Atlantic Salmon: opportunist carnivores roaming loose in the Patagonian sea

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By Tarsicio Antezana J.
Translation by George Chambers
Atlantic salmon (salmo salar) have been overexploited at the source and introduced to farms in the rivers, lakes and the Inner Sea of Patagonia without involving local communities or environmental impact studies being carried out. As a result of lax environmental and labour regulations, fish farming using cages has made this export industry very competitive and burdensome for its Chilean and foreign owners (especially those from Norway, Japan, Canada and China). It has left a clear mark on the environment and on the local communities, the so-called “expendable areas” and “by-products” of the industry. This environmental and social fallout has barely been documented by the Chilean State, by academics or by the aquaculture industry itself, but it has been persistently called out by the local communities, environmentalists and indigenous peoples.
Salmon outbreaks from Puerto Montt to Aysén
The escape of millions of salmon from farms suggest these accidents occur more often than one might expect. Between 1993 and 1996, around 1.5 million Atlantic salmon broke out of farms. Then, in 2005, another 700,000. In April 2007, another 5 million may have escaped from regions X and XI (1), and between 2010 and 2020, 4.5 million salmon (mostly Atlantic) escaped, amounting to 87 escapes in the last decade alone from Los Lagos to Magallanes. Among the largest outbreaks are 690,000 from a MOWI farm (formerly ‘Marine Harvest’) in Punta Redonda, Calbuco in 2018, and 875,000 from cages that collapsed in a BLUMAR farm Caicura, Hualaihué in June of this year. These outbreaks have led to much questioning and debate about:
1.    The range and dispersion patterns of escaped salmon in the Patagonian Inner Seas and the wider ocean.
2.    The feeding habits of escaped salmon.
3.    Their impact on biodiversity, resource populations, larval stages and age and reproductive groups.
4.    Changes in the food chain and the general (and complex) balance of local ecosystems.
5.    Their impact on the spread of disease and antibiotics among both fauna and local communities.
Scientific knowledge of the above is almost non-existent, despite Chile’s more than 40 years of aquaculture. The accompanying profits and economic growth for producers and exports do not tally with the industry’s scant contribution to scientific understanding of the Patagonian ecosystem. Let’s take a closer look at some of these issues regarding Atlantic salmon.
The feeding habits of Atlantic salmon
Salmo salar “feed on a variety of marine organisms including crustaceans such as euphausiids (krill), amphipods (tiny shrimp), decapods (the family containing crabs and lobsters) and fish such as capelin, sand eels, river herring, pejerreyes and small mackerel and cod” (2). Also forming part of their diet are squid, prawns and deep-sea North Atlantic fish. Young salmon feed on insects, invertebrates and plankton.
This feeding behaviour is classed as opportunist and generalist and is associated with highly diverse and variable environments, which attract pelagic, highly migratory organisms. This migratory instinct is their adaptive response to the difficulty of predicting where to find their preferred prey. In other words, these opportunist animals catch what they find while on the move or during feeding events and, rather than choosing, feed on whichever prey is most abundant or easy to hunt. To this end, they can suddenly change their hunting methods. These range from the filtration (or suction) of smaller organisms, to chasing, entrapping and tearing apart larger prey. Mackerel exhibit similar feeding habits along Chile’s coast and throughout their long-distance migration, as do many species of sardine.
Diet of Atlantic salmon currently loose in the Patagonian Inner Seas
The salmon and trout species in Patagonia, both farmed and wild, are all carnivorous in their natural environments of origin.
Knowledge of escaped salmon in Patagonia is scarce. Months after the alarming outbreaks in 1994 and 1995, which amounted to more than 4 million salmon, a study (3, 4) was carried out over 13 months in 6 locations between Puerto Montt and Aysén (around 1000km laterally and thousands of kilometres along the coast). Researchers collected and examined the stomachs of 189 Atlantic salmon and another 1329 of rainbow trout and Coho salmon, in order to describe a typical diet of generalist carnivores. 5 food types appeared frequently (e.g. fish, crustaceans), which when divided into lower taxonomic ranks totalled 42 distinct types of prey, and many more when viewed at species level. The most common prey found in the stomachs of Atlantic salmon were “pellets”, followed by fish and crustaceans, and a small number of molluscs and insects. The majority of the stomachs came from fish collected in regions associated with intense aquaculture (e.g. Chabuco), while a tiny proportion were collected from the only location in the study where there is no aquaculture activity (Pichicolo). Of the 79 stomachs that contained food, Atlantic salmon were found to have eaten native fauna (in unknown quantity) and pellets, and grew, but at a lower rate to that of farmed Atlantic salmon (1.3 vs 1.7) as well as Coho salmon and rainbow trout. This revelation, paired with dwindling catch rates, led the researchers to suggest that escaped Atlantic salmon do not adapt to the wild and disappear in less than 6 months after escaping. More recent consensus has amended these conclusions, confirming the generalist carnivore nature of this species as it impacts the native fauna of Patagonia (1.5). This shows us how crucial it is that we make greater efforts to scientifically analyse this situation. The analysis of 79 stomachs from 6 areas of Patagonia in the 1990s – when at least 4 million fish have escaped from farms – is clearly not sufficient to prove the gravity of salmon’s environmental impact in Patagonia.
We should point out that the above results pertain to salmon linked to cage farms, judging by the pellets that constituted most of their diet. However, little to nothing is known about how the fish spread into deeper waters or waters further from the farms.
The spread of escaped salmon
The escaped salmon tend to remain close to the farms for food, and many migrate to depths far from the cages. Even though they remain within 500km of the farm they escaped from, they are able to reach distances of up to 2000-4,500km, according to research undertaken in the North Pacific. It is often possible to recover a tiny percentage (<3%) of the escapees after a large breakout.
During experiments in which researchers freed and recaught salmon in two locations in Chiloé, salmon were observed as they travelled away from the farms. The most successful recapture attempts occurred within a radius of 400m in the first 24 hours. Researchers noted their dispersion while catching them at 1.8km in the first 6 hours and at 3km after the first 24hrs. By the third day, there were no more catches (6). This seems to confirm that a portion of the escapees rapidly spread far away from the farms, meaning the evaluation of this carnivorous fish’s impact ought to be calculated just as carefully in the areas closest to the farms as in areas further and perhaps deeper than the farming zones.
Consequently, the spread and migration of the escaped salmon in Patagonia raises many questions, such as the magnitude and geographic extent of the impact on biological communities and the ecosystem.
The impact on biodiversity and the food chain
It is very well established that both in its areas of origin, and where it is an exotic species, the impact of salmon as a generalist predator and competitor for the food of other species (Table 1), affects the biodiversity and the structure of food chains.
Studies suggest that:
a)    There is an inverse relationship between the number of native species and the abundance of individuals, with the number of salmon in 6 locations studied between Puerto Montt and Aysén.
b)    Escaped salmon, although tending to remain close to the farms and consume pellets, devoured a wide spectrum of prey ranging from planktonic crustaceans of 1-2mm to fish such as anchovy, pejerrey, sardine and mote, which in total amounted to 16 stomachs where other fish made up 20% of the findings. On a larger scale, it is not known what the proportion of each of these food items is, but it could be enormous: up to 25 pejerreyes or 40 motes on average per Coho salmon stomach.
c)    Fish species that live in schools, such as anchovy (Engraulis ringens), sardine (Sardinops sagax), mote (Normanichtyhs crockeri), pejerrey (Odontesthes regia) and young Patagonian grenadier (Macruronus magelllanicus) could be susceptible to predation by salmon.
d)    These and other prey consumed by salmon are also food sources for other endemic (native) fish, whose growth and biological sustenance could be jeopardised by escaped salmon. The added impact of competition is apparent when we look at bass, Patagonian grenadier, Chilean sandperch and Pacific sandperch, whose scarcity or disappearance along with other species has been reported by coastal communities and traditional fishermen.
These results confirm, by their feeding habits, that salmon are wolfish, opportunist carnivores that are highly skilled at trapping and consuming prey of a hugely diverse range of sizes and behaviours.
There may be some other, less well-identified prey also suffering the impact of salmon, such as Magellan Strait krill (Euphausia vallentini), Falkland sprat (Sprattus fuegensis), squat lobster (Munida gregaria) and schooling fish and crustacean larva, among others.
The impact of escaped salmon’s predation is also very clear to see when considering the competition they drive among many species that also feed on the prey mentioned above. Among these sea creatures are Southern hake, Snoek (or White snake mackerel), Hairy conger (eel) and even whales. The blue whale, well-known to eat krill in the Antarctic, has been spotted filtering large masses of krill (vallentini) at the ocean surface near Melinka. This planktonic shrimp is most abundant in the Patagonian Inner Seas and is a fundamental part of the food chain. 7, 8
Krill and other planktonic organisms (copepods, amphipods, stomatopod larva, etc.) and micronekton (miniscule squid and fish) are found in the stomachs of salmon in Patagonia (3, 4), but, troublingly, these organisms are also the prey of salmon in the north Atlantic (2). This could affect the structure and sustainability of the food chain and the ecosystem as a whole, since these prey occupy the bottom end of the food chain.
Assessing the impact of escaped salmon predation
There are not yet any quantitative assessments of the impact of salmon predation resulting from these large-scale breakouts in Patagonia, even after decades of aquaculture and lasting awareness of these accidents. However, evidence and scientific reasoning confirm that these salmon outbreaks have had a significant ecological impact on native populations and the entire ecosystem. A simple estimation based on the potential consumption by escaped salmon suggests so.
The latest escape (or loss) of 875,144 fish, with an average weight of 3.828kg, from BLUMAR’s farm in Caicura, Hualaihué, will result in salmon consuming 1,050 tonnes of native fauna in a single month (this is calculated using the daily metabolic requirements of each fish). For migratory fish with high birthing rates such as salmon, tuna or horse mackerel, food intake is estimated at 3% of bodyweight per day, which when applied to the biomass of 3,500 tonnes of salmon, is equal to 35 tonnes every day. Their estimated monthly consumption is equivalent to the average monthly catch of Falkland sprat (sardine) in 2019 (SERNAPESCA, 2020), or 70 blue whales, or 3,000 tonnes of Southern hake. This level of consumption could vary or be lower if the salmon are unable to find sufficient food and thereby die of starvation, as has been suggested (4), or if their metabolic rate is lower (e.g. 1% of bodyweight among salmon in captivity), the survival rate is lower or not all salmon escape, or if the salmon migrate towards the ocean. Without doubt, however, this simple estimation of the impact of predation and/or competition with other, native species that depend on the same food sources, is shocking.
Although estimating the impact on the entire food chain within the Inner Sea is a difficult task, given the complexity and variability of the system and prey species, along with our virtual ignorance of it, it is clear that at a local and immediate level, the impact on the entire ecosystem is dramatic when a massive escape occurs. A school of salmon as large as those discussed above would devastate everything in its path; upon finding a school of pejerreyes, sardines, krill or crab, you can expect these fish to enter a feeding frenzy and devour the school of prey until there is nothing left.
There is no doubt that escaped Atlantic salmon, as with other introduced salmon species, behave like opportunist carnivores in Patagonia, consuming a wide array of planktonic and nektonic species (and their larva). Efforts to recapture these foreign fish have clearly been ineffective. Even more so because they are considered the property of the company or farm they escape from, despite now living outside of the companies’ waters and subsisting in the scare marine environment that is public heritage. Their fishing and commercialisation by traditional fishermen is forbidden. This must change for the sake of the environment and common sense.
The impact of salmon’s free roam in Patagonia upon native populations could be devastating, as they are predators and competitors for food. It will have a significant effect on the food chain and the sustainability of the ecosystem, especially in the event of massive outbreaks.
However, the lack of rigorous scientific information on food chains before the advent of aquaculture (and the little or no investment making up for this shortcoming) not only undermines a quantitative environmental impact assessment, but allows for legal alibi denying or playing down such an impact, and thus makes it possible for companies to avoid responsibility for bad practices and decision-making. Institutional weakness and the legislation governing this mega-industry have shown it to be ineffective in successfully preventing, mitigating and controlling these “accidents” and their environmental and social fallouts. In effect, the massive outbreaks, on top of other catastrophic consequences that show us that salmon are unsuitable for farming, such as the creation of anaerobic conditions, should prompt the immediate end of this practice. However, the system has allowed these and other environmental impacts to be considered “insignificant”; with this arbitrary veneer of authority, the Environmental Impact Study has been circumvented and replaced with an Environmental Impact Statement from the same industry, aiding the approval and continuation of farming licenses.
The problem is as severe as it is because of factors beyond the outbreaks, such as:
1.    The pollution of the coast, sea floor and water column by organic overloading, which generates eutrophication, red seas and a sharp reduction in oxygen concentration levels.
2.    The introduction of various foreign diseases.
3.    The persistent and progressive influx of pesticides.
4.    The use and spread of extraordinarily high amounts of antibiotics, and a range of ramifications for coastal traditions and native peoples, in terms of safety and job insecurity.
All of this must make us rethink and question the environmental and moral desirability of farming exotic (non-native) species in Patagonia’s inner seas. Chile’s professional and institutional capacity for scientific research of the ecosystem, constituted by the Ministry of Environment and the recently-created Ministry of Science (along with the power of an under-secretary of the Ministry of Economy) has altogether been unable to comprehensively address the sustainability of the country’s marine ecosystems. At the national level, we hope for the creation of a Ministry of the Seas (closely tied to that of Mining or Agriculture) and locally, in Chiloé, an Institute for Marine and Cultural Sciences.
The author, Tarsicio Antezana, is an oceanographer and leads the citizen group Association for Defense of Environment and Culture

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