Home Range Size and Foraging Ecology of Bull Trout and Westslope Cutthroat Trout in the Upper Salmon River Basin, Idaho

Abstract

We used radiotelemetry to determine how body size, foraging ecology, and seasonal activity influence the home range size of adult bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi in the upper Salmon River basin of central Idaho. Stomach samples were collected to determine diet composition and compare foraging strategies between the two species. Contrary to other studies of home ranges for stream-dwelling fishes, home range size was not significantly related to total length or body mass in either species. Although overall home range size did not differ between species, monthly movement (km) was significantly greater for bull trout than for westslope cutthroat trout during July and September. Stomach content analysis revealed that the size of prey consumed was significantly larger for bull trout than for westslope cutthroat trout but was not significantly correlated with body size in either species. Home range size for bull trout and westslope cutthroat trout in our study was much larger than home ranges documented for other stream-dwelling salmonids; our results illustrate the importance of large-scale connectivity and the variety of habitats necessary for the persistence of these species.

ACKNOWLEDGMENTS

We thank the Idaho Department of Fish and Game, Idaho State University, Idaho Office of Species Conservation, U.S. Bureau of Land Management, U.S. Fish and Wildlife Service, U.S. Forest Service, and Trout Unlimited for providing funding and logistical support for this project. We thank T. Curet, who was instrumental to the success of this project. We also thank M. Green, T. Coates, E. Major, and K. John for many hours of fieldwork. K. Rodnick, K. Bosworth, and J. Loxterman provided valuable comments on an earlier version of this paper.