We estimated the summer and winter abundance of marine birds in Prince William
Sound, Alaska, following the 1989 Exxon Valdez oil spill, examined changes in population size
between pre-spill and post-spill surveys, and compared pre- to post-oil spill population trends in
the oiled zone of the Sound relative to trends in the unoiled zone.
Ninety-nine species of birds were observed on surveys. Not all species were equally vulnerable to
the oil spill because of the seasonal and geographic distribution. Estimated populations of 15 to
32 speciedspecies groups demonstrated declines over the 17-19 year period between pre- and
post-spill surveys; the largest declines occurred for scoters, arctic tern, and murrelets. However,
because of the long time period between surveys, we could not directly associate overall
population declines with the oil spill.
We detected fewer black oystercatchers and pigeon guillemots than expected in the oiled zone
after the oil spill during winter. Similarly, we detected fewer cormorants, harlequin ducks, black
oystercatchers, and northwestern crow than expected in tile oiled zone after the spill during
summer. We estimated net loss in populations within shoreline habitats in the oiled zone relative
to the unoiled zone, pre- to post-spill in the summer and detected losses for 6 to 20
species/species groups, including loons, harlequin duck, scoters, black oystercatcher, mew gull,
and arctic tern. We think the populations of birds present in the Sound during March were most
at risk to the immediate effects of the oil spill, but we detected declines for only 2 species during
this time of year. We also detected an oil spill effect for summer populations of some nearshore
species. We concluded that oiled zone populations of nearshore species, including harlequin
duck, black oystercatcher, pigeon guillemot and northwestem crow, showed the most injury from
the oil spill because of their prolonged exposure to oil along the oiled beaches.