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25 Years After the Exxon Valdez, Sea Otter Population at Pre-Spill Levels

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Nearly 25 years after the Exxon Valdez oil spill injured wildlife off the coast of Alaska, sea otters have returned to pre-spill numbers within the most heavily oiled areas of Prince William Sound, according to a new report issued in February 2014 by the U.S. Geological Survey (USGS).

Sea otter (Enhydra lutris) in kelp
Above: Sea otter (Enhydra lutris) in kelp. USGS photograph by Benjamin Weitzman. [larger version]

Sea otters in the path of the oil incurred heavy mortality when 42 million liters of Prudhoe Bay crude oil were spilled in Prince William Sound in March 1989, with an estimated loss of several thousand otters. Through long-term data collection and analysis, scientists found that sea otters were slow to recover, likely because of chronic exposure to lingering oil. Other studies documented persistence of oil in the sea otter’s intertidal feeding habitats. 

Map of Prince William Sound, showing path of oil spilled from the tanker Exxon Valdez
Above: Map of Prince William Sound, showing path of oil (dark-gray shading) spilled from the tanker Exxon Valdez after it ran aground on Bligh Reef in 1989. Areas where sea otters were counted and (or) studied are labeled. Figure 1 from USGS Open-File Report 2014–1030. [larger version]

“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 USGS. “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 [a State and Federal partnership formed to oversee restoration of the damaged ecosystem].”

Scientists assessed recovery by estimating the number of living sea otters on the basis of aerial surveys and comparing that number 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 before the spill, most dead otters were either very old or very young, but after the spill, more middle-aged otters were dying as well. The ages of dead animals have now returned to the pre-spill pattern.

Recovery also was assessed with studies to detect oil exposure by using gene expression as a biochemical indicator. The most recent genetic evidence suggests 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 (see "Recovery Objective" on Sea Otters webpage).

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

The new publication, “2013 Update on Sea Otter Studies to Assess Chronic Injury from the 1989 Exxon Valdez Oil Spill, Prince William Sound, Alaska,” is available online.

Related Sound Waves Stories
Alaska Sea Otter Expedition Investigates Coastal Health
July 2011

Related Websites
Exxon Valdez Oil Spill Trustee Council
Recovery Objective
2013 Update on Sea Otter Studies to Assess Chronic Injury from the 1989 Exxon Valdez Oil Spill, Prince William Sound, Alaska
Neashore Marine Ecosystem Research Program

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in this issue:

cover story:
Assessing Climate Change Vulnerability of Pacific Atolls

Spotlight on Sandy
Fire Island Oceanographic Study Update

Linking Coastal Processes and Vulnerability at Assateague Island

Recent Hires Assist USGS Barrier Island and Estuarine Studies

EDEN and EVE—Getting the Water Right in Paradise

"Marathon" Bird May Plan Flights Based on Weather Across the Pacific

Warmer Conditions Create New Goose Habitat in Arctic Alaska

25 Years After the Exxon Valdez, Sea Otter Populations at Pre-Spill Levels

USGS Intern Teaches Kids about Ocean Acidification

USGS Scientists Support the National Ocean Science Bowl’s Spoonbill Bowl

Communications Awards Recognize Ocean Chemistry Topics

Three USGS Volunteers in Florida Working on Ocean Acidification

USGS Employee in Florida Recognized for Service on Science Museum Board

Publications New Kid on the Web: USGS CMGP Redesigned Website Goes Live

March / April Publications

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