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University Develops Disease Management Plan for Oyster Aquaculture Industry in Rhode Island

The state of Rhode Island has adopted a plan facilitated by the University of Rhode Island’s Graduate School of Oceanography to reduce the likelihood of human illness from the consumption of improperly handled oysters raised in aquaculture facilities in the state. The plan, created through a collaboration between shellfish management agencies and the aquaculture industry, went into effect on July 1. 

by University of Rhode Island
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The management plan is designed to combat a naturally occurring bacterium that shellfish filter from seawater.University of Rhode IslandAccording to Azure Cygler, the fisheries and aquaculture extension specialist at the URI Coastal Resources Center and Rhode Island Sea Grant who led the project, the plan is designed to combat a naturally occurring bacterium that shellfish filter from seawater. The bacterium, Vibrio parahaemolyticus, does not harm oysters or humans when consumed in small quantities, but it can multiply rapidly when shellfish are exposed to warm temperatures, particularly when the oysters have been harvested and are left in the sun for extended periods.

“That’s when it can become a public health threat,” said Cygler. “It can make people really sick, especially the elderly and those with suppressed immune systems.”

While very few Rhode Islanders have become sick from Vibrio in oysters in recent years, those in nearby states have been affected, and warming waters due to climate change will increase the likelihood that it could become a problem here. Just three verified cases from one site in a given year would trigger the U.S. Food and Drug Administration to impose onerous rules on the oyster aquaculture industry. So the FDA recommended that a plan be developed for implementation this summer.

Beginning last March, URI brought together representatives of the Rhode Island Department of Health and Department of Environmental Management, the state Coastal Resources Management Council, and the aquaculture industry to develop a Vibrio control plan. It was quickly discovered that the industry had already developed a voluntary plan for its members that is more restrictive than the one required by the FDA, so that plan became the basis of the state’s plan.

The new rules require that from July 1 through Sept. 14, all oysters from enclosed water bodies like coastal ponds must be refrigerated or placed in ice within two hours of harvest (the limit is five hours for oysters from the open bay) so that the animal’s internal temperature does not rise above 50 degrees, which is the threshold when Vibrio begins to grow. All oysters must also be put in a shaded location immediately upon harvest, and those oysters that have been removed from the water for husbandry purposes must be re-submerged for two to seven days before being harvested.

“All of the state agencies were pleased to see that the industry was already being cautious and proactive in protecting against Vibrio,” Cygler said. “And it was a nice gesture for the state to acknowledge their plan and use it.”

The state Division of Agriculture will provide oversight for implementation of the plan, and the Coastal Resources Management Council will be responsible for monitoring adherence to the new rules. No Vibrio-related illnesses have been reported in Rhode Island this year.

The next step in the process is to develop a similar plan for the quahog industry, which Cygler believes will be more challenging to accomplish.

She said that quahoggers usually harvest for long hours each day and may object to cutting their workday short to deliver their catch to dealers to put on ice. They also work seven days a week, whereas the dealers they sell to are closed on Sundays, so a process will have to be developed for keeping Sunday-caught shellfish cool.

“It won’t be impossible to develop a plan, but these are independent-minded fishermen who are set in their ways,” Cygler said. “We’ll have some who are going to want to make it work and others who will try to find a way around the rules, which could lead to illnesses.”

Cygler believes that the shellfish dealers, who typically avoid participating in the resource management process, may have to become more actively involved “so they know they are not purchasing quahogs that have been sitting in somebody’s truck longer than five hours. The dealers almost have to take on a regulatory role,” she said.

A Vibrio control plan for the quahog industry will take effect July 1, 2015.