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Seabirds

The predatory role of the commander squid, Berryteuthis magister , in the eastern Bering Sea ecosystem. Mary Hunsicker, Timothy Essington, Kerim Aydin and Bryan Ishida Alaska Marine Science Symposium January 2009. Marine Mammals. Seabirds. Fish. Crustaceans. Squid. Juvenile fish. Squid.

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Seabirds

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  1. The predatory role of the commander squid, Berryteuthis magister, in the eastern Bering Sea ecosystem Mary Hunsicker, Timothy Essington, Kerim Aydin and Bryan IshidaAlaska Marine Science SymposiumJanuary 2009

  2. Marine Mammals Seabirds Fish Crustaceans Squid Juvenile fish Squid

  3. Motivation • Changes in abundance and distribution of commercial fish species and marine mammals in eastern Bering Sea. • Ecosystem-based management • Target and non-target species

  4. Goal Provide a better understanding of the feeding habitsandtrophic position of Berryteuthis magister

  5. Objectives • Identify the seasonal prey items of B. magister • 2. Determine the trophic level of B. magister and determine how it varies with ontogeny and season • 3. Can feeding chronologies of individual squid be reconstructed from eye lens layers?

  6. Bering Sea Gulf of Alaska Aleutian Islands Winter 2007 Bathymetry map: Stephani Zador

  7. Objective 1: Identify seasonal prey types • Stomach Content Analysis

  8. Ontogenetic Shift in Diet Summer

  9. Winter

  10. Prey items of B. magister? Northern pearleye (Benthabella dentata) Northern smooth-tongue (Leuroglossus schmidti) Brokenline lanternfish (Lampanyctus jordani) Lower beak

  11. Northern smooth-tongue dominatedthe identified otoliths Northern smooth-tongue

  12. B. magister consumes a variety of squid species

  13. Summary Objective 1: Stomach Content Analysis • Evidence of an ontogenetic shift in diet • Fish prey - northern smooth-tongue and myctophid Squid prey - variety of species (B. magister, G. borealis. Gonatus sp.)

  14. Objective 2: Trophic level • Stable Isotope Analysis • Complementary tool for investigating the trophic role of squid • Diet analysis can be problematic due to well-digested prey and empty stomachs • Muscle isotope signatures provide a time-integrated measure of feeding relationships (vs. snapshot from diets)

  15. Stable Isotope Analysis 15N:14N δ15N, Indication of trophic level (3 - 3.4‰)

  16. Increase in trophic level with body size Delta 15N (‰) Squid muscle tissue (mantle) Data in part from NPRB Project #622 (Aydin)

  17. Summer – East Bering Sea Fish data: Courtesy of Ann Edwards

  18. Summary Objective 2: Trophic Position • δ15Nincreases with increasing mantle length(1 TL) • Seasonal samples reveal similar trend • Trophic position in EBS similar to pollock

  19. Objective 3: Feeding Chronologies • Novel Method(Matt Parry, PhD Thesis) • Measure 15N in each lens layer and relate layer to body size • Fine-scale variations in dietary patterns?

  20. Conventional Pattern δ15N (‰) Data in part from NPRB Project #622 (Aydin)

  21. Non - Conventional Pattern δ15N (‰) Data in part from NPRB Project #622 (Aydin)

  22. Seasonal differences in feeding chronologies Non - Conventional Pattern Conventional Pattern Summer-caught: 80% Winter-caught: 30% Summer-caught: 20% Winter-caught: 70%

  23. Conclusions I. Evidence for ontogenetic shifts in diet II. Trophic position similar to commercial fish (pollock) III. Fine-scale variations in trophic position

  24. Acknowledgements • Funding North Pacific Research BoardAlaska Fisheries Science Center UW School of Aquatic & Fishery Sciences • PeopleJerry Hoff Bill Walker Sandra Parker-Stetter Jim Thomason Cairastiona Anderson Anne BeaudreauTroy Buckley Bridget Ferriss Andy WhitehouseJonathan Reum AFSC Observer Program Paige Drobny

  25. Conclusions • Construct size-structured food web models • Quantify the predatory / competitive impact of B. magister • Evaluate effects of squid predation / competition under alternative management scenarios.

  26. Summer – Gulf of Alaska Fish data: Courtesy of Ann Edwards

  27. Prey size spectrum of B. magister? Otolith length (width) to fish body length Lower rostral beak length to squid mantle length • Regression equations provided by Bill Walker (unpublished)

  28. p < 0.05 p > 0.05

  29. p > 0.05 p > 0.05

  30. No size / seasonal trend in carbon source Delta 13C (‰) Squid muscle tissue (mantle) Data in part from NPRB Project #622 (Aydin)

  31. 15N:14N 13C:12C δ15N, Indication of trophic position (3 - 3.4‰) δ13C, Indicates photosynthetic pathway used to fix carbon 15 13 δ15N 11 Trophic level (TL) 9 3 - 3.4‰ 7 5 -20 -16 -12 -8 δ13C Pelagic Benthic Stable Isotope Analysis Fish Squid Amphipod

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