BOEM Report 2016-077 Abundance Estimates of Ice-Associated Seals: Bering Sea Populations that Inhabit the Chukchi Sea During the Open-Water Period FINAL REPORT By Peter L. Boveng, Michael F. Cameron, Paul B. Conn, and Erin E. Moreland Marine Mammal Laboratory Alaska Fisheries Science Center 7600 Sand Point Way NE Seattle, WA 98115 Prepared for U.S. Department of Interior Bureau of Ocean Energy Management Alaska Outer Continental Shelf Region Environmental Studies Section 3801 Centerpoint Drive, Suite 500 Anchorage, AK 99503-5823 This study was funded by the U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM), through Interagency Agreement M12PG00017 with the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, as part of the MMS Alaska Environmental Studies Program. i DISCLAIMER This report has been reviewed by the Bureau of Ocean Energy Management and is approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Service, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. REPORT AVAILABILITY This document is available to the public through: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 FAX: (703) 605-6900 And at http://www.boem.gov/Environmental-Stewardship/Environmental-Studies/Alaska-Region/Index.aspx CITE REPORT AS Boveng, P.L., M.F. Cameron, Paul B. Conn, and E.E. Moreland. 2017. Abundance Estimates of Ice- Associated Seals: Bering Sea Populations that Inhabit the Chukchi Sea During the Open-Water Period. Final Report. BOEM Report 2016-077. Bureau of Ocean Energy Management, Alaska Outer Continental Shelf Region, Anchorage, Alaska, USA. ix + 119 pp with appendices. BOEM Report 2016-077 PROJECT ORGANIZATION Peter Boveng; NMFS, Seattle, Washington: Principal Investigator and report author Michael Cameron; NMFS, Seattle, Washington: Co-Principal Investigator and report author Erin Moreland; NMFS, Seattle, Washington: Project Coordinator and report author Josh London; NMFS, Seattle, Washington: Data Manager Paul Conn, NMFS, Seattle, Washington: Statistician and report author Brett McClintock, NMFS, Seattle, Washington: Statistician Jay Ver Hoef; NMFS, Seattle, Washington: Statistician i BOEM Report 2016-077 ABSTRACT Bearded, spotted, ribbon and ringed seals are key components of Arctic marine ecosystems and they are important subsistence resources for northern coastal Alaska Native communities. Although these seals are protected under the Marine Mammal Protection Act (MMPA) and bearded and ringed seals have been listed as threatened1 under the Endangered Species Act (ESA), no reliable, comprehensive abundance estimates are available for any of the species. Obtaining reliable abundance estimates for ice-associated seals is vital for developing sound plans for management, conservation, and responses to potential environmental impacts of oil and gas activities and climate change. The Bering Okhotsk Seal Surveys (BOSS) project addressed the most critical need for fundamental assessment data on ice- associated seals (also known as ice seals) in the Bering and Okhotsk Seas. Improved monitoring of ice seals is fundamental for the National Marine Fisheries Service (NMFS) to meet its management and regulatory mandates for stock assessments under the MMPA and extinction-risk assessments under the ESA. The best way to estimate the abundances of ice-associated seals is to conduct aerial photographic or sightings surveys during the reproductive and molting period when the geographic structure of the population reflects the breeding structure and the greatest proportions of the populations are hauled out on the ice and are available to be seen. The distributions of these seals are broad and patchy and so surveys must cover large areas. Similarly, the extent, locations, and conditions of the sea ice habitat change so rapidly that surveys must be conducted in a relatively short period of time. The expense and logistic complexity of these surveys have been the primary impediments to acquisition of comprehensive and reliable estimates, though the complexity of the seals’ behavior is also a factor. Scientists at the Polar Ecosystems Program of NOAA’s National Marine Mammal Laboratory, Alaska Fisheries Science Center, collaborated with colleagues from the State Research and Design Institute for the Fishing Fleet (“Giprorybflot”) in Saint Petersburg, Russia, to conduct synoptic aerial surveys of ice- associated seals in the Bering and Okhotsk Seas. Conducting spring-time surveys in those areas will yield abundance estimates for the entire population of ribbon seals, and all but a small fraction of the spotted seal population. For bearded seals, the surveys included the large and important fraction of the population that overwinters and breeds in the Bering and Okhotsk Seas. The U.S. Bureau of Ocean 1 Pending litigation. ii BOEM Report 2016-077 Energy Management (BOEM) provided critical financial support in 2012 and 2013 to complete the U.S. surveys of the central and eastern Bering Sea. Surveys for the portions of the bearded and ringed seal populations that breed in the Chukchi and Beaufort seas will require separate and subsequent surveys, possibly with different seasonal timing. Two years of survey effort were required to achieve adequate precision for abundance estimates and to ensure that sufficient periods of suitable weather occurred during survey periods. Aerial surveys were conducted in spring 2012 and 2013. In the United States and Russia combined, the teams flew more than 47,000 nautical miles (nmi) (87,000 km) of survey track. The completion of this project marks the largest survey of ice-associated seals ever completed and will provide the first comprehensive estimates of abundance for bearded, spotted, ribbon, and ringed seals in the Bering Sea and Sea of Okhotsk. Analysis of full data sets from both years indicate substantial annual variation in numbers of seals in the U.S. portion of the Bering Sea during April and early May. Model-averaged estimates in 2012 were 240,000 spotted seals, 117,000 ribbon seals, 170,000 bearded seals, and 186,000 ringed seals. In contrast, the estimates for 2013 were lower: 163,000 spotted seals, 38,000 ribbon seals, 125,000 bearded seals, and 119,000 ringed seals. Seals may have been distributed farther to the west in 2013 (i.e. more in Russian waters), but there is substantial uncertainty about ribbon and spotted seal numbers in 2012 because weather constraints prohibited us from conducting many flights over the southwest portion of our study (at the ice edge) where densities were the highest. Based on the proportions of 165 seals instrumented with satellite tags in separate studies, we estimate that 69,000-101,000 (42%) of spotted seals and 6,000-25,000 (21%) of ribbon seals that occupy the eastern (U.S.) Bering Sea in spring used the Chukchi Sea during the summer, open-water period in 2013 and 2012, respectively. KEY WORDS: bearded seal, Erignathus barbatus, ribbon seal, Histriophoca fasciata, ringed seal, Phoca hispida, spotted seal, Phoca largha, ice-associated seals, abundance, distribution, aerial survey, Bering Sea, Sea of Okhotsk, Chukchi Sea, Arctic iii BOEM Report 2016-077 CONTENTS PROJECT ORGANIZATION .............................................................................................................................. i ABSTRACT ..................................................................................................................................................... ii CONTENTS ................................................................................................................................................... iv LIST OF FIGURES ......................................................................................................................................... vii LIST OF TABLES ............................................................................................................................................ ix INTRODUCTION ............................................................................................................................................ 1 Species Background .................................................................................................................................. 1 Spotted Seal (Phoca largha) ................................................................................................................. 1 Bearded Seal (Erignathus barbatus nauticus) ...................................................................................... 2 Ribbon Seal (Histriophoca fasciata) ..................................................................................................... 4 Ringed Seal (Phoca hispida hispida) ..................................................................................................... 5 Previous Research .................................................................................................................................... 7 Using recent abundance surveys to estimate statistical power and effort required for Bering- Okhotsk seal surveys (BOSS) ................................................................................................................ 7 Using seasonal movement studies to determine proportions of seals from the Bering Sea that use the Chukchi Sea during summer .......................................................................................................