Geoduck Grow-out Using an Innovative Suspended Culture Technique

Final Report
Maplestar Seafood
AIMAP 2011-P19

Executive Summary:

Geoduck aquaculture in British Columbia (BC) has been plagued by a lack of sea bottom tenures and the very long growing period (7-10 years) to reach marketable size. The goal of this project was to address both the issues by employing off-bottom suspended technology to produce a new product (Baby Geoduck) within a relatively shorter period of time (18-24 months).

The primary object of the project was to develop innovative technology for culturing geoduck over a grow-out period of five months. The longer-term object of the project was to introduce the new product, or the Baby Geoduck of 100-150 g, to market. The high quality and highly marketable Baby Geoduck was grown using a suspended, off-bottom shellfish raft system at the Maplestar Seafood Ltd farm at Nanoose Bay, BC. Following successful production of the Baby Geoduck, the innovative results will be incorporated into commercial operations at the Maplestar Seafood Ltd farm.

The grow-out of geoduck seed did not start until Sept 2011, as opposed to the initially planned Aug 2011, and the seed was exposed to winter conditions during much of the grow-out period. Despite this, the seed in Batch 1 have achieved a maximum growth rate of 50.6-80.7 µm/day in the pearl nets during the Oct 1-Nov 19, 2011 period, and 75.7 µm/day during the Oct 15 - Nov 5 period for the seed stocked in the Duck nets. The seed did show better overall growth rate in the Duck nets than in the pearl nets.

The project has increased the productivity and dollar value of Maplestar Seafood Ltd in comparison with its existing farm operations. It has also diversified business opportunities for the company and other BC shellfish growers and processors.

The project fits AIMAP priorities of sustainable production (new technology and practices for shellfish production, increased value of production) and species diversification (increased production of geoduck as a target diversification species for aquaculture).

Introduction

The geoduck clam (Panopea abrupta) is one of the largest burrowing clams in the world. It is found in the lower intertidal and subtidal zones to depths over 110 m along the west coast of North America from Alaska to Baja California and in Japan. This species is abundant in Washington State and British Columbia (BC). The population in BC supports lucrative dive fisheries with an average landed value over $30 million annually in recent years.

Geoduck is a long-lived clam and the nature recruitment appears to be very low. As a result of concerns over the low recruitment, significant fishing pressure, and high market value, there has been growing interest in developing geoduck enhancement and aquaculture in both Washington State and BC. In the wild, growth of geoduck is relatively fast during their first 10 years of life but slow thereafter. The growth also varies along environmental gradients and between geographic regions.

Hatchery production of geoduck juveniles (seed) is a basic requirement for commercial geoduck culture. Research on geoduck hatchery, nursery, and grow-out methods started in the early 1970s in Washington State and in BC later on. Results suggested that survival of seed during the first year of planting on sea bottom increased with seed size. Therefore, different nursery systems have been developed to boost the seed growth from 3-6 mm to 12-20 mm:

• Offshore downwellers and upwellers.
• FLUPSY (floating upweller system) with forced up-flow conditions. This method is used extensively to grow oyster seed at high densities, being able to produce good survival but with relatively high initial capital and operating costs.
• Benthic tables at marine site managed by divers. This method can be effective but survival can be variable.
• BOBS (mesh bags on bottom) at marine site managed by divers. This method has a lower cost but variable survival.

Currently, the grow-out of geoduck in BC involves both intertidal and subtidal bottom culture methods, with subtidal bottom culture the primary method. However, preventing the seed from predation during the first 1-2 years after planing with bottom culture has proven to be a major technical challenge. Expansion of the industry has also been severely hindered by the lack of new aquaculture tenures due to policy issue. Furthermore, growth of the industry has been hampered by the lengthy grow-out period of at least 7-10 years to grow geoduck to a marketable size of ~700 g. Therefore, innovative techniques need to be developed to push forward the geoduck farming industry. 

Growing geoduck seed in large pyramid-shape nets (pearl nets, 2 mm mesh) by suspended culture has been tested by Island Scallops Ltd (ISL) and the results were very encouraging. Although the geoduck did not reach a marketable size in that trial due to limited time frame, this grow-out technique has demonstrated an amenability of geoduck to suspended culture at younger age. If this technique can be successfully applied, it addresses the issue of predation by holding the seed in mesh nets off-bottom, therefore avoiding exposure to benthic predators. This technique will use existing offshore shellfish tenures in BC, thus alleviating the issue of acquiring new bottom tenures, which are essentially not available at the moment because the relevant aquaculture policy is being drafted by DFO. Additionally, this technique will employ a shorter grow-out period of 18-24 months and introduce the market to a new product we call the high quality “Baby Geoduck”, therefore resulting in much quicker return on investment. It should also be noted that this technique is able to grow geoduck seed to varying size suitable for planting on sea bottom, hence serving as a new, simple nursery method for geoduck bottom culture.

However, there is significant technical gap to develop a mesh net that will support geoduck growth until harvest within about two years. In order to address such gap, Maplestar Seafood Ltd (MSL) has designed an innovative prototype “Duck net” in the present project. The Duck net is of cylindrical shape and comprises six tiers. Each tier is 12” high and 60 cm in diameter, and has three key components to facilitate geoduck growth under suspended culture conditions:

• An outer mesh of 15 mm (12” high) to facilitate water exchange between the inside and outside of the net and to strengthen the net structure so that each tier can hold more than 30 lbs.
• A fine, lower inner mesh of 2 mm (6” high) (i.e. the upper half of the tier is the single-layer 15 mm outer mesh), and
• A fine bottom mesh of 2 mm (60 cm in diameter); both the lower inner and bottom meshes are to hold the small geoduck seed and to alleviate impact of fouling and predators (crabs, starfish etc.) on the seed.

The specifically designed outer and inner meshes will allow the geoduck siphons, fetching a high market value, to extend to a higher water flow with the larger outer mesh over the growing period (i.e. the pearl nets using only 2 mm mesh can be entirely fouled during the culture). Based on calculations of growth rate, it is anticipated that geoduck seed can grow from as small as 3 mm to Baby Geoduck (80 mm or 100-150 g) in the Duck net in 18-24 months. Suspended culture is also expected to produce faster growth due to warmer water temperature and higher food supply of surface water compared to bottom culture.

The market value of Baby Geoduck is estimated at $5/lb, compared to $12/lb currently for adult geoduck. Fanny Bay Oysters has extensive experience in marketing geoduck and also great interest in marketing the new Baby Geoduck from the present project.

Successful development of suspended geoduck culture with the Duck net will potentially benefit virtually all shellfish farmers with existing deepwater tenures in BC, particularly those employing raft culture of oysters and mussels. Farmers will be able to diversify production with the addition of a new, high value product to their existing tenures. This in turn will positively impact shellfish hatcheries in BC due to increased demands for geoduck seed. The shellfish processing and marketing sectors will also benefit from the present project through introduction of a new product of Baby Geoduck and an overall increase in the amount of geoduck for marketing.

Geoduck is a target species for aquaculture diversification under the AIMAP in DFO's Pacific Region. The present project will test and develop novel equipment and techniques for use by MSL and other menmbers of the BC shellfish aquaculture industry. These inovations have the potential to significantly tranform the geoguck aquaculture industry in Canada's Pacific Region. 

Methods/Solutions:

1. Duck Net Construction 
   
   The first phase of the project entailed development of the innovative Duck net. MSL designed and constructed a prototype Duck net for the project and ISL fabricated and supplied the final product after the design had been finalized.
   
   The prototype Duck net comprises six tiers, each 12” high and 60 cm in diameter. As stated previously, each tier comprises three key parts: an outer mesh of 15 mm (12” high), a fine, lower inner mesh of 2 mm (6' high), and a fine bottom mesh of 2 mm (60 cm in diameter). The Duck net is made of polyethylene (PE) single filament knotted nets with coated wire frames and reinforced by four 3/16” three-strand PE ropes along the length of the nets.
   
   At the time of writing (Jan 2012), the design and construction of the Duck nets has been completed. A total number of 215 Duck nets have been completed, and 11 of them have been stocked with geoduck seed.
   
   
2. Supply of Geoduck Seed and Transfer to the Farm Site
   
   The second phase of the project entailed obtaining geoduck seed. Key to the project success is a secure supply of good quality seed from a shellfish hatchery. A total of 50,000 seed were obtained from ISL in two batches, at significant discount to contribute the success of the project. The seed were transferred to MSL, stocked temporarily in pearl nets of 2 mm mesh, and finally transferred to Duck nets for grow-out. In addition, 34 pearl nets were used as a control tool for the purpose of comparison for both batches.
   
   Batch 1 was transferred to MSL on Sept 7 2011 and Batch 2 on Sept 30 2011. Batch 1 contained 5,000 relatively larger seed (14.5 mm) and Batch 2 45,000 relatively smaller seed (8.2 mm). Upon arrival, the seed were held in pearl nets at a stocking density of 500 seed per tier. Stocking of the seed into Duck nets began in Oct 15 2011, and at the time of writing, a total number of 3,000 and 30,000 seed have been stocked in Duck nets for batch 1 and 2, respectively, both at a density of 500 seed per tier. The remaining seed are kept in the 34 pearl nets as controls.
   
   Both Duck and pearl nets are suspended on oyster raft at 30-foot depth.
   
3. Grow-out the geoduck Seed inside Duck Net
   
   The third phase of the project involved grow-out of geoduck seed for five months. The proposed starting time was Aug 2011 to Jan 2012, but the actual starting time was delayed until Sept 2011 due to a permitting issue (see also above actual seed transferring time). Protection of geoduck seed from predators is always a challenge in geoduck culture, perhaps even with the present Duck nets. Crabs, starfish, and flat worms are the main predators for geoduck seed smaller than 20 mm. Predation is less a problem once the seed reach 20 mm. The larval forms of predators may settle within the Duck nets and grow to a size that can have a severe impact on the seed. For example, the settlement of crab larvae occurs from early June to late September at the farm site of MSL. The problem of predation by crabs would be addressed by grading and sorting the seed during the settlement period of crab larvae.
   
   Bio-fouling of the Duck nets is another potential challenge during the grow-out phase. Mussels, hydrozoans, skeleton shrimp, and sponge are expected to be the main bio-fouling organisms. The issue would be addressed by cleaning and changing the nets during summer time. It is anticipated that the smaller inner and bottom mesh used in the Duck nets would attract more bio-fouling organisms than the geoduck seed, so that the seed could remain clean over the production season. The smaller inner and bottom mesh can also be removed to facilitate cleaning and net change.
   
   Another potential challenge during the grow-out phase arises from the tendency of geoduck seed, if grown inside a mesh of inappropriate size, to stick their siphons out of the mesh and get trapped as they grow. This problem would be resolved by the present design of the two-layer Duck nets. The fine, inner mesh (2 mm), directly holding the seed, was much smaller than the siphons of a geoduck seed at the start of the grow-out, and the outer mesh (15 mm) was much larger than the siphons of a geoduck with the target size of 80 mm, so that neither mesh would trap the siphons of a geoduck, when fully extended during normal feeding activity.
   
   Records were kept approximately on a bi-weekly basis regarding seed growth and survival, as well as predation, bio-fouling, and how many seed were stuck inside the mesh. Seawater temperature, oxygen and pH levels were also recorded at the same time.
   
   The followings are the results obtained so far. At the time of writing, no predators were evident for both pearl nets and Duck nets. This is likely due to that the settlement season of predator larvae had already finished when the project started in late Sept (2011).
   
   Bio-fouling has appeared to be some problematic at the time of writing. As expected, mussels, hydrozoans, and sponge have been the fouling organisms observed so far. But they target on different surfaces for attachment. Mussels and hydrozoans (Hydroid obelia) are found to settle on the outside of the control pearl nets, probably due to the smaller mesh size. The byssal threads secreted by a single mussel could even attach and trap several geoduck seed inside. The seed in the pearl nets are otherwise generally clean, except for a few fouling sponge (approximately 5%). For the Duck nets, the nets themselves are clean, likely due to the larger (outer) mesh size; however, the seed inside (about 30%) are fouled by hydrozoans especially on the siphons. Although these fouling organisms did not appear to cause direct mortality to the seed, their mid- to longer-term effects on the growth and survival of the seed remain to be seen. As expected, no geoduck siphons have been observed to be stuck in the inner and outer meshes so far.
   
   The (dirty) pearl nets have been changed and cleaned three times so far, but the relatively clean Duck nets haven't yet been cleaned. Additional efforts have been made to remove the fouling organisms (hydrozoans and especially sponge) on the seed by hand, but the fragile shell of the seed made the cleaning work much more difficult.
   
   From the day of initial stocking of the seed into the Duck nets (Oct 15) to the latest sampling day (Jan 29 2012), the overall average daily growth rate was relatively higher (21 and 43%, respectively) in the Duck nets than in the pearl nets for both Batch 1 and 2 seed (25.4 vs 21.0 µm/day and 14.4 vs 10.1 µm/day, respectively). The observed differences can be attributable to the better water exchange between the inside and outside of the Duck nets with larger mesh size.
   
   For the Batch 1 larger seed, maximum average daily growth rate was observed between Oct 1 and Nov 19 for the seed stock in the pearl nets (80.7-50.6 µm/day), and between Oct 15 and Nov 5 for the seed stocked in the Duck nets (75.7 µm/day). However, growth rate during the other sampling periods was generally lower (<22.1 µm/day) for both pearl nets and duck nets. For the Batch 2 smaller seed, growth rate for each sampling period was generally lower (<23.6 µm/day) for both pearl nets and duck nets.
   
   The lower growth rate (11.8-14.3 µm/day) during the initial stocking period (Sept 7-Oct 1) for the Batch 1 seed is probably due to acclimation of the seed to new environment after transferring from the hatchery to the sea. The lower growth rate (<22.1 µm/day) for the Batch 1 seed later on and for the Batch 2 seed during the grow-out (<23.6 µm/day), in both pearl nets and Duck nets, is likely related to the low winter water temperature (below 9.1oC after November) and food availability (i.e the observed transparent water conditions). In fact, growth was marginal during the last sampling periods in December and January (<5.8 µm/day) for both Batch 1 and 2 seed stocked in pearl nets and Duck nets.
   
   Overall survival rate from Oct 15, when the seed were first transferred into the Duck nets, to the latest sampling day was similar (61.1-74.8%) between pearl nets and Duck nets for both Batch 1 and 2 seed. Further evaluation of seed growth and survival is currently in progress.
   
   
4. Cleaning, Sorting, and Grading geoduck Seed in Duck Net
   
   Cleaning, sorting, and grading geoduck seed are the routine activities over the whole project period once the seed are stocked inside the Duck nets. The nets were proposed to be changed twice over the project period. Each net change would facilitate net cleaning, seed grading by size, and density adjustment. A pressure washer was used to as the main cleaning tool for the nets.
   
   Due to the fragile nature of the shell of geoduck seed, the removal, sorting, and grading would be conducted by hand picking instead of sieving which is the grading tool for other bivalve seed such as manila clam, oyster etc. This step is both labour intensive and time consuming. Successful grading of the seed was to keep the end product, after 5 months of grow-out (Aug 2011-Jan 2012 as proposed), at a uniform size of 35 to 45 mm so the end product would be more presentable.
   
   At the time of writing, no Duck net changes have been made because the nets are still clean and the seed haven't put too much growth, due largely to the relatively shorter grow-out time (two months in the Duck nuts so far), the clean seawater conditions, the lower water temperatures and/or food availability during the current winter season. Additional efforts have been made to sort and grade the seed. Further evaluation of cleaning, sorting, and grading geoduck seed is underway.

Conclusion

Due to licensing and permitting issue, the grow-out of geoduck seed did not start until Sept 2011, as opposed to the initially planned Aug 2011. As a consequence, the seed were exposed to winter conditions during much of the current grow-out period. The winter conditions are believed to be the primary cause of the observed slower growth rate of the seed. As such, extended grow-out period is required in order to obtain firmer results. Despite these, the seed in Batch 1 have achieved a maximum growth rate of 50.6-80.7 µm/day in the pearl nets during the period of Oct 1-Nov 19 2011, and of 75.7 µm/day between Oct 15 and Nov 5 for the seed stocked in the Duck nets, when seawater conditions are still believed to be favourable of the growth of the seed. Nonetheless, the seed did show better overall growth rate in the Duck nets than in the pearl nets. Evaluation of growth and survival of the seed in the Duck nets is currently in progress, especially during the coming spring and summer seasons when water conditions are in favour of maximum growth of geoduck seed. Predation, bio-fouling, and trapped geoduck siphons by nets, as well as cleaning, sorting, and grading geoduck seed in Duck nets will also be evaluated with extended grow-out period.

Results of the project will potentially benefit virtually all shellfish farmers with existing deepwater tenures in BC, particularly those employing raft culture of oysters and mussels. Farmers will be able to diversify production with the addition of a new, high value product to their existing tenures. This in turn will positively impact shellfish hatcheries in BC due to increased demands for geoduck seed. The shellfish processing and marketing sectors will also benefit from the project through introduction of a new product of Baby Geoduck and an overall increase in the amount of geoduck for marketing. The project also provides a simple, alternative nursery method to grow geoduck seed to varying size suitable for bottom culture.