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Nonnative Oysters in the Chesapeake Bay
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:
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.