Re: What're the statistics for the animals that are harmed by the Exxon Valdez?

Dear Jay,

in your question, you ask for the statistics on all the animals harmed in the Exxon Valdez oil spill. Unfortunately, the data are very limited. It is relatively easy to find data on how many animals were initially found dead after the spill: there's a good summary in this article, for instance, mainly drawn from the scientific reports of the Exxon Valdez Oil Spill Trustee Council. Another good reference can be found here. However, most of this research focused on large, charismatic animals like birds and sea otters, or on economically important animals like fish and shellfish. There is very little information on animals like starfish, snails, jellyfish, plankton, etc., which also play an important role in the ecosystem of Prince William Sound.

Another problem in evaluating the impacts of the oil spill is that we have very little data on the initial conditions of the area before the spill. While we can estimate how many animals were harmed in the spill, there's no way to estimate how badly this affected the populations if we don't know how large the populations were in the first place. For instance, let's take the example of sea otters, a fascinating and highly visible species. Sea otters have been important to humans in the region for hundreds of years, first as a source of fur and later as a tourist attraction, yet despite their popularity and charisma, there were no detailed studies of the sea otter populations in Prince William Sound until after the Exxon Valdez oil spill. A study from 1992, three years after the spill, determined that there was not enough information to tell whether the spill had impacted otter populations, despite the huge number of oil-soaked carcasses that had washed ashore. Even ten years after the spill, researchers still couldn't say with certainty how severely the otter populations were affected.

One alarming aspect of the oil spill is that the effects have lasted much longer than scientists initially thought. A study Charles Peterson and colleagues, from 2003, found that even after 14 years, remnants of the oil spill still threatened many elements of the Prince William Sound ecosystem. Deposits of crude oil have persisted on the sea floor, threatening shellfish, and levels of some contaminants have remained high enough to still cause developmental damage to fish eggs. (If you can't access the Peterson article, there is a fairly good summary here from the BBC.)

It is a common misconception that scientists have a clear and infallible knowledge of the natural systems that they study. In practice, scientific conclusions are only as good as the data from which they are drawn. In the case of Exxon Valdez, we know that the spill had a devastating impact on the animal populations of Prince William Sound, and that the impacts may be more far-reaching and lasting than we initially predicted. However, it is very difficult to estimate the entire magnitude of the spill's effects without having baseline data on the animal populations in the area. This points to the importance of basic ecological research: if teams of scientists had studied Prince William Sound intensively before the disaster, we would have a much better understanding of the spill's effects, and potentially a much better idea of how to help the ecosystem recover.