Systematics and Distributions of Dolly Varden (Salvelinus malma) and Bull Trout (Salvelinus confluentus) in North America

Abstract

Dolly Varden char in North America separate into two species: Dolly Varden (Salvelinus malma (Walbaum)) and bull trout (Salvelinus confluentus (Suckley)). Principal component analyses reveal two distinct morphotypes, and a linear discriminant function is derived (based on three field measureable variables) for their consistent classification. No single character can always distinguish both species, although branchiostegal ray number often will. The morphology of the two species remains relatively constant across their large ranges. The two species occur in strict sympatry in several areas with no evidence of interbreeding. The two species also exist parapatrically or syntopically and appear to exhibit broad scale competitive exclusion in these situations. Dolly Varden are distributed largely along the coast and range further north, while bull trout are mostly interior and range further south. Laboratory crosses demonstrate that the morphology of both species remain distinctive when they are reared under similar conditions and that their artificial hybrids are morphologically intermediate. No such natural hybrids were conclusively found, and there is no evidence of introgression.