At-Sea Distribution and Abundance of Seabirds off Southern California A 20-Year Comparison

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Language: English with bilingual abstract in English and Spanish

The authors conducted aerial at-sea and coastal surveys to examine the distribution and abundance of seabirds off southern California, from Cambria, California, to the Mexican border. From May 1999-January 2002, they flew 102 days, covered >54,640 km of transect lines, and conducted nine complete surveys of southern California in January, May, and September. They identified 54 species comprising 12 families and counted >135,000 individuals. Seabird densities were greater along island and main-land coastlines than at sea and were usually greatest in January surveys. Densities were greatest at sea near the northern Channel Islands in January and north of Point Conception in May, and lowest in the southwestern portion of the Southern California Bight in all survey months. On coastal transects, sea-bird densities were greatest along central and southern portions of the mainland coastline from Point Arguello to Mexico. They estimated that 981,000 ± 144,000 (average ± SE) seabirds occurred in the study area in January, 862,000 ± 95,000 in May, and 762,000 ± 72,000 in September. Detailed results indicate that seabird abundance has declined off the southern California coast in the past two decades, and these declines may be warning signs of environmental degradation in the region or effects of larger forces such as climate change.

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