The Arctic Charr (or Char) Salvelinus alpinus, is one of fourteen species of bony freshwater fish included on Section 41 (relevant to England) of the NERC Act and one of ten species included on Section 42 (relevant to Wales) and the Scottish Biodiversity List. It is a close relative of two other native freshwater fish species of conservation concern; the Atlantic Salmon Salmo salar and the Brown Trout Salmo trutta. Although less well known than these close relatives, the Arctic Charr is a fascinating salmonid species, both in terms of its life history and its biology, which provides ecologists with conundrums both in terms of its taxonomy and its conservation.
It is a beautiful, slender fish, possessing the characteristic salmonid adipose fin on its underside, in front of the tail. It is the most brightly coloured of European salmonids, especially during the breeding season when the males (or ‘cocks’) in particular have vivid red bellies. Their back is greenish brown in colouration with silvery flanks containing bluish-grey, or light brown colours, with small red, pink or yellow spots. The UK rod and line caught record is a 9lb 8oz specimen caught in Loch Arkaig (Inverness) in 1995; however, much larger fish have been caught in other countries.
Distribution and Life History
The Arctic Charr is a Holarctic species, inhabiting both lakes and rivers throughout the northern hemisphere with around 50,000 known populations globally, the majority of which (~30,000) are to be found in Norway. This species exhibits the most northerly distribution of any freshwater fish and, at some northern latitudes, is the only fish species to be found in freshwater habitats.
The distribution of Arctic Charr within the British Isles is focused towards northern upland areas, with 258 Scottish lochs known to support this species (although it should be noted that this has not been verified in recent times, and some of these populations may have been lost, and undoubtedly others remain to be discovered). Their distribution throughout the remainder of the British Isles is sporadic, with 74 Irish populations and localised populations in the Lake District (eight) and north Wales (four).
It was thought that all stocks in the UK were landlocked, typically in deep lakes, whereas many of the more northern stocks exhibit brief migrations to sea. These migratory (‘anadromous’) stocks move to saltwater during the summer months (for up to eight weeks), during which time they may double their weight in preparation for reproduction during the winter months. However, in recent years a small number of large Arctic Charr have been caught by fly fishermen on the River Spey, and it was found that this population was from Loch Insh which were river spawning many kilometres upstream in the River Spey.
It is suspected that this species colonised the freshwater lakes of the UK as the glaciers of the last ice-age receded, and then subsequently lost their migratory tendencies becoming freshwater resident populations.
Arctic Charr spend most of the year in deep water (>10 metres) but come into shallow rocky and gravelly areas in November and December to spawn. In some lakes, they spawn in the springtime as well as in the autumn, which can lead to two temporally reproductively isolated populations. A low water temperature (<8°C) and good oxygenation due to wind or current action is required for successful development of the eggs. Animal plankton is their predominant food, although insect larvae are taken occasionally. Migratory Arctic Charr usually reach sexual maturity and spawn for the first time at four to ten years old, whereas lake-dwelling individuals spawn after two to five years
Arctic Charr are highly sensitive to decreased oxygen levels and increased temperature and thus eutrophication and climatic warming are major threats to the persistence of this species in the UK. Introduction and the spread of species such as Pike Esox lucius, Roach Rutilus rutilus and Rudd Scardinius erythrophthalmus are also potentially detrimental, competing with the Arctic Charr for living and spawning areas, as well as well as causing direct mortality. The Zebra Mussel Dreissena polymorpha in Northern Ireland is an example of how an invasive species can affect the Arctic Charr; having colonised the hard surfaces in the Shannon-Erne waterway it is now potentially having a negative effect on areas used as spawning grounds by the Arctic Charr.
The impact of coniferous afforestation and forestry practices on freshwater habitats in the British Isles has been cause for concern in recent years. The effects of each stage of the forestry cycle (ground preparation, tree planting to canopy closure, the maturing crop and felling) have the potential to lead to adverse impacts to local fresh waters.
The Arctic Charr is also highly prized sports fish, and is caught and sold for food. Consequently, without adequate monitoring and protection, populations could come under threat in the future due to overfishing. Infrequent spawning may also make it more susceptible to overfishing.
At least 12 populations of Arctic Charr in Scotland are known to have become extinct since they were first recorded, with four recorded extinctions in England, complete loss from one site in Wales and an estimated 25 extinctions in Ireland.
The Arctic Charr Complex
It has long been recognised that the Arctic Charr displays an unusually high degree of variance in phenotype (i.e. physical characteristics). This variance is directly related to the primary food source upon which a population (particularly when isolated) feeds. This ‘trophic polymorphism’ has been found to be most variable in the most northern populations. Within UK lakes, most populations are believed to be monomorphic (i.e. having multiple forms, with polymorphic (i.e. exhibiting multiple forms) populations generally containing two forms, although in Loch Rannoch, Scotland, a population containing three morphs has been identified.
Considerable variation can take place between (‘allopatric’) and within (‘sympatric’) Arctic Charr populations. Phenotype variation manifests itself across a wide range of characteristics including: morphology, size and colouration as well as in behaviour as life history (including habitat use, spawning location and the timing of reproductive behaviour). These populations are therefore ‘reproductively isolated’ and this, in turn, leads the way to genetic divergence.
So significant is the variation within Arctic Charr populations of the British Isles that taxonomists in the early 20th century described the existence of 15 different ‘Charr’ species. However, it is now accepted that these fish are all variants of one species. There have though been some recent moves to revise the taxonomy of Arctic Charr and ‘split’ this species into a number of individual species units based on morphology.
If this new taxonomy were to be accepted, the addition of numerous new species of Charr to the UK would result in significant consequences for freshwater fish conservation both nationally, and internationally. Further investigation in the coming years using genetic approaches should clarify the genetic situation with regard to this, the UKs most ancient of freshwater fish.
Arctic Charr Factfile: http://www.arkive.org/arctic-charr/salvelinus-alpinus/
FishBase – Arctic Charr: http://fishbase.sinica.edu.tw/summary/speciessummary.php?id=247
Behnke, R.J. (2002) Trout and Salmon. The Free Press, New York.
Esk Rivers and Fisheries Trust – Scotland’s Arctic Charr
Maitland, P.S., Winfield, I.J., McCarthy, I.D., Igoe, F. (2007) The status of Arctic charr Salvelinus alpinus in Britain and Ireland. Ecology of Freshwater Fish, 16: 6-19.