Brian Hodge¹, Walt Duffy¹, Peggy Wilzbach¹, and James Hobbs² ¹California Cooperative Fish and Wildlife Research Unit, Humboldt State University, 1 Harpst Street, Arcata, CA 95521, USA; ²Interdisciplinary Center for ICP-MS, University of California at Davis, 1 Shields Avenue, Davis, CA 95616, USA
Abstract: We examined life form and life history of wild Oncorhynchus mykiss in the lower Klamath River Basin, a fishery that supports the largest steelhead population in California. Analysis of otolith strontium isotopes () was used to retrospectively determine maternal origin (anadromous vs nonanadromous) and migratory history (anadromous vs nonanadromous) of 65 fish. In addition, scale pattern analysis was used to determine age, growth, and life history of O. mykiss captured throughout the basin between August 2007 and April 2009. Sympatrically occurring anadromous (steelhead) and nonanadromous (rainbow trout) forms of O. mykiss were observed in the mainstem Klamath and major tributaries. Further, we observed rainbow trout of steelhead maternal origin, and steelhead of rainbow trout maternal origin. Our findings may be of interest to those considering the biological implications of dam removal on the Klamath River.