Final report: Spectacled eider March 2020 aerial survey
To determine winter population size and late winter distribution, we conducted an aerial survey of the Bering Sea wintering area of Spectacled Eiders (Somateria fischeri). The survey area was delineated based on satellite transmitter locations from eight marked Spectacled Eiders during the three wee...
| Main Authors: | , |
|---|---|
| Format: | Text |
| Language: | unknown |
| Published: |
U.S. Fish and Wildlife Service
2021
|
| Subjects: | |
| Online Access: | https://dx.doi.org/10.7944/p95f88yv https://ecos.fws.gov/ServCat/Reference/Profile/135508 |
| Summary: | To determine winter population size and late winter distribution, we conducted an aerial survey of the Bering Sea wintering area of Spectacled Eiders (Somateria fischeri). The survey area was delineated based on satellite transmitter locations from eight marked Spectacled Eiders during the three weeks prior to the survey. On 03 and 04 March 2020, the survey completed 13 transects spaced 7.8 km apart through the 8,600 km2 survey area. During the survey, observers documented 76,952 Spectacled Eiders in 105 flocks. The total count of eiders in 2020 was 78 percent less than the most recent count in 2010, which was just over 369,000. The 2020 survey encountered more flocks (average number of flocks encountered in the previous 8 surveys is 55, range is 19 to 115) that included fewer individuals (78 percent of flocks included fewer than 1,000 eiders in 2020) than the last survey in March 2010. Previous winter surveys documented flocks containing tens-of-thousands of individuals; however, no large flocks were encountered in 2020 when the largest flock size was just over 5,000. Spectacled Eider flocks were located farther northeast than previously documented, closer to the southeast coast of St. Lawrence Island. The potential causes of the lower count in 2020 compared to 2010 include incomplete census due to unobserved flocks within the survey area and additional flocks outside of the survey area, and population decline since the 2010 survey. We cannot disentangle the relative contributions of an incomplete count and population decline to the difference between counts in 2020 and 2010. Because the 2020 count is likely incomplete, it should be interpreted with caution and treated as a minimum count rather than a complete census. |
|---|