SPATIAL AND TEMPORAL FACTORS AFFECTING SURVIVAL IN COHO SALMON (ONCORHYNCHUS-KISUTCH) IN THE PACIFIC-NORTHWEST

Survival rates for coho salmon (Oncorhynchus kisutch) were estimated f or all coded wire tag release groups in the Pacific Northwest between 1971 and 1990. The spatial and temporal patterns show considerable geo graphic variation, with most regions south of northern British Columbi a showing declining survival since 1983, while northern areas have sho wn increasing survival during that period. The number of years of oper ation explained very little of the variation in survival, and many hat cheries showed major increases in survival after several years of oper ation. Survival of marked wild fish generally showed the same trend as hatchery fish. We conclude that the dominant factor affecting coho sa lmon survival since the 1970s is ocean conditions and that there are m ajor geographic differences in the pattern of ocean conditions. The de cline in survival seen in British Columbia and south over the last dec ade suggests that a major reduction in exploitation rates is necessary to maintain the populations.