When the Restoration Plan was first drafted, it was assumed that oil in the environment would disappear over time and resources injured in the spill would begin a path toward recovery. We now understand that several resources injured in the original oiling continue to struggle even though they are no longer in direct contact with oil. The current status of killer whales is a clear example of these long-term effects.
Case Study : Killer Whales
Killer whales are individually identifiable and fortunately in Prince William Sound they were photographed starting in 1984, five years prior to the spill. Thus, researchers knew the numbers and associations of the whales at the time of the spill. Two groups of killer whales were photographed in slicks of oil in the weeks following the spill. These two groups lost approximately 40% of their numbers by 1990, and an additional five whales after 1990. One of these, the AB pod, is a “resident” fish-eating group of killer whales, and does show some signs of recovery. The second group is a small, unique population known as “AT1.” They are “transient” killer whales that feed on marine mammals. They show no signs of recovery and continue to decline.
The losses to killer whale populations resulted primarily from the initial, acute exposures to the spill. Most carcasses were not found following the spill—which was not surprising since killer whale carcasses are known to sink—but the missing individuals have never been seen or photographed again. It is thought that the damage to killer whales from the spill, like many of the mortalities of other marine mammals, was caused by the inhalation of the oil’s toxic fumes, as all of these species had to breath air from a few inches above the slick.
Whale pods are integral, matrilineal families. So a spill that kills any of the key members of the pod, especially reproductive-age or older females, can have far reaching consequences. The reproductive capacity of the pod was reduced by the loss of females which even under ideal conditions have a low reproductive rate, with only about half of newborn calves surviving. Since pods are matrilineal, the loss of these females means that the leaders of the pod are also lost. Some of the females that disappeared following the spill also had young offspring that died in the first few years after the spill, likely due to the loss of their mothers. In addition, the AB pod has shown signs of an unusual social breakdown within the group, with one matrilineal group leaving to join a different pod. This is a phenomenon not seen in any other resident pod in the North Pacific.
Resident killer whales in Alaska have generally been increasing since the 1980s. However, the recovery of the AB pod is slower than the growth of other fish-eating pods in Prince William Sound or in Southeast Alaska. Their full recovery to pre-spill levels will likely take an additional decade or more, if their recovery is not further compromised. For the transient AT1 population, there appears to be no hope for recovery. There has not been a successful recruitment to the pod since prior to the spill. This unique population will likely become extinct as the remaining members continue to age and die.