Growing American Oysters in Maine
The Eastern oyster (a.k.a. American Oyster) is a popular species for growers in the US because they are relatively easy to grow, and there is a strong, well-established market for them. Growers in Maine are focused on producing oysters for the half-shell market, and the state's producers have an excellent reputation for quality shellfish. Depending on the market, the buyers and the product, it's not uncommon for farmers to get between 50 and 75 cents per piece. Oysters can be a relatively inexpensive species to begin with, and product can be ready for market within two growing seasons, if grown on a good site and with proper care, and even sooner if the grower starts with larger-sized seed stock.
The Eastern Oyster is a protandric hermaphrodite, meaning that it can change sexes, and is usually male at the time of sexual maturity. It will frequently switch from one sex to the other from year to year, and hatchery operators cannot be sure if a specific individual will produce eggs or sperm. Eggs are fertilized in the water column, and usually take about 3 weeks in nature (two weeks in the hatchery) to go through a metamorphosis, and settle onto a substrate. Oysters feed by filtering seawater over their gills, and capturing the algal cells that form most of their food. Oysters can choose which particles they send to their mouth, and which they will eject, by sorting the particles as they move along the gill surface. Feeding and growth are both tied to temperature; oysters enter a dormant state below 40 degrees Farenheit where feeding effectively stops, and they can function in water temperatures over 90 degrees - they can even withstand freezing for short periods of time.
The market for oysters targets the half-shell trade, often in high-end, 'white-tablecloth' restaurants. Prices to the farmer can range from $0.50 to $0.75 per piece, with premiums paid for taste, plumpness, shell shape, and uniformity of the product. A 3" shell is the traditional 'select' size that many growers focus on, although the market for a smaller oyster has arisen as well; about a 2.5" shell, usually referred to as a 'cocktail' or 'petite' size. Oysters larger than 4" are sold as well, usually called a 'jumbo' - these are particularly well suited for stew, chowder and grilling or frying. Some oyster growers do their own marketing, and others work with wholesalers; some do both. Oysters from Maine reach around the US and outside the country as well, particularly to markets in Canada. Generally speaking, oysters from Maine enjoy an exceptional reputation in the marketplace.
The production of eastern oysters in Maine starts with seed production in the hatchery, followed by a nursery phase, final growout, and harvesting. Many producers get their oysters at 1.5-2.0mm size, at which point they are placed in an upweller system for the first nursery phase (see Upweller Pages on the ME SG web site for more detail). Once the seed have reached 10-15 mm, they are often put into floating bag systems, where they will remain for the first year. At the end of the first year, some seed may be planted directly to the bottom, if it has reached 1.5" or so; otherwise, it may go into overwintering cages, into a bottom growout cage, or even into moist air storage for the winter. Most producers will get about 70% of their crop to market in two growing seasons, with the rest coming up to size in the third year. See below for a downloadable presentation on the general production cycle for Eastern oysters, and some of the comment equipment and husbandry methods.
Research and extension colleagues in the northeast have teamed up with shellfish farmers to create a network of commercial farms that are doubling as research stations, with the goal of improving shellfish production equipment and husbandry. Learn more about NARF-Net.
Disease and Health
Oyster diseases of particular concern to producers in Maine include MSX (Multinucleated Spore Unknown), and JOD (Juvenile Oyster Disease). Dermo Disease is of concern to growers to the south, but has not been observed in Maine to date. None of these oyster diseases are risks to human health. Growers and scientists work together to make sure that the genetic lines available to growers are as well adapted as possible for disease resistance and fast growth, so that their stock stays healthy. It is highly recommended that shellfish growers purchase their seed stock in-state, to reduce the chances of disease transmission from outside waters. In addition, some strict rules about movements of shellfish within the state are in place, to prevent further disease outbreaks. Producers should contact the Maine Dept. of Marine Resources, the Maine Sea Grant Program or the Maine Aquaculture Association if they have any questions at all regarding shellfish movements and pathogens.
Mud Blister Worms in Oysters (fact sheet)
Overwintering Eastern Oysters (fact sheet)
Prospective shellfish farmers should also consult the pages on Permitting and Licensing, Site Selection, and Shellfish Health.