Arctic Grayling

Arctic grayling (Thymallus arcticus) is a species of freshwater fish in the salmon family (family Salmonidae) of order Salmoniformes. It comprises five subspecies native to the Nearctic and Palearctic ecozones. T. arcticus is widespread throughout the Arctic and Pacific drainages in Canada, Alaska, and Siberia, as well as the upper Missouri River drainage in Montana.In the US state of Arizona, an introduced population is found in the Lee Valley Reservoir and in lakes in the White River Mountains. They were also stocked at Toppings Lake by the Grand Tetons.

Several life history forms of Arctic grayling occur: fluvial populations that live and spawn in rivers; lacustrine populations that live and spawn in lakes; and potamodromous populations that live in lakes and spawn in tributary streams.

The upper Missouri River basin population once merited a high priority for Endangered Species Act (ESA) listing by the US Fish & Wildlife Service (FWS). This unique southernmost population is now extirpated from all areas of the basin with the exception of the Big Hole River watershed. In preparation for an ESA listing, the US FWS began implementing a "Candidate Conservation Agreement with Assurances" (CCAA). This agreement would protect cooperating landowners from being prosecuted under the ESA "takings" clause so long as they fulfil specific obligations, spelled out in a contractual arrangement and intended to restore the dwindling population. The CCAA, however, is now in doubt. On 25 April 2007, the FWS removed Big Hole River grayling from ESA candidacy based on arguments that (1) the rarer fluvial populations should not have been "lumped together" with the more common lake-dwelling populations and (2) the Montana grayling populations are insignificant and their loss would be inconsequential given the presence of thriving populations in Alaska.

On 8 September 2010 the U.S. Fish and Wildlife Service announced a revised 12 month finding on the petition to list the upper Missouri River Distinct Population Segment (Missouri River DPS) of Arctic grayling \ as endangered or threatened under the Endangered Species Act finding that listing was warranted but precluded in the current fiscal year by higher priority listings. The Service has added the species to the candidate species list and will work on developing a proposed rule for listing as priorities allow.

T. arcticus grows to a maximum recorded length of 76 cm (30 inches) and a maximum recorded weight of 3.8 kg (8.4 pounds). Of typical thymalline appearance, the Arctic grayling is distinguished from the similar grayling (T. thymallus) by the absence of dorsal and anal spines and by the presence of a larger number of soft rays in these fins. There is a dark midlateral band between the pectoral and pelvic fins, and the flanks may possess a pink iridescence. T. a. arcticus has been recorded as reaching an age of 18 years.

The Arctic grayling occurs primarily in cold waters of mid-sized to large rivers and lakes, returning to rocky streams to breed. The various subspecies are omnivorous. Crustaceans, insects and insect larvae, and fish eggs form the most important food items. Larger specimens of T. arcticus become piscivorous and may even take small aquatic mammals, such as lemmings. The immature fish feed on zooplankton and insect larvae.

Spawning takes place in the spring. Adult fish seek shallow areas of rivers with fine, sand substrate and moderate current. Males are territorial and court females by flashing their colourful dorsal fins; the fins are also used to brace receptive females during the vibratory release of milt and roe. The fish are nonguarders: the eggs are left to mix with the substrate. Although the Arctic grayling does not excavate a nest, the highly energetic courtship and mating tends to kick up fine material which covers the zygotes. The zygote is small (approximately 3 mm in diameter) and the embryo will hatch after two to three weeks. The newly-hatched embryo remains in the substrate until all the yolk has been absorbed. They emerge at a length of around 12 to 18 mm (0.5 to 0.7 inches), at which time they form shoals at the river margins. The juveniles grow quickly during their first two years of life.

As is the grayling (T. thymallus), the Arctic grayling is economically important, being raised commercially for food and fished for sport.

The species is sensitive to pollution and, although it has been extirpated from portions of its range, it remains widespread elsewhere and hence is not listed on the IUCN Red List of threatened species.

Obsolete synonyms for T. arcticus include T. montanus, T. signifer, and T. tricolor. The species is also known as the Alaska grayling.