Sportfish Life History Metrics in the Columbia River, Canada and Their Relationships to Flow Regulation and Other Environmental Factors

The construction and operation of Hugh L. Keenleyside Dam has changed the Columbia River ecosystem between the dam and the Canada-U.S. border. Between 2001 and 2013, Mountain Whitefish, Rainbow Trout, and Walleye were captured using boat electroshocking as part of an annual mark-recapture program designed to link changes in fish populations to inter-annual variability in flows during each species’ spawning season. Changes in abundance, distribution, survival, growth, and body condition were analyzed using hierarchical Bayesian models (HBM). Over the 13 year study period, HBM results indicated substantial multi-year trends for most species and metrics. Limited inter-annual flow variability during spawning seasons hindered correlating flows to the selected metrics. Factors unrelated to flows likely contributed to the observed changes, most notably: reduced industrial effluent releases; recruitment success in tributaries; the introduction of invasive Eurasian Watermilfoil and Northern Pike; increased abundance and distribution of Didymosphenia geminata; climatic changes on water temperatures; annual variability in upstream reservoir fertilization programs; and, increasing abundance of SARA-listed White Sturgeon under a hatchery release program. The study illustrated the difficulties of assessing causes of change when a multitude of important environmental factors may contribute to the observed changes.