But marine conservation biologist Rick Steiner, who has tracked effects of the disaster for years, has suggested that due to uncertainties noted in the study itself that the status of the Prince William Sound sea otters be moved from “recovered” to “very likely recovered.”
Brenda Ballachey, the USGS research biologist who was the lead author of the study, said signs of recovery were seen in the years leading up to 2009, 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 died during the spill. Those 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 after the spill more middle-aged otters died as well the study said.
Recovery was also assessed using studies to detect oil exposure using gene expression as a biochemical indicator, and the most recent genetic evidence suggested a reduction in oil exposure since 2008, the study said.
Steiner, who was the University of Alaska’s marine advisor for Prince William Sound at the time of the spill, read the federal report, then made his recommendations in an email to Ballachey, noting that the study itself pointed out uncertainty regarding the gene transcription data.
“Based on this uncertainty, it seems premature to conclude that there is no continuing exposure to oil, and thus that otters are fully recovered,” he said.
Steiner quoted from the study notes saying that the three 2012 Western Prince William Sound subpopulations of sea otters differed significantly from the reference sea otters.
He noted that the study also said “because 2012 gene transcription rates generally were low for sea otters from all areas relative to 2008, we cannot fully interpret these observations without data from a wider panel of genes.”
Researchers also said “we caution that the implications of overall low transcription observed in 2012, in terms of interpretation of potential exposure to oil, are not certain; and “this slight uncertainty with respect to the data from the biochemical indicator is outweighed by the strength of the data for the demographic indicators.”