The Effects of Drought on Rio Grande Cutthroat Trout: The Role of Stream Flow and Temperature

The impacts of climate change on cold water species will likely manifest in populations at the trailing edge of their distribution. Rio Grande cutthroat trout (Oncorhynchus clarkii virginalis, RGCT) occupy arid southwestern U.S.A. streams at the southern-most edge of all cutthroat trout distributions; thus making RGCT particularly vulnerable to the anticipated warming and drying in this region. However, RGCT may possess a portfolio of life-history traits that aide in their persistence, attributes commonly observed in trailing edge populations. We marked RGCT across eight populations in 2016 and 2017 and used this capture-mark-recapture data to determine how environmental constraints influenced life-history trait expression (length- and age-at-maturity), demography, and extirpation risk in RGCT populations from northern New Mexico, U.S.A. We found the rate at which RGCT reached maturity was highest at warm to intermediate stream temperatures, which was the demographic trait most strongly linked to RGCT persistence. Interestingly, older life-stages contributed more to population growth as temperatures decreased, providing further evidence of strong temperature effects controlling life-history trait expression in RGCT.