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Migration Trends for King and Common Eiders and Yellow-Billed Loons Past Point Barrow in a Rapidly Changing Environment

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Migration Trends for King and Common Eiders and Yellow-Billed Loons Past Point Barrow in a Rapidly Changing Environment Migration Trends for King and Common Eiders and Yellow-billed Loons past Point Barrow in a Rapidly Changing Environment Principal Investigator: Abby Powell1 Co-Authors: R. Bentzen2, R. Suydam3 1 Affiliate Professor, Institute of Arctic Biology, University of Alaska Fairbanks 2 Wildlife Conservation Society 3 North Slope Borough Final Report OCS Study BOEM 2018-059 October 2018 Contact Information: Email: [email protected] phone: 907.474.6782 Coastal Marine Institute College of Fisheries and Ocean Sciences University of Alaska Fairbanks P. O. Box 757220 Fairbanks, AK 99775-7220 These studies were funded in part by the U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM) under cooperative agreements M16AC00002 between BOEM, Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks. This report, BOEM 2018-059 is available through the Coastal Marine Institute, select federal depository libraries, and electronically from https://www.boem.gov/BOEM- Newsroom/Library/Publications/Alaska-Scientific-and-Technical- Publications.aspx The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Government. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Government. Contents List of Figures ....................................................................................................................................... ii List of Tables ........................................................................................................................................ ii Abstract ................................................................................................................................................iii Introduction ........................................................................................................................................... 1 Methods ................................................................................................................................................. 3 Observer Locations ............................................................................................................................ 3 Observations ...................................................................................................................................... 4 Population Estimation ....................................................................................................................... 5 Photo Analysis ................................................................................................................................... 6 Radar Analysis ................................................................................................................................... 6 Results ................................................................................................................................................... 7 Observation Periods........................................................................................................................... 7 Population Trajectory ........................................................................................................................ 8 Photo Analysis ................................................................................................................................... 9 Radar Analysis ................................................................................................................................. 10 Yellow-billed Loons ........................................................................................................................ 10 Discussion ........................................................................................................................................... 10 Population Estimates and Trajectory .............................................................................................. 11 Photo Analysis ................................................................................................................................. 13 Radar Analysis ................................................................................................................................. 13 Yellow-billed Loons ........................................................................................................................ 14 Recommendations ........................................................................................................................... 14 Conclusion........................................................................................................................................... 15 Acknowledgments .............................................................................................................................. 15 Study Products .................................................................................................................................... 16 References ........................................................................................................................................... 17 i List of Figures Figure 1. Eider migration count locations, Alaska, 2015 and 2016 .................................................. 3 Figure 2. The count location at the edge of the shorefast ice, Point Barrow, Alaska, 2016 ............ 4 Figure 3. Example of a flock photo used in the photo analysis, Point Barrow, Alaska, 2016......... 5 Figure 4. Raw number of eiders counted during spring migration, Point Barrow, Alaska, 2015 and 2016 ................................................................................................................................................ 7 Figure 5. Total eider index ± 95% confidence intervals for king and common eiders passing Point Barrow, Alaska on spring migration, 2015–2016 ..................................................................... 8 Figure 6. Number of eiders observed passing Point Barrow, Alaska, on spring migration throughout the day on 8 May 2016 ...................................................................................................... 8 Figure 7. King eider population indices and 95% confidence intervals of king eiders on spring migration past Point Barrow, Alaska................................................................................................... 9 Figure 8. Common eider population indices and 95% confidence intervals of common eiders on spring migration past Point Barrow, Alaska ....................................................................................... 9 Figure 9. Number of yellow-billed loons observed on migration past Point Barrow, Alaska, 2003, 2004, 2015, and 2016 ............................................................................................................... 10 Figure 10. Ice cover just before, during, and after peak migration in 2015 and 2016 ................... 13 List of Tables Table 1. Estimated index of total number of king and common eiders passing and 95% confidence intervals from prior surveys .............................................................................................. 6 Table 2. Raw count data for eiders on spring migration, Point Barrow, Alaska, 2015 and 2016 ... 7 ii Abstract 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 < 5.07, P > 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; |t| = 3.26, df = 297, P < 0.001) for flocks of less than 1,400 individuals (observer count). Estimates of yellow-billed loon populations were highly variable and are biased low as numbers of loons passing Pt. Barrow were still high when our counts ended in late May. It is important that counts continue to
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