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The Exxon Valdez Oil Spill

Shortly after midnight on 24 March 1989, the supertanker Exxon Valdez ran aground on a reef in Prince William Sound. The tanker ripped open, resulting in the largest oil spill in U.S. history. Within a few hours, 10.8 million gallons of Alaska North Slope crude oil leaked into one of the most bountiful and diverse ecosystems in the world (Alaska Department of Environmental Conservation 1993). Over the subsequent weeks, storm winds and ocean currents broadcast the oil out of the sound, oiling 2,400 kilometers of beaches from the site of the wreck westward to the Alaska Peninsula (Figure).

   

Many wildlife populations were exposed to the toxins in the petroleum and to the viscous coating effect of the crude oil. The intertidal communities were the most immediately affected. The largest deposit of oil was stranded in the upper and middle intertidal zones on sheltered rocky shores. In these areas, seaweeds, barnacles, limpets, periwinkles, clams, mussels, amphipods, isopods, and marine worms were killed. The oil that sank into the subtidal bottom affected eelgrass beds, small crustaceans, worms, and clams. Populations of oil-degrading bacteria, which bloomed shortly after the spill, played a major role in cleaning up the nearshore areas. Bird mortalities due to the spill may have totaled as many as half a million, affecting roughly 90 species of birds (Alaska Department of Environmental Conservation 1993). Species which spend most of their time on the water's surface were most vulnerable, especially seabirds like the common murre. The marbled murrelet was another open-water foraging bird affected by the spill; as many as 12,000 died. More than 150 bald eagles were found dead after the spill. They encountered floating oil while preying on fish and consuming oil-contaminated carcasses. The marine mammal populations in the vicinity of the oil were also affected. The immediate death toll of sea otters was probably 4,500. The oil slicks that spread from the spill blackened many prime haulouts for hundreds of harbor seals just as the pupping season approached. The larger marine mammals, like humpback whales, were less affected. Over a 2-year period, 14 killer whales from a resident pod were missing and presumed dead following the oil spill (Loughlin 1994). Salmon and herring were the most seriously affected fishes. The causes of deaths for many species will never be known because the corpses sank, were washed out to sea, or were eaten by scavengers that may have then also died from ingesting oil.



Figure. Prince William Sound, Alaska, site of the 1989 grounding of the Exxon Valdez, range of the spilled oil after 5 days (Alaska Department of Environmental Conservation 1993).

The Exxon Corporation mounted an extensive cleanup effort in the spring and summer of 1989, employing thousands of people to wash the beaches with hot and cold water, remove oiled sediments, and apply chemical fertilizers to aid bacterial breakdown of the oil residues. Cleanup crews returned on a smaller scale during the summers of 1990-1992 to remove oiled sediments and keep track of changing conditions on the beaches. A trustee council, representing state and federal resource agencies, was appointed to plan and mobilize a natural resource damage assessment program. With the assistance of the Environmental Protection Agency, the trustee council developed scientific plans to restore the environment. With immediate cleanup efforts and more than 5 years of natural healing, many of the resources of Prince William Sound are well on their way to recovery or have already recovered. However, some parts of the ecosystem have not recovered and may never be the same. It is still unclear when full recovery will occur and just what it will really mean after such a large-scale catastrophic event.

   
  Author
William P. Hines
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Alaska Regional Office
P. O. Box 21668
Juneau, Alaska 99802

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