Spatial and temporal covariability in early ocean survival of Chinook salmon (Oncorhynchus tshawytscha) along the west coast of North America

Knowledge of the spatial and temporal extent of covariation in survival during the critical ocean entry stage will improve our understanding of how changing ocean conditions influence salmon productivity and management. We used data from the Pacific coastwide coded-wire tagging program to investigate local and regional patterns of ocean survival of Chinook salmon (Oncorhynchus tshawytscha) from the Central Valley of California to southeastern Alaska from 1980-2006. Ocean survival of fish migrating as subyearlings covaried strongly from Vancouver Island to California. Shortterm correlations between adjacent regions indicated this covariability increased, beginning in the early 1990s. Chinook salmon survivals exhibited a larger spatial scale of variability (50% correlation scale: 706 km) than those reported for other northeast Pacific Ocean salmon. This scale is similar to that of environmental variables related to ecosystem productivity, such as summer upwelling (50% correlation scale: 746 km) and sea surface temperature (50% correlation scale: 500-600 km). Chinook salmon ocean survival rates from southeastern Alaska and south of Vancouver Island were not inversely correlated, in contrast to earlier observations based on catch data, but note that our data differ in temporal and spatial coverage from those studies. The increased covariability in Chinook salmon ocean survival suggests that the marine phase contributes little to the reduction in risk across populations attributable to the portfolio effect. In addition, survival of fish migrating as yearlings from the Columbia River covaried with Chinook salmon survival from the northernmost regions, consistent with our understanding of their migration patterns.