Mass mortality events are becoming more common at open-pen salmon farms
Overview
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“Mass mortality events (MMEs) involve the sudden death of thousands to millions of fish. MMEs are a serious problem in marine finfish aquaculture globally and may become more common with climate change. They can entail significant asset losses; pose compliance threats to environmental and animal health, and occupational health and safety obligations; and may undermine social license to operate. MMEs may be defined as major accidents in that they require rapid mobilization of workers, vessels and other supports and working under pressure to a) investigate the extent and cause of the die-off; b) remove, transport, and dispose of dead finfish; and c) adjust farm design and practices to reduce future risk. As with other such events, MMEs have the potential to cause injury or fatalities to persons, damage to cages and vessels and also substantially reduce the welfare or number of fish. Still, no existing research has explored the potential aquaculture occupational health and safety (AOHS) hazards and risks associated with responding to MMEs.” 11 January 2023, Science Direct
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● “This year, as in the previous year, the farmers report high mortality rates for farmed salmon in the sea, mainly explained by persistent issues with sea lice and diseases.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
● “Treatment-related MEs [mortality events] were first reported in 2017 and saw a sharp increase in subsequent years, becoming the leading cause of MEs by 2020. Nearly all treatment-related MEs were linked to sea lice treatments […]” 30 December 2024
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“Mortality is an imprecise welfare indicator, but it is reasonable to assume that fish that die have experienced poor welfare before death, thus high mortality is considered a sign of poor welfare.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
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“Quantitative analysis of mass mortality events in salmon aquaculture shows increasing scale of fish loss events around the world”
“Using a global dataset of publicly available and government-collated data on salmon mortality events including nations responsible for the majority of salmon aquaculture, we document trends in mortality events, showing that in some of the major salmon producing nations of the world (in particular Norway, Canada, and the UK), mass mortality events have increased in frequency from 2012 to 2022.”
“We also show that the scope of mass mortality events has increased over time—that is, the upper bound of how many fish were killed in a specific mortality event has increased over time.”
“Additional environmental problems include existing and new diseases, sea lice, water quality problems, and harmful algae blooms. Living fish expel their wastes into water as a result of their bodily function while the decomposition of dead fish releases nutrients in the water, which causes algae blooms—making survival difficult for the remaining fish. In MMEs [mass mortality events], these challenges often appear to work in tandem: higher temperatures may lead to hypoxia, which in turn can be fatal for fish that are immune compromised due to disease.”
“MMEs have been recorded in most of the major salmon producing countries including Norway, Canada, Scotland, Ireland, Chile, the United States, and Australasia”
“The process of collecting and disposing of large volumes of dead fish may also have potential occupational health and safety consequences for workers involved in these labour-intensive and potentially risky tasks “
“In Chile in 2016 an MME at a production site in the Chiloe region caused by red tide resulted in the death of over 6 million fish, representing more than 12 per cent of annual production. The economic and social costs to the Chiloe region were significant: 4,500 people directly employed by the industry lost their jobs and the livelihoods of 6,000 inshore fisherman were affected, and even the tourism sector was affected because of the environmental impact associated with disposing of dead fish. The resulting economic devastation to the Chiloe region was such that it required government cash supports for affected households.” 7 March 2024
Nature (Nature is the world's leading multidisciplinary science journal)
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“Ironically, some of the methods employed to reduce fish loss and maximize fish production may increase the rate and scale of MMEs. For example, adopting new technologies and early warning systems as well as programs aimed at reducing the vulnerability of salmon to warming events, diseases and pest infestations through improved feeds or selective breeding, can lead to an increased sense of security and justify the growth of salmon in increasingly risky contexts. New technologies, improved feed, and early warning systems are aimed at addressing some of these risks that are a consequence of operating in increasingly variable environments. These include devices that measure temperature, water velocity, oxygen and salinity within the cage environment to remote sensing technology at larger scales that provide data on weather, currents and ocean temperatures. The more advanced systems use artificial intelligence to monitor fish behaviour using underwater cameras during feeding and to warn of potential disease outbreaks. Overall these systems aim to improve decision support in a context of a rapidly changing environment for fish farming in the ocean, but since they often attempt to promote productivity and create justifications for increased production capacity into riskier locations such as offshore and high energy sites, they have the potential to expose greater amounts of fish to hazards that can generate larger MMEs.”
“Fish farming technologies are geared to managing and controlling production in ocean systems that are changing in trend and variation that are difficult to predict and comprehend at short time-scales, which can lead to aquaculture disasters in the form of MMEs. Scholars in the field of science, technology and society have examined a wide range of disasters and have raised a number of problems with how these events are understood and how industry and regulators respond to them. First, disasters are often seen as a natural event associated with the natural environment (such as climate change or pathogens) that impact human designed production system. However, all disasters are the intersection of environmental hazards and human infrastructure and decisions. In the case of aquaculture, while MMEs in salmon aquaculture are often blamed on climate change or other environmental variables, close analysis of the events always reveals some form of human cause coupled with an environmental stress. Attributing cause to environmental variables ignores the important human dimension to disaster and can deflect responsibility and accountability. Second, these disaster risks are often introduced and can increase in frequency and scale when dependent on technology and infrastructure to produce in environments not naturally conducive to the scale of production. There is, then, a paradox where the increasing sophistication of systems of production can lead to greater risk of disasters, a concept termed the manufacturing of risk. The third and final point is that disasters are often a consequence of economic systems that are shaped by intense competition, financialization of industry, and a lack of regulatory oversight, since these processes can rush development while reducing emphasis on risk assessment. The attribution to natural factors, increased reliance on technology, and increasingly competitive industry are characteristics of global salmon aquaculture.”
“Finally, the expected maximum size of a mass mortality event differs from country to country, but is likely much larger than site and jurisdiction thresholds of concern for animal welfare, early warning thresholds, and capacity to respond to mortality events.” 7 March 2024
Nature (Nature is the world's leading multidisciplinary science journal)
Mass mortality events are increasing, often because of increased use of technology
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● More than 100 MILLION farmed fish died prematurely in Norway’s open pen cages in 2023, according to the Norwegian Veterinary Institute. That’s a higher number and a higher rate of farmed-salmon-mortality than ever before.
● “21,000 Mowi salmon died after severe drop in oxygen levels in the net pens.”
“This large loss of fish follows relatively shortly after another big animal tragedy. In July, about 60,000 salmon died during sea lice treatment in one of Mowi’s facilities in Skipningsdalen in Flekkefjord.”
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● “According to records published by the Fish Health Inspectorate, the number of fish that died [pre-slaughter] in 2022 was nearly double that of 2021 and triple that of 2020 – reaching nearly 15 million fish between January and November of 2022. The data show that fish mortalities have been rising sharply for several years.”
“15 million sentient animals dying in a 11-month period across Scotland’s salmon farms is a complete welfare crisis.” Reference
● “More than a million dead fish, the biggest mass die-off of farmed salmon in Scotland in a decade [which is when records began], have been recorded at a farm belonging to the UK’s largest supplier.
Many of its [Mowi’s] farms, including those in the Hebrides, are certified under the RSPCA Assured label, which guarantees higher animal welfare standards.”
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● “About 4.8 million salmon died in sea cage farming in the country's fjords last year, according to figures from the Icelandic Food and Veterinary Authority. It is still investigating the deaths of more than a million salmon at a fish farm in the East Fjords at the end of last year.”
“Over four and a half million salmon have died in sea pens each year for the past three years.”
● “The Icelandic Food and Veterinary Authority's Expert Council asks critical questions about animal welfare in salmon farming. The mortalities in salmon farming are considered to be so high that this is not justifiable from an animal welfare point of view and that this needs to be examined.” “The professional council MAST [Icelandic Food and Veterinary Authority] asks if salmon farming ‘has a real future’ in Iceland”
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“Four-day storm wipes out 1 million fish in Faroes”
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“Mass mortality event kills hundreds of tonnes of B.C. farmed salmon”
“Mass die-offs of farmed salmon are increasing around the world, with Canada experiencing some of the biggest and most frequent mortality events, according to a study published in March 2024.
“McCorquodale [DFO’s senior director of aquaculture management] officially told Proboszcz [a fish scientist with Watershed Watch Salmon Society] the die-offs were not isolated to a single farm, but ‘that elevated levels of mortalities have been occurring recently among farmed fish at farm sites in Clayoquot Sound, Port Hardy, Clio Channel, Esperanza, and Nootka,’ the email reads.”
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● More than 5,500 tonnes of dead salmon – equivalent to over a million adult salmon – were dumped at waste facilities in Tasmania during February 2025.
The deaths were primarily caused by a bacterium.
During this time, fatty chunks of salmon have been washing up on beaches.
● “About 1,149 tonnes of salmon farmed in Macquarie Harbour on Tasmania's west coast died between September last year and March this year, with the cause of death not reported.
The month of January recorded the highest proportion of mortalities, with 313 tonnes of dead salmon.”
“The expansion of the industry in 2012 is now being reconsidered by the federal environment minister, amid concerns around the impact on the endangered Maugean skate.”
“Macquarie Harbour is the last known habitat of the endangered Maugean skate.”
“The skate relies on dissolved oxygen, and conservation advice to Ms Plibersek last year identified the salmon industry as "the most important anthropogenic contributor" to the oxygen level in the harbour.”
Farmed salmon die in high numbers everywhere
Dumping dead fish
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“Dumping dead (including diseased) fish in landfill is a biosecurity risk as they are ‘potentially a reservoir for disease, an attraction for vermin, a contamination risk to land and water courses, can release methane and takes a considerable time to fully decompose’ (Newton, 2014).”