A Spatially Explicit Approach for Evaluating Relationships among Coastal Cutthroat Trout, Habitat, and Disturbance in Small Oregon Streams
Robert E. Gresswell, Christian E. Torgersen, Douglas S. Bateman, Troy J. Guy, Steven R. Hendricks, and J. E. B. Wofford
Abstract.—Small stream systems are complex networks that form a physicochemical template governing the persistence of aquatic species such as coastal cutthroat trout Oncorhynchus clarkii clarkii. To gain new insight into these interactions, we initiated an integrated program of landscape- scale sampling that is focused on fine- and broad-scale relationships among upslope landscape characteristics, physical stream habitat, and the spatial patterns of cutthroat trout abundance. Our sample of 40 catchments (500–1,000 ha) represented approximately 15% of the 269 barrier-isolated catchments in western Oregon that support populations of cutthroat trout. Because data were collected in a spatially contiguous manner throughout each catchment, it was possible to collect biological and geographic information necessary to assess the spatial structure of cutthroat trout abundance. Results underscore the influence of the physical habitat template at a variety of spatial scales. For example, cutthroat trout move throughout the accessible portions of small streams. Some cutthroat trout congregate in areas of suitable habitat and form local populations that may exhibit unique genetic attributes. At times, some cutthroat trout move into larger downstream portions of the network where they may contribute to the genetic character of anadromous or local potamodromous assemblages. Results underscore the advantages of viewing habitats that are critical to the fitness and persistence of cutthroat trout populations as matrices of physical sites that are linked by movement. It is apparent that human activities that impede movement among suitable habitat patches can have unanticipated consequences for metapopulations of cutthroat trout and may ultimately affect their persistence.