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Thymallus arcticus

By Michael Hsieh

Geographic Range

Arctic grayling inhabit a wide geographic area that includes the Arctic and Pacific drainages in Canada, Alaska, and Siberia. Historically, they were found throughout the Arctic as far west as the Kara River in Russia, as far east as the western shores of the Hudson Bay in Canada, and as far south as Michigan. Though they no longer occur naturally in North America apart from Canada and Alaska, the species has been introduced into some lakes of western mountain states such as Arizona and California and the upper Missouri River drainage in Montana. (Sepulveda, et al., 2013; Stamford and Taylor, 2004)

Habitat

Arctic grayling live in high-elevation, mid to large, cold (8 to 11°C), and clear freshwater lakes and rivers. They are obligate cool or cold water dwelling species. They migrate several times per year. In the early spring, individuals migrate from overwintering habitats to rocky streams for spawning. Individuals then move to summer feeding areas before finding a suitable wintering spot, where they spend 8 to 9 months under ice. Arctic grayling typically overwinter in a lake or sections of a stream that are downstream of feeding areas. Larger fish are usually found in cooler upstream reaches of the river, while juveniles typically live in downstream and lower reaches of rivers. A possible explanation for this pattern is that water downstream is typically warmer than water upstream, helping to speed growth. Another hypothesis is that larger fish that are upstream have a feeding advantage because they have first access to drifting prey. (Baccante, 2011; Hughes and Reynolds, 1994)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Arctic grayling have an elongated, laterally-compressed, and trout-like body. Like many fish in the family Salmonidae, they have short heads, large eyes, small, toothed mouths, and forked tails. Arctic grayling are approximately 15 to 36 cm long, with an average weight of 1 to 2 kg. The largest individual on record was around 76 cm long and 3.8 kg. The dorsal surface of the body is often the darkest, with dark-purple or blue-black to blue-grey coloring. The sides have tiny scales exhibiting a variety of colors, from iridescent gray to light greenish blue. Patterns of numerous V-shaped or diamond-shaped spots are also common. The dorsal fin is sail-like, with as many as 17 to 25 rays, and is sometimes taller than the width of the fish’s body. They are usually marked with black and a narrow, vividly colored band on the top edge with orange to bright green spots on the bottom. The pelvic fins can have bright colors, such as pink or orange stripes. Grayling that live in the clearest waters tend to exhibit brighter colors. There is sexual dimorphism in coloration, with males having more orange, light green, and blue colored scales than females, which have more dull and dark colored scales. ("Arctic Grayling (Thymallus arcticus)", 2013; "Arctic Grayling Recovery", 2012)

  • Sexual Dimorphism
  • male more colorful
  • Range mass
    3.8 (high) kg
    8.37 (high) lb
  • Average mass
    1.5 kg
    3.30 lb
  • Range length
    76 (high) cm
    29.92 (high) in
  • Average length
    15-36 cm
    in

Development

Arctic grayling fry hatch 2 to 3 weeks after spawning, and they are approximately 1.3 cm long at hatching. The fry immediately move toward the calm and warm shoreline waters where they will become juveniles at 5 to 10 cm by the end of summer. Fry are miniature versions of adults. They continue to grow quickly and reach maturity in 3 to 4 years. At this point, they begin to grow much more slowly as they dedicate more of their annual energy intake to spawning efforts. The growth rate of arctic grayling is among the fastest for arctic fish in many streams and lakes. Researchers note that grayling embryos and hatchlings are exposed to increasingly colder temperatures as they develop. At these life stages, arctic grayling are exposed to microbial bacteria pathogens that are often temperature and sex-specific and result in behavioral and immunological responses. While this does not directly affect the sex-determination of individuals, studies show that male grayling appear to have a sex-specific behavior or tolerance to warm temperatures that female grayling do not have. ("Arctic Grayling (Thymallus arcticus)", 2013; Wedekind, et al., 2013)

  • Development - Life Cycle
  • temperature sex determination

Reproduction

Arctic grayling spawn in spring in shallow areas of rivers with moderate current as well as a gravel or rocky areas with a substrate composed of fine sand sediments. Spawning in lakes is rare. Arctic grayling alter their behavior to give them better abilities to spawn and reproduce. During mating season, males defend their spawning area for up to 7 days against other males. Females do not exhibit agonistic behavior during this season. During the act of mating, other males will try to beat other males off prospective mates. Females can also just swim off. Males court females by flashing their colorful dorsal fins. These fins are also used to brace receptive females to aid in the mating process. Although they do not excavate a redd (nest) in the substrate, the act of mating kicks up a large amount of substrate that serves as a sort of nest for the eggs. The roe (eggs) are left on the bottom of the streambed to mix with the milt (sperm) released from the males. The female leave and find another prospective male to mate with and leave the zygotes to be covered by the substrate and to survive on their own. However, less than 50% of all spawning attempts are actually completed due to interference by other fish or the female moving away from the male. Arctic grayling are promiscuous, with males mating several times with several females and females mating more than once with several males. (Kratt and Smith, 1980)

Arctic grayling, like most other fish, are oviparous and they lay eggs in the spring, when ice begins to break up. Depending on the size of the female, she may lay between 1,500 and 30,000 eggs, each around 2.5 mm in diameter. The eggs sink to the bottom and become lodged between pebbles and gravel. Only about 10% of the fry that hatch from the eggs will reach adulthood and be able to spawn. When spring approaches, arctic grayling gather in large groups to "run" upstream to spawning areas. ("Arctic Grayling (Thymallus arcticus)", 2013; Kratt and Smith, 1980)

  • Breeding interval
    Arctic grayling breed once yearly in springtime spawning events.
  • Breeding season
    Breeding occurs in spring.
  • Range number of offspring
    1500 to 30000
  • Average time to hatching
    2.5 weeks
  • Average age at sexual or reproductive maturity (female)
    3.5 years
  • Average age at sexual or reproductive maturity (male)
    3.5 years

Arctic grayling parents generally do not invest much in the young apart from defending the spawning area. (Kratt and Smith, 1980; Miano, 2013)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female

Lifespan/Longevity

The lifespan of arctic grayling is usually around 18 years for both males and females. However, individuals in Alaska have been known to live up to 32 years. Most mortality occurs in eggs, larvae, and fingerlings or in areas where these fish are heavily fished. ("Arctic Grayling (Thymallus arcticus)", 2013; "Arctic Grayling Recovery", 2012)

  • Range lifespan
    Status: wild
    32 (high) years
  • Typical lifespan
    Status: wild
    18 (high) years

Behavior

Much of arctic grayling behavior revolves around strategies that aid survival in the harsh, uncertain environment of the Arctic. One strategy is migration for food and spawning. Individuals can use different streams for spawning, development, overwintering, and summer feeding, although some individuals spend their entire life within a single section of a stream or lake. They are active during the day. (Davis, et al., 2010; Gingerich, et al., 2010)

Home Range

Arctic grayling may move tens of miles on a seasonal or annual basis between spawning, feeding, and sheltering habitats. Some arctic grayling have been known to travel more than 160 km (100 miles) in one year. (Davis, et al., 2010; Gingerich, et al., 2010)

Communication and Perception

There is no research on communication and perception in arctic grayling, but it is assumed they have sensory perception similar to other freshwater fish, including chemoreception and the lateral line system. One form of perception is through chemoreceptors that can respond to chemical stimuli in the water and act a sense of taste and smell. Another form of perception is the lateral line system. This system is common in fish and detects the motion of other fish and prey through changes in current and vibration that are caused by the other organisms. They are visual predators, reacting to visual cues to detect and attack prey. (Bleckmann and Zelick, 2009)

Food Habits

During the brief northern summers, arctic grayling eat drifting aquatic insects, such as black flies (Simuliidae), mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera). At times, grayling gorge upon the eggs of spawning salmon, smaller fish, or terrestrial insects that have fallen into the water. They may even eat an occasional vole, lemming, or shrew. Young arctic grayling feed on zooplankton and eventually transition to feeding on insect larvae. ("Arctic Grayling Recovery", 2012; Davis, et al., 2010)

Predation

Predators of arctic grayling include other fish (pike and trout), predatory birds (eagles and osprey), and mammals (otters and mink). ("Arctic Grayling (Thymallus arcticus)", 2013; Sepulveda, et al., 2013)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Arctic grayling are one of the top predators in their aquatic habitats. They prey on a wide variety of insects, fish and other small animals. They are also hosts to protozoan and metazoan parasites such as Cystidicoloides tenuissima and Pomphorhynchus bulbocoli. (Arai and Mudry, 1983; Davis, et al., 2010; Muzzall, 1990)

Commensal/Parasitic Species
  • Cystidicoloides tenuissima
  • Pomphorhynchus bulbocoli

Economic Importance for Humans: Positive

Arctic grayling are raised commercially for food and fished for sport. ("Arctic Grayling (Thymallus arcticus)", 2013)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of arctic grayling on humans.

Conservation Status

While arctic grayling are not currently considered endangered, they are sensitive to pollution in the areas they live and pollution can cause local extirpations. They are most vulnerable to overfishing, competition, road culverts, mining, agriculture, and destructive forestry practices. Recent findings indicate that populations of arctic grayling in North America have been steadily declining and the species is listed as a candidate for “species of concern” status and may warrant protection under the Endangered Species Act. ("Arctic Grayling (Thymallus arcticus)", 2013)

Contributors

Michael Hsieh (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

insectivore

An animal that eats mainly insects or spiders.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Alaska Department of Fish and Game. Arctic Grayling (Thymallus arcticus). Anchorage, Alaska: Alaska Department of Fish and Game. 2013. Accessed October 15, 2013 at http://www.adfg.alaska.gov/index.cfm?adfg=arcticgrayling.main.

US Fish & Wildlife Service. Arctic Grayling Recovery. Washington, DC: US Fish & Wildlife Service. 2012. Accessed October 15, 2013 at http://www.fws.gov/redrocks/arcticgrayling/.

Arai, H., D. Mudry. 1983. Protozoan and metzoan parasites of fishes from the headwaters of the Parsnip and McGregor Rivers, British Columbia: a study of possible parasite transfaunations. Canadian Journal of Fisheries and Aquatic Sciences, 40: 1676-1684.

Baccante, D. 2011. Further evidence of size gradients of arctic grayling (Thymallus arcticus) along stream length. Journal of Ecosystems and Management, 11: 13-17.

Bleckmann, H., R. Zelick. 2009. Lateral line system of fish. Integrative Zoology, 4: 13-25.

Davis, J., A. Rosemond, S. Eggert, W. Cross, J. Wallace. 2010. Long-term nutrient enrichment decouples predator and prey production. Proceedings of the National Academy of Sciences, 107: 1210126.

Gingerich, A., D. Philipp, C. Suski. 2010. Effects of nutritional status on metabolic rate, exercise and recovery in a freshwater fish. Journal of Comparative Physiology B, 180: 371-384.

Hughes, N., J. Reynolds. 1994. Why do arctic grayling (Thymallus arcticus) get bigger as you go upstream?. Canadian Journal of Fisheries and Aquatic Systems, 51: 2154-2163.

Kratt, L., R. Smith. 1980. The analysis of the spawning behaviour of the arctic grayling Thymallus arcticus (Pallas) with observations on mating success. Journal of Fish Biology, 17: 661-666.

Miano, A. 2013. Lake Trout (Salvelinus namaycush) and Arctic Grayling (Thymallus arcticus) Diet, Population and Migration Dynamics in Arctic Ecosystems. Biology Honors Paper at Connecticut College.

Muzzall, P. 1990. Parasites of arctic grayling, Thymallus arcticus (Pallas), stocked into Michigan lakes. Canadian Journal of Zoology, 68: 596-599.

Sepulveda, A., D. Rutz, S. Ivey, K. Dunker, J. Gross. 2013. Introduced northern pike predation on salmonids in southcentral Alaska. Ecology of Freshwater Fish, 22: 268-279.

Stamford, M., E. Taylor. 2004. Phylogeographical lineages of arctic grayling (Thymallus arcticus) in North America: divergence, origins and affinities with Eurasian Thymallus. Molecular Ecology, 13: 1533-1549.

Wedekind, C., G. Evanno, T. Szekely, M. Pompini, O. Darbellat, J. Guthruf. 2013. Persistent unequal sex ratio in a population of grayling (Salmonidae) and possible role of temperature increase. Conservation Biology, 27: 229-234.

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