OCS Study BOEM 2018-059. U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM), Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks. 19 pp.
OCS Study BOEM 2018-059. U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM), Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks. 19 pp.
Most of the king (Somateria spectabilis) and common eiders (S. mollissima v-nigra) nesting in northern Alaska and northwestern Canada pass Point Barrow, Alaska, during spring and fall migrations. Yellow-billed loons (Gavia adamsii), a species of international conservation concern, also migrate past Point Barrow. Spring migration counts of eiders have been conducted at Point Barrow approximately every ten years since 1976. These counts indicate that both eider species experienced population declines of approximately 50% between 1976 and 1996, and that the declines had stabilized by 2004. Population estimates derived from migration counts have not been previously estimated for yellow-billed loons. We conducted spring counts of eiders and loons in 2015 and 2016 to obtain population indices to compare with eider counts from 1994, 1995, 2003, and 2004, and loon counts from 2003 and 2004. These data allowed us to evaluate current and long-term trends. We estimated (95% confidence intervals) that 796,419 (± 304,011) king and 96,775 (± 39,913) common eiders passed Point Barrow in 2015 and 322,381 (± 145,833) king and 130,390 (± 34,548) common eiders passed Point Barrow in 2016. Both king and common eider population indices increased from 1994 through 2016; however, the increase over time was not significant (F 0.087, df = 1). Our population indices for king eiders were very different between the two years of this study, possibly due to a very short and intense migration peak in 2016. This peak resulted in a population count that was biased low because sampling periods did not adequately capture the peak of migration. The numbers of common eiders were similar between the two years, and within range of counts conducted in 2003–2004. Photo analysis of flocks indicated that observer counts were on average 4% lower than photo counts (paired t-test;