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

Abstract

Diversity in habitat and life-history strategies promote a species' long-term persistence. However, life-history strategies are most commonly studied at broad spatial and temporal scales. We applied longevity growth models and closed N-mixture models to examine within- versus between stream variability in life-history characteristics of Rio Grande Cutthroat Trout in northern New Mexico streams. We developed a von Bertalanffy growth model and a closed N-mixture model in a hierarchical Bayesian framework to examine the importance of fine-scale variability in temperature and density-dependence on growth and abundance. The model indicated that accumulation of degree days likely 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 that Cutthroat Trout productivity along the temperature continuum was affected by physiological limitations (e.g., optimal growth temperatures). Parameter variability was greatest at the segment level for asymptotic size and abundance, but greatest at the stream level for the rate at which asymptotic size is reached. In total, the results suggest that fine-scale habitat heterogeneity (i.e., temperature) may play important roles in the continued persistence of Rio Grande Cutthroat Trout. Management actions should, therefore, consider the role of fine-scale processes for improving the likelihood of future population persistence.