SEABIRDS AND CLIMATE IN THE CALIFORNIA CURRENT—A SYNTHESIS OF CHANGE

Abstract

We investigated changes in ocean climate and ecosys tems by reviewing select case histories for seabirds in the California Current ecosystem (CCE) and the transition zone between the CCE and the Gulf of Alaska using data from the early 1970s to the present. We used in formation spanning the entire CCE, from the south (California Cooperative Oceanic Fisheries Investigation [CalCOFI]) to the north (Ocean Station Papa/Line P surveys) and colonies sites, to make this assessment. Seabird timing of breeding, productivity, and abundance at sea have changed in ways consistent with predictions under an ocean-warming scenario, but we cannot dismiss the hypothesis that low-frequency variability explains some of these patterns. In contrast, recent reproductive fail ures of auklets and other species cannot be explained by El Nino-Southern Oscillation (ENSO) or low-frequency variability. Declining trends in the productivity of murre and auklet “trophic chains,” including the relative abun dance of mesozooplankton (krill) and forage fish (juve nile Sebastes ) cannot be explained by low- or high(ENSO-scale) frequency climate variability. Changes in relative abundance at sea in the CalCOFI and Line P study areas, however, could be related to change points related to regime shifts in the North Pacific Ocean. Contrasting trends in life history (timing), demographic (productivity), and population (density) patterns by species highlight the need to consider spatial ecology and habi tat quality (food web attributes) in order to develop a deeper understanding of how climate change ‐ecosystem change is affecting seabirds in the CCE and adjacent North Pacific regions.