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NOAA Technical Memorandum NMFS-NWFSC-49

The Net-pen Salmon
Farming Industry
in the Pacific Northwest

Edited by Colin Nash

From contributions by
Kenneth M. Brooks (consultant)*,
William T. Fairgrieve, Robert N. Iwamoto,
Conrad V.W. Mahnken, Colin E. Nash,
Michael B. Rust, Mark S. Strom, and
F. William Waknitz

Northwest Fisheries Science Center
Resource Enhancement and Utilization Technologies Division
2725 Montlake Boulevard East
Seattle, Washington 98112

*Aquatic Environmental Sciences
644 Old Eaglemount Road
Port Townsend, Washington 98368

September 2001

Donald L. Evans, Secretary

National Oceanic and Atmospheric Administration
Scott B. Gudes, Acting Administrator

National Marine Fisheries Service
William T. Hogarth, Acting Assistant Administrator for Fisheries

NOAA Technical Memorandum NMFS Series

The Northwest Fisheries Science Center of the National Marine Fisheries Service, NOAA, uses the NOAA Technical Memorandum NMFS series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible due to time constraints. Documents published in this series may be referenced in the scientific and technical literature.

The NMFS-NWFSC Technical Memorandum series of the Northwest Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest & Alaska Fisheries Science Center, which has since been split into the Northwest Fisheries Science Center and the Alaska Fisheries Science Center. The NMFS-AFSC Technical Memorandum series is now being used by the Alaska Fisheries Science Center.

Reference throughout this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.

This document should be cited as follows:

Nash, C.E. (editor). 2001. The net-pen salmon farming 
industry in the Pacific Northwest. U.S. Dept. Commer.,
NOAA Tech. Memo. NMFS-NWFSC-49, 125 p.

Most NOAA Technical Memorandums NMFS-NWFSC are
available on-line at the Northwest Fisheries Science Center
web site (https://www.nwfsc.noaa.gov)

Copies are also available from:

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This HTML file represents the Introduction only; the rest of the document is available only in PDF format.


Thirty-five copies of this document in draft were circulated globally in April and May, 2001 for review and comment. The authors acknowledge the added contributions of the following individuals:

Hans Ackefors (University of Stockholm, Sweden)
Kevin H. Amos (Washington Department of Fish and Wildlife)
Andrew Appleby (Washington Department of Fish and Wildlife)
Faye M. Dong (University of Washington, Seattle, Washington)
John Forster (Forster Consulting Inc., Port Angeles, Washington)
Peter Granger (Washington Fish Growers Association, Bellingham, Washington)
James P. McVey (National Sea Grant Program, NOAA, Washington D.C.)
John E. Rensel (Rensel Associates Aquatic Science Consultants, Arlington, Washington)
Andrew J.L. Thomson (Fisheries and Oceans, Nanaimo, B.C. Canada)


The US Government advocates a strong policy for national aquaculture development. The Department of Commerce (DOC) has set specific 25-year goals to offset the annual $7 billion imbalance in seafood trade, and to double employment and the export value of goods and services. The policy is reflected in strategies proposed by the National Oceanic and Atmospheric Administration (NOAA) and its three line agencies responsible for certain aquaculture-related activities. With its broad mandate for stewardship of the nation's marine and coastal living resources, NOAA recommends that aquaculture development and environmental protection proceed hand in hand to meet public needs. Thus, in keeping with the Government's firm commitment to the United Nations Food and Agriculture Organization's (FAO) Code of Conduct for Responsible Fisheries, the line agencies of NOAA are encouraging the fisheries and aquaculture sectors to develop national Codes of Conduct, and their sub-sectors to develop and abide by Best Management Practices (BMPs).

The National Aquaculture Act of 1980 recognized that the principal responsibility for national development lay with the private sector. Therefore, to increase overall effectiveness of federal research, transfer, and assistance programs for the private sector, the Act created the Joint Subcommittee for Aquaculture (JSA). JSA published a National Aquaculture Plan in 1983, which has been recently updated. A review of all the current government policy statements and the National Aquaculture Development Plan 2000 reveals considerable verbal (but not financial) encouragement for private initiatives. The Plan recognizes that aquaculture is not a unique industry with unique hazards. Its systems and practices, and its products, parallel those of many other industries and human activities. Apart from the single and pandemic caveat of protection for the environment there are no directives which promote one aquaculture system or practice over another, elevate one genera or species above another, or forward or forbid the use of any specific technology. In summary, there is no political attempt to rate or rank a sub-sector, or to advance or suppress any specific activity because of any known risk.

The sub-sector of salmon farming in saltwater is a minor part of the national aquaculture industry, but it is a valuable economic asset contributing 11% to the total value of all aquaculture products. Only 45 commercial farms produce salmonids in marine net-pens directly for food, which is just 1% of all production facilities registered in the country, and <6% of all facilities in marine and coastal waters. Another 244 federal, state, or tribal facilities in the freshwater environment produce anadromous Pacific and Atlantic salmon for restoration of the commercial fisheries, recreational fisheries, or conservation, and another 362 freshwater facilities produce salmonids for both food fish and recreational fisheries. Because of its particular niche in marine and coastal waters, American net-pen technology has resulted in considerable growth of secondary producers in the aquaculture industry, and contributes a disproportionate share to the export of national goods and services.

Despite the economic success of net-pen salmon farming in the USA, this review of scientific and other literature reveals that there are many perceived and real issues with this industry which concern the American public. These areas of risk and uncertainty occur in many facets of the industry - from the effects of salmon farming on the environment, to competition with other economies for the same resources, and the human health and safety of farming or consuming farm products. However, based on the evidence available in the existing literature and in ongoing research, it is apparent that the degrees of risk vary considerably from issue to issue.

Risk and Uncertainty in the Pacific Northwest Industry

A. Issues which carry the most risk

After a review of the available scientific literature, the following three issues of net-pen salmon farming in the Pacific Northwest appear to carry the most risk. All potentially impact the environment.

1. The impact of bio-deposits (fish feces and uneaten feed) from farm operations on the environment beneath the net-pens.

Bio-deposits from salmon farms settle onto sediments near the net-pens and can have definite effects on their chemistry together with their benthic and infaunal biota. Firstly, with regard to the chemistry, changes can be anticipated in total volatile solids and sulfur chemistry in the sediments in the immediate vicinity of operational net-pens, together with decreased redox potential. Sedimentation rates remain fairly constant irrespective of farm size, which currently is about 1,500 mt, and a typical total volatile solids (TVS) loading is 32.9 g/m2-day for the perimeter of such a farm near peak production. This value is reasonably close to a theoretical average of 25.7 g TVS/m2-day calculated for an entire 18-month production cycle. Reduced accumulation of volatile organic material under farms can extend to distances of 145 to 205 m from the net-pen perimeter during peak production. The magnitude of the change in any of these parameters is correlated with the degree of flushing in and around each farm site.

Secondly, with regard to the benthic biota, the accumulation of bio-deposits can enrich benthic communities but the actual affects depend on the hydrodynamics of each particular site. At poorly circulated sites these accumulations can exceed the aerobic assimilative capacity of sediments, leading to reduced oxygen tension and significant changes in the benthic community. Under extreme conditions sediments can become anoxic and depauperate. However, under any circumstances these effects are ephemeral and conditions have returned to normal within a period of weeks to years during fallow periods in all cases studied.

Thirdly, with regard to the infaunal communities, the accumulation of organic wastes in the sediments can change their abundance and diversity. But prolonged case studies reveal significant differences between poorly-flushed and well-flushed sites. At poorly-flushed sites benthic effects are highly dependent on farm management practices. Very high salmon production levels and other activities, such as cleaning nets in-situ, result in significant changes in both abundance and diversity of infauna to distances as great as 30:m from the net-pen's perimeter. At reduced production levels, and in the absence of in-situ net cleaning, the impacts are restricted to as little 15 m, or less, downstream from the net-pens. At well-flushed sites the abundance and diversity of infaunal organisms is positively correlated with total organic carbon, suggesting that the farm stimulates the infaunal community throughout the area.

2. The impact on benthic communities by the accumulation of heavy metals in the sediments below the net-pens.

Both copper, from marine anti-fouling compounds used on net-pens, and zinc, from fish feeds, can be toxic in their ionic forms to marine organisms. Levels of copper are elevated around some net-pen farms which use government-approved anti-fouling paints on structures or, more likely, treat their nets with approved commercial compounds containing copper. The detected additions of copper in the water following the installation of newly-treated nets are biologically insignificant, except to organisms which settle on the nets. Zinc is an essential trace element for salmon nutrition, and it is added to feeds as part of the mineral supplement. Sediment concentrations of zinc are typically increased near salmon farms and the concentrations at a few farms in British Columbia have exceeded Washington State's sediment quality criteria (270 µg zinc/g dry sediment).

The degree of risk is dependent on several factors. Firstly, the concentration of sulfide in the sediment is important, as typically elevated concentrations near salmon farms reduce the bio-availability of both copper and zinc thus making the observed concentrations non-toxic. Long-term studies have demonstrated that the metal concentrations return to background during the period of chemical remediation, and there is no evidence of a long-term buildup of these metals under salmon farms. Secondly, the formulation of the feed is relevant, as the majority of feed manufacturers now use reduced amounts of a more bio-available proteinated form of zinc, or a methionine analog. Monitoring of zinc continues to determine the efficacy of this change in reducing even the temporary accumulation of zinc in sediments under salmon farms. Finally, management practices play a role, as the potential rate of accumulation of copper in sediments can be significantly reduced by washing the nets at upland facilities and properly disposing of the waste in an approved landfill.

3. The impact on non-target organisms by the use of therapeutic compounds (both pharmaceuticals and pesticides) at net-pen farms.

In European salmon farms therapeutic compounds are used for the control of sea lice, both for the health of the fish and to reduce their potential as vectors. The commonly used compounds are all non-specific within the Class Crustacea, and several are broad-spectrum biocides with potential to affect many phyla adversely.

The degree of risk is greatly reduced by government regulation for the use of specific therapeutic compounds following extensive research in vitro and in situ on their effects on marine organisms. Case studies show that some of these compounds can be detected in sediments close to the perimeter of net-pen farms, but the levels resulting from their authorized use do not show significant widespread adverse affects on either pelagic or benthic resources. In the Pacific Northwest the use of pharmaceuticals to control sea lice has not been practiced in Washington State for over 15 years because they have not presented significant problems to growers, but some sea lice control agents have been used infrequently in British Columbia.

Note: One more issue might be included in this first category, although the degree of risk is uncertain as there is little scientific information available. This is the impact on human health through consumption of feed-borne organic toxicants. Farmed fish are exposed to dioxins through feed ingredients, and dioxins are found in virtually all feedstuffs of animal origin, especially those containing fish meal and oils. Dioxins can be accumulated and transferred up the food chain. But the degree of risk is uncertain, as the impact of dioxin and dioxin-like compounds on human health is a recent discovery. Currently the Codex Alimentarius Commission is making efforts to reduce the risk by specifying stringent quality control of the ingredients for all animal feeds, and the potential for substituting plant proteins and oils for fish meal and fish oil in salmon diets. Although observation of the Codex by the 165 member countries is voluntary, the USA is an active signatory (see the section on Managing Risk and Uncertainty, which follows).

B. Issues which carry a low risk

Puget Sound is a stressed ecosystem and one continuously being degraded by further human intervention. For the last 25 years it has been an area of intense annual population growth (1.5%) and is now home to 4 million people, with 1.4 million more projected by 2020. It is an area noted for recreational sailing and fishing, and there has been a corresponding growth in the number of support facilities for these water-borne activities. Salmon net-pen farming is another intervention competing for space and water-use, albeit minute by comparison. There are only 10 salmon net-pen farms active on sites in Puget Sound and unlike marinas, which deplete oxygen levels and elevate water temperatures, they are porous structures.

Nonetheless, there are a number of facets of the net-pen salmon industry in Puget Sound which appear to carry a low risk. The majority of these eight issues concern the environment in the immediate vicinity of the farms themselves.

4. The physiological effect of low dissolved oxygen levels on other biota in the water column.

Fish stocked intensively in contained areas are known to have a high oxygen demand. Decades of monitoring in Washington State have found a maximum oxygen reduction of 2 mg/L in water passing through salmon net-pens where large biomasses of fish were being fed. In most cases the reduction in dissolved oxygen has been < 0.5 mg/L. Salmon are more sensitive than most other species to depressed oxygen levels and 6.0 mg/L is considered a minimum concentration for optimum health. Therefore, if there was a localized effect associated with net-pen culture, the farmed salmon would be the first organisms affected. At coastal (oceanic) sites, farmed salmon are infrequently subjected to low dissolved oxygen concentrations when oxygen deficient up-welled water naturally intrudes into the growing area. However, these are oceanographic events which have nothing to do with the culture of fish or shellfish. In even the most poorly flushed farm in Puget Sound the culture facility does not consume quantities of oxygen sufficient to affect other organisms.
5. The toxic effect of hydrogen sulfide and ammonia from the bio-deposits below a net-pen farm on other biota in the water column.

The accumulation of any highly-organic sediment produces ammonia and hydrogen sulfide once the oxygen is depleted. These gases most frequently cycle between oxidized and reduced states within superficial sediment layers where they modify the infaunal community. They are infrequently released into the water column. Although there is evidence from in situ studies that total sulfide concentrations in surface sediments in areas of high organic loading can exceed 20,000 µM, there is little soluble hydrogen sulfide in the water column even under poorly flushed sites. Less than 1.9% of the gases at the sediment-water interface are sulfide, and this can be reduced to 0.05% at a distance 3 m above the sediment. The majority of these gases are methane and carbon dioxide. In a well-sited farm concentrations of hydrogen sulfide gas rising through the water column are rapidly reduced by oxidation, diffusion, and mechanical mixing. For these reasons it is unlikely that toxic conditions caused by hydrogen sulfide will ever occur unless there were extremely large emissions at the sediment-water interface in shallow water.

6. The toxic effect of algal blooms enhanced by the dissolved inorganic wastes in the water column around net-pen farms.

Enhancement of a harmful algal bloom by the inorganic nutrients discharged from salmon farms in Puget Sound is feasible but highly unlikely to occur in the Pacific Northwest. First, apart from the summer months, the natural atmospheric and geographical parameters of the region reduce light availability for photosynthesis, and the waters are vertically well mixed which reduces the time phytoplankton spend in the euphotic zone. Second, the physical characteristics of locations permitted for salmon farming are not conducive to the accumulation of nutrients, even when the water body is nutrient limited. Decades of monitoring have shown minimal increases in inorganic nutrient concentrations downstream from even the few sites having restricted water exchange. Small increases observed at 6 m downstream during slack tide have been statistically insignificant at a distance of 30 m downstream. Nutrient-limited embayments in Washington State have been identified and salmon aquaculture activities in these locations are discouraged and carefully managed when allowed.

7. Changes in the epifaunal community caused by the accumulation of organic wastes in sediments below net-pen farms.

The effects on a wide variety of epifaunal communities have been studied in detail and the results are well-documented. One case study, with long-term (up to 10 years) monitoring, reveals significant numbers of fish, shrimp and other megafauna inhabiting the site, which appears to function as an artificial reef. Other salmon farms in close proximity all share the same characteristics, even attracting larger predators to the enhanced epifaunal communities.

8. The proliferation of human pathogens in the aquatic environment.

Wild salmonids carry genera of marine bacteria, such as Vibrio, Acinetobacter, and Aeromonas, some species of which are pathogenic to humans. The concern is that fish feces and waste feed might enhance populations of these pathogens. There is no evidence in the literature, or in the epidemiological records of Washington State, of any documented case in which the handling or consumption of farmed salmon has led to infectious disease in consumers or farm workers. There are many differences in the physical and chemical composition of salmon farm waste compared with human sewage discharge, and the former does not disperse over large areas but remains localized where it is metabolized by naturally-occurring marine bacteria and invertebrates. There is no credible evidence supporting a hypothesis that salmon farming increases the risk of infectious disease in humans or wild populations of animals.

9. The proliferation of fish and shellfish pathogens in the aquatic environment.

Public health concerns for the safety of fish and shellfish in the vicinity of discharges of industrial and residential waste are real, and vigilance is maintained by stringent regulations and monitoring programs. The accumulation of wastes from net-pen farms is perceived as another source of human and environmental pathogens. However, there is little evidence substantiating this hypothesis. Viruses pathogenic to fish have no documented effect on human beings because they are taxa-specific. Fecal coliform bacteria are unlikely to persist in net-pen sediments rich in total organic carbon as they are specific to warm-blooded animals. Sources of fecal coliform bacteria near salmon farms are more likely to be mammals (such as seals and sea-lions) or birds. In situ monitoring at some well-flushed net-pen farms revealed slightly more fecal coliform bacteria in water and shellfish tissues at stations closest to the farm perimeter. The sources of observed bacteria were not determined. However, all water and shellfish tissues examined were consistently of high quality and met all bacteriological requirements imposed by the National Shellfish Sanitation Program.

10. The increased incidences of disease among wild fish.

Maintaining animal or plant populations in intensive concentrations can be conducive to an outbreak of disease. The specific diseases and their prevalence in Atlantic salmon stocks cultured in net-pens in Puget Sound are not shown to be any different than those of the more numerous cultured stocks of Pacific salmon in hatcheries, which in turn are not known to have a high risk for infecting wild salmonids. All Pacific and Atlantic salmon stocks currently cultured in Washington are inspected annually for bacterial and viral pathogens, and the movement of fish from place to place is regulated by permit.

11. The displacement of wild salmon in the marketplace by farmed salmonids.

Salmon farmers and traditional Pacific salmon fishermen sell the same generic product, and therefore compete in the marketplace. Regulations specific to Washington State require farmed fish to be identified for the consumer. In terms of supply, salmon production by the net-pen salmon industry in the USA has been a counterbalance to the declining commercial and tribal landings of Pacific salmon to meet increasing consumer demands for seafood. But in terms of demand there are distinct differences in the species produced by the two industries, and there are also differences in products available to consumers. Farmed fish are sold mostly as whole dressed fish and fresh fillets, while the typical disposition of the total annual wild catch (not by species) of the five Pacific species is whole fish, fresh and frozen, and canned products.

In terms of price and availability, Atlantic salmon has an all-year round advantage and therefore a competitive edge over Pacific salmon harvested in the commercial fisheries. They are also relatively cheap to produce for the market. Per harvested fish, the cost to the private producer of farmed Atlantic salmon is currently about $1 per pound, head on, gutted weight. However, irrespective of its origin, production of salmon in Washington has little or no measurable effect on prices determined by global supply and demand, or reducing the large importation of farmed salmon from Norway and Chile.

C. Issues which carry very little or no risk

Despite the fact that two of the issues in this final category have many sub-sets, all three issues are deemed to carry very little or no risk. Two are specific to the environment of the Pacific Northwest, and the third concerns human health and safety in general.

12. The escape of Atlantic salmon - a non-native species.

Since a reporting regulation was imposed in 1996, the records show that some 600,000 farmed salmon escaped between 1996 and 1999. These were mostly fish between 0.5 - 1.5 kg in weight. Only 2,500 of these particular escapees were subsequently accounted for. In addition, between 1951 and 1991 the State made 27 releases of 76,000 smolts of Atlantic salmon of various sizes into the Puget Sound Basin in attempts to establish this prized species on the west coast. Many escapees were taken immediately by recreational fishermen angling close to the net-pen farms, and a few others were taken at random by commercial fishermen in Puget Sound and beyond. A few fish (which may have originated in either Washington or British Columbia) have been recovered as far away as the Alaskan Peninsula. However, the numbers recovered have always been small and the rest remain unaccounted for, and it is assumed that the domesticated existence and docile behavior of farm fish makes them easy victims of predators, especially the large populations of marine mammals which now exist throughout the Pacific Northwest.

The following list summarizes the sub-issues of concern regarding escaped Atlantic salmon in Puget Sound which appear to carry little or no risk.

(i) Hybridization with other salmonids
There is no evidence of adverse genetic impacts associated with escaped Atlantic salmon on the west coast of North America as they do not have congeneric wild individuals with which to interact. Hybrids between Atlantic salmon and the Pacific salmonid species can be produced in vitro, but with difficulty. Hybrids between Atlantic salmon and brown trout, another non-native species, are more easily produced in vitro, and occur readily in nature. Atlantic salmon x Pacific salmonid hybrids are not observed in nature, whether for introduced Atlantic salmon in North America, or for introduced North American salmonids to Europe and the other continents. By comparison, successful hybridization between some North American salmonids is regularly recorded.

(ii) Colonization of salmonid habitat
Atlantic salmon are unlikely to colonize salmon habitat in the Pacific Northwest. Accidents occur, and farm fish of various sizes occasionally escape in large numbers. About 1 million Atlantic salmon have escaped from net-pen farms in Puget Sound and British Columbia since 1990. Only a few were accounted for in recreational and commercial fisheries. In addition to escapes, deliberate releases of Atlantic salmon to establish local self-sustaining populations have been made in the Pacific Northwest since the beginning of the century, with the last release in 1991. Although routine monitoring programs occasionally find naturally-produced juveniles, naturally-produced adults have yet to be observed.

(iii) Competition with native species for forage
Like all salmonids Atlantic salmon are high on the food chain. But few prey items of any sort have been found in the stomach contents of escaped Atlantic salmon which have been recaptured. As survival in the wild is extremely low for escaped farm fish, it is assumed that their domestic upbringing makes them poor at foraging successfully for themselves. Therefore, the few natural prey items any escaped fish might consume is negligible, especially when compared with the competitive food requirements of the juvenile Pacific salmon deliberately released into Puget Sound and its tributaries from hatcheries.

(iv) Predation on indigenous species
All salmonids are predators. However, all analyses of the stomachs of recovered farm Atlantic salmon, and of the few naturally-produced juveniles caught in the wild, have failed to show evidence of preying on native salmonid species. This is not the case of other introduced non-native species which are known to be voracious predators of juvenile Pacific salmonids. Some of these non-native predators have been deliberately and/or accidentally introduced and are now managed for sustained natural reproduction to enhance recreational fisheries and for their contribution to sport fishing revenues.

(v) Vectors for the introduction of exotic pathogens
Provided no new stocks or eggs of Atlantic salmon are introduced into the region, farm Atlantic salmon cannot be a vector for the introduction of an exotic pathogen into Washington State. The extensive movement of aquatic animals and plants globally is known to carry the risk of introducing exotic diseases but movement of fish into and within Pacific Northwest states is now well-regulated with the requirement for disease-free certification. No Atlantic salmon stocks have been transferred into the State of Washington since 1991.

13. The impact of antibiotic-resistant bacteria on native salmonids.

Drugs are used in all hatcheries and rearing facilities, and over-use of drugs is known to increase the resistance of many bacteria. Therefore there is the potential for development of antibiotic-resistant bacteria in net-pen salmon farms or Atlantic salmon smolt hatcheries which could in time impact native salmonids. All drugs used in fish culture in the USA are scientifically safe and efficacious, and approved by the FDA. Drug resistance has been commonly observed in public fish hatcheries in Washington State for over 40 years and no resulting adverse impacts on wild salmonids have been reported.

14. Impacts on human health and safety.

The consumption of salmon farm products and/or working in and around the vicinity of net-pen salmon farms are perceived by some people to be concerns of human health and safety. The following list summarizes these sub-issues of concern regarding human health and safety which appear to carry little or no risk, either directly or indirectly.

(i) Heavy metal contamination of farm products
The three main sources of heavy-metal contamination found in coastal waters where fish and shellfish are farmed include industrial and municipal waste discharge, anti-fouling paints, and various organic pesticides, herbicides, and hydrocarbons. Problems with industrial and municipal waste discharges have long been recognized, and exposure to toxic chemicals from these sources are minimized by licensing farming areas away from sources of contamination. The hazards of heavy metal contamination, principally methyl mercury and tributyl-tin, are currently addressed by regulatory controls. As intensive farming relies on high quality formulated diets, the ingredients are regularly monitored to avoid possible contamination of feed with methyl mercury; and the use of tributyl-tin, once a common biocide used in anti-fouling bottom paints and for treating net-pens structures, is totally banned in North America.

(ii) Rendered animal products in animal feeds
The use of rendered animal proteins, once common in formulated feeds for many species of fish as well as other farm animals, has been curtailed by public concern over possible amplification of bovine spongiform encephalopathy (BSE), or 'mad cow disease'. Although not specifically prohibited by regulation, rules designed to prevent cross-contamination of feeds and feed ingredients at time of manufacture have effectively eliminated the use of these ingredients from salmon feeds. There are no scientific studies on the potential for BSE transmission to humans through discharge of BSE prions into the aquatic environment, but based on studies of the discharges from rendering plants to aquifers used for drinking water, the possibility of infection by this route is remote.

(iii) Genetically modified (GM) ingredients in fish feeds
Although safety concerns regarding the use of GM ingredients in animal feeds have not been substantiated scientifically, most feed suppliers continue to offer only GM-free feeds. The use of GM oilseeds and grains in animal and human foods has gained considerable public attention in North America because of uncertainties regarding their effects on human health and the environment.

(iv) Other ingredients and additives in animal feeds
The use of pigments, hormones, antioxidants, and vitamin/mineral supplements in animal feeds is strictly controlled by FDA regulations. Although growth hormones are given commonly to other farm animals, such as poultry and cattle, their use in food fish is prohibited. Additives such as pigments, antioxidants, and other nutritional supplements have been proven safe and their use in fish feeds is permitted by FDA regulation.

(v) Residual medicines and drugs in farmed products
Antibiotic residues in any farmed animals, including fish, is of concern to consumers because they might induce allergic reactions, have toxic effects, or simply increase antibiotic resistance in human pathogens. All drugs used in aquatic species farmed in the USA have been proven safe and efficacious, and are undetectable at the time of harvest when withdrawal times prescribed by the FDA are followed. At present only two antibiotics are registered and sold for use in the USA as feed additives for disease control in farmed fish. The use of parasiticides and vaccines is similarly restricted by FDA regulation. There could be a risk to consumers if these chemical compounds and vaccines were misused or administered by untrained workers.

(vi) Biological hazards in farm products
Potential biological hazards include parasites, bacterial and viral infections, or naturally produced toxins. To date there have been no reported cases of any fish parasites or pathogenic organism from farmed fish causing disease in humans. Most hazards have been eliminated by strict adherence to BMPs on the farm and at harvest, and/or by HACCP regulations during processing.

(vii) Transgenic farm fish
The perceived hazards of transgenic farms products, such as human allergies or unnatural competitors in the ecosystem, are hypothetical issues for net-pen salmon farming in Puget Sound. There is no evidence in the literature that transgenic fish have been raised or are being raised in the Pacific Northwest, and there are no plans to raise them.

(viii) Workers' safety
Compared with commercial fishing, which is identified as one of the most hazardous of occupations, net-pen salmon farms provide a safe working environment. Some fatalities and injuries in the national aquaculture industry from physical accidents have been reported but not specifically among net-pen salmon farmers.

(ix) Public safety and navigational hazards
There is no evidence that floating net-pen structures in Puget Sound are a hazard to the safe navigation of Washington's large and diverse boating communities. Firstly, permits from the US Coast Guard and Army Corps of Engineers are required for each farm to ensure that it complies with navigation and water safety regulations. Secondly, the complexes are small in total area. The ten active sites, which range in size from 2 - 24 acres, occupy only 131 acres of navigable surface waters from the State. The actual surface areas of the net-pen structures themselves occupy only 21.2 acres in total, with each complex ranging from 0.48 - 3.9 acres. By comparison the State has 77 aquatic land sites leased for commercial shellfish production, with a total area of 81,500 acres.

(x) The impact on nearby property values
In the competition for coastal sites between the salmon farming industry (requiring access and good quality water conditions), and residential real estate (requiring access and industry-free views) there is no evidence that the sight and presence of net-pen operations has impacted the values of coastal properties in Puget Sound.

Managing Risk and Uncertainty

A. The environment

There is considerable evidence available in the scientific literature to evaluate any potential risk of net-pen salmon farming on the environment of the Pacific Northwest. Most issues have been studied in great detail for some 20 years, and in many similar environments in different parts of the world. The results are well documented, and a common denominator is that the potential for environmental impact depends primarily on the site of each individual farm. The most important rule in the management of risk is therefore the careful selection of the site.

Responsible permitting of each site is also playing an important management role. The National Pollution Discharge Elimination System (NPDES) permit has been effective in regulating the degree of allowable effect, but its impact must now be supplemented with the strict adherence by site operators to a well-defined set of industry BMPs which are based on good scientific information. These BMPs can be specific to a particular farm, or they can be overarching for the entire industry.

Scientific evidence in the literature indicates that the potential changes in the sediments below operating net-pen farms bear the most risk for the environment. Continuous monitoring of the sediments under and around farm sites for many years has produced an extensive database of chemical and biological information, and specific parameters are now being used to predict the environmental effects. Key parameters include, inter alia, sediment grain size, total volatile solids or total organic carbon, redox potential, free sulfide concentrations and ultimately invertebrate community assessment. Modeling programs are also beginning to provide insight into the environmental response to farm waste, but these are not yet adequate to make reasonable quantitative predictions.

Long-term monitoring of the sediments has also revealed that chemical and biological recovery of the substrate under and around farm sites occurs naturally without human intervention or mitigation. In situ data show that physicochemical recovery can occur within weeks or months at some sites, and within two or three years at others. Biological remediation of the sediments follows after a period of chemical remediation, and the speed of recovery depends on the seasonal recruitment of new infauna.

B. Human health and safety

Net-pen salmon farming is a relatively new global industry, but one which is very highly regulated in the USA. Atlantic salmon cannot be farmed in the Pacific Northwest or along the Northeastern Atlantic coast under any conditions which might pose a hazard to human health by exposure to environmental contaminants, pathogens, or infectious disease organisms. Farm salmon cannot be treated with any chemo-therapeutic compounds not approved by the US Food and Drug Administration (FDA). The health and safety of the farm workers are protected similarly by labor and industrial regulations.

The United Nations Food and Agriculture Organization (FAO) in 1995 formally adopted a Code of Conduct for Responsible Aquaculture, which was followed in 1997 by a detailed document called Responsible Aquaculture at the Production Level. These documents detailed areas of concern regarding the responsible, safe, and effective use of feeds and feed additives, chemicals and chemotherapeutants, and other aquaculture practices which might reduce health and safety risks to humans. Food safety issues associated with farmed aquatic organisms have been subsequently evaluated by the World Health Organization in a working committee of the Codex Alimentarius Commission. The USA, which has agreed to abide by the intentions of all these international codes, has also developed national guidelines regulating the safety of all seafood, including farmed products. These are administered by the FDA.

The literature reveals that the net-pen salmon farming industry in the Pacific Northwest is integrating all these safety assurance and quality control measures at all levels of the farm-to-table food-safety continuum. It has been applying Hazard Analysis and Critical Control Point (HACCP) methods wherever possible since their inception, and is in the final stages of publishing its own BMP.

C. Farm escapes

Accidents have occurred enabling farmed salmon to escape. Such incidents are likely to continue following some unique meteorological event or human error. The possible negative consequences of such events have been limited in part by implementation of pre-prepared recovery plans, some of which have included deregulating catch limits for public fishing on escaped farm fish, and by programs to monitor the background populations of fish in nearby watersheds. These responses will continue to be effective management practices to minimize impact, together with further advances in the technology. Improvements in the design and engineering of net-pens and their anchorages, and the use of new net materials, are continuing to reduce the incidents of loss following structural failure or damage from large predators.

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