Overview of studies to determine injury caused by the Exxon Valdez Oil Spill to marine mammals

Marine mammal damage assessment studies after the Exxon
Valdez oil spill concentrated on sea otters, harbor seals, Steller sea
lions, killer whales, and humpback whales. Sea otter and harbor seals
were the most affected marine mammal; it was estimated that several
thousand otters and several hundred harbor seals died within months of
the spill. Steller sea lion, harbor seal, and sea otter numbers were
monitored using aerial surveys. Studies of humpback whales and killer
whales used photoidentification techniques to determine changes in
abundance, distribution, mortality, and natality. Tissues from
animals found dead in spill and control areas were analyzed for
hydrocarbon levels. Sea otters, sea lions and harbor seals had
elevated hydrocarbon levels, but only sea otters and harbor seals
showed population declines associated with the spill. Humpback whales
were not severely affected by the Exxon Valdez oil spill. Killer
whale numbers in the resident AB pod declined after the spill.
Coincidental evidence supports the oil spill as the causative agent.