Monitoring data shows that our waters are trending warmer. How might this effect our local oysters ?
As winter gives way to spring, oyster growers get excited for the start of the fast growing season. Seed purchased the previous season that grew to pre-harvest size in the fall will quickly reach market size and be ready for harvest and sale the following spring. Warmer waters in the spring & summer translate into more algae in the water for oysters to eat. If warmer waters benefit oyster growth, might warmer waters year-round be a positive trend? Indeed, warmer trends will certainly enhance the growing season allowing operators to turn more product for profit. However, there are two key concerns to warmer water trends to note:
Some growers and scientists report higher mortality of some aquaculture species. Read more about this topic here.
Public Health: The same warm water that promotes algae growth also sets the stage for the undesirable growth of certain bacteria. Vibrio species are natural to our coastal waters. During periods of elevated concentrations (typically mid-late summer), specific strains are a public health concern. V parahaemolyticus (Vp) is the most common strain of Vibrio associated with infections from consuming raw seafood. The remainder of this article provides more information on this topic.
Vibrio Forecasting Tool Vibrio parahaemolyticus (Vp) forecast models produced by NOAA are being improved and expanded to help both consumers and industry stay informed of (Vp) trends and potential.
The Virginia Department of Health Division of Shellfish Sanitation (VDH DSS) is responsible for regulating the shellfish industry to reduce consumer risk. VDH officials visit operators every 6 months to inspect equipment, review records, and issue operational certificates for compliance. For example, oyster tags are required for all harvests. Tags follow oysters from harvest to the point of consumption and are the means of tracking their origin and facilitating product recalls if an outbreak of infection occurs. See this article to learn more about tags.
While this might keep others from getting sick from the same harvest through a product recall, what about prevention? News of infection is devastating to the industry and keeping people well in the first place is obviously preferred. For this purpose, VDH also samples oysters for water quality and determines where and when one can harvest. For example, specific areas and times are off-limits for harvesting in order to control high-risk Vibrio concentrations. Adhering to these rules and regulations is key to ensuring public health. But growers can also use best practices to lower Vibrio exposure and your Lynnhaven Oyster Club operation is aligned with the latest research.
Researchers with the Alabama Agricultural Experiment Station at Auburn University’s Shellfish Research Lab investigate how handling practices, gear type, and geographic region can affect the levels of Vibrio in farmed oysters, as well as determining the re-submersion period required to return elevated levels of Vibrio in harvested oysters to normal.
Study results show that all Vibrio types return to ambient levels after 7-14 days of re-submersion, regardless of handling type, gear type or region. This means that following routine handling treatment, farmers should allow the oysters to remain in the water for 14 days before harvesting for human consumption.
These research findings demonstrate that unhealthy Vibrio counts are influenced more by non-aquatic environmental factors and processing time associated with both pre-harvest maintenance activities and out-of-water processing during harvests than the naturally occurring in-water concentrations.
LOC adheres to a self-imposed best practice by separating and spacing all pre-harvest handling and processing steps from harvesting activity. Any interim handling of oysters for maintenance is dated and logged. This handling date initiates a 14-day moratorium on these oysters as they await a "harvest ready" green-light status by our tracking system. Once harvest readiness dates are reached we work our oysters in-water and in quantities that allow the harvest ready oysters to go from water to ice immediately, minimizing exposure to warm air temperatures and thereby suspending any Vibrio growth. Maintaining refrigeration temperature from point of harvest to end consumption is the next step in keeping Vibrio levels safe.
A contrasting practice, particularly of larger operators, is to bring large quantities of oysters on deck to sort, clean and package, or to transport to a land-based processor to do the same. These activities increase risk by adding to the total time between the oyster’s in-water status to when the product can be put on ice or into mechanical refrigeration to reach the required temperature (45 degrees) within the required time (5 hours). For these operators that do not have refrigeration on-board their vessels, the clock is ticking. Also during the warmer months, shading devices are mandated and harvest curfews are activated to ensure oysters are off the water before daytime temperatures rise. While these rules and regulations drive standard practices that are dramatically different than LOC's best practices, they are still science-based and represent a successful system for protecting public health. If it was not successful, oyster-caused food-borne illness reports would increase and we would not see oysters on the menu year round.
Bottom Line:
Vibrio’s ability to exponentially multiply in warm environments is in opposition to the longer growing season that might result from warming trends. In other words, what might extend the oyster growing season might also close it to harvest. With climatic warming trends, positive and negative changes will result. While the industry can celebrate positive outcomes such as faster return on investment, operators can also responsibly respond ahead of government oversight and build best practices into their businesses. This way, the industry can demonstrate self-regulation and the cost of operations from necessary regulation and oversight is minimized.
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