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  • Scott Tansowny

What Factors Threaten Alberta's Arctic Grayling?

The Arctic grayling, Thymallus arcticus, is a symbol of pristine northern waters. It is a stunning fish with silver scales, small black spots, and a huge colourful dorsal fin. Native to three regions of Alberta, it is a symbol of the wild, a symbol of untouched wilderness, and a symbol of a healthy ecosystem. The success of this fish relies on habitat quality making it a perfect indicator species for the health of boreal forest ecosystems. So, basically, if grayling populations are healthy the ecosystem is doing pretty well but if populations start to decline, something is wrong.

Arctic Grayling
Arctic Grayling — Photo by USFWS Mountain Prairie on / CC BY

There is no question that in areas of the province, arctic grayling populations have been on a large decline. The Alberta government has listed the Arctic grayling as sensitive and for good reason. Grayling populations are not doing well as can be seen in the below figure comparing the population density of arctic grayling in Alberta from pre-1960 to 2014.¹

Population Density of Arctic Grayling in Alberta from pre-1960 to 2014
Population Density of Arctic Grayling in Alberta from pre-1960 to 2014 (ESRD 2014)

The Alberta government has even made a catch limit of zero fish across the entire province. Populations need to be protected now; when Arctic grayling populations decline to critical levels or disappear, it is much more difficult to restore their populations than it would have been to prevent the population decline in the first place.

How can we do this? The key to protecting this species and, in turn, protecting the entire ecosystem is understanding the threats and challenges it faces. If we do not fully understand what threatens a species, we are unable to make decisions and policies that will properly protect it. So, what factors threaten Alberta’s Arctic grayling?

Degradation of water quality

Arctic grayling are a fish of pristine streams. Pristine does not necessarily mean the crystal clear waters of streams high in the rockies, it simply means unpolluted and in its natural state. For example, a silty bottomed boreal stream, very rich in aquatic insects, could be an important summer area for grayling; however, when it comes to spawning, Arctic grayling require a stream floor composed of gravel that is free of silt and sediment.

Arctic Grayling Spawning Run
Arctic Grayling Spawning Run — Photo by USFWS Mountain Prairie on / CC BY

Increases of silt on the bottom of a river has a direct negative impact on the spawning success of Arctic grayling as substrate on the bottom of the stream suffocates the eggs.² Due to this, Arctic grayling do not spawn over mud, silt, sand, or clay.³ The more areas of a stream build up layers of silt on the bottom, the less spawning habitat that is available for the grayling and without spawning habitat a fish species has no chance to thrive.

Increases in the amount of silt in a stream also increases the turbidity of the water. Increased turbidity can have a large impact on Arctic grayling because they are visual predators, relying on sight for feeding success.⁴ With murky water comes decreased efficiency in the finding and catching of food and this only compounds the threat of sediment in the water further.

Increased sedimentation of the stream floor can have many causes including the construction and upkeep of gravel roads, the reduction in streamside vegetation causing increased erosion, and outflow from mining operations. These are all things that need to be controlled to minimize the degradation of grayling habitat.

Water quality can also be degraded by the presence of pollution and chemicals. These can present themselves as a side effect of mining operations, oil and gas extraction and refinement, and the use of herbicides and insecticides. Pesticides and chemical spills can contaminate terrestrial and aquatic insects having a negative consequence on Arctic grayling populations.⁵ Arctic grayling are almost exclusively insectivores so poisoned insects means a poisoned food source and if the food source is poisoned, there is little chance for a healthy fish population. There has also been evidence showing that discharge of sediment from placer mining — the mining of a streambed for deposits of minerals — would cause grayling unable to escape to either die or suffer gill damage, starvation, and slowed maturation.⁶

Degradation of water quality is a real concern to Alberta’s Arctic grayling right now and is clearly a serious threat to their survival.

Introduced Species

Introduced species competing with and predating on Arctic grayling is another possible threat. Due to similarities in food, the introduction of rainbow, brook, and brown trout has caused grayling numbers to decline in some water systems in the Northwest Territories.⁷ This was contrasted, however, by a study in Montana’s Big Hole River that found introduced brook trout to have little to no impact on grayling populations.⁸ Another study in Montana found competition and predation from other fish species — brook trout and cutthroat trout specifically — to not be a limiting factor on populations.⁹

Although there is not much evidence of the impacts of introduced species on grayling populations in Alberta, it does not seem to be as large of a factor to their survival as other factors.

Fragmentation of habitat

Fragmentation of habitat is when a large continuous area of habitat is divided into smaller patches of habitat. For example, a forest habitat can be fragmented by a highway built down the middle. The presence of the highway will impact the movement of species from one part of the forest to another. When it comes to Arctic grayling, the concern is blocking movement up and down rivers and streams.

Arctic grayling are a migratory species, moving upstream into smaller tributaries to spawn and spend the summer and then working their way downstream to larger rivers and deeper pools to overwinter when their summer habitats freeze solid. The fish often travel more than 50km and even in excess of 100km to go from their wintering location to their breeding and summer location. The grayling also show a large amount of site fidelity to the location they spent previous summers, not just the area, but the exact location.¹⁰

The problem occurs when this crucial migration route is blocked by a natural or human caused barrier such as a beaver dam, a hydroelectric dam, or other anthropogenic structures. The main cause of this fragmentation in Alberta is hanging culverts. Hanging culverts do not allow any fish passage and unfortunately half of the culverts in northern Alberta are of this habitat fragmenting type.¹¹

Hanging Culvert
Hanging Culvert — Photo by Sam Beebe on / CC BY

When the habitat is fragmented in this way, fish are unable to move as they naturally would. Some habitat can end up completely devoid of fish and crucial spawning areas may end up inaccessible or very difficult to access, delaying the migration. Delays in migration may force grayling to spawn in suboptimal habitats, decreasing the reproductive success of the species.¹²

The fragmenting of grayling habitat through dams or culverts has obvious negative impacts on the species.

Fishing mortality

Historically, fishing has made large impacts on the populations of Arctic grayling. Grayling are quite eager to take a fly or lure making them very susceptible to overfishing. In Alberta, regulations have been put in place not allowing anglers to keep any grayling. In some areas of the Pembina River system angling is not even permitted for fear of mortality due to catch and release fishing. While these measures definitely help to reduce anglers’ impact on the species, it is still possible that some mortality could occur in released fish.

Not a lot of extensive studies have looked at this but there was one in Alaska in 1991.¹³ The study tested mortality rates from baited single hooks, artificial lures with treble hooks, and artificial flies. The study included two single catch experiments where in each only a single grayling died out of a total of 359 fish and one multi-catch experiment where of the 147 different fish caught (some as many as 5 times), the experiment saw a mortality of only a single fish.

This study did have some limitations, one being that the baited hooks were “sight fished” allowing the angler to see the fish take the bait and set the hook before the grayling could pass the hook to its gullet. The other limitation was that the study did not indicate the water temperature when the fish were caught; a higher water temperature is believed to greatly increase fishing mortality in trout although this is contradicted in some studies.¹⁴

Even with these limitations this study showed that mortality from catch and release fishing on Arctic grayling is extremely low and is unlikely to be a population limiting factor.

Three Arctic Grayling
Three Arctic Grayling — Photo by USFWS Mountain Prairie on / CC BY


In order to protect a species it is imperative we understand what threatens it. In the case of Alberta’s Arctic grayling, the largest threats appear to be degradation of water quality and fragmentation of habitat. To protect Arctic grayling and the ecosystem they thrive in, it is imperative we address these threats.


1. Cahill, C. L. (2015). Status of the Arctic grayling (Thymallus arcticus) in Alberta: Update 2015. Alberta Government.

2. Beauchamp, D. A. (1990). Movements, habitat use, and spawning strategies of Arctic grayling in a subalpine lake tributary. Northwest Science, 64(4).

3. Hubert, W. A. (1985). Habitat suitability index models and instream flow suitability curves: Arctic grayling riverine populations (Vol. 82). Western Energy and Land Use Team, Division of Biological Services, Research and Development, Fish and Wildlife Service, US Department of the Interior.

4. Stewart, D. B., Mochnacz, N. J., Reist, J. D., Carmichael, T. J., & Sawatzky, C. D. (2007). Fish diets and food webs in the Northwest Territories: Arctic grayling (Thymallus arcticus). Can. Manuscr. Rep. Fish. Aquat. Sci, 2796, 21.

5. Stein, J.N., Jessop, C.S., Porter, T.R., and Chang-Kue, K.T.J. 1973a. An evaluation of the fish resources of the Mackenzie River valley as related to pipeline development. Environmental-Social Committee, Northern Pipelines, Task Force on Northern Oil Development Rep 73-1: xv + 121 p.

6. Reynolds, J. B., Simmons, R. C., & Burkholder, A. R. (1989). EFFECTS OF PLACER MINING DISCHARGE ON HEALTH AND FOOD OF ARCTIC GRAYLING 1. JAWRA Journal of the American Water Resources Association, 25(3), 625-635.

7. Stewart, D. B., Mochnacz, N. J., Reist, J. D., Carmichael, T. J., & Sawatzky, C. D. (2007). Fish diets and food webs in the Northwest Territories: Arctic grayling (Thymallus arcticus). Can. Manuscr. Rep. Fish. Aquat. Sci, 2796, 21.

8. Byorth, P. A., & Magee, J. P. (1998). Competitive interactions between Arctic grayling and brook trout in the Big Hole River drainage, Montana. Transactions of the American Fisheries Society, 127(6), 921-931.

9. Davis, M. N. (2016). Winter survival and habitat as limiting factors for Arctic grayling at Red Rock Lakes National Wildlife Refuge (Doctoral dissertation, Montana State University-Bozeman, College of Letters & Science).

10. Buzby, K. M., & Deegan, L. A. (2000). Inter-annual fidelity to summer feeding sites in Arctic grayling. Environmental Biology of Fishes, 59(3), 319-327.

11. Park, D. J. (2006). Stream fragmentation by hanging culverts along industrial roads in Alberta's boreal forest: assessment and alternative strategies (Doctoral dissertation, University of Alberta).

12. Stewart, D. B., Mochnacz, N. J., Reist, J. D., Carmichael, T. J., & Sawatzky, C. D. (2007). Fish life history and habitat use in the Northwest Territories: Arctic grayling (Thymallus arcticus). Canadian Manuscript Report of Fisheries and Aquatic Science, 2797, 55.

13. Clark, R. A. (1991). Mortality of Arctic grayling captured and released with sport fishing gear. Alaska Department of Fish and Game, Division of Sport Fish.

14. Marnell, L. F., & Hunsaker, D. (1970). Hooking mortality of lure‐caught cutthroat trout (Salmo clarki) in relation to water temperature, fatigue, and reproductive maturity of released fish. Transactions of the American Fisheries Society, 99(4), 684-688.


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