1. Department of Fisheries Biology, Humboldt State University, Arcata, California 95521-8222, USA
2. Present address: Trout Unlimited, Post Office Box 771233, Steamboat Springs, Colorado 80477, USA
3. U. S. Geological Survey, California Cooperative Fish and Wildlife Research Unit, Humboldt State University, Arcata, California 95521-8222, USA