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Research Technical Report

A PDF version of this paper is available here:

Nevins et al. 2011

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Chronic Oil and Seabirds

Nevins, H.M., C. Young, C. Gibble, and J.T. Harvey (March 2011)

Report to California Department of Fish and Game Office of Spill Prevention and Response. [unpublished report] 47 pp.


The goal of this study was to determine trends and sources of chronic oiling and other mortality factors affecting marine birds in central California, provide this information to California Department of Fish and Game Office of Spill Prevention and Response (CDFG-OSPR) to determine the species and populations affected by oil, and to help guide appropriate mitigation and restoration actions. This information is central to CDFG-OSPR's mission "to provide best achievable protection of California's natural resources by preventing, preparing for, and responding to spills of oil and other deleterious materials, and through restoring and enhancing affected resources." Specifically, our objectives were to 1) quantify and document trends in chronic oiling and other mortality factors by conducting necropsies of seabirds collected by beach survey programs, rehabilitation centers, and state and federal resource agencies, 2) identify sources of oil by analyzing oiled feather samples and comparing them to known specimens at the CDFG-OSPR Petroleum Chemistry Lab (PCL), and 3) increase understanding of the population-level affect of oil spills on marine birds by examining post-litigation specimens.

Our results indicate chronic oiling is the cause of 1 to 4% of annual mortality of marine birds in central CA. Species groups most affected by chronic oiling were alcids, loons, grebes, cormorants, pelican, procellarids, phalaropes, and gulls; these same species are also those most affected by catastrophic oil spills. We found several other mortality factors which continue to affect CA seabirds, including fishery entanglement, trauma, biotoxins, and to a lesser extent, plastic ingestion. We found that demographic impacts of oiling events depend upon the season in which the oil spill occurs. Winter events such as Luckenbach spills affected first year birds more than adults whereas late summer and fall spills (e.g, Kure, Stuyvesant) affected more adults than expected. These results may be useful in determining population-level impacts of both chronic and catastrophic oiling events in the future and designing appropriate mitigation plans.