THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and Medicine

February 21, 2003

Mr. William A. Pruitt, Commissioner

Virginia Marine Resources Commission

2600 Washington Avenue, Third Floor Newport News, VA 23607

Dear Mr. Pruitt:

On behalf of the National Research Council’s Committee on Non-Native Oysters in the Chesapeake Bay, we are writing to express this committee’s views about the pending 2003 proposal from the Virginia Seafood Council (VSC) to use Crassostrea ariakensis in a field trial. The National Research Council was asked by several state and federal agencies (see attachment B for the study’s statement of task and list of sponsoring organizations) to undertake a review of the potential benefits and impacts of introducing this oyster into the Chesapeake Bay. Although the committee’s final report will discuss many different aspects of risk assessment for using a non-native species, it will not be completed until June of this year. The committee decided to send this letter because of the importance and time sensitive nature of the pending decision before the Commission. This letter represents the consensus views of the committee and has been formally reviewed and approved by the National Research Council.

The Virginia Seafood Council has submitted a proposal “Economic analysis and pilot-scale field trials of triploid C. ariakensis aquaculture” to Virginia’s Marine Resources Commission for the 2003 growing season. This proposal is designed as an industry trial with 10 participants and approximately 100,000 animals per site. Four different growing methods would be employed: bags in clam cages, bags on bottom, rack and bag, and floating raft. The animals would be harvested when they reach market size, estimated at 9-18 months. This proposal was originally submitted for 2002 and then revised in response to comments from the Virginia Institute of Marine Science and the Chesapeake Bay Program Living Resources Subcommittee - C. ariakensis Ad Hoc Review Panel. The major changes in the new proposal are as follows:

  • Genetic (mated tetraploid by diploid) triploids will be used instead of “induced” (chemical) ones,

  • The number of field trial participants has been reduced to 10, each with a larger number of animals,

  • An economic feasibility analysis is stated as the principal goal, and

  • A project manager will be hired specifically to oversee all aspects of the trial.

The purpose of this letter is to identify, based on this committee’s work to date, important risks associated with the field trial as proposed. Major sources of risk or concern that are specific to the current Virginia Seafood Council proposal include:



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THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine February 21, 2003 Mr. William A. Pruitt, Commissioner Virginia Marine Resources Commission 2600 Washington Avenue, Third Floor Newport News, VA 23607 Dear Mr. Pruitt: On behalf of the National Research Council’s Committee on Non-Native Oysters in the Chesapeake Bay, we are writing to express this committee’s views about the pending 2003 proposal from the Virginia Seafood Council (VSC) to use Crassostrea ariakensis in a field trial. The National Research Council was asked by several state and federal agencies (see attachment B for the study’s statement of task and list of sponsoring organizations) to undertake a review of the potential benefits and impacts of introducing this oyster into the Chesapeake Bay. Although the committee’s final report will discuss many different aspects of risk assessment for using a non-native species, it will not be completed until June of this year. The committee decided to send this letter because of the importance and time sensitive nature of the pending decision before the Commission. This letter represents the consensus views of the committee and has been formally reviewed and approved by the National Research Council. The Virginia Seafood Council has submitted a proposal “Economic analysis and pilot-scale field trials of triploid C. ariakensis aquaculture” to Virginia’s Marine Resources Commission for the 2003 growing season. This proposal is designed as an industry trial with 10 participants and approximately 100,000 animals per site. Four different growing methods would be employed: bags in clam cages, bags on bottom, rack and bag, and floating raft. The animals would be harvested when they reach market size, estimated at 9-18 months. This proposal was originally submitted for 2002 and then revised in response to comments from the Virginia Institute of Marine Science and the Chesapeake Bay Program Living Resources Subcommittee - C. ariakensis Ad Hoc Review Panel. The major changes in the new proposal are as follows: Genetic (mated tetraploid by diploid) triploids will be used instead of “induced” (chemical) ones, The number of field trial participants has been reduced to 10, each with a larger number of animals, An economic feasibility analysis is stated as the principal goal, and A project manager will be hired specifically to oversee all aspects of the trial. The purpose of this letter is to identify, based on this committee’s work to date, important risks associated with the field trial as proposed. Major sources of risk or concern that are specific to the current Virginia Seafood Council proposal include:

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The process of generating mated triploids is not 100% effective, hence a small number of reproductive diploid oysters will be deployed with the triploids. In the 2000 year class of mated triploids, 3 out 3396 oysters examined were diploid (S. K. Allen, Jr., Virginia Institute of Marine Science; Response to Questions by C. ariakensis Ad Hoc Panel 2/3/03). If this frequency of occurrence (about 0.09%) were characteristic of populations of triploids produced by mating tetraploids and diploids, each field site under the 2003 VSC proposal would contain approximately 90 diploids per 100,000 oysters. If these diploids are allowed to become sexually mature and if they are in sufficient proximity to each other, there is a risk that a diploid population of non-native oysters could become established in the Chesapeake Bay. The probability that the reproductive diploids may be in close enough proximity to fertilize successfully has not been quantified, but should be determined for each grow out method. Reversion of triploids to diploids increases as the oysters get older, requiring more clearly defined accountability for the inventory to ensure that all oysters are removed by eighteen months. The triploid oysters may undergo gonadal maturation during the proposed trial. Currently, there are no provisions in the proposal for assessing maturation during the length of the trial. The risk of introducing a reproductive population of oysters could be lowered by harvesting animals before they have a chance to produce gametes. In the 2000 year class mentioned above, 25 mosaic animals (partial reversion of triploids to diploids) have been identified to date. In 6 of these mosaics, a small fraction of diploid cells were found in gonadal tissue, but none contained haploid gametes (S. K. Allen, Jr., Virginia Institute of Marine Science; Response to Questions by C. ariakensis Ad Hoc Panel 2/3/03). With the large number of oysters proposed for use in this trial a larger number of oysters will be expected to revert to diploid over time, increasing the risk that reproductive non-native oysters could be released into the Chesapeake Bay; If diploid C. ariakensis are found in the wild in the future, it will not be possible to determine whether or not they originated from this field trial. Genotyping of the broodstock would make it possible to determine whether or not the oysters from this field trial were responsible for introducing diploid C. ariakensis into the Chesapeake Bay or neighboring state waters; The causes of a significant mortality event may not be identified because regular monitoring for disease is not required. The proposal does not identify resources or responsibility for follow up investigation of a disease event. Furthermore, the position of project manager is contingent on outside funding, posing a risk that the trial will proceed without a responsible party to ensure implementation and coordination of monitoring, data collection, and data management. Both the stated goals of the field trial and safeguards meant to reduce the risk of accidental release of C. ariakensis would be compromised without a program manager to ensure enforcement. A more comprehensive discussion of risks associated with the introduction of a non-native oyster will be provided in the committee’s final report, including the potential ecological and economic risks and benefits. These types of risks and benefits have been raised in previous reports (e.g. Chesapeake Bay Program (2002). Report of the Ad-hoc Panel On the Industry Trials of Triploid Non-Indigenous Oyster Species in Waters of the Chesapeake Bay Basin, Annapolis, Maryland; Thompson, Julie A. (2001) Introduction of Crassostrea ariakensis to Chesapeake Bay: The solution to Restoring an Oyster Fishery and Water Quality in the Bay? U.S. Fish and Wildlife

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Service, Chesapeake Bay Field Office, Annapolis MD; and Hallerman, E., Leffler, M., Mills, S., and Allen, S. (2001). Aquaculture of Triploid Crassotrea ariakensis in Chesapeake Bay: A Symposium Report. Maryland and Virginia Sea Grant, College Park, MD). The committee is also concerned that the proposed field trial might be considered “a first time introduction” of C. ariakensis as stipulated in the 1993 Chesapeake Bay Program Policy for the Introduction of Non-Indigenous Aquatic Species. The committee firmly supports the Chesapeake Bay Program policy on non-native species introduction and the review process implemented by the ad hoc panel. This process enables participation by the major parties likely to be affected by this important decision. Unless this issue is clarified, the 2003 VSC field trial could preclude the Chesapeake Bay Program’s review of future proposals to introduce this species, either as nonreproductive triploids in aquaculture or as reproductive diploids in the wild. At present, there is insufficient scientific information available to thoroughly quantify and evaluate the risks and benefits of introducing this species into Virginia waters. Even less information is available for assessing the potential spread of C. ariakensis in the Chesapeake Bay and into the coastal waters of states along the Atlantic seaboard. If the Commission decides to approve a 2003 field trial, the committee strongly recommends amending the proposal to include measures to reduce the risks described above and to require collection of scientific data necessary for assessing the risk of introducing this non-native oyster. For example, more information is needed on the reproductive cycle of C. ariakensis in the field, the causes of mortality events, the fidelity and stability of triploid induction, and the growth rates at different locations under various deployment methods. This information would also be valuable for assessing the economic viability of using C. ariakensis in aquaculture. Sincerely, Jim Anderson, Ph.D. Dennis Hedgecock, Ph.D. Co-Chairs Committee on Non-Native Oysters in the Chesapeake Bay