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Ribbon Seals and Their Relationship with Sea Ice in the Bering Sea

Ribbon Seals and Their Relationship with Sea Ice in the Bering Sea. Peter Boveng, Shawn Dahle, Michael Cameron, John Bengtson, Josh London, Erin Moreland, Heather Ziel, Kym Yano, & Luciana Santos Polar Ecosystems Program, National Marine Mammal Laboratory

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Ribbon Seals and Their Relationship with Sea Ice in the Bering Sea

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  1. Ribbon Seals and Their Relationship with Sea Ice in the Bering Sea Peter Boveng, Shawn Dahle, Michael Cameron, John Bengtson, Josh London, Erin Moreland, Heather Ziel, Kym Yano, & Luciana Santos Polar Ecosystems Program, National Marine Mammal Laboratory NOAA Alaska Fisheries Science Center, Seattle, Washington

  2. The 2008 summer sea ice extent was the 2nd lowest on record, just slightly higher than 2007. • Concerns about ice-associated marine mammals: • Tynan & DeMaster 1997 • ACIA 2005 • Bengtson 2006 • Learmonth et al. 2006 • Simmonds & Isaac 2007 • Kovacs & Lydersen 2008 • Laidre et al. 2008 • Moore & Huntington 2008 • Center for Biological Diversity 2007

  3. Where, when, and how do ribbon seals use sea ice? Within this context, what are the expectations for future ice conditions? And the implications for the fate of ribbon seals?

  4. Ribbon seals rarely come ashore, and are not known to breed on land

  5. Timing of Ribbon Seal Life History Events

  6. Haul-out records of 46 ribbon seals

  7. Prolonged haul-out during adult molt (May & June) • Intermittent haul-out during whelping & breeding (April – mid May) • Weaned pups spend a lot of time on the ice, but with frequent forays into the water (May) Haul-out Timing

  8. Where, when, and how do ribbon seals use sea ice? Within this context, what are the expectations for future ice conditions? And the implications for the fate of ribbon seals?

  9. (Stabeno and Overland, submitted) • Climatological Conditions: • Cold and dark in winter • Mean monthly maximum temperature at Nome <-3oC, Nov – April • Analogs for future conditions: • De-coupling of Bering Sea annual ice from Arctic Ocean perennial ice, 2007/2008 • Sea ice in the northern Bering Sea in other years

  10. IPCC Model Projections for Bering Sea The Bering Sea will continue to have ice in April Sea ice in May will continue to vary substantially from year-to-year Rapid melting in June; many years have been “zero” in the past and these will increase in frequency; resolution issue (figure courtesy of Muyin Wang & Jim Overland)

  11. Where, when, and how do ribbon seals use sea ice? Within this context, what are the expectations for future ice conditions? And the implications for the fate of ribbon seals?

  12. No quantitative basis for estimating the impact on vital rates from increased frequency of years with less ice, poor ice quality, or early melt • Assumption of current demographic equilibrium leads to a conclusion that the population will decline if conditions for reproduction and survival deteriorate, even slightly • A qualitative consideration of potential impacts and factors potentially conferring resilience to these impacts, led to a prediction of a gradual population decline for the foreseeable future Implications

  13. Aerial survey of eastern & central Bering Sea pack ice • US Coast Guard Icebreaker Healy • Helicopter line-transect surveys • 12 April – 4 May 2007

  14. Ribbon seal abundance estimate 0.2796 seals/nmi2 X 64,500 nmi2 = 18,034 seals

  15. The proportion of ribbon seals hauled out during surveys was estimated from satellite-linked recorders 18,034 ÷ 0.365 = 49,370 total ribbon seals mean = 0.365 {

  16. Comparison with historical estimates *western Bering Sea

  17. Conclusions • To reliably predict the impacts of climate warming on ice-dependent species, it is critical to consider the specific context of where, when, and how the species interacts with ice • Model projections indicate that ribbon seals will continue to encounter ice for reproduction in the Bering Sea and Sea of Okhotsk • Survival of pups and adults may be reduced from less frequent years with sufficient ice for early development and molting • The total abundance of ribbon seals is poorly known, but is likely sufficient to sustain a gradual decline for the foreseeable future • New estimates are badly needed for the western Bering Sea and Sea of Okhotsk if we hope to be able to track potential climate-related changes in ice-associated seals of this region

  18. http://www.fakr.noaa.gov/protectedresources/seals/ice.htm

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