An Alternative Vision for Fish Farming

An Alternative Vision to Industrial Scale Open-Net Fish Farming – By Roger Cottis

As with all intensive farming methods, when the wider environment is directly involved, the effects on many impacted organisms often manifest themselves as problems to the Industry itself. With its current structure and methodology, the salmon farming Industry is a prime example.

Sea Lice & Disease 

Sea lice exist naturally and healthy wild fish are often host to a very small number, which pose no threat to their survival.  However, when up to a million captive fish are exposed to the same parasitic threat, they are unable to escape into fresh water where the parasites would not survive.Sea lice multiply uncontrollably, and hosts are plentiful and readily accessible in open-net fish farm cages.  The effect of such parasitism is that the affected fish are effectively eaten alive, hence the intervention with large doses of therapeutant chemicals.  Sea lice are increasingly becoming resistant to the conventional treatments, which eventually require wholesale culling of fish followed by road transportation to incineration sites many hundreds of miles away. This in itself is resulting in controversy, as reported on BBC’s The One Show on 12th December 2017[1]

The Scottish Government’s intention to allow intensive open-net salmon farming to double by 2030 will vastly increase sea lice larvae, allowing them to disperse on tidal currents and infest migratory salmonids.  This would simply exacerbate an existing problem, predictably leading to local extinctions of already vulnerable salmonid species.  In addition, an unintended consequence would be to impact fresh water pearl mussel populations, which are wholly dependent on salmonid species as hosts to their larvae in a symbiotic relationship.

Compounding the issue of sea lice, amoebic gill disease (AGD), Pasteurella skyensis and other piscine diseases are also becoming an increasing threat with additional unknown wider environmental impacts.  Multiple transports of dead salmon (‘Morts’) by sea and road from many local farm sites have been witnessed in recent times and act as a reminder of the seriousness of the problems facing the industry and government in denial of these massive problems.

There are a number of additional problems impacting our Scottish west coast marine biodiversity associated with the salmon farming industry:

Marine Pollution

Solid organic waste released by a single modern fish farm (12 x 120 m cages) directly into the sea is untreated and amounts to approximately 1,000 tonnes per annum.[2]  In 2015 there were 250 active fish farms in Scotland.[3] Therefore, total waste from Scotland’s salmon farms is currently of the order of 250,000 tonnes per annum. Every salmon farm creates a dense, anoxic bacterial mat on the seabed beneath the cages causing local extinctions of species and habitats, a situation which, apparently on scientific grounds, is condoned by the Scottish Environment Protection Agency (SEPA).  Dissolved inorganic waste, consisting mainly of dissolved nitrogen (N) as ammonia and urea, and phosphorus (P) as phosphates, is liberated from Scotland’s fish farms, estimated to be equivalent to the entire human sewage of Scotland.[4] But that was eighteen years ago, since when the aquaculture industry has expanded significantly.[5]  Today, dissolved N & P released from Scotland’s more numerous and larger fish farms greatly exceed the equivalent in Scotland’s untreated sewage.  Harmful Chemical residues in the form of therapeutants have also been a source of public concern, yet little is known of their long-term effects, other than that they are toxic.  The most frequently applied anti-sea lice pesticide, emamectin benzoate, is known to be toxic to birds, mammals, fishes and other aquatic organisms, particularly sea bed crustaceans.

Seals and cetaceans

Because seals naturally predate fish, they are attracted to industrial sized fish farms by all of the distress signals emitted by the fish when they register a predator is nearby.  This has the effect of stimulating hungry seals.  This is no fault of the seals, yet they are condemned to die, albeit under a government licence to shoot them if necessary.  Similarly, inshore cetaceans, typically porpoise, become distressed when acoustic deterrent devices (ADDs) are deployed. To an animal relying on its hearing for its survival, ADD emissions are at the very least painful and disorientating, depriving them of large areas of sea in which to hunt.

Modelling of the exposure time to exceed injury criteria for seals and porpoises at given ranges from active ADDs suggest that there is a credible risk of exceeding injury criteria for both seals and porpoises. Thus, the risk that ADDs at Scottish aquaculture sites is causing permanent hearing damage to marine mammals cannot be discounted”.[6]

There should be a moratorium on the deployment of ADDs until deleterious impacts on seals and cetaceans have been thoroughly researched. Here the precautionary principle[7] needs to be implemented to avoid detrimental impacts on such species as, bottlenose, white-beaked, Risso’s and common dolphins, orca, minke whale and harbour porpoise, which are now specifically protected under the Harbour Porpoise Special Area of Conservation (HPSAC).

Grey seals Halichoerus grypus and Common seals Phoca vitulina are listed under the:

  • Bern Convention Appendix III Protected fauna species[8]
  • EU Habitats Directive Annex II and V species

All species of cetaceans are listed under the:

  • EU Habitats Directive Annex II and V species[9]

This legislation needs to be fully implemented, monitored and respected.


Closed containment

Truly ecologically sustainable aquaculture cannot be guaranteed until salmon farming in open nets at sea is replaced by land-based closed containment. Closed containment systems, also known as Recirculating Aquaculture Systems (RAS) would eliminate all of the harmful impacts of salmon farming on our marine ecosystems as currently conducted. A transition to RAS should be the overriding aim of the Scottish Government for the development of salmon farming in Scotland. Land-based RAS already exist in other countries, notably the US and Canada, and are being developed globally to address these concerns fully. Therefore, it is incumbent on the Scottish Government to prioritise an Innovation Centre which specifically investigates RAS methodologies, ensuring that Scotland maintains its spirit of innovation and entrepreneurship.  It is no longer acceptable to dismiss RAS as not commercially viable simply due to cost.  The marine environment has been paying the cost of salmon farming for far too long.  Out of sight should no longer mean out of mind.  Given the accrued benefits of innovative development there will be parity with the costs of current open-net fish farming. A genuine cost-benefit analysis with all aspects included should be undertaken.

RAS designs are scalable, enabling large industrial sized units producing high outputs of quality, healthy fish. Because these systems are able to pump flows of water, the fish naturally swim against the current allowing their flesh to resemble that of wild fish which is not the case with farmed fish.  The land-based RAS design eliminates all (see Table 1.) of the problems already highlighted and, if combined with small-scale hydro and solar panel energy, further benefits will accrue.  Environmental responsibility is built into the systems allowing ecological principles to develop fish farming where by-products and waste can be integrated into energy production, fertilisers or algae farming.


To compliment large scale RAS, the design can be extrapolated to incorporate aquaponics (aquaculture combined with hydroponics) with additional benefits. Recirculated water is pumped from fish tanks via filters to a series of containers, which can produce fruit and vegetables by utilising fish waste as a source of nutrients before the same water is recirculated in the system[10].  Because these systems are scalable, they can be tailored to suit spatial conditions in remote and fragile coastal communities, producing sustainable jobs and where produce could be delivered in food yards and not food miles.

The Aquaculture Growth Plan to 2030 report[11] acknowledges that the industry faces significant problems. It would therefore be a rational conservation measure for the Government to instigate a moratorium on any further expansion of salmon farming until a consensus is reached on the way forward. A programme of phasing-in of closed containment facilities could then be initiated to start redressing the damage to our sensitive marine ecology.  Brown field sites could be targeted for new facilities and eventually even more jobs could be created in an ecologically sustainable way, especially when combined to produce, fish, fruit and vegetables.


  • Develop RAS at innovation and demonstration sites;
  • Develop aquaponics centres, especially in western Scotland as demonstration sites;
  • Introduce incentives to promote the development of RAS and finance this by levying a tax on the salmon farming industry. A similar approach has been successfully adopted by the Norwegian government to promote transition to sustainable electric vehicles.

Table 1.

Comparing the two systems, open-net and closed containment previously discussed under Mitigation.



Full of holes, open to the sea x No holes, fully contained
Waste disposed of in the sea x Waste contained 
Marine environment polluter x Not a marine environment polluter
Waste treatment non-existent,

therefore completely free x

Waste treatment for additional benefit available  
Waste is lost to the environment x Waste can be reused 
Waste is not recycled  x Waste can be recycled 
Pest & Diseases affect farmed fish x Pest & Diseases almost eliminated
Pest & Diseases affect wild fishes  x Pest & Diseases do not affect wild fishes
Pesticides & Medicines required x Pesticides & Medicines much reduced
Pesticides & Medicines pollute x Pesticides & Medicines do not pollute
Fishes escape  x Fishes do not escape 
Genetic contamination of wild fishes x No genetic contamination of wild fishes
Invasion by carnivorous

animals & birds x

Invasion by carnivorous animals & birds excluded   


Carnivorous animals & birds culled x Carnivorous animals & birds excluded
Cages damaged or destroyed by rough seas   x Tanks not exposed to rough seas 
Creates a few jobs  = Creates a few jobs  =
Contributes to local economy? = Contributes to local economy?  =
Fish feed contains wild caught fish as meal = Fish feed contains wild caught fish as meal =

By Roger Cottis on behalf of The Scottish Salmon Think-Tank[12], a member of Salmon Aquaculture Reform Network Scotland (SARNS).[13]

Extract from written evidence submitted to the Scottish Government, February 2018

[2] Data: e.g. ES DOC 6 APP 7.5.1a AUTODEP MODELLING REPORT (page 7)
[3] Munro, L.A., & Wallace, I.S. (2016). Scottish Fish Farm Production Survey 2015. Marine Scotland Science.
[4] Mcgarvin M. (2000). Scotland’s Secret? Aquaculture, nutrient pollution, eutrophication and toxic blooms. WWF Scotland.
[5] Total salmon production (Scotland, 2000) = 128,830 tonnes. Data: Stagg, R.M & Allan, C.E.T.  (2001). Scottish Fish Farms Annual Production Survey 2001. Marine Scotland Science.
Total salmon production (Scotland, 2015) = 171,722 tonnes. Data: Munro & Wallace, 2016 (note 3).
[6] (Establishing the sensitivity of cetaceans and seals to acoustic deterrent devices in Scotland)
[7] Principle 15 resolved by the United Nations, in Rio de Janeiro, 1992.
[10] (From 38mins 30secs.)



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