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Linking seasonal migratory patterns with prey availability in Steller sea lions

Linking seasonal migratory patterns with prey availability in Steller sea lions. Jamie N. Womble 1 , Michael F. Sigler 2 , Mary F. Willson 3 1 National Park Service-Glacier Bay Field Station 2 Alaska Fisheries Science Center-Auke Bay Laboratory

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Linking seasonal migratory patterns with prey availability in Steller sea lions

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  1. Linking seasonal migratory patterns with prey availability in Steller sea lions Jamie N. Womble1, Michael F. Sigler2, Mary F. Willson3 1National Park Service-Glacier Bay Field Station 2Alaska Fisheries Science Center-Auke Bay Laboratory 3University of Alaska Fairbanks-School of Fisheries and Ocean Sciences

  2. Migration • Occurs in many species • Annual • Seasonal • Daily

  3. Seasonal Migration • Movements among two or more areas that are occupied in different seasons during the annual cycle (Dingle 1996).

  4. Possible explanations for the evolution of migratory behavior • Reduces the risk of predation • Enhances access to resources such as breeding sites • Enhances access to patches of high-quality food and/or shifting patterns of food abundance

  5. Photo: Jeff Mondragon

  6. Serengeti Migration

  7. Objectives • Assess the seasonal distribution and migratory patterns of sea lions • Classify seasonal distribution patterns • Determine to what extent seasonal distribution patterns of sea lions can be explained by seasonal prey concentrations

  8. Prediction • Sea lions should aggregate at terrestrial sites near where seasonal prey densities are high in order to achieve energy intake to meet seasonally changing energy demands.

  9. Methods • Aerial Surveys (2001-2004) -24 sites (23 haulouts, 1 rookery) - monthly (n = 39 surveys) • Classification of distribution patterns -Standardized data by computing the proportion of maximum count for each site -Hierarchical cluster analysis • Estimation of proportion of sea lions associated with each pattern

  10. Lynn Canal Stephens Passage Icy Strait/ Cross Sound Frederick Sound Chatham Strait Gulf of Alaska

  11. ~30% in Lynn Canal JAN FEB MAR APR

  12. ~31% in Lynn Canal ~38% in Cross Sound ~30% in Cross Sound ~60% in Frederick Sound ~50% in Frederick Sound MAY JUN JUL AUG

  13. OCT SEP NOV DEC

  14. Classification of seasonal distribution patterns

  15. Type 1 Up to 55% in winter Up to 56% in spring Up to 44% in fall Up to 78% in summer

  16. Benjamin Island (2001-2004) Type1 Womble & Sigler (2006) 325: 281-293 MEPS

  17. Type 1 Womble & Sigler (2006) 325: 281-293 MEPS

  18. Type 2 Gran Point 2001-2004

  19. Spawning eulachon Spawning herring Spawning capelin Type 2 APR MAY Womble et al. (2005) 294: 271-282 MEPS

  20. Type 2

  21. Type 3

  22. Type 4

  23. Type 3 and Type 4 Salmon migratory corridor JUL AUG SEP Pollock primary prey specieswith FO of salmon up to 35% in late summer and fall in Frederick Sd with (Tollit, UBC)

  24. Spring-spawning forage fish (herring, eulachon, Capelin)) Fall-spawning salmon Summer-spawning salmon Over-wintering herring Pollock (available year-round) MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB

  25. Conclusions • Seasonal prey species available from a few weeks to several months • Pollock is available throughout the year and is supplemented with seasonal prey species • Migratory behavior of sea lions enhances access to patches of high-quality prey and shifting patterns of food abundance

  26. ACKNOWLEDGEMENTS • AFSC-Auke Bay Laboratory • NOAA Fisheries-SSLRI • Rasmuson Fisheries Research Center • Jacques Norvell-Tal Air • Julie Scott-Ashe, Kathleen White, Mervi Kunnasranta, Ben Williams, Dave Csepp, JJ Vollenweider, Ben Williams, Karen Blejwas • MMPA/ESA Permit No. 782-1532-02

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