The problems around sea lice proliferation in open-pen salmon farms
Overview
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“[The sea louse] C. rogercresseyi was recorded for the first time in Chile on Atlantic salmon reared in the Puerto Montt area (42ºS) (Figure 1). Today C. rogercresseyi is widely distributed in Region X, and has also spread south to Region XI (45ºS) (Figure 1).”
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“In 1998 [the sea louse] C. rogercresseyi was also reported on anadromous brown trout (Salmo trutta) in the south of Argentina (51ºS) (Figure 1) (Bravo et al., 2006). The discovery of C. rogercresseyi in the south of Argentina, one year after the record of this louse in Chile, was attributed to the migratory behavior of the native species rock cod Eleginops maclovinus.” [Eleginops maclovinus is the scientific name for Falklands mullet.]
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“As the Falkland’s native Zebra Trout and the Falklands Minnow are both considered to spend time in coastal waters when they are young, they may be particularly vulnerable to sea lice from salmon farms during a critical life stage.” Reference
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● “Sea lice feed on mucus, skin and blood and, if the number of parasites becomes high enough, can cause mortality in the hosts. Physiological effects of salmon lice on salmon, sea trout and char have been thoroughly studied, and include, among other things, increased levels of the stress hormone cortisol, problems with the water and salt balance and reduced immunological capacity, especially when the lice develop from sedentary larvae to mobile lice.”
“The large production of salmon and rainbow trout in open cages along the Norwegian coast gives the sea louse many hosts and thus a good food base, which leads to unnaturally high populations of the parasite in farming-intensive areas.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
● “Sea lice are parasites that feed on skin, blood and mucus of fish such as salmon (Barrett, Oppendal, Robinson, & Dempster, 2021). They leave painful open wounds and ulcerations, leading to stress, anaemia, reduced growth, reduced osmoregulatory and respiratory ability, impaired body defences, risk of secondary infections and, ultimately, death (Erkinharju, Dalmo, Hansen, & Seternes, 2020). They naturally occur in the environment but at a much lower incidence; the high concentration of fish on farms however provides the ideal environment for these parasites to flourish (Tett et al, 2018).” Reference
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“Parasites occur naturally in the wild, but confining large numbers of farmed salmon in open net-pens over long periods of time creates artificial environments for parasites like the sea louse to multiply and spread. Their eggs are dispersed by the currents and can travel freely into and out of net-pens.” Reference
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“Sea lice, though often framed primarily as a problem for wild Atlantic salmon, also have negative impacts on many other salmonid and non-salmonid wild fish populations. Notably, Atlantic salmon farms have a profound impact not just on the fitness of sea trout, but also on their behaviour, and the influence of high sea lice densities transmitted from farms is acting as a strong selection pressure against anadromy in brown trout.” Reference
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“Experts of the fish farming industry claimed that sea-lice would not become a problem in Iceland due to the low temperature of the sea. That turned out to be wrong and the industry has had to poison the fjords on several occasions to battle sea-lice outbursts.” Reference
Sea lice treatments cause a third of all mortalities in farmed fish
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“None [of the sea louse treatments currently in use] are found to be fully effective, and many are harmful to salmon and regularly result in mortalities. Of the mortality data reported to the [Scottish] Fish Health Inspectorate (2020) between 2017 and 2019, over 2.6 million fish mortalities included ‘treatment’ in the explanation.” Reference
Chemical sea lice treatments are toxic to aquatic life
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“Released into the environment via fish faeces and uneaten food, emamectin benzoate is known to be toxic to crustaceans, including lobsters, crabs and prawns; it has been found to have negative impacts on benthic communities even at low levels.”
“SEPA announced eight years ago that it would be introducing stricter limits on its use, initially suggesting an outright ban; however, this regulatory change has seen substantial watering down and delay, concurrent with heavy lobbying by the major salmon farming companies in Scotland.” Reference
Farmed fish are fed pesticides
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● “Salmon farmers hold fish in tarped cages or well boats where they are bathed in products like Paramove® (hydrogen peroxide) or Salmosan Vet® (azamethiphos)
for a period of time in efforts to rid fish of lice. Afterwards, operators commonly discharge the treatment water into the open sea. Safety data sheets list both products as toxic or very toxic to aquatic life, with long-lasting effects.”
“Both chemicals have been associated with lethal and non-lethal impacts in other marine organisms including algae and aquatic plants, herring, shrimp, mussels, snails, sea stars and sea urchins.” Reference
● Deltamethrin and Azamethiphos are pesticides used for sea lice treatment baths. These toxins are later discharged into the sea where they are acutely toxic to crustaceans up to 39km2 around the salmon farms. Reference
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Hydrogen peroxide is used in bath treatments against sea lice infestations and gill parasites on farmed fish. After use it is discharged into the surrounding sea.
“Hydrogen peroxide is highly damaging to kelp and shrimp; with impacts on the latter occurring up to 1km away from a treated salmon farm. The far-reaching impacts of this non-regulated chemical on ecosystems across Scotland is highly concerning, considering the key role shrimp and kelp play in these environments and ecosystems.” Reference
Farmed fish are bathed in pesticides that are then discharged into the sea
Literally tonnes of sea lice chemicals are used in salmon farming regions around the world
“Chemical use within the industry has failed to decline even as the industry increasingly seeks alternative solutions, […]” Reference
Non-chemical sea lice treatments can kill farmed fish
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● “Warm water treatment increased mortality risk in salmon”
“Thermal treatment is a controversial method to control sea lice in the Atlantic salmon farming industry. This study aimed to complement the growing evidence base to document the impact of thermal treatments on salmon welfare, behaviour, physiology and health.” ScienceDirect
● “The latter method [thermolicing] involves heating water to temperatures of between 28 and 34 °C, which the salmon are pumped into and stay for about half a minute. The salmon probably perceive the water as scorching hot.”
“Experiments carried out by the Institute of Marine Research and the Norwegian Veterinary Institute show that the fish respond with pain behaviour – swimming in panic into the vessel walls, shaking their heads, splashing on the surface and losing body control. Most survive the treatment but are weakened by it. Some suffer a brain haemorrhage and die.”
“Norwegian farmed salmon is deloused on average every 73 days it is in cages in the sea. The methods involve sorting, crowding, pumping and other stresses that are all stressful for the salmon.”
“Situations arise that can damage gills, fins, eyes and skin, says the Veterinary Institute's latest fish health report. If the salmon is sick or weakened by infections, it cannot tolerate this handling as well. That's what a lot of fish are. Fish live in cages with up to 200,000 individuals and are susceptible to disease.”
“PAINFUL: To kill the lice, salmon are forced to bathe in water up to 34 °C. It's as if we humans were to bathe in 60-70 °C. Such mechanical delousing methods are now the main cause of salmon dying, according to the Veterinary Institute.” Reference
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“Hydrolicers use freshwater jets to physically remove sea lice from salmon, and can also cause physical damage to fish such as scale loss. It is a process similar to the thermolicer where fish are crowded and pumped from cages into delousing chambers.” Reference