Effects of Persistent Shoreline Oil on Breeding Success and Chick Growth in Black Oystercatchers

Abstract

To determine if Black Oystercatchers (Haematopus bachmani) were affected by persistent shoreline oil from the T/V Exxon Valdez oil spill, I identified contaminated foraging sites of oystercatchers, quantified diet and foraging behavior, assessed hydrocarbon uptake, and measured breeding success and mass gain of chicks. Hydrocarbon concentrations in sediments at foraging sites indicated that some oystercatchers potentially were exposed to shoreline oil that persisted into 1992 or 1993. Direct evidence of hydrocarbon exposure was obtained from feces of chicks raised on persistently oiled shorelines. Elevated concentrations of total hydrocarbons, even-numbered aliphatics, and unresolved complex mixtures were indicative of petroleum hydrocarbon exposure. Mussels (Mytilus trossulus) were an important component of the diet of adults and chicks. Oystercatchers foraged for mussels on low-sloping, mixed sand-and-gravel beaches that often retained oil but spent less time foraging on contaminated substrates than on unoiled substrates. Effects of persistent shoreline oil on measures of breeding success were negligible and likely were overridden by the influence of egg and chick predation. Chicks raised on shorelines that were heavily oiled in 1989 gained mass at a slower rate than did chicks raised on shorelines that were not heavily oiled; however, slower mass gain did not translate into reduced fiedging success of chicks raised on heavily oiled shorelines. Although some oystercatchers were exposed to persistent shoreline oil, areas of contamination were patchily distributed, and relatively few adults and young were exposed. The lack of a large-scale change in oystercatcher numbers inhabiting the oiled area of Prince William Sound suggests that the negative effects of oil exposure operated locally. Consequently, oiled mussel beds present little additional risk to the population of Black Oystercatchers inhabiting Prince William Sound.