Animal Field Guide

Montana Arctic Grayling

Thymallus arcticus montanus
(Salmonidae)

Global Rank: G5T1Q
State Rank: S1

Agency Status
USFWS: C
USFS: SENSITIVE
BLM: SENSITIVE

The Arctic grayling is a species native to northern North America. The only populations native to the lower 48 states were in Michigan and Montana, and the Michigan population is now extinct. Consequently, the fluvial or river-dwelling population in the upper Big Hole River are the last remnants of this native Fish of Special Concern. Originally, the fluvial Arctic grayling was widespread throughout the upper Missouri river drainage as far downstream as Great Falls. Lewis and Clark made note of these "new kind of white or silvery trout" in 1805. The lake-dwelling form is fairly common in 30 or more lakes across the western half of the state. These lake fish are genetically, but not visibly, different from our native fluvial grayling. Grayling are gullible to the angler's lures and also seem to be easily out-competed by other salmonid species. This probably explains much of their demise from their native range. They are spring spawners and broadcast their eggs over a gravel bottom in moving streams. Grayling can overpopulate, producing severely stunted populations in some mountain lakes. Grayling are truly a unique Montana species. The iridescent hues of a spawning grayling's dorsal fin are brilliant. Exceptional individuals can weigh up to 3 pounds and reach 20 inches in length. They are generalists, eating a variety of aquatic invertebrates (FWP).

Today in Montana Arctic grayling are found primarily small, cold, clear lakes with tributaries suitable for spawning. They do not coexist well with other fishes except cutthroat trout and others with which they evolved.

Although fluvial Arctic grayling inhabit the entire Big Hole River, highest densities occur in the vicinity of Wisdom. The majority of spawning occurs near Wisdom in the main stem and several tributaries (Liknes and Gould 1987, Shepard and Oswald 1989, Byorth 1994). Fluvial Arctic grayling are reared in the vicinity of where they hatch; thus, the Wisdom area provides the majority of rearing habitat as well (AFS website 2003).

Arctic grayling rarely live beyond 5 years in the Big Hole River. Fast growth rates and short life spans result in domination of spawning by fish aged 3 and 4 years. Thus, poor recruitment in a given year may substantially affect recruitment to the population for several years (AFS website 2003).

Arctic grayling grow quickly in the Big Hole River, reaching full sexual maturity and nearly maximal size by age 3 (AFS website 2003).

The Fluvial Arctic Grayling Workgroup (FGW) developed a plan to research, protect, and restore fluvial Arctic grayling (FGW 1995). A primary objective was to develop a brood stock from wild Big Hole River Arctic grayling to preserve their genetic identity. Arctic grayling derived from the brood may be used to augment the Big Hole River population, if necessary, and to reestablish other populations within their native range (AFS website 2003). Another objective of FGW is to expand the range of fluvial grayling beyond the Big Hole River basin. Water quality and quantity problems are being addressed in the Big Hole basin. A habitat inventory conducted in 1994 will provide baseline information necessary to identify degraded habitats and potential rehabilitation projects (OEA 1995). While catch-and-release-only regulations protect grayling from over-harvest, angling regulations will also be used to exert pressure on non-native trout. More liberal regulations may inhibit encroachment of rainbow and brown trout into key grayling habitat (AFS website 2003).