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Final Report Submitted to the NOAA Chesapeake Bay Office, Anapolis, MD
Fisher, Robert Southworth, Melissa Wesson, James Erskine, A.J. Leggett, Tommy
Fisher, Robert
Southworth, Melissa
Wesson, James
Erskine, A.J.
Leggett, Tommy
Abstract
This project was an academic – government – industry – non-‐profit collaboration wherein all parties began and ended the project with a singular commitment to stewardship of the Chesapeake Bay oyster resource for both ecological and economic purposes. The project addressed a critical issue, the potential loss of oysters to predation by cownose rays, in a controlled experimental design but at a scale commensurate with industry practices and large‐scale restoration efforts. This rare and extensive collaboration was a resounding success in terms of participation and information exchange. All participating individuals and the entities they represent should be applauded for a productive project outcome. The project focused on the value of shell overlays to oyster plantings as a ray predator deterrence mechanism. Typical industry practice of oyster seed planting was followed in an experimental design employing treatment Areas in the 0.5-‐1.0 acre range. Areas were prepared in the Lower Machodoc River, VA by the initial application of shell to insure a stable substrate under planted seed oysters. Seed oysters were then obtained from the James River, VA and planted using industry methods on each of four Areas. The Areas were located two upstream and two downstream of a constriction in the Lower Machodoc that dictated differing physical environments in the respective locations with downstream locations being more exposed to northeast wind driven stresses and, historically, a greater incidence of ray predation. Once oysters were planted, two of the Areas, one upstream and one downstream of the aforementioned constriction, were additionally treated with a shell overlay as a predation deterrent. The oyster seed were planted in February 2012. Market oysters were harvested in December 2013 and January 2014. In between limited monitoring of the population was accomplished using both diver and patent tong survey methods. Final harvest data demonstrated that shell overlays do not offer additional protection to planted oyster seed with respect to possible cownose ray predation. Evidence of predation in the form of ray signatures – characteristically broken oyster valves – were recorded on all treatment Areas. Concurrent stomach content analysis of rays captured at the study location and observations of fouling community associated with the cultured oysters taken during the harvest operation indicate broad dietary preferences for rays when such a variety exists in the foraging region. Oysters are not the singular preferred diet item, although localized and intensive feeding on oysters remains an option for rays with a wide foraging range. Additionally, the overlay procedure does not appear to increase local productivity in that the exposed Areas demonstrated higher production than the “protected” Areas with shell overlay. Accordingly we recommend against the use of shell overlays as predator deterrents for cownose rays in large deployments of unprotected oyster seed.
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2014-05-07
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Mann_etal_CownoseRay.pdf
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cow-nose ray predation, oysters, industry, planting protocol
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Mann, R., R. Fisher, M. Southworth, J. Wesson & A. J. Erskine. 2014. Oyster planting protocols to deter losses to cownose ray predation. Final Report submitted to the NOAA Chesapeake Bay Office, Annapolis, MD, Virginia Institute of Marine Science, Gloucester Point, VA. 36 p.