Louisiana Sea Grant Addresses New Oyster Refrigeration Requirements

Louisiana Sea Grant is helping oyster harvesters adjust to new “time/temperature” rules for their catch with a series of workshops and with research into alternative means of cooling oysters.

Changes in the state’s Sanitary Code require that “white tag” oysters – those that can be sold for raw consumption in interstate commerce – be placed under mechanical refrigeration with an air temperature of less than or equal to 45 degrees F within one hour of harvest during May through October to lessen the likelihood that consumers will be sickened by Vibrio bacteria. The internal meat temperature of white-tag oysters also must be brought down to 55 degrees F within 6 hours. Vibrio normally live in warm sea water. Eating raw seafood contaminated with Vibrio parahaemoloyticus can cause intestinal distress, and Vibrio vulnificus can be deadly for immunocompromised persons. It is unknown how many cells of the bacteria are required to cause illness in humans, but cooler temperatures slow the multiplication of the pathogens. Louisiana is one of 20 states required to have a Vibrio management plan.

“This is part of the Department of Health and Hospital’s zero-tolerance policy for Vibrio vulnificus,” said Julie Falgout, seafood industry liaison with Louisiana Sea Grant. “In the past, they just put oysters on the deck and had several hours before they had to be cooled. The new rules are basically for oysters destined for the shucked industry that are eaten raw.”

Falgout helped organize the Oyster Industry Workshop in December in Terrebonne Parish as part of the Louisiana Fisheries Forward program that brought together people with the answers to help fishermen comply with new regulations. “It’s part of bringing the university to the coast,” she added.

John Supan, a research professor, oyster specialist and the director of the Sea Grant Oyster Research Lab also has an interest in the new rules as they affect two technologies – intensive or off-bottom culture and triploid oysters. Off-bottom production eschews traditional reef cultivation in favor of growing the bivalves in mesh bags that are suspended in the water column either by floats or by a series of lines anchored to piers. The bags are emptied by hand, and the harvest does not require dredging. Triploid oysters are genetically altered to be sexually sterile. Ordinary oysters (dipliods) direct their energy toward spawning in the summertime and are significantly smaller at that time of year. Triploid oysters do not reproduce and remain meaty and marketable during the summer. They also have faster growth and greater survival rates.

However, the new rules will defeat the economic advantages of triploid oysters raised in off-bottom aquaculture systems. The smaller vessels used to harvest off-bottom cultured oysters do  not have the deck space needed to carry the required refrigeration units, icing is currently not permitted, and returning the oysters to shore within the one-hour requirement is not feasible.

“Triploid oysters have a market advantage in the summer – they are fat when the others are typically skinny,” Supan explained. “Without the need to dredge, fishermen can use a skiff instead of a lugger to harvest off-bottom oysters for tremendous fuel savings. This could mean fuel costs of $17 per week vs. $1,000 per week. However, if you can’t follow the time/temperature rule then you lose a major market advantage. Growers can only harvest from November through April without on-board refrigeration. By the dead of winter, the diploids are fat again. Instead of having an 8-month market advantage, you only have a two-month advantage. A tool or technology is needed to meet the regulatory time/temperature requirements for summer harvest on small vessels and to change mechanical refrigeration requirements.”

With funding from the National Oceanic and Atmospheric Administration, Supan is investigating the use of on-board icing in lieu of mechanical refrigeration in a project titled “On-board Rapid Cooling of Cultured Oysters to Address Regulatory Needs.” His main objective is to produce a commercial prototype machine that washes oysters and chills them with ice. He also plans to compare the effectiveness of dipping oysters in static vs. circulating ice slurries; to test the levels of V. vulnificus and V. parahaemolyticus in treated and control shellfish; to generate more up-to-date data that federal and state shellfish control authorities can use when making regulations and; to test the gaping of iced v. un-iced oysters in cold storage.

“If successful, this research could improve the economic feasibility of oyster culture during the summer months.  This would lead to improved harvesting and refrigeration practices,” Supan said.