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23 February 2011
ALR/02
Hon Shane Arden Chair Primary Production Committee
For Information
ENVIRONMENTAL EFFECTS OF SALMON FARMING Purpose:
This paper responds to your request for information on the environmental effects of salmon farming.
Contact:
Phil Kirk, Ministry of Fisheries
DDI: 03 5458787
Mobile: 0274 392187
Summary 1 The New Zealand industry has made significant advances in production techniques that are focused on minimising environmental effects through the application of advanced technology and husbandry practices. 2 At the present relatively low level of salmon production around New Zealand, and with good site selection and husbandry by the industry, the environmental effects of salmon farming are considered to be well within the carrying capacity of the environment. 3 The most common effects are localised changes to the seabed and water column through the deposition of organic wastes from the farm (faeces and uneaten feed). However, farms are managed so that a balance is found between the amount of material falling to the seafloor and the ability of seafloor fauna to assimilate this material. The result is that there is little or no build up of material on the seafloor below the farm. These matters are routine considerations in the Resource Management Act planning and consenting processes. This minimises habitat modification and protects biodiversity of more sensitive habitats. 4 Most problems from overseas salmon farms, including those in Chile, have been the result of having poorly located farms, too many farms in close proximity to each other, or overstocked farms, so that the assimilative capacity of the environment is exceeded.
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Background 5 A great deal of information is available on the environmental effects of salmon farming. What follows is largely a summary of a report on salmon farming in New Zealand prepared for the Ministry of Fisheries by the Cawthron Institute in 2007. This has been updated with additional information on fish feed provided by the National Institute of Water and Atmospheric Research; the Cawthron Institute and the New Zealand Salmon Farmers Association.
Analysis Seabed Effects 6 Salmon farms affect the seabed directly beneath them through faeces and uneaten feed falling to the seafloor. These organic-rich particles can alter the physical, chemical and biological nature of the seabed. Organic enrichment increases microbial activity that, in turn, can lead to oxygen depletion in the sediment (and subsequent changes to biodiversity). 7 In New Zealand, it is usual to site salmon farms over muddy habitats that are adapted to naturally higher rates of deposition. The stocking densities of farms are also managed so that a balance is found between the amount of material falling to the seafloor and the ability of seafloor fauna (worms etc) to assimilate this material. The result being that there is generally no build up of material on the seafloor below the farm. This minimises habitat modification and protects biodiversity of more sensitive habitats. Information to date shows seabed effects that might develop are largely reversible. 8 Organic enrichment can be pronounced directly beneath a salmon farm, but seabed conditions rapidly improve with increasing distance from farm structures (over tens or hundreds of metres). How great these effects are depends mainly on the flushing characteristics of the site, and salmon stocking density and biomass (total weight of salmon in the farm) and feed management. These effects can be reduced by siting farms in deeper, well-flushed areas and through farm management practices that control stocking densities and limit feed wastage. These matters are routine considerations in the Resource Management Act planning and consenting processes. 9 In conventional marine farming, fish are fed with specially formulated feed pellets that match their dietary feed requirements (in the same way as food is fed to pet fish in an aquarium). There have been significant improvements in how feed pellets are manufactured and distributed in the fish cage. For example, feed pellets are now developed to float or sink at different rates based on the requirements of the fish species and the cage used. Fish farmers also use underwater cameras and other equipment to monitor feeding activity within the cage. Feeders are turned off when the fish stop eating. 10 These technological and farm management improvements mean reduced costs for marine farmers. These improvements are also better for the environment through reduced release of nitrogen and reduced waste on the seafloor below the cages. 11 As part of the ecological assessment for a salmon farm application, scientists check whether there are any unusual habitats or species at the site. Proposed farms are more
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In-Confidence likely to be declined if the sites contain or are very close to habitats or species of special conservation value or ecological importance. 12 The depositional 'footprint' of a proposed salmon farm is also checked. This is usually done using a predictive model that estimates the distance and direction salmon farm wastes could travel before reaching the seabed. The model takes into account local water current speed, water depth, and the time it takes for particles to settle to the seabed. The model also estimates the amount of deposition that would be likely to occur at increasing distances from the farm. 13 Scientists also study the composition of the sediments beneath the proposed site. This usually includes taking samples inside and outside the proposed site, to investigate the proportion of fine mud, sand, and shell/gravel, the organic matter content of the sediment, and the redox depth (the depth at which sediment becomes anoxic). These values are compared with the average values for other sediments in the region. 14 In New Zealand, established salmon farms are regularly monitored for their environmental effects. These monitoring programmes are set as conditions of the farm’s resource consent. Seabed samples can be taken, to detect the level and extent of the actual depositional “footprint” of an operating salmon farm (for example, by testing for organic content, redox depth, and what animals are living in the sediments).
Water Column Effects Water Quality 15 Fish wastes and uneaten food from salmon farms can increase nutrients and reduce dissolved oxygen levels in the water column. Such potential water column effects can be mitigated by siting farms in well-flushed areas. They can be further reduced through farm management practices that control stocking densities and limit feed wastage. 16 Having lots of nutrients in the water column can cause excessive algal growth and the wider flow-on effects of this – reduced water clarity and physical smothering. Nutrient enrichment can also increase the likelihood of harmful algal blooms (algal species that produce biotoxins). 17 Due to current farm management practices and the small scale of farming, salmon farming in New Zealand has not been found to result in these types of enrichment effects or an increase in harmful algal bloom events. The monitoring of algae (phytoplankton) in the water column in the Marlborough Sounds has not revealed an increase in their numbers around salmon farms. 18 International studies show that reduced oxygen levels can occur in the waters in and around farms due to the respiration of farmed fish and the microbial breakdown of seabed wastes. This effect is of most concern to the farmers themselves, as low oxygen can damage farmed fish stock. 19 In New Zealand, consenting processes ensure that salmon farms are sited in areas with sufficient water flushing, so dissolved oxygen concentrations are well maintained.
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Nutrient Cycling 20 Nutrients are released into the water column from waste material on the sea floor as part of the nutrient cycling process. Good water circulation minimises the impacts of nutrient enrichment by distributing and diluting waste products and soluble nutrients over a wide area, and encouraging oxygen and nutrient exchange between the seabed and the water body. 21 As part of the assessment of ecological effects required for a marine farm application in New Zealand, scientists take samples of sediment from the seabed at the proposed site and measure them for sediment size, organic matter content and redox depth (the depth at which sediment becomes anoxic). These parameters provide a very general indication of the natural level of nutrient enrichment at the site, which helps to predict the likely effects of the proposed farm on nutrient cycling. Enrichment values at the site are also compared with regional values to assess the site in the context of the wider area, and can also take into account the nutrient loads entering the system from the ocean, rivers and from land runoff.
Biodiversity Effects Community Changes 22 The artificial structures, fish wastes and uneaten food present at marine salmon farms all have the potential to affect local seabed communities and ecosystems. 23 One potentially positive effect is an increase in local biodiversity, through the variety of marine life attracted to farm structures. Wild fish aggregate around artificial structures like salmon farms, and fish in the vicinity of fish farms may feed on waste feed, thereby attracting larger fish. 24 Salmon farming also results in changes to communities and habitats directly below the farm. Particularly, they can reduce the abundance of species that are relatively intolerant of the enriched conditions which can develop below salmon farms. Other enrichment-tolerant species, like worms, can increase in abundance. 25 Both central and local government and the New Zealand aquaculture industry are clear that salmon farms, and other aquaculture, should be sited only in environmentally appropriate locations. As a result, salmon farms are generally not approved if they are proposed over reefs or complex habitats with a high diversity or abundance of species, and consequently applicants generally avoid such sites. 26 As part of the assessment for a new aquaculture site, the likely effects on general biodiversity as well as likely effects on fisheries – particularly important spawning or nursery habitats – are taken into account by decision makers. Diseased and Escaped Fish 27 Overseas studies highlight the risks of escaped fish altering the genetic structure of wild fish populations and transmitting disease from farmed stocks to the wild populations. These both appear to be relatively minor issues for New Zealand at present.
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28 New Zealand has few serious salmon diseases present, so disease is not a significant issue. As king salmon is not native to New Zealand, genetic effects from farm escapees will not impact indigenous marine biodiversity. At present the effects of escapee salmon are likely to be minimal, given the small scale of the industry and the limited salmon numbers in wild populations within existing grow-out regions. Marine mammals and seabirds 29 New Zealand is home to several species of dolphins, whales, and seals. The welfare of these species is carefully considered when assessing marine farm applications. 30 New Zealand fur seals can be a problem around salmon farms, leading farmers to use predator exclusion nets around most sea-cages. In approximately 25 years of sea-cage salmon farming in New Zealand there have been five entanglements of marine mammals in predator nets. Subsequent management responses by the industry (e.g. changes to net design, development of protocols for net changing) mean that entanglement is unlikely to be a significant ongoing issue. 31 Exclusion of marine mammals from critical habitat by finfish farms is highly unlikely at present in New Zealand, given the small scale of the industry. Risks from future development can be minimised by appropriate site selection. Effects of aquaculture activities on seabirds are considered by regional councils when they assess effects of a proposed marine farm. Marine farming is avoided in areas of particular importance for seabird feeding or breeding, especially for threatened seabird species. 32 Potential effects on seabirds relate mainly to habitat modification, entanglement in structures and habitat exclusion. Salmon farms may also provide roosts for seabirds.
Chemicals and Additives 33 New Zealand salmon farms use diets especially prepared for king salmon. These diets do not contain antibiotics, vaccines, steroids or other growth enhancers. 34 The feed contains zinc (concentrations of ~130 - 150 mg/kg), which is an essential micronutrient for the prevention of cataract formation and other health problems. Zinc can accumulate in sediments beneath fish farms and can be toxic in high concentrations. Feed companies are presently working to minimise zinc discharges to the seabed, mainly by reducing the content in the feed. 35 Copper can also accumulate in sediments below farms and, like zinc, can also be toxic in high concentrations. Copper comes from antifouling paint, used to reduce build-up of fouling organisms. New Zealand salmon farming companies actively minimise the use of copper antifoulant paints and use manual defouling as much as possible. Research is ongoing into other antifouling treatments as alternatives to copper-based paints. 36 The relative absence of salmon diseases and parasites in New Zealand waters means chemical treatments against these things are not used in New Zealand salmon farms. 37 Other chemical contaminants such as dioxins, polychlorinated biphenyls (PCBs) and heavy metals like mercury, are globally ubiquitous compounds that accumulate in animal In-Confidence
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In-Confidence tissue (including humans) via the food chain. In New Zealand, PCB and dioxin levels in seacage salmon are well within health guidelines stipulated by various regulatory agencies, and as such are unlikely to be a risk to the wider ecosystem or to consumers’ health. 38 The New Zealand salmon industry and feed supply companies implement various measures to minimise contaminant inputs to the environment, which will likely lead to reduced contaminant loads in the future.
Pests and Diseases 39 There is a relative absence of salmon diseases and parasites in New Zealand waters. However, like coastal shipping and recreational boating, marine farm activities are a potential vector for transporting unwanted and exotic marine species to new localities around the country. 40 Marine farms can also provide ideal habitats for some species, especially biofouling species. There is the potential for marine pests to establish on a marine farm, then multiply and subsequently spread into the surrounding natural environment. The pest may then cause changes to existing communities. Also, extensive biofouling by unwanted pest species could adversely affect the salmon farming operations themselves. 41 Good farm management is an effective way to minimise the spread of pests and diseases as well as maximise farm yield. The New Zealand aquaculture industry recognises that managing pests and diseases is important to the health of the environment and the aquaculture industry as a whole. 42 The salmon industry has been proactive in developing an environmental code of practice, part of which focuses on minimising the potential for further introduction of pests and diseases. This document complements existing MAF Biosecurity New Zealand guidelines.
Fish feed 43 If a fish’s nutritional needs cannot be met by the surrounding environment, supplementary feed is provided from commercial feed producers. Currently there are no commercial fish feed producers in New Zealand. Most fish feed is imported into New Zealand from Australia, with lesser amounts from Chile. 44 Fish feed may come from fish meal, fish oil, plant material and oils, as well as livestock by-products. Until recently, most fish feed consisted primarily of fish meal and fish oil. This is because fish meal and fish oil were cost effective, known to meet the dietary requirements of fish, and were easy for the farmed fish to digest. Research into the specific nutrient requirements for fish and nutrient balances and alternative protein sources has resulted in a steady decrease in the amount of fish meal and fish oil in most fish feed. This trend is expected to continue. 45 In New Zealand, most marine farmers use 15 percent fish meal in finfish diets. Trials are currently underway to reduce this percentage even further. Fish oil is also used in fish feed diets with the health needs of the consumer in mind. Some fish oil is needed in fish feed to help with the production of Omega-3s (long-chain polyunsaturated fatty acids) within the farmed fish’s tissue. In-Confidence
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In-Confidence 46 Currently most fish meal and fish oil are sourced from wild fish populations. World production of meal and oil is derived from forage-fish stocks in the coastal waters of Peru and Chile. The governments of these countries have management controls in place to determine when the fishery can be fished and for how many tonnes. 47 New Zealand Salmon Farmers have adopted an Environmental Code of Practice that includes where feed is sourced. The code states, “Raw materials must be sourced from sustainable fisheries such as Peru and Chile. The utilisation of alternative, sustainable raw materials in feeds should be optimised.”
References 48 Extensive references to international and New Zealand literature on the environmental effects of salmon, and other finfish farming can be found in the following documents. Forrest B, Keeley N, Gillespie P, Hopkins G, Knight B, Govier D. 2007. Review of the ecological effects of marine finfish aquaculture: final report. Prepared for Ministry of Fisheries. Cawthron Report No. 1285. 71p.
Ministry of Fisheries Aquaculture Unit Information Sheet - Aquaculture and the use of feed. 2011.
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