Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon P. S. RAND* Wild Salmon Center, The Natural Capital Center, 721 Northwest 9th Avenue, Suite 290, Portland, Oregon 97209, USA S. G. HINCH Department of Forest Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z2, Canada; and Institute for Resources, Environment, and Sustainability, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada J. MORRISON Vynx Design, Inc., Sydney, British Columbia V8L 3J2, Canada M. G. G. FOREMAN Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, British Columbia V8L 4B2, Canada M. J. MACNUTT Department of Forest Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z2, Canada J. S. MACDONALD Fisheries and Oceans Canada, Simon Fraser University, School of Resource and Environmental Management, Room WMC 3101A, Burnaby, British Columbia V5A 1S6, Canada M. C. HEALEY Institute for Resources, Environment, and Sustainability, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada A. P. FARRELL Biological Sciences Department, Simon Fraser University, Burnaby, British Columbia V5A 1Y6, Canada D. A. HIGGS West Vancouver Laboratory, Fisheries and Oceans Canada, West Vancouver, British Columbia V7V 1N6, Canada Abstract.—We evaluated the effects of past and future trends in temperature and discharge in the Fraser River on the migratory performance of the early Stuart population of sockeye salmon Oncorhynchus nerka. Fish of lower condition exhibited disproportionately higher mortality during the spawning run, elucidating a critical link between energetic condition and a fish’s ability to reach the spawning grounds. We simulated spawning migrations by accounting for energetic demands for an average individual in the population from the time of entry into the Fraser River estuary to arrival on the spawning grounds (about 1,200 km upstream) and estimated energy expenditures for the average migrant during 1950–2001. The model output indicates relatively high interannual variability in migration energy use and a marked increase in energy demands in recent years related to unusually high discharges (e.g., 1997) and warmer than average water temperature (e.g., 1998). We examined how global climate change might effect discharge, water temperature, and the energy used by sockeye salmon during their spawning migration. Expected future reductions in peak flows during freshets markedly reduced transit time to the spawning ground, representing a substantial energy * Corresponding author: prand@wildsalmoncenter.org Received January 25, 2005; accepted December 26, 2005 Published online May 30, 2006 655 Transactions of the American Fisheries Society 135:655–667, 2006 Ó Copyright by the American Fisheries Society 2006 DOI: 10.1577/T05-023.1 [Article]