Effects of Temperature and Spatial Scale on Rio Grande Cutthroat Trout Growth and Abundance

Population persistence across broad spatial scales (e.g., watersheds) can depend on asynchronous dynamics among populations at finer scales (e.g., streams or habitats). We applied a von Bertalanffy growth model and closedN‐mixture abundance model in a hierarchical Bayesian framework to examine effects of fine‐scale variability in temperature and density dependence on growth and abundance as well as within‐ versus among‐stream variability in growth and abundance of Rio Grande Cutthroat TroutOncorhynchus clarkii virginalis(RGCT) in northern New Mexico streams. An accumulation of degree‐days positively influenced instantaneous growth rates and, to a lesser extent, negatively affected asymptotic body length. A nonlinear response of abundance to temperature was also observed, suggesting thatRGCTproductivity along the temperature continuum was affected by physiological limitations (e.g., optimal growth temperatures). Variability inRGCTabundance and the asymptotic size parameter could not be distinguished with certainty between spatial scales but was greatest at the stream level for the rate at which asymptotic size was reached. In total, our results suggested thatRGCTproductivity in our study streams was influenced by mechanisms operating at multiple spatial scales. Management actions should consider processes not only at the stream scale but within streams for improving the likelihood of future population persistence.