Flipping the cages on sustainable aquaculture: a study on oyster aquaculture technique and policy to reduce pathogens

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Commodities

• Animals: shellfish

Practices

• Animal Production: aquaculture, parasite control

Sustainable aquaculture industries, such as oyster aquaculture, are critically important to support protein production for the global human population (FAO, 2020), and are an increasingly important economic driver for coastal states of the U.S. (USDA, 2019). The oyster aquaculture industry provides socio-economic and environmental benefits that include viable agriculture jobs, local and affordable protein options, and beneficial ecosystem services such as water quality enhancement, habitat provision, and eco-tourism opportunities. Advancements in gear technology and the ability to generate year-round revenue through triploid summer harvest have enabled the expansion of the oyster aquaculture industry in South Carolina. A key factor influencing the economic viability of oyster farming is pest and pathogen management for both human health and aesthetic quality of product. One best management practice is to periodically air dry oyster cages to reduce biofouling (i.e., the unwanted settlement of epibenthic organisms, such as barnacles on oyster shells). This routine is strictly controlled by South Carolina Department of Health and Environmental Control (SC-DHEC) since aquaculture oysters are destined for the (typically) raw consumption, half shell market. Exposing oysters to the air (and elevated temperatures) can increase human health risks associated with consuming live, raw seafood due to increases in naturally occurring pathogenic Vibrio bacteria, Vibrio vulnificus and Vibrio parahaemolyticus (Su & Liu, 2007). SC-DHEC requires a minimum of a 14-day resubmergence period after air drying to allow oysters to depurate their tissues and return to ambient Vibrio spp. levels. In highly productive environments, oysters and cages can become re-fouled during this period, causing the farmer to incur additional labor expenses to clean the oysters before harvest. Farmers must strike a balance between maximizing production efficiency while providing a safe, sustainable product, and have requested an in-depth study on best management practices for air-drying and resubmergence. Providing the best available science to inform local regulations is needed to effectively and responsibly manage the oyster farming industry. The collection of Vibrio spp. data at the local (e.g., state-specific) level may enable an optimization of resubmergence requirements; though to do so, cooperation across multiple state and federal agencies is necessary.

This study will undertake a whole-systems approach to collect field data, understand inter-agency communications, and develop policy recommendations to maximize agricultural sustainability and efficiency for the coastal shellfish aquaculture industry. The project team will experimentally measure Vibrio spp. dynamics following aquaculture industry handling practices, and create an advisory committee to facilitate transparent communication across stakeholder groups. Oyster tissue samples will be collected at three different farms for analysis of Vibrio spp. at different pre-handling, post handling, and post-resubmergence time points (i.e., 5, 7, and 14 days after resubmergence), with trials repeated on two occasions during Vibrio control months (i.e., May-September). In addition to field data collection, an analysis of current policies and decision-making practices will be conducted to evaluate how the data may inform regulations in an efficient manner to foster a sustainable oyster farming industry that works in harmony with environmental, economic, and sociopolitical parameters.

The objectives of this project are as follows:

1. Engage with off-bottom oyster aquaculture partners to plan for and prepare aquaculture lease study sites for project implementation.
2. Conduct resubmergence trials (e., handling and desiccation of oysters and gear at farm sites) and collect oyster tissue samples for analysis of Vibrio spp. at specific time intervals at multiple sites, as described in the methods below.
3. Continually engage with a PAC of public health, environmental and fisheries managers, and industry experts at state and federal levels throughout the development, implementation, and dissemination of the proposed work to maximize the use of the data in guiding public health requirements for off-bottom aquaculture.
4. Conduct an analysis of the policy process to translate results into policy recommendations, following the completion of data collection.
5. Conduct education and outreach efforts to disseminate project results and best management practices to the South Carolina aquaculture industry.