Geoduck

Culture of the geoduck (Panope Abrupta) has been under development for more than twenty years in Puget Sound, Washington and there are now hatcheries and farms there producing a significant amount of market product. Here in British Columbia the first significant step to develop a geoduck aquaculture industry was taken around 1995. A five-year initiative was undertaken by a number of stakeholders, including investors and researchers. During this time the technology for geoduck culture in BC has been refined and developed and cuture of the geoduck is now poised to move forward into commercial development and expansion.

Planning Production
Geoduck have a five to seven year culture cycle from planting to harvest, requiring a significant level of planning, management and investment capital. It is a high value product that has the potential to realize a significant return on investment. Geoduck aquaculture in Puget Sound is undertaken only on inter-tidal lands and culture methods and technology has been developed to meet those conditions. In British Columbia, much of the development work has been focussed on sub-tidal culture technology. As commercial aquaculture of geoduck moves forward in BC, a combination of inter-tidal and sub-tidal techniques will likely be employed.

Hatchery and Seed
The backbone of a viable aquauculture industry is the production of seed with reliable quality and quantity. Hatchery capacity to produce geoduck seed will have to increase to promote the growth of a culture industry. British Columbia companies have risen to meet this need with at least three hatcheries now capable of producing geoduck seed animals. Much of the hatchery technology for geoduck seed production has been developed around Puget Sound and a great deal of this knowledge has been shared with BC firms.

Ideally, broodstock will be selected from the areas where they are to be grown, and maintained in the hatchery for one year or more. Broodstock should be good-looking, contain fatty gonads and be disease-free. Geoduck can spawn repeatedly (every two weeks) when held under appropriate conditions (e.g. water temperature at 12oC). Spawning is induced by warming the water to 16oC and feeding them large quantities of algae. Males and females are kept separate and the milky male spawn is mixed with the more granular female spawn.

Larvae are reared in larval tanks and fed a blend of algae. Temperature is maintained at 14oC. It will take 21-25 days to reach 250-280 microns in size at which point the larvae are nearly ready to set and metamorphose. Larvae are very delicate and all screeing is done under water.

Nursery Rearing
Early rearing of juvenile geoducks in nursery systems is a rapidly evolving technology as more is learned about the culture requirements and optimum conditions for these animals. Hatcheries are generally equipped to handle large numbers of small size juvenile animals and the cost of production in a hatchery rises dramatically with increased size of the animals. Nursery methods are under development for both early post-metamorphosis and larger juveniles. Nursery systems are also sometimes distinguished as primary early stage rearing systems and secondary later stage systems

According to the reports from one hatchery, the larvae set on fine screens (120 microns) in a downwelling system. The seed animals are maintanined on these screens in a primary nursery and continue to grow until they are out-planted in a secondary nursery. As the seed grows, densities per screen are reduced. Maintaining flow and adequate feed over the screens is critical to producing healthy larvae. Screens must also be washed daily. At this stage and under these conditions the larvae are especially vulnerable to bacterial problems. In addition to the screens, a sand nursery system with totes and tanks is sometimes used. Sea water is pumped through the tanks and flows over the sand-filled totes containing the seedling geoduck. They feed on plankton contained in the sea water. Although this is a lower maintenance system and the seed grow more quickly, the tanks and totes are prone to infestations of other marine organisms leading to fouling and competition for food. In some cases seed is out-planted inter-tidally when it reaches a size of 5-7mm (shell length) after 2-4 months in the nursery system

Experimentation with a nursery system designed as a Floating Upweller System (FLUPSY) has been undertaken in British Columbia. This system allowed nursery rearing to be done on a floating system in the same areas as the grow-out beds. The FLUPSY has been used very successfully for nursery rearing of oysters and clams and it was hoped that its efficiencies could be transferred to geoduck applications. The necessity for geoduck seed to be embedded in a sand substrate during the rearing process has presented significant challenges. The FLUPSY design was modified to draw water across a bed of sand containing the juvenile geoduck

Seed was boosted in this sytem over the spring and summer and has been grown in the FLUPSY to 25mm or more. It has proven to be a difficult system to manage well with fouling by tunicates or mussels, anaerobic conditions in the sand, and density-related conditions just some of the problems that have been encountered.

Transferred from the FLUPSY, the seed are held over winter in a benthic nursery system consisting of a protected enclosure with sand substrate for the seed. When the seed are harvested in spring for planting in grow-out areas, a screen is pulled from the container separating seed from substrate. While there have been successes with the FLUPSY nursery system, the cost of operating the FLUPSY is high relative to the amount of geoduck seed that can be boosted in the sand-filled totes. The FLUPSY may play a more limited role in boosting seed for short periods without the use of sand substrate, provided the seed is not compromised.

Recent geoduck nursery systems under development have begun to utilize tank or raceway systems where there is greater conttrol over culture conditions. Since such systems require pumping and filtering seawater, production costs can be quite high but it is hoped that advances in technology and efficiencies will eventually lead to lower costs.

An experimental geoduck nursery system is under development at a new Vancouver Island facility operated by Manatee Holdings. A small inlet area has been modified to create a salt water pond designed to encourage natural plankton blooms. This feed-rich water is then pumped into the tank system of the nursery. This operation has committed itself to the highest standards of facility aesthetics as is evident from the construction of the bridge and pathway over the pond flow control gate.

The geoduck seed is brought in from a hatchery at 1-2mm in size and planted in a sand bed installed in a flow-through tank. In this experimental system, the algae-rich water is pumped in from the outdoor salt water pond, passed through a sand filter (which filters out large particles over 50 microns in diameter) and distributed in the tank through a grid of pipes laid out on the bottom.

The pipe grid is covered with a layer of gravel followed by a filter layer of landscape cloth followed by the sand substrate in which the geoduck seed are planted. The water flow from below the substrate prevents anaerobic conditions from developing below the surface of the sand. A secondary inflow of water is introduced into the tank at the surface by means of the perforated cross-pipe. This creates a light surface current across the sand enhancing the ability of the geoduck juveniles to feed by menas of the siphon tube it extends to the surface of the sand. Insertion of a screen beneath the sand will allow the nursery tank to be harvested efficiently when the seed reaches a size appropriate for out-planting in the grow-out beds.

Critical to this tank nursery system is determining the optimum seeding density. The stock will perform poorly if the density is too high and the costs will be unnecessarily high if the density is too low. Staff are experimenting with stocking densities of one to two animals per square inch. The objective for the nursery production cycle is to plant animals in the tank at 1-2mm and harvest them for plant-out at 10-12mm (shell length). It may be possible to boost them to this size in two months in the nursery. It is hoped that at least two cycles of seed for grow-out can be produced by such a nursery rearing facility. As long as phytoplankton is produced in the external water supply (i.e. not from November to March), the system should be able to operate.

Experimental development will continue on geoduck nursery systems and new designs and techniques will be introduced as growers strive to produce high quality juvenile animals more efficiently. Although upwellers with no substrate will not suffice for a full cycle of nursery production, experiments are being undertaken to determine if they can be used at key points in the nursery rearing process. However, without the sand substrate, the juvenile geoduck gradually become fouled and may be stressed. Work is also underway to find lighter and more economical substrate alternatives to sand.

Grow-out
Once seed attain the minumum 10mm size, they can be transferred to grow-out beds which can be either low-intertidal or sub-tidal beds. Geoduck seed that is planted out must be protected from predation. Since the geoduck will take some time to bury themselves in the substrate and since they are small animals that will not be deep in the substrate, they can easily be taken by predator animnals such as crabs and starfish.

In inter-tidal culture systems such as those common in Puget Sound, the seed geoduck are planted directly into PVC tubes in the spring. The tubes may be 12-16 inches long and 4-6 inches in diameter. The tubes are pushed into the sand substrate and covered with a protective mesh. Four juvenile geoduck are placed in each tube. The mesh is removed after the first year.

The tube is left for another year and then it too is removed and re-used for the next lot of seed geoduck. Seeding density is site specific but if the site is sufficiently productive, it can be up to one tube every square foot. Geoduck prefer the low inter-tidal environment. Ideally they should be planted no higher than the +3-foot level and as low as is practical to access them. They can be planted as high as +6 feet tide level but growth and survival will be lower.

In sub-tidal culture, the development of grow-out technology has been a significant challenge. Tubes have proven to be too labour-intensive for divers and the tubes shift and can pop out of the substrate. An underwater self-propelled seeder has been developed by the Underwater Harvesters Association which transfers the 25-30mm seed geoduck from a hopper through seeding tines into the substrate at the desired depth.

Seed broadcast on the substrate surface are subject to predation and losses can be high. Planting the seed at depth gives them some advantage, but the seed still requires further protection and is covered with a protective canopy. The canopy, however, does not guarantee protection. The planting activity will attract predators and crabs, starfish (e.g.Pisaster brevispinus), flatfish (which nibble off the siphons), moonsnails and diving birds are continuing to present challenges to the grow-out process. Without the canopy, survival of planted seed is probably less than 10%, but with the canopy in place survival rates can be increased to 80 or 90%. Further losses will occur in the second and third year which may reduce overall survival to 50%. However, further work on survival enhancement is being done.

Harvesting
It is currently estimated that it will take six years to grow a geoduck to market size (i.e. at least 1 kilogram live weight). Because mature geoduck can live almost a metre below the substrate, harvesting presents a small challenge. Currently, both inter-tidally and sub-tidally, geoduck are harvested simply and economically by use of a wand which expels high pressure water. The injected water liquifies the sand substrate around the geoduck. It can then be gently removed by grasping the siphon. In this way no damage is done to the animal by the harvesting process.

Web sites to consult:

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

Thanks to Eric Gant and Sondra (Manatee Holdings Ltd.) for information and photographs.