After the construction of the Buffalo River Hydroelectric project in the 1930s, fish passage to the Buffalo River was blocked. An initial fish ladder was constructed in 1996 and an improved design was constructed in 2005, involving a 270-foot long fish ladder that would to allow fish to more easily bypass the 12-foot high Buffalo River Dam. In 2013, monitoring of the fish ladder shifted from assessing the effectiveness of the ladder in passing individual fish to assessing if and how the Buffalo River contributes to the Henry’s Fork fishery. PIT tagging to monitor movement of trout and genetics analysis to better understand their life history were underway.
HFF also operates a fish trap from early February to mid-June each year to collect data on species, length, and sex before passing the fish upstream into the Buffalo River. This data allows us to quantify run size, run timing, number of spawners, number of return spawners, and other valuable information needed to monitor and understand the Henry’s Fork Rainbow Trout population.
The following are a summary of 4 key findings related to the Buffalo River Fish Ladder. To learn more about each, see the references below or visit the HFF Community Campus for additional resources.
HFF and partners advocated for the construction of a fish ladder with the goal of reconnecting fish passage to the Buffalo River, and allowing juveniles to migrate into tributaries for winter habitat so they can return and add to the overall fish population in the Henry’s Fork.
1. However, research and monitoring showed that the juveniles moving downstream in the spring were not the same individuals that had moved upstream during the previous autumn. Young-of-year sized trout migrate from the Henry’s Fork to the Buffalo River in the fall, but only a small number (approximately 150 individuals) appear to out-migrate and contribute to the Henry's Fork fishery the following spring. At average annual survival for trout in the Henry’s Fork, only half of these would be expected to contribute to the cohort of two-year old fish that recruit to the fishable population in the subsequent year.
2. The vast majority of out-migrants appear to have been born in the Buffalo River, and the vast majority of those are offspring of resident Buffalo River fish.
3. There is a relatively stable annual run of approximately 200 spawners from the Henry’s Fork into the Buffalo River. Thus, primary contribution of the Buffalo River to the Henry’s Fork fishery appears to be spawning and not overwintering habitat, although spring outmigrants have spent a winter in the Buffalo River.
4. The fish ladder allowed juvenile Rainbow Trout to access overwinter habitat and contributed a 3% increase of Rainbow Trout in the Henry’s Fork population.
Sources
Gregory, J. (1997) Spring spawning on the Henrys Fork and tributaries upstream from Riverside Campground. Henry’s Fork Foundation, Ashton, ID. Gregory, J.S. (2000)
Gregory, J.S. (2000) Winter fisheries research and habitat improvements on the Henry’s Fork of the Snake River. Intermountain Journal of Sciences 6: 232-248.
Gregory, J. and R. Van Kirk. (1998) Henrys Fork Habitat Assessment: Island Park Dam to Warm River, Summer 1997. Henry’s Fork Foundation, Ashton, ID.
Henry’s Fork Foundation (2016) Buffalo River Fish Ladder 2006-2016 Comprehensive Report prepared by Conservation Technician, Christina Morrisett.
Mitro, M. and A. Zale. (2002) Seasonal Survival, Movement, and Habitat Use of Age-0 Rainbow Trout in the Henrys Fork of the Snake River, Idaho. Transactions of the American Fisheries Society 131: 271-286.
Oldemeyer et al. (2017) Long-term Effectiveness of Flow Management and Fish Passage on the Henry’s Fork Rainbow Trout Population. Wild Trout Symposium Conference Presentation, West Yellowstone, MT.