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Food Webs in the Ocean. Andrew W Trites Marine Mammal Research Unit University of British Columbia. Who eats whom and how much?. Steller Sea Lions. Diet: Stomachs. Diet: Scats. Diet: Scats. Diet: Scats. Fatty acids Stable Isotopes. Bering Sea Food Web. Bering Sea Food Web.

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Food Webs in the Ocean


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    1. Food Webs in the Ocean Andrew W Trites Marine Mammal Research Unit University of British Columbia Who eats whom and how much?

    2. Steller Sea Lions

    3. Diet: Stomachs

    4. Diet: Scats

    5. Diet: Scats

    6. Diet: Scats Fatty acids Stable Isotopes

    7. Bering Sea Food Web

    8. Bering Sea Food Web

    9. Food Web Patterns (Species) • Sizes • larger at higher trophic levels • Numbers • more at the bottom of food webs • Proportions • constant at each trophic level • Diets • most are restricted – sizes & levels • humans can eat all

    10. Food Web Patterns (Chain Lengths) • Typically short (2-5 linkages) • Oceanic upwelling (2.2-2.8) • Coastal shelves (2.8-4.0) • Tropical estuaries (3.0-5.0) • Function of • Environmental stability • Energy transfer efficiency

    11. Consumption

    12. Estimating Energy Requirements • Stomach contents • Feeding rates • Metabolism • Mathematical models • single species • multispecies (ecosystem)

    13. Studies • Captive • Field • Models

    14. Metabolism

    15. Digestive Efficiencies

    16. Foraging Energetics

    17. Activity Budgets

    18. Growth Curves

    19. Food Web Patterns (Consumption)

    20. Food Web Patterns (Production Efficiency)

    21. Food Web Patterns (Residence Time)

    22. Food Web Patterns • 10% trophic transfer efficiency • Consumption • young > old • not constant over time • quality of prey changes

    23. Food Web Patterns(Fisheries) • High fish catches associated with • high primary production • fishing at lower trophic levels • Potential concerns • may break long food chains • may affect ecosystem stability

    24. Food Web Patterns(Steller sea lions) • Diet studies • Single species modeling • Ecosystem modeling • Captive feeding trials • Predation

    25. Diet Studies • 1950s  1990s • Shifted from fatty fishes to low fat fishes

    26. Diet Studies

    27. Single Species Modeling • Low diversity • Higher cost to young

    28. Ecosystem Modeling

    29. Captive Feeding Trials • Require 35-80% more pollock than herring

    30. Predation Studies

    31. Food Web Analysis (Steller Sea Lions) • Composition of North Pacific has changed • Diet has changed • Diet and ecosystem composition are consistent • Health consequences of eating too many gadids • Carrying capacity of pinnipeds is lower • Recovery linked to a more diverse diet & reduced predation • Environment appears to be the driving force

    32. Conclusions • Food webs & consumption estimates essential for fisheries management & understanding ecosystem dynamics • Require a combination of field studies, captive studies and models • Key to understanding what our marine ecosystems once were, what they are currently, and what they might be in the future