Oysters

In the 1970s, companies in Blue Hill and on the Damariscotta River pioneered oyster aquaculture in Maine using rafts to culture European oysters (Ostrea edulis). Hatchery-produced seed oysters were reared to market size in Japanese lantern nets, stacked trays, or floating trays suspended in the water. Suspension culture, in which oysters or mussels are grown off bottom, in floating trays and on ropes, is a labor-intensive form of cultivation that requires continuous tending and cleaning of both gear and shellfish.  Beginning in the mid-1980’s growers switched species to the native Eastern oyster (Crassostrea virginica) due to this species greater tolerance to extremes of temperature and salinity.  At this time, researchers at the University of Maine initiated a selective breeding program to develop genetic strains of oysters more suited to Maine’s growing conditions.

Oyster production begins in the a shellfish hatchery with the ripening of parental broodstock during the off season winter months.  Parents are typically spawned in March and April with juvenile seed oysters available to industry growers in late May and June.  Land-based or floating upwellers are commonly used for the initial growing stage to both protect the 2mm seed and to enhance growth by forcing nutrient-rich waters through the growing bins.  Nursery culture of oysters typically includes rearing 10-50mm oysters in floating plastic cages tethered together in long strings.  Surface cages can be regularly flipped over to air dry the undersides and thus control the accumulation of biofouling organisms. As the oysters grow in size, farmers regularly size-grade and thin their crop to to maintain optimal growing conditions. Often at the end of the first growing season, farmers will either bottom plant their crop or overwinter the oysters in cages or rafts until they can be redeployed the following growing season.