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The predatory role of the commander squid, Berryteuthis magister, in the eastern Bering Sea ecosystem Mary Hunsicker, Timothy Essington, Kerim Aydin and.

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Presentation on theme: "The predatory role of the commander squid, Berryteuthis magister, in the eastern Bering Sea ecosystem Mary Hunsicker, Timothy Essington, Kerim Aydin and."— Presentation transcript:

1 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

2 Seabirds Marine Mammals Fish Crustaceans 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 habits and trophic position of Berryteuthis magister

5 Objectives 1.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 Winter 2007 Gulf of Alaska Aleutian Islands Bering Sea Bathymetry map: Stephani Zador

7

8 Objective 1: Identify seasonal prey types  Stomach Content Analysis

9 Summer Ontogenetic Shift in Diet

10 Winter

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

12 Northern smooth-tongue dominated the identified otoliths Northern smooth-tongue

13 B. magister consumes a variety of squid species

14 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.)

15 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)

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

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

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

19 Summary Objective 2: Trophic Position  δ 15 N increases with increasing mantle length (1 TL)  Seasonal samples reveal similar trend  Trophic position in EBS similar to pollock

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

21 δ 15 N (‰) Conventional Pattern Data in part from NPRB Project #622 (Aydin)

22 δ 15 N (‰) Non - Conventional Pattern Data in part from NPRB Project #622 (Aydin)

23  Seasonal differences in feeding chronologies Conventional PatternNon - Conventional Pattern Summer-caught: 20% Winter-caught: 70% Summer-caught: 80% Winter-caught: 30%

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

25 Acknowledgements  Funding North Pacific Research Board Alaska Fisheries Science Center UW School of Aquatic & Fishery Sciences  People Jerry HoffBill Walker Sandra Parker-StetterJim Thomason Cairastiona AndersonAnne Beaudreau Troy BuckleyBridget Ferriss Andy WhitehouseJonathan Reum AFSC Observer ProgramPaige Drobny

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

27 Summer – Gulf of Alaska Fish data: Courtesy of Ann Edwards

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

29 p < 0.05 p > 0.05

30

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

32

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

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