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Are brown trout replacing or displacing bull trout populations in a changing climate?

February 23, 2016

Understanding how climate change may facilitate species turnover is an important step in identifying potential conservation strategies. We used data from 33 sites in western Montana to quantify climate associations with native bull trout (Salvelinus confluentus) and non-native brown trout (Salmo trutta) abundance and population growth rates (λ). We estimated λ using exponential growth state space models and delineated study sites based on bull trout use for either Spawning and Rearing (SR) or Foraging, Migrating, and Overwintering (FMO) habitat. Bull trout abundance was negatively associated with mean August stream temperatures within SR habitat (r = -0.75). Brown trout abundance was generally highest at temperatures between 12 and 14°C. We found bull trout λ were generally stable at sites with mean August temperature below 10°C but significantly decreasing, rare, or extirpated at 58% of the sites with temperatures exceeding 10°C. Brown trout λ were highest in SR and sites with temperatures exceeding 12°C. Declining bull trout λs at sites where brown trout were absent suggests brown trout are likely replacing bull trout in a warming climate.

Publication Year 2016
Title Are brown trout replacing or displacing bull trout populations in a changing climate?
DOI 10.1139/cjfas-2015-0293
Authors Robert K. Al-Chokhachy, David A. Schmetterling, Chris Clancy, Pat Saffel, Ryan Kovach, Leslie Nyce, Brad Liermann, Wade A. Fredenberg, Ron Pierce
Publication Type Article
Publication Subtype Journal Article
Series Title Canadian Journal of Fisheries and Aquatic Sciences
Index ID 70175344
Record Source USGS Publications Warehouse
USGS Organization Northern Rocky Mountain Science Center