In recent years, shellfish farms in Washington and California have been exploring the use and expansion of novel, off-bottom grow-out methods, including “flip-bags” – buoyed mesh bags that rise and fall with the tide -- to produce high-quality oysters for the singles, half-shell market. T he interactions of these complex systems with the surrounding environment have yet to be comprehensively explored. Intertidal shellfish farms in parts of the Pacific Northwest overlap with native eelgrass (Zostera marina) habitat. Z. marina beds are designated as Essential Fish Habitat (EFH) for multiple Pacific salmon species (Pacific Fishery Management Council 2008) and provide nursery habitat for many other species within the Pacific Coast Groundfish Fisheries Management Plan. Regulators require robust scientific information to support decision making for ongoing and proposed shellfish aquaculture activities in our region. Our study is the first to systematically explore nekton use of oyster flip-bag culture and directly supports the permitting and regulatory process of these systems within and adjacent to Z. marina habitat.
In 2020 and 2021, we collected nekton within oyster flip-bag arrays, inside and outside Z. marina beds at six farm locations, representing key shellfish growing areas in Washington state. Four habitat types were surveyed: flip-bags with eelgrass, flip-bags without eelgrass, eelgrass with no culture and bare mudflat. Sampling occurred in both spring and summer seasons using a modifie d seine net with cod end to collect nekton >5 mm in size. All nekton were counted and identified to species from three replicate tows within each habitat. Sampling within the highly structured arrays presented some logistical challenges compared to the unstructured habitats with the seine net. A multi-methods approach within thes e complex, dynamic systems is recommended to capture and observe all potential nekton utilizing these habitats.
In general , spring had the greatest total nekton abundance compared to summer. Total nekton abundance was greatest in dense eelgrass beds with no oyster culture in both spring and summer . Both habitats with eelgrass, no culture and flip-bag culture, had greater nekton abundances compared to habitats without eelgrass during the spring season. Oyster flip-bags without eelgrass had the least total nekton compared to all other habitat types in both seasons.
Our study results further indicate the critical value of Z. marina to support abundant nekton communities in Pacific Northwest estuaries. At our study sites, Z. marina was able to grow within the flip-bag arrays and support nekton communities in greater abundance than flip-bags without eelgrass. Further analysis of community structure within these habitats will improve our understanding of ecological function . Our study results provide scientific information to key stakeholders producing and regulating shellfish aquaculture in our region.