• 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