Population Genetics of Boise Basin Bull Trout (Salvelinus confluentus)

Abstract

We analyzed the population genetic structure of bull trout (Salvelinus confluentus) in the Boise River Basin, Idaho. We determined the influence of contemporary (including anthropogenic) and historic factors on genetic structure, taking into accountexisting data on bull trout habitat patches in this basin. We tested three models of the organization of genetic structure in this system, where genetic structure would: a) parallel the stream hierarchy, b) correspond to habitat patch structure, or c) follow a pattern of isolation by distance. We found strongest support for the isolation by distance model. In addition, we found weak population differentiation within the Boise system (FST = 0.064), relative to other similarly scaled systems containing bull trout. Frequent disturbance may be responsible for the strong isolation by distance yet weak overall levels of population subdivision in this system. In addition, we found that the South Fork was a genetic outlier from the remainder of the Boise system and may have been colonized at a separate time than the Middle and North Forks. At least one dam (Kirby Dam) has noticeably reduced levels of gene flow. These results show that distinct patterns of genetic structure may occur in separate portions of a species' range, especially at the range extremes. Based on these results, we suggest the South Fork should be treated separately from the remainder of the basin. Bull trout in Mores Creek should be protected but our results suggest that this population may be comprised of adults entrained by Arrowrock Dam and unable to return to natal streams to spawn and are thus spawning in the only available habitat. Connectivity should be restored whenever possible in cases where human activities have eliminated migratory corridors.

Citation

Whiteley, A.R., P. Spruell and F.W. Allendorf. 2003. Population Genetics of Boise Basin Bull Trout (Salvelinus confluentus). Final report. RMRS# 00-JV-1122014-561. 37pp.