Variable responses of seabirds to change in marine climate: California Current, 1985–1994

• Published in: Marine ecology. Progress series (Halstenbek) 2001-03, Vol.212, p.265-281
• Main Authors: Oedekoven, Cornelia S., Ainley, David G., Spear, Larry B.
• Format: Article
• Language: English
• Subjects: Agnatha. Pisces; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Breeding; Climate change; Demecology; Fundamental and applied biological sciences. Psychology; Marine; Marine fishes; Ocean currents; Oceans; Ptychoramphus aleuticus; Puffinus griseus; Regression coefficients; Sea birds; Thermoclines; Upwelling water; Uria aalge; USA, California; Variable coefficients; Vertebrata
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps212265

We conducted annual ship-board surveys to determine the density and distribution of seabirds off central California in relation to marine climate, from 1985 to 1994. Summarized here are results for the sooty shearwaterPuffinus griseus, the common murreUria aalge, and Cassin’s aukletPtychoramphus aleuticus, the 3 most abundant seabirds in the central part of the California Current (91% of seabird abundance and biomass). During the study, sea-surface temperature, wind speed and thermocline depth all increased, salinity decreased and thermocline intensity (slope) showed no consistent trend. Periods of cool water and warm water, as well as offshore and inshore excursions of the shelfbreak front, alternated and were mediated by the Southern Oscillation and upwelling intensity. The responses to climate variation by the 3 seabird species were in accord with their respective morphologies and natural history patterns. All moved closer to shore and away from the shelf-break front (which also weakened). Abundance of the shallow-diving shearwater and auklet decreased dramatically, but those of the deeper-diving murre did not. The shearwater, which nests in the southern hemisphere and is the most mobile of the 3 seabirds, likely changed its migration routes and reduced its association with the California Current. The auklet, which breeds within the study area and lacks mobility, declined in number, most likely due to reduced breeding success and subsequent reduced population size. Remaining auklets moved away from the shelfbreak, but not as far inshore as the shearwater. The murre, which also breeds locally, is the most adaptable owing to its deeper-diving capabilities. It shifted distribution within the study area to feed on alternative prey found throughout the water column.