Case Study: Sea Otters
Oiled sea otters were the icons of the spill and its effects, and remain one of the area's most compelling animals. While overall population numbers in western Prince William Sound have recovered, local populations in heavily-oiled areas have not recovered as quickly.
Sea otters excavate pits while foraging for food, including their preferred food item, clams. Sometimes these pits are excavated in the intertidal zone. Using depth recording instruments, researchers have looked at the data from more than 10 million dives. These data have shown that sea otter diving activities within the intertidal zone are centered around the zero tide elevation, and up to +1-2 feet above that. Although they have a fur coat, sea otters lack the thick, insulating layer of blubber found in other marine mammals. Thus, they rely on a high caloric intake to maintain their body temperature. To do this, otters must consume about 25% of their body weight each day. This requires each otter dig thousands of pits each year.
Sea otters usually have very small home ranges of a few square kilometers. In these small ranges, it is unlikely that the otters are avoiding areas of lingering oil when foraging. Unfortunately, when clam beds and lingering oil patches overlap, it is likely that digging pits continues to expose sea otters to oil. The otters digging activities do reduce the amount of subsurface oil in the long term: in the process of digging a pit, sediments and the subsurface oil are released and re-suspended in the water and exposed to weathering.
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Current Trustee Council-funded studies monitor environmental damage from the remaining oil. Additional studies have been funded to determine where else in the spill-affected area subsurface oil may persist, and what, if anything, to do about it.
Following the oil and its impacts over the past 20 years has changed our understanding of the long-term damage from an oil spill. Because of the scope and duration of the restoration program, lingering oil and its effects were discovered and tracked. As a result, we know that risk assessment for future spills must consider what the total damages will be over a longer period of time, rather than only the acute damages in the days and weeks following a spill. Beaches in the Gulf of Alaska are unique because of their composition and structure, and the lack of waves and winter storm action. This, along with the colder temperatures, is partly why oil has persisted and remained toxic here. The potential for long-term damage remains wherever oil persists after an oil spill, whether it is buried in the ocean bottom, marshes, mangroves, or other habitats that are not dynamic.