On the 25th anniversary of the Exxon Valdez oil spill, a review of species impacted by the incident shows recovery is varied. Seven species are considered recovered, the latest being the sea otter whose recovery was announced in 2013. Four species are recovering but have not reached pre-spill status, two species’ recovery status is unknown and one species is not recovering. Lingering oil in nesting and foraging areas was a factor until 2004 in the slow recovery of some species, with climate change, reduced prey availability, predation by introduced species and natural low reproductive rates playing a part in delaying recovery. Full details of the recovery project are available at the Exxon Valdez Oil Spill Trustee Council website.
Recovered species:
- Bald eagle (1996)
- Common loon (great northern diver) (2007)
- Common murre (guillemot) (1997)
- Cormorants (pelagic, red-faced, double crested) (2005)
- Harbour (common) seal (2005)
- River otter (1999)
- Sea otter (2013)
Recovering species:
Barrow’s goldeneye
As of December 2000, this species was tentatively considered recovered, however, the population of Barrow’s goldeneye on Knight’s Island (a heavily oiled island) was stable while that of Montague Island (an unoiled island) was increasing, suggesting full recovery had not yet occurred. Until 1997, this species continued to show signs of exposure to oil. Studies of intertidal sediments and mussels (an important food source) in 1999 showed ongoing elevated levels of hydrocarbons, which may be a contributing factor to the Knight’s Island population not increasing in step with other areas.
Complete assessment of recovery of Barrow’s goldeneye is hampered by lack of information on site fidelity and dispersal.
Black oystercatcher
The black oystercatcher was also tentatively designated as recovered in 2000, but, as with the goldeneye, persistent oil in the habitat and prey species of these birds has resulted in chronic exposure and subsequent higher levels of nest failure. This species nests in rocky areas near the intertidal zone and feeds on mussels and other intertidal invertebrates. In addition, human disturbance in nesting areas has a profound effect on this species. Ongoing exposure to petroleum products was documented as late as 2004 and is considered a factor in the continued high rate of nest failure in this species.
Harlequin duck
Another species that spends most of its time in intertidal and shallow subtidal zones, the harlequin duck has also been subject to long-term chronic exposure to oil. For this species, of concern is the low female survivorship in oiled areas. While survival rates are increasing and numbers are no longer declining it is expected to take some time before full recovery is achieved.
Orca
The recovery of such a long-lived, slow reproducing species is expected to take some time, particularly in situations such as occurred during and immediately after EVOS where 15 of the 22 whales known to be part of the AT1 group went missing. Overall, mortality for the AB pod was 19% in 1989 and 21% in 1990. Normal mortality is 2.2% or less. Because whales were observed surfacing in the slicks following the spill, it is assumed that inhalation of petroleum vapors is a factor, as is the potential consumption of contaminated prey, in this case-common/harbour seals and sea otters. A confounding factor is the finding of high levels of other contaminants-PCBs and DDT/DDT metabolites-which are linked to reproductive failure in other species. Also of importance with this species is that, while the AB pod is considered to be recovering with low but stabilised reproductive rates, the AT1 population is listed as Not Recovering based on continued decline in numbers.
Recovery unknown:
Kittlitz’s murrelets
Assessment of this species’ recovery is hampered by the lack of pre-spill data and the fact that the population was in decline began before the spill. The species is only found in Alaska and the Russian Far East and it is estimated that between 5 and 10% of the world’s population of Kittlitz’s murrelet died during the spill. These birds have a naturally low population growth rate so recovery from acute losses would be slow. In addition, there is some evidence suggesting that climate change plays a role in the overall decline, and that predator impacts may also be limiting their recovery. The rarity of this species makes it difficult to study. Ongoing marine bird surveys will track the population but no specific studies or surveys are planned.
Marbled murrelets
As with the Kittlitz’s murrelet, marbled murrelets were also in decline before the Exxon Valdez spill. Climate change, reduced food base (Pacific herring and sand lance) and decreased habitat availability are all implicated in this decline. 6-12% of the marbled murrelets in the area of the spill were killed. Following the spill, foraging and other natural behaviours were likely disrupted by clean-up activities. This species also has a naturally low productivity rate resulting in slow recovery from sudden high losses to the population. Annual census of these birds has been highly variable year on year since the spill, adding to the uncertainty of recovery status.
Not recovering:
Pigeon guillemots
The pigeon guillemot population was likely declining before the spill but the reasons for the decline are not well understood. During the spill an estimated 10-15% of the population from the spill area died. In addition, reduction in normal prey (shellfish) for minks and otters likely caused increased nest predation after the spill. Oil exposure appears to been a problem up until 2004, however, the species continues to decline in both oiled and non-oiled areas. Decline in sand lance, a particularly valuable prey species as it is high in fat, and increased nest predation by introduced predators such as fox, are considered factors in the continued decline.