European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

Although this species' European population trend may be decreasing due to habitat degradation, the rate of reduction is not understood to approach the minimum threshold for Vulnerable under Criterion A (≥ 30% over the longer of 10 years or three generations). It does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. The regional population size far exceeds 10,000 mature individuals, and hence does not approach the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Therefore, the Arctic Charr does not currently approach the thresholds for any Red List criteria, and it is assessed as Least Concern for both Europe and the EU 27 member states.

This species has an extensive, partially discontinuous circumpolar distribution in the Holarctic region, within some parts of which, e.g., Ellesmere Island (Canada), it represents the northernmost freshwater fish in the world.

In the European region its range comprises Iceland, northern and western Fennoscandia, parts of the British Isles, northern slopes of the Alps, and the northwestern Russian Federation.

It has for several centuries been widely translocated both within and outside its native range, especially in Europe. In some countries, e.g., Austria, Norway, Sweden, this has led to uncertainty regarding the precise extent of its native range. It has been stocked in hundreds of naturally fishless, high-altitude lakes across the Alpine region resulting in its expansion to northern Italy, where it is unlikely to be native. A single introduced subpopulation is established in the Pyrenees mountains, Spain.

The typically small size of individual lakes, rivers and locations where extirpation events have occurred (see 'Population') precludes their depiction on the range map accompanying this assessment.

This species' European population size is unknown, but significantly exceeds the minimum threshold for Red List criteria (< 10,000 mature individuals). The regional population trend has not been quantified, but is suspected to be reducing based primarily on declining habitat quality (see 'Threats'). A number of documented extirpation events and site-scale declines have occurred since the mid-20^th century, e.g., in the British Isles, Alpine region, Fennoscandia and parts of the Russian Federation.

The number of subpopulations is unknown, but it is estimated that there are c. 30,000 in Norway alone.

Phylogenetic and phylogeographical analyses have identified five major genetic lineages, among which two are present in Europe. The Atlantic lineage includes continental Europe west of Finland, the British Isles, Iceland, southern Greenland and Newfoundland. The Siberian lineage occurs from Transbaikalia to the Taymyr Peninsula (Russian Federation) and Svalbard archipelago (Norway), the Bering lineage from eastern Siberia (Russian Federation) to western Alaska (United States), the Arctic lineage from northern Alaska to the Canadian Arctic, and the Acadian lineage from southern Quebec (Canada) to New England (United States). There exist a number of contact zones, e.g., between the Arctic and Atlantic lineages in western Greenland. Molecular research has also demonstrated that multiple phylogeographic sublineages exist within the Atlantic assemblage, some of which appear restricted to small geographic areas (see ‘Taxonomic Notes’ and 'Conservation').

This species is anadromous at northern latitudes, but below 65°N the majority of subpopulations are non-migratory and isolated in moderately deep, naturally oligotrophic, post-glacial freshwater lakes with a cold and well-oxygenated hypolimnion. A handful of potamodromous northern subpopulations are fluvial, adfluvial or migrate between different lakes within a particular river system.

Anadromous subpopulations are iteroparous and undertake annual migrations to their spawning sites in rivers and freshwater lakes. They spend 30-60 days in coastal areas of the sea during summer before returning to freshwater for autumn reproduction followed by overwintering in lakes or rivers, which in many cases freeze over for several months. Both adult and immature individuals undertake these seasonal movements, and they can double their body weight during the short summer period. The longest upstream migration recorded to date is c. 940 km.

Resident subpopulations inhabit lakes of most sizes and exploit all habitat and depth zones, having been recorded at depths of over 250 metres in some cases. They typically inhabit environments with depauperate fish communities and often occur in the absence of other species. A number of northern lakes and rivers are occupied by both resident and anadromous individuals. Some resident subpopulations occurring in the extreme north inhabit lakes with more-or-less permanent ice cover, e.g., Lake Arkvatn (Svalbard, Norway).

Anadromous individuals overwintering under ice tend to be somewhat sedentary, presumably in order to conserve energy, and at some locations do not feed at all. In general, they migrate to the sea in early spring, during or after surface ice breakup, with the precise timing dependant on latitude, e.g., June at 70°N in mainland Norway, July at 79°N in Svalbard. The seaward migration is preceded by physiological and behavioral changes (smolting), including the development of seawater tolerance (hypoosmoregulatory ability). The correct timing of these developments appears to be crucial for successful completion of the life cycle (see 'Threats').

The diet of anadromous individuals at sea mostly comprises zooplankton and smaller pelagic fishes, but may also include littoral zoobenthos and surface insects. The diet of fluvial subpopulations is not well-understood, but is likely to be dominated by benthic and drifting invertebrates.

Resident lacustrine subpopulations demonstrate high flexibility in feeding preferences with a tendency towards exploiting the pelagic (for zooplankton) or profundal (for zoobenthos) zones when in competition with other fish species. Diet segregation along this benthic-pelagic resource axis has also occurred repeatedly within subpopulations occupying deeper lakes. A number of these systems contain between one and four sympatric morphological forms, among which one or two are epibenthic zoobenthos feeders, one is a pelagic planktivore and one is a piscivorous form. Feeding preferences may also switch between different seasons, with zooplankton favoured during warmer months of the year and zoobenthos in winter. Cannibalism, i.e., the consumption of conspecifics, is also common, especially in larger-bodied forms occupying more northerly latitudes.

This species is also noted for its phenotypic diversity, which can be particularly extreme within some lacustrine subpopulations. This sympatric polymorphism is typically related to resource partitioning, and the different forms tend to vary in meristic characters (e.g., gill raker counts), colour pattern, growth rate, adult size, age of maturation, reproductive timing, spawning site selection and parasite fauna. The majority of known cases have occurred within the Atlantic genetic lineage (see 'Population'), but examples have also been identified in the Arctic and Siberian lineages.

There exists a degree of reproductive isolation from very low to complete between such sympatric forms, and this has led to differing levels of genetic divergence. These often-unique combinations of genetic and phenotypic variability have also generated considerable taxonomic confusion (see 'Taxonomic Notes').

Sexual maturity is reached at 2-15 years of age and maximum lifespan appears to be c. 33 (usually c. 15) years, depending on latitude, hence the generation length is variable. Resident individuals tend to reach a smaller adult size (generally < 35.0 cm standard length) compared with anadromous individuals (up to > 70 cm), and size at maturation between subpopulations is also highly variable, with reproductively active individuals weighing from three grammes to 12 kilogrammes or more. Fecundity may be extremely low (< 20 eggs per individual) in small-bodied resident forms, whereas it is much greater (up to 9000+ eggs per individual) in larger anadromous forms.

Sub-arctic anadromous individuals normally spawn on an annual basis once mature, whereas at higher latitudes they may require more than one summer to regain fitness and in some years forgo migration to the sea.

In lakes, spawning most often takes place on coarse, well-washed stony substrata in shallow littoral or sublittoral habitats, although some specialised forms spawn at much greater depths. A few subpopulations are known to migrate short distances into affluent rivers where they spawn in gently flowing reaches. Anadromous subpopulations tend to select clean gravel beds in flowing river stretches and display fidelity to particular spawning sites. In many cases, the presence of relatively large, deep and unclogged interstitial spaces is believed to be essential for egg development and to reduce predation.

With the exception of some benthic or profundal lacustrine forms, reproductive individuals tend to develop a particular red, orange or yellow epigamic colour pattern, which is often very striking and sometimes more intensive in males.

Most subpopulations spawn over a condensed period of two to three weeks in autumn or early winter, although a handful do so in spring. In addition, different morphological forms with contrasting reproductive strategies may coexist within the same body of water. For example, in Lake Fjellfrøsvatn, northern Norway, a "normal" form spawns in the littoral zone at depths of less than five metres during late September, while a small-growing profundal form spawns at depths of over 30 metres in February.

During the reproductive period, sexually mature males aggregate at spawning sites prior to the arrival of females, which tend to arrive individually and leave immediately post-spawning. Larger male individuals compete aggressively over positioning and the opportunity to spawn with females, while some smaller males may display sneaking behaviour. Males are polygynous, and successful individuals can spawn with multiple females over the course of a single season.

In subpopulations which reproduce during autumn and winter, the eggs hatch in spring after an incubation period of three to four months.

Since this species is a coldwater obligate, it is considered to be particularly vulnerable to the effects of altered temperature and flow regimes driven by climate change, especially at lower altitudes. Such changes may disrupt the timing of migration and smoltification in anadromous subpopulations, increase the likelihood of summer stratification in lakes inhabited by resident subpopulations, hamper the proper development of early life stages and interfere with food availability. Warmer temperatures may also favour the abundance of potentially competitive fish species and exacerbate the effects of eutrophication (see below).

The trophic status of many lakes in this species' Eurasian range increased gradually from the 19^th century due to expanding urbanisation, increased discharge of urban wastewater and changes in agricultural practices. Raised levels of phosphorous and other nutrients lead to eutrophic conditions characterised by greater primary productivity, hypolimnetic deoxygenation, sedimentation of spawning sites and increased turbidity, plus altered zooplankton, macroinvertebrate and fish population structures. All of these factors can negatively impact Arctic Charr abundance and habitat quality, especially in small, shallow systems or deeper lakes inhabited by multiple sympatric forms.

Lakes in areas with rock-types of low pH-buffering capacity (e.g., granite) and acidic soils (e.g., peat) are susceptible to acidification. This process can be accelerated by anthropogenic factors such as afforestation, mining or peat-cutting, and can drive recruitment failure and extirpation of Arctic Charr subpopulations.

Industrial pollution, such as effluent from metal production and mining, has been reported to negatively impact some subpopulations, while others may be threatened by oil and gas development.

Some anadromous subpopulations are plausibly threatened by barrier construction and other forms of river channel modification, which may hamper access to their spawning sites. The widespread impoundment of lakes for urban water supply or hydroelectricity generation has in some cases led to fluctuating water levels and subsequent declines in resident subpopulations due to dewatering of spawning and nursery sites, e.g., Lake Inari (Finland), Loch Fad East (Ireland).

Resident subpopulations are often threatened by the introduction of non-native fish species due to competition, predation, hybridisation and transfer of disease or parasites. For example, in Europe the stocking or invasion of the predatory Northern Pike (Esox lucius) for recreational fisheries has been widely destructive, while introduction of whitefishes and/or ciscoes (Coregonus spp.) to improve the yield of commercial fisheries has driven site-scale extirpations through increased competition for food resources.

Other fish species typically introduced to European lakes exploited as recreational fisheries include Common Roach (Rutilus rutilus), Common Bream (Abramis brama), Eurasian Rudd (Scardinius erythrophthalmus) and Eurasian Perch (Perca fluviatilis), all of which may compete for both benthic and pelagic prey. In contrast to Arctic Charr, their abundance is positively influenced by nutrient enrichment and as their biomass increases, they can further accelerate the eutrophication process by reducing zooplankton to the point that nutrient cycling is impeded. The benthic Eurasian Ruffe (Gymnocephalus cernua), has expanded its European range in recent decades and is known to prey extensively on the eggs of other fish species. The congeneric and non-native Brook Trout has also been introduced to some European lakes and may pose a threat through introgressive hybridisation.

Moreover, the often unregulated stocking of hatchery-reared Arctic Charr can lead to a loss of native genetic diversity, especially when brood sources are derived from divergent evolutionary lineages. This has driven a complete replacement of ancestral genotype in some lakes where wild stocks have been reinforced with non-native hatchery individuals, especially in systems that have suffered from anthropogenic pollution.

The stocking of hatchery-reared individuals of any fish species also increases the risk of introducing novel pathogens or parasites to native fish communities.

In Fennoscandia, introduction of the benthopelagic crustacean Mysis relicta to a number of lakes between the 1950s-1980s resulted in the decline of resident Arctic Charr subpopulations due to competition for zooplankton resources.

The invasive Zebra Mussel (Dreissena polymorpha) and Quagga Mussel (D. bugensis) are invasive Ponto-Caspian molluscs that have been introduced to some locations occupied by Arctic Charr and represent a plausible threat due to their propensity to alter zooplankton abundance, community structure and composition. They may also colonise charr spawning sites and thus negatively impact reproductive success.

The introduction of modern monofilament gill nets during the mid-20^th century resulted in the overexploitation of some resident subpopulations in northern Europe, including Svalbard, while some anadromous subpopulations, e.g., the Tana River (Norway and Finland) plus several rivers in the northern Russian Federation, are also threatened by overfishing.

This species supports valuable commercial and recreational fisheries throughout much of its range, with both anadromous and resident subpopulations harvested for human consumption.

For example, c. 20 metric tonnes are landed annually in the major lakes of Switzerland, while much larger commercial fisheries operate in Fennoscandia and the Russian Federation. Sometimes unauthorised overfishing has occurred at some locations since the mid-20^th century, and is believed to have driven a number of subpopulation declines (see 'Threats').

Widespread stocking and translocation for both commercial and recreational fisheries has taken place in Fennoscandia since the late 19^th century, although many such introduction attempts have failed. In northern Fennoscandia, it was historically stocked into many high altitude lakes located along the reindeer migration paths of the Sámi people.

Some commercially-exploited fisheries are today sustained only by stocking. For example, almost three million individuals were released annually in Swiss lakes between 1994-2013. In Lake Geneva, stocked fish accounted for 65–92% of harvest during the 1980s, but this has since declined by at least 25%.

Research aimed at determining the suitability of Arctic Charr for aquaculture has been ongoing since the late 1970s. It is currently farmed in a number of European countries including Iceland, Ireland, Switzerland, Denmark, Norway, Sweden, Estonia and Finland. In Norway it is raised in hatcheries and marine net-pens, and in Denmark it is hybridised with the non-native Brook Trout (Salvelinus fontinalis) for put-and-take recreational fisheries.

Outside of its native range, the Arctic Charr is considered a delicacy in the Autonomous Province of Trento, Italy, where it is intensively-produced in aquaculture facilities and has been designated the European Union's Protected Geographical Indication (PGI) quality logo. It is promoted to drive fishery‐related and gastronomic tourism and its range expansion continues to be supported by official stocking programmes, in some cases within the boundaries of protected areas.

Recreational anglers in Switzerland harvested more than 10 metric tonnes of char annually between 2004 and 2015, but such fisheries are relatively minor outside of the Alpine region.

This species is not included in any international wildlife legislation, but occurs within the boundaries of numerous National Parks and other protected areas throughout its range. In the EU 27 member states, some of these are included in the European Union's Natura 2000 network.

It is nationally or regionally protected in some countries, e.g., in Ireland it is listed in the National Fisheries Act, in the United Kingdom it is a priority species of conservation concern in the national Post-2010 Biodiversity Framework, subpopulations from Transbaikalia are listed in the Red Data Book of the Russian Federation.

In some countries it is also considered to be threatened, e.g., it was most recently assessed as Vulnerable in the National Red Lists of Ireland (2011) and Switzerland (2022), and Endangered in France (2019).

Investment in wastewater treatment facilities and other policy-led measures developed since the 1980s has driven an improvement in water quality and partial stock recovery in some European lakes. Some subpopulations may also have benefitted from European Union legislation covering protected areas (Habitats Directive 92/43/EEC) and water quality (Water Framework Directive 2000/60/EC).

Many European subpopulations are maintained by annual stocking, although the evolutionary consequences of such schemes remain poorly understood and non-native evolutionary lineages have often been utilised (see 'Threats'). In some countries, there is a general trend towards stocking only with individuals derived from their respective native subpopulations, e.g., in Germany the interchange of eggs or fry between lakes has been prohibited since around the turn of the century.

In Ireland, regular stock surveys are carried out at the majority of locations inhabited by extant subpopulations within the framework of a National Research Survey Programme administrated by Inland Fisheries Ireland. Efforts to improve water quality have taken place at some locations, e.g., Lough Conn, and other proposed actions have included public awareness campaigns regarding the introduction of non-native species, reduced afforestation in catchments with a low buffering capacity and management of charr farms operating in Ireland to establish where the origin of domesticated fish and prevent escapes.

In Scotland, a handful of Arctic Charr stocks have been successfully translocated to establish "refuge" subpopulations at new locations.

In Norway, some subpopulations have been enhanced by stocking programs to compensate for the negative consequences of hydropower development.

Closed fishing seasons, bag limits and minimum legal-size rules are established in some countries, where they have been applied to both anadromous and resident subpopulations. Fishing regulations may also vary depending on whether water bodies are publicly- or privately-owned.

The taxonomy of Eurasian charrs is in need of review (see 'Taxonomic Notes'), and it has been widely recommended that their conservation management must be considered independent of their systematic classification. Each subpopulation should therefore be assessed individually, taking into account its evolutionary and genetic significance coupled with the ongoing population trend and threats to result in a priority ranking permitting the effective allocation of conservation resources through the development of site-specific, catchment-scale management plans. Sympatric morphological forms should also be managed separately, depending on their respective habitat preferences, diets and life histories. The abundance trends of many subpopulations remain unknown, and their individual assessments should ideally form the basis of future research efforts in order to ensure appropriate prioritisation. In practice, such efforts should ideally be coordinated at local, national or regional scales.