Effects of Non-native Brown Trout and Temperature on the Production of Rio Grande Cutthroat Trout Populations
Dates
Publication Date
2020-08-20
Start Date
2017-08-01
End Date
2018-08-30
Citation
Colleen A. Caldwell, and Lauren Flynn, 2020, Effects of Non-native Brown Trout and Temperature on the Production of Rio Grande Cutthroat Trout Populations. U.S. Geological Survey Data Release, https://doi.org/10.21429/3y4d-7s43.
Summary
Native Cutthroat Trout Oncorhynchus clarkii spp. populations in the western U.S. have declined in part due to displacement by nonnative trout, but mechanisms to explain displacement vary by species and geography. Using a production framework, we demonstrated allopatric populations of Rio Grande Cutthroat Trout O. c. virginalis (RGCT) exhibited consistently higher biomass and secondary production rates (0.19–0.92 g DM·m-2·yr-1) than sympatric populations with Brown Trout Salmo trutta (0.01–0.05 g DM·m-2·yr-1) and that an interactive temperature effect on RGCT biomass and production was overshadowed by the presence of Brown Trout across cold and warm streams. Interestingly, over half of trout production was fueled by a small group of [...]
Summary
Native Cutthroat Trout Oncorhynchus clarkii spp. populations in the western U.S. have declined in part due to displacement by nonnative trout, but mechanisms to explain displacement vary by species and geography. Using a production framework, we demonstrated allopatric populations of Rio Grande Cutthroat Trout O. c. virginalis (RGCT) exhibited consistently higher biomass and secondary production rates (0.19–0.92 g DM·m-2·yr-1) than sympatric populations with Brown Trout Salmo trutta (0.01–0.05 g DM·m-2·yr-1) and that an interactive temperature effect on RGCT biomass and production was overshadowed by the presence of Brown Trout across cold and warm streams. Interestingly, over half of trout production was fueled by a small group of taxa including Trichoptera (caddisfly) nymphs and Hymenoptera (ants, wasps, and bees), which were actively selected by both trout species. Similar prey preferences and niche widths suggest that RGCT are experiencing competitive exclusion by Brown Trout. These results offer fresh insight into the unique environmental conditions of headwater streams in the Southwest and justify management strategies to segregate Cutthroat Trout and nonnative trout species.
This study used secondary production (i.e., trophic basis of production) and prey availability to evaluate how temperature and competition with nonnative Brown Trout impacted the ecological success of Rio Grande Cutthroat Trout O. c. virginalis (hereafter, RGCT) populations in the Southern Rocky Mountains of the United States. As a consequence of their unique distribution across high elevations (1828-3810 m) at a southern latitude, RGCT populations are subject to a broad thermal range (i.e., minimums below 10°C and maximums above 20°C in the summer). Brown Trout are pervasive throughout the range of RGCT and are considered competitively dominant to Cutthroat Trout subspecies and suppress Cutthroat Trout growth and body condition across a thermal spectrum. Here, we examine the interactive effects of Brown Trout and temperature on RGCT production. To our knowledge, this is the first study that uses production to quantify the impact of Brown Trout on a Cutthroat Trout subspecies.
