Migratory behaviour in the Arctic charr is highly variable (1). Certain populations make annual migrations from the sea to a freshwater lake or river. Other populations are sedentary and remain within their freshwater habitat throughout their lives (1) (2). Riverine populations have been known to perform migrations within the river system or may also be sedentary (1).
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 (1). After this period, the Arctic charr only spawns every two to four years, once the reproductive organs have redeveloped from the last season (3). Most individuals will only spawn around three times throughout their life (3).
The breeding behaviour of the Arctic charr varies greatly between populations, with some individuals spawning in freshwater lakes after migrating from the sea, and riverine populations finding areas with slow currents (1) (2). Spawning usually takes place onto a rocky or gravelly substrate (1) (2) (9). The male Arctic charr sometimes build a nest, which can be up to two or three metres in diameter, where it spawns with several females (1). Males can be very territorial during the spawning season (1).
In lake-dwelling populations, spawning occurs between autumn and early winter (1), with young fish usually emerging the following spring (9). However, different stocks are known to spawn at different times throughout the year (1). Once hatched, the young fish will remain hidden within the gravel and stones, only leaving to feed on insect larvae and small crustaceans (9).
The diet of the Arctic charr is mainly composed of small fish, amphipods, planktonic crustaceans, molluscs and insects (2). When feeding at sea, fish and larger invertebrates are taken (1) (3).
The Arctic charr is able to withstand freezing conditions and can gain weight in this environment, where other species would lose weight (3) (7). This species is known to form dense shoals in deep water (6).