Session Name: Upper Columbia River Redband Trout
Presentation Title:
Rainbow Trout monitoring in the Canadian portion of the Columbia River in relation to dam discharge
and operations
Presenter Name: David Roscoe
All Authors, affiliations, phone number, email:
David Roscoe, Golder Associates Ltd., (250) 365-0344, david_roscoe@golder.com
Joe Thorley, Poisson Consulting Ltd., (250) 551-7474, joe@poissonconsulting.ca
Larry Hildebrand, Golder Associates Ltd., (250) 365-0344, larry_hildebrand@golder.com
Abstract :
The Canadian portion of the Columbia River between Hugh L. Keenleyside (HLK) Dam and the CanadaUSA border is home to a highly-valued population of Rainbow Trout (Oncorhynchus mykiss). This
population is thought be a single interbreeding native population of interior Redband Rainbow Trout
with no evidence of introgression from hatchery stocks. Rainbow Trout in this section of the Columbia
River can be affected by fluctuating flows from HLK Dam. Each spring, HLK Dam provides Rainbow Trout
spawning protection flows, which involve stable or increasing flows from April 1 – June 30 and are
intended to reduce the number of redds dewatered during flow reductions. Populations of Rainbow
Trout were monitored annually since 2001 using a boat electrofishing mark-recapture study. The data
were analyzed using hierarchical Bayesian models to assess the effects of river flows on the abundance,
growth rate, survival rate, body condition, and spatial distribution of subadult and adult Rainbow Trout.
In addition, a spawning assessment study has been conducted since 1999 to visually enumerate
Rainbow Trout redds and spawners. The electrofishing data suggested a gradual increase in adult
Rainbow Trout abundance between 2001 and 2013, with no consistent trend during this period for
subadults. Multivariate analyses suggested a correlation between discharge in the fall and adult
abundance, but overall, flow variables were not strongly associated with Rainbow Trout metrics.
Estimates of spawner abundance suggested a six-fold increase from <2000 fish in 1999 to ~12,000 in
2013. The electrofishing and spawner survey results suggest an increase in adult Rainbow Trout since
2001 but it is unclear whether this trend was related the spawning protection flows. Discrepancies
between subadult and adult estimates suggest potential bias in one or more of the models, which will
be investigated using visual electrofishing surveys in future years of the study.
Student Presenter?: No
Presentation Type: Oral presentation only