Nonlinear response of trout abundance to summer stream temperatures across a thermally diverse montane landscape

Abstract

Stream temperature is a fundamental physical factor that affects the distribution and abundance of salmonids, but empirical inconsistencies exist regarding the nature of this relationship in wild populations. We sampled trout populations composed primarily of cutthroat trout Oncorhynchus clarki but also including brown trout Salmo trutta and brook trout Salvelinus fontinalis at 102 reaches on 24 first- to fourth-order streams across a thermally diverse montane landscape. Curves fit to scatterplots of density and biomass versus mean July-August stream temperatures suggested nonlinear, dome-shaped responses. Peaks occurred near mean stream temperatures of 128C; x-intercepts were near 38C and 218C. We conclude that inconsistencies in previously reported temperature–abundance relationships for wild trout populations may have resulted from sampling only a subset of the thermal environments occupied by a species. Researchers analyzing this relationship should be cognizant of the range of temperatures studied and the expected form of the relationship over that range.

Citation

Isaak, Daniel J.; Hubert, Wayne A. 2004. Nonlinear response of trout abundance to summer stream temperatures across a thermally diverse montane landscape. Transactions of the American Fisheries Society. 133:1254-1259.