The Response of Trout to Beaver Dams in Sagehen Creek, California

MASTERS THESIS: This study examines the response of trout to beaver dams under low summer flows and following winter flood conditions in Sagehen Creek, California. For purposes of this study, a response is defined as a shift in habitat utilization as indicated by a change in density or age structure of the trout populations. Little work has been done to investigate the response of trout to beaver (Castor canadensis) dams in Western mountain streams, although substantial data exist for eastern and Midwestern streams. No follow up studies have been done on streams in California since the pioneering work of Gard. Further, no published study has specifically examined the role beaver dams play in providing physical habitat for trout in years of high and low flows. Two consecutive, extreme water years in 1986 and 1987 provided the opportunity for such an investigation. Flows in Sagehen Creek in February through May of 1986 were substantially above mean monthly flows for the period of record, 1954-1985. By July of 1986, however, flows had dropped to normal summer levels for this stream. Hydrologic conditions the following year were fairly typical of a drought year, with flows consistently below monthly mean flows. The objective of this investigation were to describe the physical characteristics of stream reaches with and without beaver activity, to examine changes in physical characteristics of both types of reach under yearly flow variations, and to identify responses of trout to those physical habitat characteristics and changes.