BRANTA — Brad A. Andres
Consequences of the Exxon Valdez oil spill on Black Oystercatchers inhabiting Prince William Sound, Alaska
Institution: Ohio State University, U.S.A.
Supervisors: JR Bart
Details: PhD 1996 (Completed)
Address: U.S. Fish and Wildlife Service, P.O. Box 25486, DFC-Parfet Denver, CO 80225-0486 USA (Oct 2006) Email
Subject Keywords: Alaska, breeding, disturbance, Exxon Valdez, oil spill, populations, reproduction, shoreline habitat
Species Keywords: Black Oystercatcher Haematopus bachmani
Approximately 40% (16.7 million L) of the Prudhoe Bay crude oil spilled by the T/V Exxon Valdez, in 1989, in northern Prince William Sound, Alaska (Sound), was deposited along 563 km of shoreline of the Sound. Black oystercatchers (Haematopus bachmani) are completely dependent upon marine shorelines for their life’s requirements and were at risk from direct and indirect effects of the Exxon Valdez oil spill (Spill). Therefore, I undertook a study to determine the immediate effects of the Spill on reproduction of oystercatchers and to determine if oil persisting in fine sediments and mussel beds, into 1992 and 1993, was negatively affecting adult reproduction and growth rates of chicks. I also collected information on the habitat requirements of black oystercatchers.
Although direct mortality of adults was, most likely, minimal (only 2 oystercatcher carcasses were retrieved in the Sound and no oiled adults were observed on Green Island in 1989), black oystercatchers nesting along shorelines that were impacted by oil had their breeding season disrupted in 1989. On Green Island, 39% of the breeding population were not able to maintain nests into June. Oystercatcher pairs that tolerated heavily or moderately oiled nest sites and were able to hatch eggs experienced greater losses of chicks than pairs that nested at unoiled shorelines. Disturbances to shorelines, by oil impact and associated clean up operations, also reduced productivity into 1990, but by 1991 productivity had recovered and reoccupation of oiled shoreline habitats had occurred.
Gradual, gravelly shorelines indicated high quality habitat for breeding black oystercatchers; these shoreline types supported the highest densities in the Sound. In areas of steep rocky shorelines, the presence of numerous offshore islets (?100 m diameter) and mixed sand and gravel beaches were good indicators of oystercatcher habitat.
The importance of mussels as a food source for adults and young and the reliance on fine sediment shorelines for foraging sites indicated that black oystercatchers could be exposed to oil persisting on shorelines. Where shoreline oil remained in 1992 and 1993, elevated hydrocarbon concentrations in the feces of chicks indicated that black oystercatchers were being exposed to persistent oil. Petroleum hydrocarbon concentrations in sediments collected from oystercatcher foraging sites were highest in Herring Bay, in Bay of Isles, and on northwest Knight Island. Exposure to persistent oil changed the ability of adults to provision their young, possibly lowered the body condition of renesting females, and lowered the ability of chicks to gain weight. Effects of exposure to persistent oil on breeding success were overshadowed by the influence of egg and chick predators.
Because areas of persistent shoreline oil exposure were restricted, widely distributed, and highly variable, effects on the black oystercatcher population, on the short term, were minimal. The longevity of oystercatchers minimizes the importance of a single, or dual, season breeding failure. Remediation or cleaning of remaining oiled mussel beds in Prince William Sound should have a minimal impact on black oystercatcher population as whole. Additional restoration actions for oystercatchers should include the acquisition of low elevation, gravelly shorelines.
Andres, B.A. 1999. Effects of persistent shoreline oil on breeding success and chick growth in black oystercatchers. Auk 116:640-650.
Andres, B.A. 1998. Habitat requirements of breeding black oystercatchers. Journal of Field Ornithology 69:626-634.
Andres, B. A. 1998. Black oystercatcher. Exxon Valdez Restoration Notebook Series, Exxon Valdez Oil Spill Trustees, Anchorage, Alaska. 8 pp. Andres, B.A. 1997. The Exxon Valdez Oil Spill disrupted the breeding of black oystercatchers. Journal of Wildlife Management 61:1322-1328.
Andres, B.A. & G.A. Falxa. 1995. Black oystercatcher (Haematopus bachmani). Pages 1-20 in A. Poole and F. Gill, editors. The birds of North America. The Academy of Natural Sciences, Philadelphia, & The American Ornithologists’ Union, Washington D.C.