Inevitable escapes of carnivorous predators, sometimes tens of thousands at a time

● “Invasive alien species are one of the major drivers of biodiversity loss, and cause dramatic, and in some cases irreversible changes to ecosystems. They can produce substantial environmental and economic damage, […]”. Reference

● “Escapes of farmed salmon have serious negative consequences for the environment and the fish farming industry, and considerable efforts are being made to reduce these undesirable events.” Reference

● “When rough weather and poorly enclosed structures enable salmon to escape farms in large numbers, the predator fish endanger local species, destabilizing ecosystems and carrying contaminants beyond their farming locations, [Dr. Felipe Cabello, from New York Medical College] said.” Reference

● “It is an expected and accepted part of the aquaculture industry that farmed salmon frequently escape into the wider environment (Glover et al., 2020; Table 1). […] At all stages of growth where salmon are kept in nets there is evidence of both large-scale escape events caused by damage to cages, and the steady release of individuals – known as “drip” escapes – for example by stocking pens with fish small enough to pass through the netting (Wringe et al., 2018; Glover et al., 2017). The official statistics of farmed salmon escapes are considered by scientists to be a significant underestimate, reporting in some instances an estimated 12-29% of the true volume of escapes (Thorstad et al., 2008).” Reference

● “There is great uncertainty in such estimates, but the figures indicate that more farmed salmon escape than is reported to the Directorate of Fisheries, says [researcher] Utne.” Norwegian Institute of Marine Research

● “There is no clear correlation between the number of escaped farmed salmon within a production area and registered escape incidents, but we find escaped salmon in all of these areas even though no escapes have been reported there in the past year, says [researcher] Utne.”

“The reason for this may be, for example, underreporting of escaped fish, especially in small incidents, that the escaped salmon spread over large areas or that some stay in the sea for several years before reaching the rivers.” Norwegian Institute of Marine Research

● “Although most farmed salmon that escape die before reaching sexual maturity, a significant number of escaped salmon can migrate up rivers and spawn with wild salmon, especially if large salmon escape during the summer and autumn.” Norwegian Institute of Marine Research

“[…] large salmon escaping from fish farms in Ireland, Scotland, the Faroe Islands, and Norway during winter and spring move with the current and, during the following summer or autumn, may enter home water fisheries and spawning populations far away from the site of escape, when they become sexually mature.”

“Salmon escape from fish farms at all life stages, and they are caught in oceanic, coastal, and freshwater fisheries.” Reference

It has been shown that anywhere from 62-77% of escaped farmed salmon die of starvation in the wild; this still leaves 23-38% who don’t. Reference

● “Escaped farmed salmon can spread over large areas, which means that there is uncertainty related to how a production area is affected by escapes in other production areas.”

Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research

● “Information on the survival and migratory pattern of the escaped farmed salmon is sparse, but Hansen et al. (1987) demonstrated that farmed salmon tagged and released in Norway during summer were apparently ‘homeless’, and some of the immature fish were captured north of the Faroe Islands.” Reference

● “Interestingly, this includes Atlantic salmon caught in Alaska, even though Alaska does not allow Atlantic salmon farming, proving that the fish are capable of surviving and moving great distances after escaping.

“This suggests that while released farmed Atlantic salmon will compete with wild salmon for food, many also don't make the transition from being fed pellets in farms to catching and eating wild food. For those that do, though, stonefly nymphs found in the stomachs of Atlantic salmon caught in the Salmon River (Vancouver Island) suggest that escaped Atlantic salmon also can be predators in freshwater as well as in ocean ecosystems (McKinnell and Thompson, 1997).” Reference

● “Thousands of salmon escaped an Icelandic fish farm. The impact could be deadly.” “Suspected escapees have now been found in at least 32 rivers across north-west Iceland, according to unconfirmed social media posts, one of which showed fish covered in sea lice, a parasite that can be lethal to wild fish. Iceland’s Marine and Freshwater Research Institute (MRI) confirmed the farmed fish have been found in multiple rivers.” Reference

● “Most farmed salmon that escape "disappear" into the ocean and do not survive long enough to reach rivers to spawn. However, some manage to make the transition to a life in the wild and survive until they reach sexual maturity and migrate to freshwater.”  Norwegian Institute of Marine Research

● “Of the 189 watercourses examined, we have assessed that nine salmon rivers have high levels of escaped farmed salmon, that is, over 10% of farmed salmon, says [senior researcher] Wennevik.” Norwegian Institute of Marine Research

“Available evidence from the CIS and the AFS shows that escaped salmonids can impose a strong predatory pressure upon schooling fish, including two small pelagic species important to [Chilean] artisanal fishermen, such as Southern sprat and Chilean silverside, Odontesthes regia (Humboldt, 1821) (Soto et al. 1997; Niklitschek et al. 2001). and, to a smaller extent, upon juvenile Patagonian grenadier (Soto et al. 1997), a key resource for the local fishing industry.”

“Because predation upon juvenile and competition for pelagic prey with adult Patagonian grenadier, escaped salmon may also have indirect trophic effects upon southern hake, the most valuable fishery resource in the AFS.”

“More complex ecosystem effects have also been documented in freshwater ecosystems where permanent salmonid populations have become established.” Reference

“Escaped salmon also change the population density in a river or near aquaculture facilities which can lead to increased predation pressure not just for salmon, but for all wild fish in the environment (Bradbury et al., 2020). Reference

“The one study available finds that, based on biochemical analysis, 15% of farmed salmon tracked, survived on a diet of native fauna.” “Collectively, the evidence suggests that salmonid species have detrimental impacts on native fishes in all types of ecosystems, including lakes, rivers and inner seas, due to predatory and interference competition (Soto et al. 2006, Arismendi et al. 2009, 2012, García de Leaniz et al. 2010, Habit et al. 2010, Correa & Hendry 2012, Penaluna et al. 2009, Young et al. 2009, 2010).” Reference

“The observed diet in escaped salmonids includes fish, crustaceans, insects and molluscs, depending upon the escaped species, the habitat, the season and the release site (Brodeur 1991; Jacobsen & Hansen 2001; Soto et al. 2001; Haugland et al. 2006; Ciancio et al. 2008, 2010; Niklitschek et al. 2011b). Reference

● Escaped salmon frequently carry diseases at a higher frequency than wild populations and may alter the incidence of diseases and parasites in wild populations following escape (Madhun et al., 2017: Bradbury et al., 2020).  Reference

● Escaped farmed salmon “pose a risk to wild salmon and trout populations through transmission of disease and parasites (Jones, Bruno, Madsen, & Peeler, 2015).” Reference

“Giant escape event reported. As many as 14,000 salmon escaped at the beginning of May from Lerøy Seafood's facility at Reitholmen on Hitra in Trøndelag. Environmental crime, according to the Norwegian Association for the Conservation of Nature.” “The salmon weigh around 7 kilos and may be ready to spawn.” “The facility also had high levels of sea lice just before the escape.” “The salmon in the facility were infected with two serious diseases, bacterial kidney disease (BKD) and PD (Pancreas disease). Because of this, the facility was quarantined by the Norwegian Food Safety Authority.” Reference

“Farmed salmon escape their ocean based cages through continuous low-level leakage and in much larger numbers often associated with the collapse of open net-pens. Infrastructural issues such as net damage are also primary causes while adverse weather, improper handling, and human factors contribute to escape events.” ScienceDirect

“Some of the 1 million Bakkafrost salmon initially believed to have been killed by a storm in the Faroe Islands may have survived and escaped, it has emerged.” Reference

At least 27,000 farmed salmon, weighing an average of 5.5kg each, escaped from a single cage when a storm damaged the outer ring of a feedlot pen, triggering a major recapturing effort.

“The industry apologizes and apologizes, while the salmon escapes and escapes. Now it must end. The farming industry must switch to closed cages, or other technology that prevents the escape and spread of salmon lice,” says a Member of Norwegian Parliament. Reference

14 cages at eight locations have been affected by a storm in Norway, leading to reports of escapes or suspected escapes. The damage includes 4-5 m long tears in the nets. Reference

“Following the escape [of farmed salmon from a feedlot in Maine, USA], divers inspected the nets to determine how the seals got into the cages. In accordance with farm management plans, the nets were confirmed to be properly tied, with a second layer of predator netting in place around the primary netting.”

“… ‘government needs to responsibly manage predator populations.’” – “said Joel Richardson, vice president for public relations for Cooke Aquaculture USA [the salmon farming company in question].” Reference

One of the common reasons that escapes occur is because predators are attracted to the high fish density in aquaculture facilities and damage the nets trying to reach the fish (Callier et al., 2017). Reference

“Hundreds of farmed salmon escape after pipe bursts on wellboat”

“The incident resulted in the escape of farmed salmon during the transfer of smolts from the company’s facility at Röndin in Kópasker to the well boat Ronja Fjord.” “In response, Kaldvík staff followed their emergency response plan and deployed nets to recapture the escaped fish. Despite a 13-hour effort, no fish were recovered.” Reference

“Details of the largest mass escape of farmed salmon in the last ten years, in which some 80,000 individual farmed salmon escaped into the Scottish wilds, are only now emerging, despite taking place almost two years ago.”

“The 80,000 salmon smolts, all of which were around 12 months old, were being transported by the Canadian-owned Cooke Scotland from Loch Shin. The fish were able to escape in transit via an unsecured hatch Cooke Scotland have put down to ‘human error’.” Reference

“The escape occurred when the salmon farmer was moving fish from one cage to another. One cage was damaged, and around 20,000 salmon were released through a large hole in the cage.” Reference

“Nadia Jdaini, senior communications adviser in the Directorate of Fisheries, told Fish Farming Expert's Norwegian sister site, Kyst.no, that it is normally work operations, and especially delousing, that lead to escape incidents.” Reference

“There are various reasons why salmon escape from fish farms, but escapes often occur in connection with work operations and fish handling.” Norwegian Institute of Marine Research

“Arctic Fish reported the escape to authorities on 20 August after it discovered two ‘small holes’ measuring 20 by 30 centimeters in its net pens.”

An estimated 3,500 fish with an average weight of 5.5 kg escaped.

“The company activated its response plan after discovering the holes, placing nets around the fish farm where the hole was discovered.” “Four of the salmon were caught with nets, […]” Reference

“Almost 14,000 salmon with an average weight of 7.3 kilos have escaped from a Norwegian site operated by Lerøy, one of the world’s top five Atlantic salmon farmers.” Reference