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Have sea otters recovered from the Exxon Valdez spill?

 Monitoring shows populations have returned to pre-spill numbers

Alaskan_Sea_Otter

Sea otter in kelp. Photo by Benjamin Weitzman, U.S. Geological Survey.

By Summit Voice

FRISCO — It took almost quarter of a century, but federal scientists say that sea otters have recovered to pre-spill population numbers in the most heavily oiled areas of Prince William Sound, where the Exxon Valdez ran aground in 1989, spilling tens of millions of gallons of oil.

“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 lead author of the study, Brenda Ballachey, research biologist with the U.S. Geological Survey. “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.”

Several thousand otters died in the immediate aftermath of the spill, and recovery was slow. Scientists monitoring the area say chronic exposure to oil remnants likely hampered recovery. Other studies documented persistence of oil in the sea otter’s intertidal feeding habitats.

“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 lead author of the study, Brenda Ballachey, research biologist with the U.S. Geological Survey. “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.”

Scientists assessed recovery by estimating the number of living sea otters based on aerial surveys and comparing that to pre-spill numbers. They also collected carcasses of otters that had died in the spill area. Carcasses were evaluated to determine how old sea otters were when they died. Historically, and prior to the spill, most dead otters were either very old or very young, but following the spill, more middle-aged otters were dying as well. The ages of dead animals has now returned to the pre-spill pattern.

Recovery also was assessed using studies to detect oil exposure using gene expression as a biochemical indicator. The most recent genetic evidence suggested a reduction in oil exposure since 2008.

Scientists concluded that the status of sea otters in western Prince William Sound is now consistent with the criteria established for population recovery set by the Exxon Valdez Oil Spill Trustee Council.

The sea otter was one of more than 20 nearshore species considered to have been injured by the spill.

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