Resources for Shellfish Growers | Species: American Oyster

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.

Oyster Gardening

Oyster gardening is an educational program, which uses the process of growing oysters to engage participants in topics like estuarine ecology, shellfish biology, aquaculture regulation, stewardship, public health, natural resource management, and a host of others. Oyster gardening got its start in the Chesapeake Bay region, and has since spread to many other coastal states. Our program here in Maine has been adapted from those developed elsewhere, to meet our particular needs, opportunities, and constraints.

The first classes in the state got under way in March 2004, and our second class of students began in May 2006, with funding support from Maine Sea Grant, the Coastal Program of the Maine State Planning Office, and the Maine Aquaculture Innovation Center . Important partnerships were formed with and/or support was provided by the Damariscotta River Association, the Maine Aquaculture Training Institute (MATI), and the Maine Department of Marine Resources. Dr. Chris Davis of MATI and the Pemaquid Oyster Company is the principal instructor for the class, with MET Extension Associate Dana Morse acting as the program coordinator and field instructor.

Students receive classroom instruction on the basics of oyster culture, including permitting and regulation, public health, equipment, and husbandry. Each student purchases approximately 1000 Eastern Oyster seed and is then responsible for maintaining his or her crop. During the 18-month course, the classes meet approximately monthly, to review progress, share observations, take field trips, and hear from guest speakers. The current class includes nine students from the Damariscotta region, and a small shellfish lease has been secured upriver in the Damariscotta.

One of the goals of the program is to bring oyster gardeners together with opportunities for collaboration with other programs, such as the Maine Phytoplankton Monitoring program and the Pemaquid Oyster Festival. 

For more information on this program, contact Dana Morse.

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. 

More on oyster disease:

Juvenile Oyster Mortality (JOM) is a condition that, in some years, has resulted in greater than 90% losses of a given year class in oysters on some farms along on the East coast. Dana Morse has organized and/or facilitated meetings between scientists and shellfish company representatives, and worked with researchers to produce and distribute a fact sheet on JOM. The project resulted in three funded JOM research projects. In addition, Morse has coordinated meetings regarding the future of the UMaine oyster breeding program, to continue the University's work on production of faster growing and more disease-resistant oysters. An outcome of these meetings was an offer by the UMaine Dean of the College of Natural Sciences, Forestry, and Agriculture, to match industry money for a hatchery position at the DMC. The industry has nearly achieved their financial goal, and the resulting research could ultimately help reduce the incidence of JOM in Maine waters and in other states.

Exploring Husbandry and Equipment Solutions to Infestations of Polydora sp. on a Maine Oyster Farm

Helpful Documents:

Power Point slide show on the basics of how to grow oysters in Maine (ME Sea Grant)

Fact Sheet: Juvenile Oyster Mortality

Fact Sheet: Cultivation of Eastern Oyster (Northeast Regional Aquaculture Center)

Business Planning for Aquaculture (NRAC)

Feasibility study for a new oyster farm, and business plan elements (NRAC)

Sample Production Worksheets for 100,000 oysters/year (NRAC)

Sample Production Worksheets for 1 million oysters/year (NRAC)

Guide to Bivalve Diseases, for Aquaculturists in the Northeast US (Univ of Maine)

An Alaskan Flip-Bag system for growing oysters

New Brunswick Oyster Production Guide

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.