Mediterranean Mussel (farmed)

Mediterranean Mussel

Mytilus galloprovincialis

This species is farm-raised.

Summary

Although Mediterranean Mussels farmed in the U.S. are an introduced species, they are well established, and have not had negative effects on local ecosystems. Mussels feed by filtering water for plankton and nutrients, so no fishmeal or fish oil is needed to raise them. These mussels are raised on suspended ropes, which keeps habitat intact.

Criterion	Points
Inherent Operational Risks	3.25
Feed	3.75
Pollution	4.00
Risk to Other Species	1.75
Ecological Effects	2.50
Final Score (average of criteria)	3.05
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 March 10, 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).

3.00

This species is raised in a low risk system (e.g., re-circulating closed system; suspended culture of mollusks; zero-discharge ponds).

While Mediterranean mussels are farmed both in the U.S. and in Europe, all the Mediterranean mussels in the U.S. market are domestically raised.

Mediterranean mussels are raised in suspension cultures. Farmers seed the mussels onto ropes which hang from rafts (Taylor Shellfish 2004; Penn Cove 2004). Penn Cove Shellfish describes their farms: seed-collector lines are hung off of the rafts in the Spring. Spawning peaks in May, and the seed are allowed to grow on the lines for several months. At this point, there are thousands of mussels per meter of line. Farmers reseed the lines to about 200 mussels per foot of line, and hold the small mussels in with a "mussel sock." Mediterranean mussels are fully grown after about one year (Penn Cove 2004).

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. We neither add nor subtract here, because although mussels are raised at high densities, there is no evidence of environmental impact. Mussels grow naturally at high densities.
-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.
+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.

3.25	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). Some of the seed is raised in hatcheries, and is fed algae in the hatchery. During the bulk of the animal's life, however, seawater is the sole nutrient source (Taylor Shellfish 2004; Penn Cove 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 (Taylor Shellfish 2004; Penn Cove 2004).
+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 (Taylor Shellfish 2004; Penn Cove 2004).
+0.25	Feed conversion ratio (FCR) is low (i.e., <1.3; e.g., salmon); OR no feed is used. No feed is used (Taylor Shellfish 2004; Penn Cove 2004).
+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 Mediterranean mussels (Taylor Shellfish 2004; Penn Cove 2004).

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). Mussels themselves improve water quality by filtering out algae and other plankton, reducing chlorophyll, nutrient and suspended solid levels (Downey, pers. comm. 2004).
+0.25	Chemicals (e.g., pesticides; parasiticides; antibiotics) are rarely or never used. No chemicals are used in mussel farming operations (Downey, pers. comm. 2004).
+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 Mediterranean mussel operations, as the mussels are biofilters, contributing to control of excess nutrients in the water column. However, water quality is monitored by the National Shellfish Sanitation Program, and in the event of contamination from harmful algal blooms (such as red tides), or bacteria, growing areas are closed to harvest to protect public health (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). Mediterranean mussels are native to the Mediterranean Sea and the southwestern coasts of Europe, and are farmed in France, Spain, Italy and Greece (Penn Cove 2004). It is believed that they first appeared in Washington and California in the 1950s (Downey, pers. comm. 2004), presumably transferred through ballast water (Taylor Shellfish 2004; Harlow 2004). They are considered a naturalized species, and do not seem to pose a risk to native ecosystems (Downey, pers. comm. 2004).
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. Mediterranean mussels are farmed in the open water, so "escape" is common. As they are well-established on the west coast, "escaped" individuals will generally survive.
-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. There are no major disease problems.
-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.
+0.25	Regulatory authorities are addressing the risks of escape and spread of disease associated with farming this species. In the U.S., states' departments of health or agriculture oversee the transfer of shellfish between states under The National Shellfish Sanitation Program (NSSP) (Kraeuter and Castagna 2001). States' departments of fish and wildlife of fish and game oversee the transfer of live animals intended for replanting (such as planting out seed from hathceries to growing areas). A high health program, developed by the Pacific Shellfish Institute, provides stringent guidelines for hatcheries to assure disease-free seed is supplied to industry for grow-out (Downey, pers. comm. 2004).

1.75	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). Mussels are raised in sheltered coastal areas of the intertidal and subtidal zones. They are frequently raised in partially enclosed embayments (Gosling 1992).
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. The major predator on Mediterranean mussels is the diving duck. In some cases, farmers using a raft system may secure nets around mussel rafts to protect their mussels from diving duck predation. The nets are generally made of fine mesh, and there have been no documented entanglement problems (Downey, pers. comm. 2004).
+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). Most Mediterranean mussel seed comes from hatcheries (Penn Cove 2004). As Mediterranean mussels are not native, there is no issue with depleting the brood stock.
+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

Downey, Robin. Pacific Coast Shellfish Growers Association. Personal communication. May 18, 2004.

Gosling, Elizabeth (editor). 1992. Developments in Aquaculture and Fisheries Science – 25. Elsevier Science. Amsterdam, The Netherlands

Harlow, Jay. Mussels: Blue-Black Gold for Shellfish Farmers. Available online at: http://www.sallys-place.com/food/columns/harlow/mussels.htm. Accessed 23 July 2004.

Kraeuter, J.N. and M. Castagna, Eds. Biology of the Hard Clam. Developments in Aquaculture and Fisheries Science – 31. Elsevier. Amsterdam, The Netherlands.

Penn Cove Shellfish, LLC. Farming Mussels in Penn Cove. Available online at: http://www.penncoveshellfish.com/FarmingMussels.htm. Accessed 22 July 2004.

Taylor Shellfish Farms, Inc. Available online at: http://www.taylorshellfish.com. Accessed 22 July 2004.