Response of common murres to the Exxon Valdez Oil Spill and long-term changes in the Gulf of Alaska marine ecosystem

Abstract

Short-term effects of the 1989 TV Exxon Valdez oil spill on seabirds were dramatic and well documented. Seabird populations at sea in the spill zone were immediately depressed, and more than 30,000 dead, oiled seabirds were recovered from beaches within months of the spill. It is estimated that 250,000 seabirds were killed by oil, of which 74% were murres. Based on comparisons of prespill (1970s) and postspill (1989-1994) data, long-term effects on murres attributed to oil pollution included population declines, reduced breeding success, and delayed breeding phenology. Populations remained depressed, but breeding success phenology gradually returned to normal levels by 1993. An alternative hypothesis to explain these long-term effects is that murres were responding to natural events in their marine environment. Flow of the Alaska Coastal Current (ACC) was at an all-time low in 1989, and this may have reduced and delayed biological productivity in the ACC. On a broader time scale, marked changes in marine fish communities have occurred during the past 20 years. Coincident with cyclical fluctuations in seawater temperatures, the abundance of small forage species (e.g., humpy shrimp, capelin, and Pacific sandfish) declined precipitously in the late 1970s while populations of large predatory fish (e.g., walleye pollock, Pacific cod, and flatfish) increased dramatically. Correspondingly, seabird diets shifted from mostly capelin in the 1970s to mostly Pacific sand land and juvenile pollock in the late 1980s. Furthermore, a variety of seabirds and marine mammals both inside and outside of the oil spill zone exhibited signs of food stress (population declines, reduced productivity, die-offs) throughout the 1980s and early 1990s. We conclude that available data are inadequate to distinguish between long-term effects of the Exxon Valdez oil spill on murres and a natural response of murres to long-term changes in their marine environment.