MONTANA ARCTIC GRAYLING } Thymallus arcticus
DESCRIPTION: A member of the salmon family, the Arctic grayling has a prominent sail-like dorsal fin and purple metallic coloration. Adults are usually about eight to 12 inches long.
HABITAT: Grayling inhabit cool-water streams and pools. They use the pools’ woody debris for opportunistic feeding and hide in deep water from potential predators.
RANGE: Historically, fluvial (river-running) populations of Arctic grayling existed in only two places in the lower 48 states: Michigan and the upper Missouri River of Montana. Populations in Michigan went extinct by the 1930s, and at the end of the 19th century, fluvial Arctic grayling were intermittently distributed throughout the upper Missouri drainage above Great Falls. During the 20th century, the range of fluvial Arctic grayling has been restricted to the Big Hole River of southwest Montana, less than 5 percent of its native range.
MIGRATION: The Montana fluvial arctic grayling moves upwards of 50 miles downriver during winter. The reasons for this migration are poorly understood, but may provide a possible explanation for the failure of reintroduction of the species to other rivers in its historic range. These other rivers may lack areas where the fish can move to overwinter, or perhaps fish placed into a new system are not able to locate such habitat.
BREEDING: In Montana, grayling spawn from late April to mid-May. Without digging out a nest, the fish deposit sticky eggs over sand and gravel. The eggs then develop and hatch within a few weeks.
LIFE CYCLE: Arctic grayling grow quickly in the Big Hole River, reaching full sexual maturity and size by age three and rarely living beyond five years. In contrast, Arctic grayling in Alaska mature from age four to eight and can live up to 12 years. Fast growth rates and short life spans mean that poor recruitment in a given year may have a lasting effect on the Montana population.
FEEDING: Grayling are visual predators, feeding opportunistically on drifting invertebrates like crustaceans, insects, and fish eggs and larvae.
THREATS: Factors potentially threatening the survival of Arctic grayling in the Big Hole River include water quality and quantity, competition with introduced species, climate change, habitat degradation, and exploitation by anglers. Arctic grayling are easily caught by anglers and are susceptible to overharvest. Catch-and-release-only regulations enacted in 1988 in the Big Hole River have served to protect the Arctic grayling population from overexploitation, but cattle grazing, mass willow removal, and dewatering of the river for agricultural uses have all negatively impacted fish habitat in the Big Hole River.
POPULATION TREND: The grayling population is declining.