Stellers Eider Spring Migration Surveys Southwest Alaska 2012

Larned, William W.
USFWS -Migratory Bird Management - Alaska
Publication Date: 

The majority of the Pacific population of Steller's eiders migrates along the Bristol Bay coast of the
Alaska Peninsula in the spring, crosses Bristol Bay toward Cape Pierce, then continues northward
along the Bering Sea coast. Most then cross the Bering Strait to their breeding grounds in Siberia, with
a smaller number continuing north to the Alaska North Slope to breed (U. S. Fish and Wildlife Service
2002, Gill et al. 1978). During migration the eiders linger to feed at the mouths of lagoons and other
productive habitats. Concern over apparent declines of eiders prompted the U.S. Fish and Wildlife
Service to initiate a special spring migration survey in 1992 to monitor the population of Steller's
eiders that winters in Alaska waters. A comprehensive winter survey of the species is not feasible over
the eider’s extensive and remote winter range, which includes the Aleutian Islands, the Alaska
Peninsula, and the western Gulf of Alaska including Kodiak and lower Cook Inlet; thus we estimate
their numbers as they stage during spring migration in Bristol Bay and Kuskokwim Bay.Spring aerial surveys were conducted most years from 1992 to 2012 to monitor abundance
and habitat associations of the Pacific population of Steller’s eiders (Polysticta stelleri), which stages
for spring migration in southwestern Alaska. We recorded visual estimates of Steller's eiders and all
other identifiable water birds and marine mammals along shorelines and within estuaries and shoals
where Steller's eiders and other sea ducks were known to congregate during migration. Two to four
replicates were conducted per survey year from 1992-1997, with the highest annual count used to
describe peak numbers of eiders staging within the survey area prior to their departure to arctic nesting
grounds. Since 1997, funding cuts precluded replication in all but one year (2008), and timing of thesingle annual surveys was based on satellite imagery of sea ice, information from local contacts, and
occasionally concurrent telemetry studies. Annual Steller’s eider estimates ranged from 54,888 (year
2010) to 137,904 (year 1992), and averaged 81,453. The 2012 survey was completed 16-22 April. We
retrospectively judged that the survey was timed phenologically early based on extensive sea ice
covering major portions of eider habitat beyond mid-April; an unusual condition that may have resulted
in a lower than normal proportion of the target population within the survey area during the survey. In
2012, the Steller’s eider estimate (59,638) was 27% below the 1992-2011 mean, and 20% below the
2011 estimate of 74,369. The long-term trend (1992-2012) indicates an annual decline of 2.4 percent
per year (R2=0.45). We suspect a slight negative trend bias resulted from a higher frequency of
optimally-timed counts in early years due to selection of the highest counts from survey replicates in
1992-1997, compared to the single annual counts in subsequent years. We present maps illustrating the
2012 survey flight path and observed distribution of Steller’s eiders and other selected species. A
persistent pattern of habitat use by Steller's eiders and most other sea duck species among years provides
evidence of relative importance among southwestern Alaskan habitats to staging and migrating
waterfowl. An experimental aerial photographic molting Steller’s eider survey was initiated in
September 2012 as a possible alternative to the Spring Migration Survey to monitor the Pacific Steller’s
eider population, with results not yet available.
Key Words: Steller's eider, Polysticta stelleri, king eider, Somateria spectabilis, migration, population,
aerial, survey, waterfowl, Bering Sea, Bristol Bay