Off-bottom culture involves growing shellfish like oysters in mesh bags, baskets or cages that are attached to racks or ropes or onto lines running between stakes. The gear is placed in intertidal areas where it can be accessed on foot.
Rack and bag culture consists of placing racks on the bottom of sand and mud intertidal habitat. The racks are made of various materials including wood, plastic and steel. Bags filled with oyster seed are put on top of the racks, where they are submerged during high tides and exposed during low tides. The racks keep the bags off the bottom, allowing the oysters to feed and grow while being protected from predators.
Flip bags (sometimes called flip cages, rolling bags, floating bags, or tumble bags) are a specialized type of gear used to grow oysters in areas that are not ideal for bottom culture. These mesh bags are filled with seed oysters and then attached to ropes or racks that run a few feet above the intertidal zone. The raised, off-bottom position of the mesh bags gives oysters better access to the algae they eat, which speeds up the oysters’ growth. Each mesh bag has a buoy that keeps it afloat and allows it to rise, fall and roll over with the tides. The rolling or “flip” action of the bags was developed to prevent fouling and to keep individual oysters from growing together, and it also saves oyster farmers from having to flip the bags by hand. These bags enable the oysters to grow with a smooth, deep-cupped shape with firmer meat, which is preferred in many markets.
Stake longline culture uses an array of stakes that are driven into the bottom of mud intertidal habitat with suspended lines running horizontally between the stakes. Oysters are attached directly to the lines, spaced evenly with several inches between them. Because these stake-based longline systems are exposed during low tides, growers can walk out to maintain them, unlike suspended longlines.
Image captions and credits
1. Off-bottom rolling bag culture on a Washington shellfish farm; Washington Sea Grant
2. Rack and bag oyster culture in Tomales Bay, California; California Sea Grant
3. Stake longline oyster culture in Humboldt Bay, California; California Sea Grant
4. Illustration of shellfish grower tending to off-bottom stake and longline oyster culture system at low tide; Tom Crestodina
5. Oysters growing on off-bottom stake longline; Washington Sea Grant