Sea otters have recovered from Exxon Valdez

The U.S. Geological Survey has published a report saying that recent surveys of Prince William Sound sea otter populations indicate that the animals have recovered from the impacts of the 1989 Exxon Valdez oil spill. The report says that otter populations have returned to pre-spill numbers in the most heavily oiled areas of Prince William Sound.

This result has been gleaned from sea otter population estimates from aerial surveys conducted in all but three years between 1993 and 2013.

“Although recovery timelines varied widely among species, our work shows that recovery of species vulnerable to long-term effects of oil spills can take decades,” said Brenda Ballachey, research biologist with the U.S. Geological Survey and lead author of the sea otter study. “For sea otters, we began to see signs of recovery in the years leading up to 2009, two decades after the spill, and the most recent results from 2011 to 2013 are consistent with recovery as defined by the Exxon Valdez Oil Spill Trustee Council.”

An assessment of sea otter carcasses found in spill-impacted areas supports the evidence from the population estimates, USGS says. Under normal conditions, otters tend to die mostly when they are either very old or very young. But researchers found an abnormally high number of dead middle aged animals following the oil spill. The age distribution of dead animals has now returned to a more normal pattern, USGS says.

Assessments of the animals’ oil exposure, using gene expression as a biochemical indicator, also suggest a reduced oil exposure since 2008, the agency says.

—Alan Bailey