Ocean warming and long-term change in pelagic bird abundance within the California current system

As a result of repeated sampling of pelagic bird abundance over 3 × 105 km2 of open ocean 4 times a year for 8 yr, we report that seabird abundance within the California Current system has declined by 40% over the period 1987 to 1994. This decline has accompanied a concurrent, long-term increase in...

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Bibliographic Details
Published in:Marine ecology. Progress series (Halstenbek) 1996-08, Vol.139 (1/3), p.11-18
Main Authors: Veit, Richard R., Pyle, Peter, McGowan, John A.
Format: Article
Language:English
Subjects:
Birds
Cruises
El Nino
Larus heermanni
Marine
Ocean currents
Ocean temperature
Oceanodroma
Oceanodroma leucorhoa
Oceanodroma melania
Oceanodroma microsoma
Oceans
Pelecanus occidentalis
Pelicans
Population dynamics
Puffinus griseus
Random allocation
Sea birds
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Summary:As a result of repeated sampling of pelagic bird abundance over 3 × 105 km2 of open ocean 4 times a year for 8 yr, we report that seabird abundance within the California Current system has declined by 40% over the period 1987 to 1994. This decline has accompanied a concurrent, long-term increase in sea surface temperature. The decline in overall bird abundance is largely, but not entirely, a consequence of the 90% decline of sooty shearwaters Puffinus griseus, the numerically dominant species of the California Current. Seabirds of the offshore waters we sampled showed a different pattern from seabirds of the shelf and slope waters. Leach's storm-petrels Oceanodroma leucorhoa, the commonest species offshore, significantly increased during 1987 to 1994, while sooty shearwaters and other inshore species declined. Thus the clearest pattern that emerges from our data is one of gradual but persistent changes in abundance that transpire at time scales longer than 1 yr. Nevertheless, we did find evidence of change at shorter time scales (weeks and months) that may relate to the El Nino episode of 1992 to 1993: Pronounced positive anomalies of abundance of brown pelicans Pelecanus occidentalis and Heerman's gulls Larus heermani in fall 1991, and black Oceanodroma melania and least O. microsoma storm-petrels in late summer 1992, likely reflect northward dispersal following reproductive failure in the Gulf of California.
ISSN:0171-8630
1616-1599
DOI:10.3354/meps139011