Status of Harlequin Ducks in Prince William Sound, Alaska after the Exxon Valdez Oil Spill, 1995 to 1997

This data summarizes the results of harlequin duck surveys conducted in western Prince William Sound (WPWS) and eastern Prince William Sound (EPWS) in 1995 to 1997. Since pre- and post-spill analysis could not be conducted due to a lack of data on harlequin ducks prior to the spill, comparison of demographic characteristics of harlequin ducks utilizing areas not affected by the spill, EPWS, to areas affected by the spill, WPWS, was utilized. The number of breeding pairs, age and sex composition of the population, molt chronology, and the number of broods were used to determine whether harlequin ducks in EPWS and WPWS exhibit similar demographic characteristics. Annual counts of harlequin ducks were used to compare population trends for each study area. Variation between study areas in population structure or growth would indicate dissimilar extrinsic influences acting on harlequin populations.

Surveys of nearshore transects were conducted simultaneously in EPWS and WPWS during three spring and three fall period in 1995, 1996, and 1997, and during one winter survey in March 1997. Spring surveys were timed to monitor harlequin ducks during the breeding season, while fall survey coincided with molting and brooding rearing. During spring and winter surveys, the number of breeding pairs was recorded and males were either classified as sub-adult or adult based on plumage. During the fall surveys, numbers of flightless and flight-capable ducks, and the number and age of duckling observed in each brood were recorded. To increase the likelihood of locating harlequin broods, expanded fall surveys were conducted in 1995, 1996, and 1997 to include potential brood rearing areas not visited during the normal standard surveys.