Oysters

Species
The species now most widely cultivated in BC and the Pacific Northwest is the Pacific Oyster, Crassostrea gigas (Thunberg).

The Pacific Oyster is not native to this area but originated around the northern Japanese island of Hokkaido. A few of these oysters were first brought to BC around 1913, but most of the seed was imported from Japan between 1930 and World War II. These oysters became naturally established in several areas including Ladysmith Harbour, and Pendrell Sound. Natural breeding of these oysters produced most of the seed for outplanting in BC. In 1950, Pendrell sound was set aside as a reserve to protect breeding oyster stocks. Today Pendrell Sound and Pipestem Inlet are still widely used by growers to collect oyster seed (spat).

The species native to this area, the Olympia oyster (Ostrea conchaphila) is a smaller, slower growing oyster and not as suitable for culture except for a limited specialty market.

Planning Production
The oyster-growing industry in British Columbia has been revolutionized over the past twenty years. Since off-bottom methods of growing oysters have been developed, more and more production is moving from intertidal to deep water. Many beaches with suitable substrate material where oysters have been grown are now being converted to clam culture or clams are co-cultured with oysters. The development of off-bottom growing methods for oysters has pushed productivity and technology to new levels. Where once oyster growing was more like ranching, it is now more like farming and agri-business. Extensive methods of culture are being replaced by intensive ones. Mechanization is now beginning to push productivity to higher levels than ever before.

The information that follows is intended to illustrate production systems and options available to growers. Growing oysters is now a matter of production planning. Decisions about seed, for example, will affect how the crop can be grown-out or harvested which in turn is determined by the type of product the grower aims to send to market. Output of product needs to be predicted with reasonable accuracy which will be more consistent the more control the grower has over the production process.

As the industry grows, production systems will become increasingly standardized, resulting in higher productivity and lower costs. Shellfish growers should be planning for growth (and profits). Production of oysters is an integral process with inter-linked decisions. It should be part of a general management approach that involves defined goals and objectives, clear alternatives to achieve those goals given the limitations of one’s resources (land, labour, capital). Growers should analyze each step of production, look at the alternatives available and make decisions in the light of the objectives.

Steps of Production: Seed
Planning and decision making is followed by preparation and then production itself. Seed or larvae will be the first step. Oyster growers no longer need to depend upon unreliable natural spawning events to collect spat. Hatcheries in Washington and British Columbia produce quality seed and there is a reliable supply. Growers have the option of purchasing eyed larvae and and doing the setting on site or they can buy seed that has already set. Setting eyed larvae can be done in tanks on land or done en mass in tarp enclosures on the beach or floating in deep water. Seed can also be set using ground shell fragments in downweller/upweller systems. These are ususally nursery reared in the upwellers to produce single seed. Seed can also be acquired already set and conditioned on shell cultch or tubes that are moved to the nursery or grow-out site. Another option is to purchase single seed that has been boosted up to 3/4″ in a FLUPSY (Floating Upweller Systems). These can be grown out in tray systems. For details see the section on seed and remote setting.

Nursery Rearing
Nursery rearing follows seed acquisition and follows the stream of type of seed chosen. Seed on tubes or shell cultch can be nursed in intertidal sites or suspended in deepwater from rafts or longlines. Single seed can be nursed in tray systems. Upwellers can also serve as nursey systems for single seed. Some growers with large scale operations have built a FLUPSY for single seed nursery production. For more details see the nursery rearing section.

Grow-out
Grow-out systems follow from nursery systems and types of seed. Cultch oysters might still be spread out on a beach for growout or for hardening and defouling after deep water growth. Oysters on shell cultch or tubes can be suspended from rafts or longlines until harvest. Some of these may be high-graded to singles for the half-shell market or go as shuck oysters. Single oysters can be grown in tray systems suspended from rafts or longlines. Vexar bags can also be used for rearing single oysters and can either be suspended or integrated into an intertidal system. For more details see the sections on tubes, trays, and bags.

Although there is no section dedicated specifically to the method of stringing oyster on shell cultch for deepwater production systems, some information is found in the unit on rafts. Information is also available in the book by D.B. Quayle and some of the other publications. Oysters that have been set on shell cultch (about 15 per shell is considered about optimum) are normally nursery reared on special nursery beaches that have low siltation and are relatively well protected from storms and predators. After a good summer’s growth the bags of seed on shell cultch are transferred to grow-out beaches where they are spread or more commonly now, suspended in deep water. This is usually done on rafts but longlines may also be used. The poly rope most commonly used is two-strand “oyster blue”. The worker uses a table with several adaptations to string the oysters. The tables are usually made of aluminum, with a contained surface to work with the shells, a chute to discard the junk, a holder for the string and a rod and spacer to separate strands and insert shell at specific intervals. See the section on Redonda Rafts for details of stringing rafts.

Each option requires different resources and inputs that must be weighed — capital investment, labour, technology, and site suitability. The flow chart below illustrates some of the production method possibilities open to the oyster producer.

Harvesting and shipping the product to the processor in top condition is the final challenge. Techniques range from hand-harvesting to crew-operated harvest machines and which method is best depends on the volume of production and the type of production system used. Tube harvesters are now well advanced and trays on rafts and longlines can be efficiently harvested because high volumes of product are contained in a small area.

Site Specificity
If there is one cardinal rule for growing shellfish in BC it is this: there is no recipe. Although the industry is moving towards mechanization, modularization and standardization, there is no single method or device that will perform identically at all sites. Techniques that work well in one place may be substandard in another. Each growing site is unique and it is up the grower to find the best means to produce oysters for any given location.

Printed sources to consult about oysters:

  • Cross, S.F. and Kingzett, B.C. 1992. Biophysical Criteria for Shellfish Culture in British Columbia: A Site Capability Evaluation System. (BCMAFF Publication #AFF2965)
  • Field, J. and Drinnan, R.W. Off Bottom Oyster Culture in British Columbia: Culture Methods, Harvesting, Processing and Industry Costs. (BCMAFF Bulletin #21. AFF0374)
  • Kingzett, B.C. and Pirquet, K.T. 1995. Towards Quality Assurance: An Information Manual for BC Shellfish Growers. (BCMAFF Publication #AFF3244).
  • Nosho, T. 1989. Small Scale Oyster Farming for Pleasure and Profit. (Seattle: Washington Sea Grant).
  • Paust, B. and RaLonde, R. 1997. Guidelines for Shellfish Farming in Alaska. (Alaska Sea Grant Publication AN-16).
  • Quayle, D.B. 1988. Pacific Oyster Culture in British Columbia. (Ottawa: Department of Fisheries and Oceans).
  • Shellfish Culture Capability Appraisals for Specific Regions: Okeover Inlet (1995 BCMAFF Publication #AFF3261), Nootka Sound (1995 BCMAFF Publication #AFF3260), Kyuquot Sound (1995 BCMAFF Publication #AFF3259), Quatsino Sound (1995 BCMAFF Publication #AFF3258, Clayoquot Sound (1993 BCMAFF Publication #AFF2847).

Web sites to consult:

  • Fisheries and Oceans Canada:Species and Habitat of Shellfish.
  • Fisheries and Oceans Canada:Diseases and Parasites of Shellfish