Validation of morphological characteristics used for field identification of bull trout × brook trout hybrids

Bull trout Salvelinus confluentus are of conservation concern throughout much of their range, in part because of displacement by and hybridization with nonnative brook trout S. fontinalis. Hybridization between these species can complicate efforts to control brook trout because hybrids are often difficult to distinguish from parental species. Here, we assess the reliability of five morphological characteristics that were used to identify bull trout × brook trout hybrids among 106 fish collected from Quirk Creek, Alberta. Genetic analysis of up to three microsatellite loci suggested that hybrids were correctly identified 95% of the time and that no bull trout were mistaken for hybrids. Visual inspection of photographs of hybrids suggested that dorsal fin markings were the most reliable morphological characteristic for identifying hybrids. Based on these results, we recommend that field identification of bull trout × brook trout hybrids be based solely on dorsal fin markings.