Opposite Effects of Sea-Surface Temperature on Survival Rates of Pacific Salmon from Northern and Southern Areas

Environmental conditions cause large variations in productivity of Northeast Pacific salmon (Oncorhynchus spp.). Management of salmon stocks could be improved by better understanding the sources of environmentally driven variability in their productivity. Large-scale climatic and oceanographic variability has been related to aggregate catches of Northeast Pacific salmon (Downton and Miller 1998; Hare et al. 1999). However, catch data may not reveal changes in productivity because catch reflects the confounded effects of fishing effort, spawner abundance, and hatchery production, and, if aggregated across stocks, may be dominated by changes in the most abundant stocks in a given area. Therefore, to identify environmental effects on recruitment, we used survival rates from eggs to adult recruits, adjusted for the effect of spawner abundance, as a more appropriate measure of productivity. Recent analyses show that such survival rates are positively correlated among stocks across local or regional spatial scales of several hundred kilometers, but not at larger scales (Peterman et al. 1998; Pyper et al. 2001; Pyper et al. in press). Coastal sea-surface temperatures (SST) have similar spatial correlation scales, suggesting that covariation in survival rates among salmon stocks is driven by regional-scale processes in the coastal ocean (Mueter et al. in press). The objectives of this study were to quantify SST effects on survival rates of pink (O. gorbuscha), chum (O. keta), and sockeye salmon (O. nerka) across multiple stocks, to examine differences in these effects among stocks from different areas, and to determine the relative importance of regional and large-scal