyster and the Chesapeake Bay. Various ecological risks that can be postulated have unknown probabilities and unknown impacts.
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From page 231... ...
The breadth and quality of existing information on oysters and other introduced species are not sufficient to support a comprehensive risk assessment of the three management options. · Comprehensive risk assessment is also not practicable, owing to the lack of well-defined and/or conflicting objectives and goals among Chesapeake Bay management agencies and users.
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