Beached bird surveys and chronic oil pollution in Central California

Abstract

This report summarises beached bird and oil pollution data gathered from September 1993 through August 2002 by Beach Watch, a longterm shoreline monitoring program. Surveys were conducted at 32 beach segments ranging from southern San Mateo County to southern Sonoma County. Beached birds were most commonly found in August and September, and most birds at this time were local nesting marine species. During the 1997/98 El Niño-Southern Oscillation (ENSO) event, the annual encounter rate for all beached birds more than doubled, and the encounter rate for oiled birds increased more than six-fold. Also during the 1997/98 ENSO the encounter rate for tarballs (hardened patties of oil) was more than twenty times that observed for the preceding year. Periodic increases of oiled birds and tarballs may have reflected the corresponding releases of heavy fuel oil from long submerged vessels, such as the SS Jacob Luckenbach, as well as illegal discharges from merchant and tank vessels. The percentage of beached birds found oiled was lower than that reported in the southern North Sea (1977-1997) and in Newfoundland (1984-1999). Comparison with an earlier beached bird dataset from central California from 1971 to 1981 (Stenzel et al. 1988) suggests that oiling rates have declined since that decade. The observations recorded by Beach Watch have contributed to the discovery, identification and prosecution of sources of pollution.