Patterns of Change in Climate and Pacific Salmon Production
Nathan J. Mantua
Abstract.—For much of the 20th century a clear north-south inverse production pattern for Pacific salmon had a time dynamic that closely followed that of the Pacific Decadal Oscillation (PDO), which is the dominant pattern of North Pacific sea surface temperature variability. Total Alaska salmon production was high during warm regimes of the PDO and total Alaska salmon production was relatively low during cool regimes of the PDO. Leading hypotheses for the link between climate and Pacific salmon production have focused on changes in early ocean survival for juvenile salmon, but it is clear that climate also affects freshwater life stages and influences productivity. Over broad spatial scales, the PDO-related patterns in climate and Pacific salmon production were less prominent in the period 1990–2004 than in earlier decades of the 20th century, yet the regional associations between salmon production and temperatures were generally the same: warm periods coincided with high salmon production in Alaska, and cool periods off the west coast of the continental U.S. and British Columbia coincided with high salmon production in those regions. A case study of Norton Sound pink salmon provides one regional perspective on the links between changes in climate and salmon production. In the period 1962–1995, anomalously warm winter and spring climate in western Alaska and warm spring/summer temperatures in the eastern Bering Sea generally coincided with high pink salmon production. However, especially warm conditions for freshwater and early marine life stages for Norton Sound pink salmon coincided with both high and low levels of recruits per spawner for brood years 1996–2003, a period that experienced large inter-annual variations in Bering Sea, North Pacific, and tropical Pacific Ocean conditions.