ABSTRACT
Following the Exxon Valdez oil spill of March 24, 1989, in Prince William Sound, Alaska, Exxon conducted a comprehensive shoreline survey program in cooperation with federal and state authorities. Objectives of surveys during the spring and summer of 1989 were to assess the distribution and magnitude of oiling, to evaluate impacts of the oil on key shoreline biological communities, and to identify ecological and archaeological resources requiring special care during the massive cleanup effort that followed. Similar shoreline surveys were performed during the springs of 1990, 1991, and 1992 on all shorelines in Prince William Sound and the Gulf of Alaska suspected of having residual oil. These subsequent surveys were conducted to provide information on the distribution and amounts of residual shoreline oil and to assess the condition of intertidal biological communities in order to make environmentally sound decisions regarding the need for additional cleanup.
The following report is based primarily on survey results from Prince William Sound, where most of the heavy shoreline oiling occurred. Although not strictly quantitative, the shoreline surveys provide an unprecedented, broad base of professional observations covering the entire spill-affected area from 1989 through 1992 by which to evaluate spill impacts and recovery.
Shoreline surveys documented that the extent of shoreline oiling declined substantially from 1989 to 1992. In 1989, oil was found on about 16 percent of the 3,000 miles of shoreline in Prince William Sound; by the spring of 1991, oil was found on only about 2 percent of the shoreline; and by May of 1992, on only 0.2 percent. In all years, most of this oil was located in the biologically least productive upper intertidal and supratidal zones. In both 1991 and 1992, small, isolated pockets of subsurface oil were found on some boulder/cobble beaches. Most of these deposits were also located in the upper intertidal and were usually buried beneath clean sediments.
In almost all cases, the condition of intertidal biological communities improved correspondingly from 1989 to 1992. By the spring of 1991, recovery appeared to be well under way on virtually all previously oiled shores, with species composition, abundance, and diversity levels usually comparable to those of nearby shores that were not oiled in 1989. Recruitment of intertidal plants and animals was observed as early as the summer of 1989, and increasingly through 1991 and 1992. Recruitment was evident even in areas with remnant deposits of surface and subsurface oil, indicating that toxicity levels of the oil had declined substantially and that, in most cases, the residual oil no longer interfered with biological recovery.
Observations of birds and marine mammals on or near shorelines surveyed during 1991 and 1992 confirmed that species present before the spill were still present and were feeding and reproducing in areas affected by oil in 1989. In most cases, observed densities were comparable to those recorded prior to the spill, and to those found in similar unaffected areas.
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