We all have some idea of just what "recovery" is—we've all recovered from a cold or the flu—yet to ecologists studying natural systems, it is a very difficult term to define and measure. If you ask a fisherman from Kodiak Island, a villager from the town of Valdez, an Exxon engineer—or, yes, a NOAA biologist—you are likely to receive such different answers that you may wonder if they heard the same question!

Despite the remaining impacts of the largest oil spill in U.S. history, Prince William Sound remains a relatively pristine, productive and biologically rich ecosystem. (Photo credit: OR&R, NOAA)

An ecosystem like Prince William Sound constantly adjusts itself to react to, or compensate for, changes in the environment, such as:

• daily temperature variations;
• changing of the seasons;
• long-term drought;
• rare natural events, like hurricanes and earthquakes; and
• oil spills.

When the Exxon Valdez spill occurred in March 1989, the Prince William Sound ecosystem was also responding to at least three notable events in its past:

• an unusually cold winter in 1988-89;
• growing populations of reintroduced sea otters; and
• a 1964 earthquake.

In summer 2001, roughly 10,000 pits were excavated as part of a shoreline survey of Prince William Sound. Oil was found at 58 percent of the 91 sites surveyed, which is approximately equivalent to 5.8 km of contaminated shoreline (Short et al., 2001). (Photo credit: NMFS, NOAA)

Scientists studying the effects of the spill must evaluate their results against this background of other insults, or stressors, that have affected the sound.

Scientists do not define recovery as a return to the precise conditions that existed before the oil spill. They know that this is unlikely to happen. Nevertheless, they can observe a range of conditions to measure shoreline recovery from the spill.

For example, if they find that unoiled sites are changing in the same ways and at similar rates as the oiled sites, then the changes are probably caused by natural events and cannot be linked to the oil spill. If conditions at oiled sites fall outside the range found at control sites, then scientists would suspect that oil contamination is still affecting these systems.

Just as people differ in their ability to recover from injury, so do plants and animals. Some animals and plants are resilient and grow back quickly. In Prince William Sound, green algae and certain types of worms grew back the first summer. Rockweed and barnacles had repopulated many areas within 2 to 3 years. Other animals, such as clams, limpets, and some snails, are taking much longer.

Today, two escort vessels accompany each tanker that passes through Prince William Sound. They not only watch over the tankers, but are capable of assisting them in the event of an emergency, such as a loss of power or loss of rudder control. (Photo credit: Argonne National Laboratory)

In short, biologists consider the intertidal communities in Prince William Sound to be still recovering, but not completely recovered.

Scientists will continue to regularly monitor a range of study sites in Prince William Sound at least through the year 2005. In 2001, they began a smaller-scale, experimental phase of their research, focusing on fewer sites. Scientists will use this information to improve oil spill response and cleanup in the future, with an overall goal of minimizing environmental harm. Because of this, the Exxon Valdez will leave at least one positive legacy in its unfortunate wake: knowledge that will benefit all of us and the environment the next time disaster strikes.