Manila Clam (farmed)

Pacific Coast Shellfish Growers Association

Tapes philippinarum, Venerupis philippinarum

Sometimes known as Japanese Carpet Shell, Japanese Clam or Japanese Littleneck Clam.

These species are farm-raised.

Summary

Manila clams are farmed on medium impact intertidal beach plots. Like other mollusks, no feed is necessary, and they improve water quality by filtering out impurities from seawater. While Manila clams are farmed outside of their native range, populations have been established for a long time with no negative consequences for native ecosystems.

Criterion	Points
Inherent Operational Risks	2.50
Feed	3.75
Pollution	4.00
Risk to Other Species	2.00
Ecological Effects	2.50
Final Score (average of criteria)	2.95
Color

Final Score	Color
2.60 - 4.00
2.20 - 2.59
1.80 - 2.19
1.40 - 1.79
0.00 - 1.39

Last updated May 9, 2005.

Inherent Operational Risks

Core Points (only one selection allowed)

General System Design:

An aquaculture system's design is a good overall proxy measure for the likely effect of the operation on the environment. For example, open systems (e.g., net pens and net cages) are more likely to have pollution, disease, and escape issues than closed systems (e.g., recirculating tanks). With shellfish, which don’t require supplemental food input, the more important question is whether they are harvested on or off of the bottom.

1.00	This species is raised in a high risk system (e.g., net pens; net cages).
2.00	This species is raised in a moderate risk system (e.g., most ponds; raceways; bottom culture of mollusks). Clams can be farmed in a variety of methods. The most common system involves on-bottom culture where seed is placed onto the beach, and settles naturally into the substrate, replicating natural set. Farming practices may include the use of plastic mesh, sometimes referred to as “car cover,” placed over the clams to protect them from predators, such as ducks and crabs. The nets are generally staked into the substrate (BCSGA 2002; WRAC 2001). Clam beds may be carefully worked in order to encourage natural setting (WRAC 2001). A less common grow-out method, usually employed on high energy beaches, is to place seed in bags staked to the beach (Downey 2001).
3.00	This species is raised in a low risk system (e.g., re-circulating closed system; suspended culture of mollusks; zero-discharge ponds).

Points of Adjustment (multiple selections allowed)

-0.25	Species is raised at a high stocking density; OR there is a high density of sites in the geographic region, with evidence of environmental impact.
-0.25	Operations do not incorporate best-available, cost-effective technology to reduce environmental impact.
-0.25	There are no effective zoning or permitting practices for siting of facilities.
-0.25	Government programs encourage expansion of high-impact systems.

+0.25	Species is raised at a low stocking density OR there is a low density of sites in the geographic region, which results in minimal impact to the natural ecosystem. Presumably Manila clams are present at high densities with reference to unfarmed areas, but at densities which do not surpass the beach's carrying capacity. Nonetheless, one grower is able to harvest roughly 5,000 pounds of clam on a productive acre (Chew 1999).
+0.25	Operations incorporate innovative culture methods that limit environmental impacts (e.g., polyculture).
+0.25	There are effective zoning or permitting practices for siting and operation of facilities (e.g., mandatory consideration of hydrographic characteristics; requirements for site rotation). Washington, Oregon, California and British Columbia all have licensing controls for leasing land from the state/province. In Washington, most tidelands are privately owned, but aquatic farms must be registered through the State Department Fish and Wildlife Service. All states’ shellfish farms are certified through a registered Shellfish Authority, which is usually the state's department of health or agriculture. Depending upon culture operations, shellfish farms may require various shoreline development or use permits through local county ordinances. Most shellfish aquaculture activities are permitted through the Army Corps of Engineers Nation Wide Permit 4. (Downey 2004)
+0.25	Government programs preferentially encourage the expansion of low-impact systems over high impact systems.

2.50	Points for Inherent Operational Risks

Feed

Core Points (only one selection allowed)

Ecological Footprint of Feed:

"Trash" fish, frequently used in developing countries, is an industry term used to refer to whole fish or fish parts fed to farmed fish without being processed into fish meal and fish oil.

Twenty percent was selected as a cut-off because carnivorous species (e.g., salmon; eel; tuna; cobia; etc.) generally consume greater than twenty percent fish products (fishmeal, fish oil, or trash fish), while omnivorous or herbivorous species (e.g., catfish; tilapia; carps; etc.) consume less than twenty percent fish products.

1.00	Typical aquaculture feed includes high levels of fishmeal, fish oil, or "trash" fish (i.e., >20% of the feed; e.g., salmonid feeds).
2.00	Typical aquaculture feed includes moderate levels of fishmeal, fish oil, or "trash" fish (i.e., <20% of the feed; e.g., tilapia and catfish feeds).
3.00	No feed is used (e.g., mollusks and seaweeds) or typical aquaculture feed includes no fishmeal, fish oil, or "trash" fish (e.g., paddlefish; filter-feeding carps). During the hatchery and nursery stage, algae may be added to seawater as feed; however, during the bulk of the animal's life, seawater provides the sole source of nourishment (Downey, pers. comm. 2004).

Points of Adjustment (multiple selections allowed)

-0.25	When fish products are used, the major sources score low on the Wild-Caught Fisheries Ranking System.
-0.25	Feed contains greater than 10% of fish products and public or private sectors are not working to reduce fish content in feed.
-0.25	Feed conversion ratio (FCR) is high (i.e., >2.0; e.g., eel).
-0.25	Government policy promotes research, development and commercialization of carnivorous or other highly fishmeal-dependent species.

+0.25	When fish products are used, the major sources score high on the Wild-Caught Fisheries Ranking System; OR the source is innovative and ecologically sound (e.g., fisheries byproducts); OR no feed is used. No feed is used.
+0.25	Feed contains less than 10% of fish products OR public and private sectors are working to reduce the fish content in feed; OR no feed is used. No feed is used.
+0.25	Feed conversion ratio (FCR) is low (i.e., <1.3; e.g., salmon); OR no feed is used. No feed is used.
+0.25	Government policy promotes research, development and commercialization of herbivorous species or other species not highly dependent on fishmeal.

3.75	Points for Feed

Pollution

Core Points (only one selection allowed)

Typical effluent treatment procedures:

1.00	Effluent is not treated before discharge (e.g., salmon net pens).
2.00	Effluent is partially treated before discharge (e.g., infrequently discharged effluent from catfish ponds).
3.00	Effluent is substantially treated before discharge (e.g., recirculating shrimp systems; settling ponds; reconstructed wetlands); OR treatment is not necessary because supplemental feed is not used (e.g., molluscs or seaweeds). Treatment of effluent is not necessary because supplemental feed is not used to farm Manila clams.

Points of Adjustment (multiple selections allowed)

-0.25	Operations have demonstrated negative impacts on water quality or sediment/benthic characteristics (e.g., elevated nutrient levels; algal blooms; altered benthic communities).
-0.25	Pollutants (e.g., pesticides; parasiticides; antibiotics; plastic; nets; dead fish) are frequently discharged into the environment or otherwise not appropriately discarded.
-0.25	Effluent regulations do not exist, are lax, or are poorly enforced, which allows for degradation of the aquatic environment.
-0.25	Available technologies and practices to reduce or recycle waste (e.g., feed sensors; low-pollution feeds) are not used.

+0.25	Operations generally improve water quality or sediment/benthic characteristics (e.g., oyster farms). Shellfish filter-feed, reducing concentrations of nutrients such as nitrogen and phosphorus and other suspended particles in the water.
+0.25	Chemicals (e.g., pesticides; parasiticides; antibiotics) are rarely or never used. Chemicals are not used in the production of Manila clams outside of hatchery operations. Even in hatcheries, chemical use is minimal, with spawning induced by temperature and feed variation (BCSGA 2002).
+0.25	Robust water quality regulations exist (e.g., permits required; discharge caps; strong enforcement), and regular monitoring occurs. No controls are necessary for effluent from Manila clam operations. However, water quality is monitored by the National Shellfish Sanitation Program, and contamination from PSP, brown tides, or bacterial outbreak leads to beach closures. In some areas farms are having to close due to non-point source pollution (Downey 2004).
+0.25	Innovative methods and practices to reduce or recycle wastes are used (e.g., integrated systems; effluent and solid wastes used as terrestrial fertilizer); OR innovative methods and practices are not needed because raising this species does not create waste. Farming this species does not create waste.

4.00	Points for Pollution

Risk to Other Species

Core Points (only one selection allowed)

Frequency and Impact of Escapes:

1.00	Farmed species regularly or intermittently escape into the wild AND escapes are non-native to the area or otherwise pose a risk to native populations or ecosystems (e.g., most non-native fish raised in outdoor facilities).
2.00	Escape frequency is not known OR farmed species is native to the area where it is raised and poses minimal risk to native populations or ecosystems (e.g., channel catfish in the US; most native mollusks). While Manila clams farmed in Canada and the United States are farmed outside of their natural range, they have been established in these areas since the 1930s, and seem to coexist well with the pre-existing biotic community (DFO 1999).
3.00	Farmed species never (or virtually never) escape to the wild (e.g., species is raised in bio-secure facilities).

Points of Adjustment (multiple selections allowed)

-0.25	This farmed species has been known to survive in the surrounding ecosystem if it escapes; OR would likely survive given its physiological requirements. Although the introduction of Manila clams to waters in Canada and the United States has not caused major ecological problems (like Zebra mussels), we subtract here to account for their ability to survive outside of farms.
-0.25	This farmed species is known or is likely to compete with wild species for food or habitat if it escapes; OR this species is known or is likely to compromise the genetic integrity of the wild species (e.g., through spawning disruption, genetic introgression or establishment of feral stocks) if it escapes.
-0.25	This farmed species is known or is likely to amplify and transmit disease or parasites to wild populations (e.g., infectious salmon anemia or sea lice infestations) if it escapes.
-0.25	Regulatory authorities are not adequately addressing the risks of escape or spread of disease associated with farming this species.

+0.25	This farmed species has not been known to survive in the surrounding ecosystem if it escapes; OR would not likely survive given its physiological requirements; OR farmed species is a native mollusc.
+0.25	Operations employ management protocols and techniques to limit the ecological impacts of escaped farmed fish (e.g., triploidy; sterilization); OR it’s unlikely that escaped individuals will either compete with wild species for resources, or compromise the genetic integrity of wild species.
+0.25	Operations employ effective disease and parasite management protocols (e.g., fallowing of pens; retaining water when disease outbreak occurs); OR incidence of disease or risk of retransmitting disease is low. Disease has not been a particularly troublesome issue with Manila clam farms in the Pacific Northwest, particularly compared to the difficulties experienced by American oyster and hard clam aquaculturists. The known diseases affecting Manila clams are not very pathogenic and often not present in North America (DFO 2001).
+0.25	Regulatory authorities are addressing the risks of escape and spread of disease associated with farming this species.

2.00	Points for Risk to Other Species

Ecological Effects

Core Points (only one selection allowed)

Ecological sensitivity of site used for operations:

1.00	Operations are generally located in areas of high ecological sensitivity (e.g., coastal wetlands; mangroves).
2.00	Operations are generally located in areas of moderate ecological sensitivity (e.g., coastal and nearshore waters; rocky intertidal or subtidal zones; river or stream shorelines). Manila clam farms occur in protected beaches, inlets or estuaries (Downey, pers. comm. 2004).
3.00	Operations are generally located in areas of low ecological sensitivity (e.g., land that is less susceptible to degradation such as land formerly used for agriculture or land previously developed).

Points of Adjustment (multiple selections allowed)

-0.25	Farming this species causes substantial damage to surrounding habitat, ecosystem or other resources (e.g., groundwater depletion; stream diversion; saltwater intrusion; soil salinization; loss of habitat for juvenile fish; loss of flood control; dredging hard bottoms; etc.).
-0.25	Harmful or lethal predator deterrents are used (e.g., bird/seal shootings; acoustic deterrent devices); OR operation otherwise harms wildlife (e.g., dolphin/seal entanglement; disrupting migration routes; bird/animal shooting).
-0.25	If seed is collected from wild sources, the intensity of collection is high enough to result in depletion of brood stock, wild juveniles, or associated non-target organisms (e.g., collection of postlarvae shrimp).
-0.25	Government policy encourages aquaculture operations to locate or expand in areas of high ecological sensitivity.

+0.25	Operations enhance habitat structure or function (e.g., constructed wetlands).
+0.25	Predator deterrents are not used OR predator deterrents are used but are not harmful or lethal (e.g., predator exclusion nets), AND operation does not otherwise harm wildlife. Non-harmful mesh netting is used to deter predators such as ducks and crabs (BCSGRS 2002).
+0.25	Seed comes predominantly from hatcheries or on-farm sites (e.g., seed for trout); OR if seed is collected from the wild, it does not deplete brood stock, wild juveniles, or associated non-target organisms (e.g., collection of oyster or mussel spat). Eighty-five percent of seed comes from hatcheries (Downey 2004). However, seed is collected from broodstock, and has no harmful effects on wild populations. Since manila clams are an invasive species, this is not an issue for concern anyway.
+0.25	Government policy encourages the growth of aquaculture operations in areas of low ecological sensitivity; OR protects sensitive habitats from aquaculture operations (e.g., prohibitions on cutting mangroves).

2.50	Points for Ecological Effects

References

British Columbia Shellfish Growers Resource System. 2002. Clam culture in British Columbia. Online at: http://www.island.net/~bcsga/bcsgirs/clams/clam.htm

Chew, K.K. 1999. Major moves by British Columbia shellfish growers to increase their take Aquaculture Magazine Jan/Feb, 1999, pp. 90-96.

Department of Fisheries and Oceans, Canada. 2001. Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish. http://www.pac.dfo-mpo.gc.ca/sci/sealane/aquac/pages/toc.htm#cla

Department of Fisheries and Oceans, Canada. 1999. Manila Clam: DFO Science Stock Status Report C6-03 (1999), October, 1999.

Robin Downey. 2001. Personal communication. Pacific Coast Shellfish Growers Association, Follow up conversation for Profile Update May 18, 2004.

Western Region Aquaculture Center (WRAC). 2001. Western Region Aquaculture Industry. Situation and Outlook Report, Volume 6. November, 2001.