Montana Field Guide

Eastern Montana is the home of the blue sucker. This species appears to inhabit only the larger streams, primarily the Missouri and Yellowstone rivers. It is easily recognized by its elongate shape, long dorsal fin, and slate-blue coloration. The largest weight for this species in Montana is slightly over 10 pounds. It was once taken commercially from the Mississippi River but is now too rare.

Montana populations appear to be stable and fairly abundant with a healthy size structure. Although the blue sucker populations appear to be healthy and stable, special recognition is warranted because this species may be susceptible to population declines due to its unique biological characteristics (longevity, low recruitment, migratory nature and reliance on high flows in tributary streams for spawning). Montana has some of the finest habitat for blue suckers found in their range and losses of Montana populations would be significant to the overall gene pool (AFS website 2003).

The blue sucker has a back and sides that are dark blue to dark olive, and a white underside.

Blue suckers make long spawning movements from the lower Missouri River to upstream areas and tributary streams. Dispersal downstream follows.

Blue suckers prefer waters with low turbidity and swift current (Brown 1971).

The species feeds mainly on aquatic insects (Brown 1971).

The blue sucker is adapted for life in swift currents. This fish prefers swift current areas of large rivers, feeding on insects in cobble areas (Moss et al. 1983). In the spring blue suckers migrate upriver and congregate in fast, rocky areas to spawn. Large numbers have been observed migrating up tributary streams to spawn. The Tongue, Marias, Milk and Teton rivers are the tributary streams most heavily used. Blue suckers can live longer than 17 years. Blue suckers sampled in Montana are typically older and larger fish, with lengths of 60 to 75 centimeters and weights of 3 to 5 kilograms. Berg (1981) reported that 93% of sampled fish in the upper Missouri were 9 to 14 years old. The blue sucker is monogenetic and is not known to hybridize with any other species (AFS website 2003).

Reproductive success may be a problem for this habitat-specific species. Very few young-of-the-year blue suckers have been collected while sampling with a variety of methods. Moreover, the populations are dominated by older fish, indicative of minimal recruitment. Blue sucker larvae have been collected from the Milk River, Big Muddy Creek, and in the lower Missouri and Yellowstone rivers (Gardner and Stewart 1987, Penkal 1981). Additionally, young-of-the-year blue suckers have been sampled at the Milk River confluence and in Big Muddy Creek of the lower Missouri River (Liebelt 1996 and Stewart 1980) (AFS website 2003).

Blue suckers are probably sexually mature at 2 to 3 years. They spawn in April to June at temperatures of 50 degrees F. (Brown 1971).

Management of the blue sucker consists mainly of routine monitoring of population status and habitat protection. The blue sucker is considered an indicator species for ecosystem health because of its habitat-specific requirements. Current monitoring information indicates the populations are in stable condition. Efforts towards locating spawning and rearing areas should be continued. Habitat protection includes protecting or promoting the natural spring-time hydrograph. Establishment of more natural seasonal flow conditions are presently being discussed and initiated for three storage reservoirs in Montana (AFS website 2003).