Bull trout conservation in Hells Canyon

Bull trout can be found in many mountain streams and rivers in Idaho, but did you know there are several populations that exist in headwater streams above the Hells Canyon Dams? These streams contain resident bull trout which are smaller than their migratory counterparts. Bull trout in these headwater streams would be more resilient if migratory fish were able to spawn in these waters, but migration is currently blocked by Hells Canyon Dam. 

A population of large, migratory bull trout overwinters in the Snake River below Hells Canyon Dam. Once upon a time, these migratory bull trout likely spawned in creeks upstream of the dams. But what river these migratory fish were from, and how related they were to bull trout above Hells Canyon Dam was unknown.

Recent genetic work done by Idaho Fish and Game and Idaho Power Company revealed two important findings. First, bull trout from above Hells Canyon dam were most similar to bull trout from the Imnaha River relative to other downstream populations like the Grande Ronde River or Little Salmon River. Second, almost all migratory bull trout captured below Hells Canyon Dam were assigned to the Imnaha River. These findings suggest that if migratory bull trout were transported above the dam, they would be a “good genetic match” for upstream populations. If the installation and operation of a fish passage facility at Hells Canyon Dam goes as planned, this means that resident populations of bull trout upstream of the dam could be reconnected with their migratory relatives and be more resilient moving forward.