The toxins in antifouling /
The dangers of mechanical net cleaning
Salmon farm infrastructure around the world is usually coated in toxic antifouling to suppress biofouling.
Whether copper-based or not, all antifoulants are extremely poisonous to marine life.
Mechanical net cleaning comes with its own set of alarming ecological hazards.
The Norwegian Institute of Marine Research publishes data for the antifoulants used on open-open salmon farm infrastructure
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Based on Norwegian antifouling usage data (see quote below), the equivalent of 68.4 tonnes of copper antifouling plus 15.2 tonnes of tralopyril, 1.6 tonnes of zinc pyrithion and 0.8 tonnes of copper pyrithion antifoulants would be required for the projected production of 200,000 tonnes of farmed salmon in Falkland waters.
Quoting the Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research:
“Several foreign substances are released into the environment from fish farming facilities, with the use of copper as an antifouling agent on the fish farming nets being the most significant. In 2022, the latest year we have consumption data for, 440 tons of copper were registered for use as an antifouling agent in aquaculture. This represents a 74% decrease from the peak year 2019 (1698 tons). At the same time, the consumption of the substitute tralopyril increased by 86% from 2019 to 2022 (from 53 tons to 98 tons). Two other substitutes; zinc pyrithion and copper pyrithion had a consumption of 10 and 5 tons respectively in 2022, approximately the same amount as in 2019. The increase in the consumption of tralopyril and zinc pyrithion/copper pyrithion means that these substances should also be included in future risk assessments.”
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Based on Norwegian data (see quote below) 54.7 tonnes of copper would be released into Falklands marine environment every year from antifouling for the projected production of 200,000 tonnes of salmon.
Quoting the Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research:
“Copper can be toxic to different organisms at different stages of development.”
“To avoid fouling, the nets are impregnated with an antifouling agent such as copper, in concentrations that are toxic to the organisms.”
“Over time, copper leaks into the water and is spread with the water flow, and some falls off and sinks below or in the immediate zone of the plant, depending on particle size, sedimentation rate and current pattern. This means that the seabed under and around fish farms can contain high concentrations, as the copper can accumulate over time. The largest contribution of copper from fish farming is copper oxide (Cu2O) used as a growth inhibitor on nets in the aquaculture industry.”
“If copper-impregnated nets are flushed or high-pressure washed, this leads to extra wear and increased emissions of copper particles into the environment around the facility. In the EU, it is assumed that 80% of copper used for antifouling is released into the environment. For 2022, this will amount to 352 tonnes.”
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● “Scientists sound the alarm: New poison has been detected in farmed salmon”
“The substance [tralopyril] used against bio-fouling in fish farms is sold as environmentally friendly and risk-free. The Institute of Marine Research has now found the poison in black halibut, krill, mussels and farmed salmon.”
● “The substance tralopyril causes poisoning in mussels, small sharks and other wild fish species.”
“Tralopyril is supposed to prevent organisms from attaching to the net cages of the sea pens and has been presented as harmless, but now it has been confirmed that it does not pass inspection. At least that is the conclusion of research published by Dagens Næringsliv [Norway’s leading business newspaper] under the heading ‘Poison in the fjords’. It says that the substance, which is used daily in Norwegian sea pens, has now been found, among other things, in mussels and halibut.”
● “Researchers have detected trace amounts of tralopyril, an antifouling agent, in farmed salmon fillets during a laboratory test.”
“Although the concentrations are minimal, Grøsvik calls the discovery concerning due to the lack of data on the impact of tralopyril, which is not naturally occurring and has no established safety limits for food products or animal feed.”
“In addition to salmon, tralopyril has been found in species such as blackmouth catshark, mussels, and krill.”
● “We also know that tralopyril bioaccumulates to high levels in mussels that grow on tralopyril-impregnated nuts so that it can be spread in the environment through the food chain. Tralopyril has been identified as belonging to several categories that are identified as dangerous substances in EU directive 67/548/EEC. In the sea, zinc pyrithione is quickly exchanged with copper to form copper pyrithione. Zinc pyrithione and copper pyrithione have been identified as highly toxic to several marine species. We plan to include tralopyril and Zn/Cu pyrithione in next year's risk assessment.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
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“Biocides from fish farm nets are threatening life below the surface of the sea along the Norwegian coast.”
“[…] the most common way is with a flushing robot that moves over the net and flushes away everything that grows with high-pressure nozzles. This releases a violent toxic cloud of algae, paint flakes, etc. full of biocides into the seawater, which spreads further into the fjord basin.”
“The large reduction in copper-based impregnation substances should actually have been a positive development, but the new substances that are now replacing the copper-based ones appear to be an even more serious environmental problem than the copper-based ones they were supposed to replace.”
“Both of these substances [tralopyril and zinc pyrithione] are highly toxic, and that is really the whole purpose of a biocide, to be as deadly as possible to the organisms you want to combat.”
“New mixtures can be used under the EU's transitional arrangements even if one of the individual substances is banned for use individually.”
“Neither tralopyril nor zinc pyrithione are approved for use, but are still allowed to be used today through the EU's transitional arrangement - until they have been investigated and possibly approved or banned.”
From this data, the antifouling requirements for the projected salmon production in Falklands waters can be calculated
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“Net cleaning waste can contain harmful cnidarians as well as associated pathogens.”
“Salmon were exposed to 41-fold elevated particle concentrations for up to 30.5h. “
“Hydroid particles spread to adjacent pens and dispersed up to 5.5km from a farm. “
“Biofouling is a serious challenge for global salmon aquaculture and farmers have to regularly clean pen nets to avoid impacts on stock health and farms' structural integrity. The removed material is released into the surrounding environment.”
“There is also increasing evidence of the association of parasites and pathogens with biofouling organisms and cleaning fragments.”
“The results highlight the potential risks associated with net cleaning: the dispersal of harmful cnidarian particles, associated pathogens, and non-indigenous species, thus underlining the need for novel farming or net cleaning technologies that prevent the release of potentially harmful cleaning waste.”
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“Biofouling growth on finfish aquaculture farms restricts water exchange, adds weight and drag to farm structures, and may provide an onsite reservoir for pathogens. Biofouling assemblages often include an abundance of cnidarian taxa [which include jellyfish], which possess harpoon-like stinging cells and associated toxins. Understanding and managing biofouling risks to farm productivity is important, including the impact of frequent cleaning events on fish health.”
“Average biofouling biomass reached ∼2kg per m2, and net occlusion peaked at ∼46%, after eight weeks of immersion.”
“There was no minimum size of anemone that did not have nematocysts, so a higher frequency of net cleaning to prevent anemones from reaching a critical size threshold is unlikely to improve fish health outcomes.”
“Finfish farming is consistently challenged by biofouling because of its impacts on submerged infrastructure (Fitridge et al., 2012; Bannister et al., 2019; Bloecher and Floerl, 2021). Salmon farms have considerable floating and underwater structures, including pontoons, mooring systems, weights, farm barges, and large quantities of netting to retain farmed stock (pen nets) and, in some instances, to exclude predators (predator nets). For example, a typical Norwegian salmon farm has approximately 50,000m2 surface area of submerged structures (Bloecher et al., 2015). Biofouling of nets can have important consequences for fish health because net occlusion restricts water exchange, lowering oxygen levels and waste flushing to heighten stress on farmed fish (Bannister et al., 2019). Biofouling growth also increases weight load and drag on farm nets by up to 10–fold (Bi et al., 2018), resulting in poor hydrodynamic performance and pen deformation with associated reductions in pen volume and inadvertent periodic changes in stocking density (Klebert et al., 2013).”
“However, uncoated nets are susceptible to rapid biofouling accumulation and must be regularly cleaned or washed to prevent water flow problems (Bloecher and Floerl, 2021). This is generally carried out in situ using specialised underwater high-pressure cleaning equipment. Cleaning must be carried out more regularly than for copper-treated nets to avoid significant accumulations that can negatively impact stock. While there are clear advantages to avoiding biocidal coatings on nets, in situ cleaning without waste retention produces temporary plumes of cleaning waste that may affect fish health and adjacent marine communities and habitats (Floerl et al., 2016; Bannister et al., 2019; Bloecher and Floerl, 2021; Østevik et al., 2021).”
“Biofouling assemblages on salmon farms in New Zealand often contain anemones and hydroids in high abundance. […] When disturbed, cnidarians can release harpoon-like stinging cells (nematocysts) containing toxins or stinging strands (acontia) that have large numbers of nematocysts. […] In addition to direct contact, net cleaning waste may contain whole and fragmented organisms, including cnidarian species, that can release stinging structures with associated toxins (Carl et al., 2011). Over recent years in New Zealand, farmed Chinook salmon (Oncorhynchus tshawytscha) exposed to this material during net cleaning operations have subsequently developed skin health issues (Johnston et al., 2021), although the cause of the lesions remains unknown. Injured fish are generally more vulnerable to pathogens, thermal stress, and other factors that increase mortality (Svendsen and Bøgwald, 1997; Madetoja et al., 2000; Småge et al., 2017).”
“Biofouling biomass increased significantly with immersion duration—analogous to periods between net cleaning […].”
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“Net cleaning debris causes gill necrosis. The primary threat from polyp stages comes from debris generated by net cleaning activities. Cleaning is accomplished by high pressure water blasting, or by manual brushing or scraping of the nets. Debris consists of stingy and abrasive components, both of which lead to gill injuries, amoebic gill disease, necrosis, and mortality (Bloecher et al. 2018; Bosch-Belmar et al. 2017).”
“As bad luck would have it, hydroid regrowth is stimulated by the mechanical action of net cleaning (Guenther et al. 2010). Laboratory experiments have demonstrated that tiny bits of hydroids left on the nets after cleaning are sufficient to regrow entire colonies, and the more frequent they are cleaned, the faster they reproduce.”
“Likewise, the tiny fragments created by the cleaning process act like seeds, flowing downstream and settling out to become new vigorously growing colonies.”
“Hydroid seeding can be compared to the broom scene in the Disney film Fantasia, where each effort to destroy the brooms simply resulted in more brooms. Downstream hydroid seeding is a serious issue affecting farmed and native species alike. In the short term, it leads to a higher biomass of medusae stinging the salmon and native species, and in the long term, the extra biomass permanently alters the function of the ecosystem.”
“Hydroid seeding downstream beyond the farms is a serious biosecurity issue and environmental hazard for other industries and natural habitats, with knock-on effects back to the farms in terms of increased bloom impacts; the biosecurity plan must consider this.”
“Positive Feedback Loop Between Jellyfish & Salmon Farming” by Dr Lisa-ann Gershwin, Director, Australian Marine Stinger Advisory Services Pty Ltd