Scientific Research on Cultured Clams
Table of Contents
Science is the key to an environmentally and economically sustainable aquaculture industry. Fisheries and Oceans Canada scientists and researchers have examined the potential impacts of clam aquaculture on the marine ecosystem, including the potential effects and benefits of clam harvesting and predator protection techniques. Multi-disciplinary research has also been undertaken to study all aspects of the clam culture cycle, including seeding, rearing, over-wintering, and harvesting.
A mechanical clam harvester designed for the British Columbia industry is now in use. The ‘Mark II’ harvests more clams, in less time, with fewer workers. In addition, the machine harvests low density beach areas and reduces losses from juvenile clam mortalities. An environmental impact study showed that the harvester’s impact was no greater than manual harvesting.
New Manila Clam processing equipment installed in a British Columbia processing plant has more than quadrupled processing capacity, while significantly reducing clam breakage. The equipment also provides efficient and consistent clam grading, and the modular design allows components of the equipment to be moved as required, which permits more efficient equipment cleaning. As a result of these advantages, the company achieved reduced labor costs, per-unit production costs and clam breakage. In addition, new capacity increased employment at the plant.
- A two year collaborative project was conducted to assess the genetic and health status of the native Basket Cockle in British Columbia for aquaculture operation facilitation. By sampling cockles from 14 widespread locations in all five BC Shellfish Zones, the information gained through this research will inform the development of a regulatory regime for aquaculture.
- Researchers in British Columbia worked to develop genomic tools to aid in the study of native littleneck clam responses to environmental and anthropogenic stress factors. The tools were intended to facilitate the use of Littleneck Clams as a bio-indicator in the assessment of ecosystem health and resilience in the presence of aquaculture operations
A series of experiments were undertaken by researchers in British Columbia to improve understanding of the basic biology of Geoduck Clams as it relates to commercial aquaculture production. Studied several aspects of the culture cycle, from broodstock conditioning to larval rearing, juvenile rearing and out-planting. Broodstock conditioning experience focused on the effect of temperature on gonad development, and how this translates into larval success in terms of growth, survival, and condition. Optimal nursery conditions for post-set clams were also examined by monitoring growth and survivorship under various treatments of temperature, feed type, water exchange rate, socking density and substrate type. The potential of a low-cost, raft-based nursery system for Geoduck Clam seed was also examined to determine the effect of various gear types, culture depths, and socking densities on juvenile clam growth and survival. Burrowing behaviour experiments were also conducted to help determine the appropriate season, animal size, and substrate type for out-planting.
A team of researchers sought to determine the physiological and genetic characteristics that differentiate Soft-shell Clam on the basis of their growth in order to evaluate the possibility of developing a farm management method that maintains high-growth rates without weakening farmed stocks.
The sexual maturity, immersion time, and food supply of Soft-shell Clams in the St. Lawrence Estuary and the Gulf of St. Lawrence were the subjects of in-depth evaluation from 2005 to 2007 to help in the selection of seeding sites suitable for clam culture in the area. Preliminary results indicated that size at maturity was similar in the Estuary and Gulf, but smaller in that of clams from the Magdalen Islands.
Researchers sought to determine the optimal over-wintering techniques for juvenile Soft-shell Clams in the Passamaquoddy Region to establish and maintain a reliable hatchery source for the clam industry in Southwest New Brunswick, while maintaining disease surveillance and assessing the survival rates following seeding.
Clam seed (spat)
Researchers evaluated the use of shells to increase the recruitment and survival of Quahogs and Soft Shell Clams. By examining the various sediment parameters and their effects on recruitment and survival, this project may help identify specific factors that would be helpful in the selection of aquaculture sites for these species.
Between 2006 and 2010, researchers sought to find which factors (temperature, salinity and nutrition) promote maximum fecundity and egg quality in a hatchery setting for broodstock Geoduck Clams. The ranges of temperature and salinity tested reflected those typical of an estuarine environment in British Columbia, which the quality of nutrition was manipulated by presenting live algal feeds that vary in levels of essential fatty acids and eicosapentaenoic acid. Various rations were administered to manipulate caloric intake.
Researchers evaluated four spat collection techniques for Soft-shell Clam in an open environment on the north shore of the estuary and Gulf of St. Lawrence in order to estimate their respective collection success. Results indicated that the net appeared to be the most promising method. In subsequent research, nets were placed in two different patterns on an intensively harvested tidal flat to promote the settlement of current year spat and the retention of residual and seeded clams. Sampling was carried out in the fall of 2007, 2008, and 2009, to measure demographic changes in the clams. The results showed that variations in spat density were attributable primarily to annual variability in reproductive success. They also showed a significant increase in spat density in the plots with nets in the fall of 2007 and 2008. One year after nets were removed spat densities were similar on all treatment sites.
- Research abstract (project 2)
- Canadian Aquaculture R&D Review articles: 2007 (project 1), 2011 (project 2)
Clam diet and feeding
A team of researchers are evaluating the effects of various microalgal diets on the growth and survival of Geoduck larvae and seed in order to identify optimal diets and the specific nutritional requirements (especially fatty acids) of larvae/seed and to ascertain vital nutrients imparting high nutritional value to the diets. As part of the research, optimal microalgal rations for both larvae and seed will be identified and the possibility of replacing these live microalgae with commercially available, spray-dried microalgal diets examined.
Predator protection technologies
Between 2004 and 2006, researchers in British Columbia examined the efficacy of various predator protection technologies on clam survival and growth. Intertidal research considered the use of PVC tube technology, including tube diameter, tube length and mesh size of screen covering the tubes. Subtidal research examined various biodegradable materials. Another component of this research focused on the development of high-quality broodstock for hatchery production.
The influence of intertidal clam netting on the distribution of settling Manila Clam larvae was investigated by sampling from netted and non-netted sites in Baynes Sound, Vancouver Island. Overall, no measurable increase in sedimentation beneath netter was noted; however, decreased settlement beneath netting was observed in the year during research when overall settlement was high.
- Canadian Aquaculture R&D Review article: 2007
Potential effects and benefits of clam culture on wild fish and shellfish and/or the marine environment
- In 2011, researchers in British Columbia undertook a 2-year project to assess whether shellfish transfers are a likely vector for aquatic invasive species movement, particularly the Invasive European Green Crab, from the West to the East coast of Vancouver Island. Results will help Fisheries and Oceans Canada (DFO) Fisheries Management to make informed decisions about this potential vector for AIS spread and will allow for a scientific basis for specific shellfish culture licence conditions and for evaluating the introduction or transfer of shellfish to other areas.
- For more than five years, researchers in British Columbia have been studying the potential effects of intertidal and subtidal Geoduck harvesting on the benthic environment, including sediment, infaunal species, and nearby eelgrass beds. This includes researching the effects of high-pressure water hoses called “stingers”, which are used to extract clams. Results consistently found that the impacts of Geoduck harvest and culture are relatively minor and limited in both duration and scale.
A team of researchers set out to determine the potential near- and far-field effects of mechanical and hand harvesting of clams (Manila Clam and Quahogs). The study focused on any risks of these harvest methods to valued habitat productivity, in order to provide the scientific information necessary for the development of appropriate regulatory approval criteria for such activities. Research into this issue is being performed on both the East and West coast of Canada.
Over the course of seven months, researchers analyzed and published the results of a 2003 study conducted in Quebec which evaluated the impact of harvesting clams by hydraulic rakes on benthic communities in local conditions, as well as the recovery of the communities.
Between 2005 and 2007, researchers evaluated and monitored the health condition of two clam sites, one Soft-shell Clam and one Quahaug, in the Bay of Fundy to achieve three objectives: to update the status of endemic diseases such as haemic neoplasia in Soft-shell Clams and QPX (quahaug parasite X) in Quahaugs; to screen non-carrier species for OIE-listed diseases, such as MSX (multinucleate sphere X) and SSO (seaside organism); and to evaluate the prevalence of shellfish diseases in relation to population dynamics and environmental parameters.
A team of researchers worked to identify the role of environmental watershed variables on the development of haemic neoplasia (HN) and to determine the potential genetic susceptibility of clams to develop this disease. Results indicated that a relatively high prevalence and intensity of HN exists in Prince Edward Island, and low prevalence and intensity was detected in several areas of the Gulf of St. Lawrence. Results to contaminant exposure experiments also suggested that the contaminants used may not directly induce development of HN in clams.
- Canadian Aquaculture R&D Review article: 2007
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