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Trophic Links in the Northeastern Chukchi Sea: Ice Seals and Forage Fishes

Explore the trophic relationships between ice seals and forage fishes in the Chukchi Sea, focusing on the dietary habits and isotopic analysis of key seal species. Discover how changes in sea-ice habitat and prey availability impact these sentinel species and the larger Arctic food web.

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Trophic Links in the Northeastern Chukchi Sea: Ice Seals and Forage Fishes

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  1. Trophic Links – Forage Fishes, Their Prey, and Ice Seals in the Northeastern Chukchi Sea Part II – Ice Seals CMI Review – December 10, 2009 S. Carroll L. Dehn B. Norcross B. Holladay Kakulu Sagiatok, Cape Dorset

  2. The Players – Pagophilic Seals Photo: NOAA Photo: NOAA • Bearded Seal (Erignathus barbatus) • 2-2.5m length, ~450-500lbs • Prefer transition zone with medium ice-cover • Ringed Seal (Phoca hispida) • 1-1.5m length, ~100-150lbs • Prefer land-fast ice ? Photo: NOAA Photo: NOAA • Spotted Seal (Phoca largha) • 1.3-1.7m length, ~180-250lbs • Prefer ice-edge • Ribbon Seal (Phoca fasciata) • 1.3-1.7m length, ~180-250lbs • Prefer ice front

  3. Background – Key Issues • Sentinel species: long-lived, high trophic level marine predators • Important link to higher trophics • Loss of sea-ice as a platform • Sea-ice related changes in food web assemblages and productivity • Industrial development in ice seal habitat • Subsistence importance

  4. It’s all about Food • It takes food to grow and reproduce! Dietary shift is often the first sign of change, followed by:  Stress  Body Condition  Resistance to Disease  Reproductive Output  Mortality  Population declines • Understanding MM response and adaptive potential is critical

  5. Sedna’s Realm Objectives -Determine trophic level of ice seals -Determine ice seal trophic history -Compare trophic levels of forage fishes to those of ice seals -Develop isotopic mixing models Kakulu Sagiatok, Cape Dorset

  6. Sample Collections • Samples of ringed, bearded, spotted, and ribbon seals collected during Native subsistence harvests • In collaboration with: • Alaska Department of Fish & Game • North Slope Borough, Department of Wildlife Management • Targeted specimens: • Liver - short term dietary record • Muscle – longer term dietary record • Claws – dietary history • Stomach contents – dietary snapshot

  7. Collections • *Spotted seal harvest for 2009 not yet inventoried by ADF&G • Challenges in obtaining all tissues for the same individuals • Continue sampling in 2010 to increase sample size, in particular for claws

  8. Sample Preparation • Archived seal samples have been sub-sampled and freeze-dried • Homogenization and isotope analysis is in progress • Some archived samples were requested through the Museum of the North • Total body homogenates of Arctic cod, Bering flounder, and Arctic staghorn sculpin are presently examined for the effect of lipid removal on stable isotopes • Method development for seal claws complete and preparation of “new” samples in progress Photo: S. Carroll

  9. Stable Isotope Primer • d15N used to identify trophic level and predator-prey relationships • ↑ in consumer as trophic level ↑ • d13C used to identify feeding location and feeding habitat • No ↑ with trophic level, but carbon source indicator

  10. Carbon Isotopes in Bowhead Baleen Schell et al., 1989 • Carbon from surrounding area is incorporated in baleen as it grows • Baleen oscillations can be measured ~18 years 1 minimum (Beaufort) + 1maximum (Bering/Chukchi) =1year

  11. Isotopic Record in Seal Whiskers Cherel et al., 2009 • Male Antarctic fur seals • Whiskers show records of annual migrations • AA polar front vs. subtropical front • Associated with switch in prey • AA krill vs. mesopelagic fishes

  12. Ringed Seal Migrations Olokhaktomiut and Paulatuk Hunters and Trappers Committee, EMC, and DFO • All seals tagged in 2001/2002 in Canada moved westward • Age range from pup to 4-year • Undertake sporadic migrations between Beaufort and Chukchi/Bering seas http://www.beaufortseals.com/telemetry.htm

  13. Ringed Seal Migrations – Carbon Isotopes Dehn et al., 2007 Muscle Tissue • Beaufort Sea depleted in 13C compared to Bering/Chukchi seas • Can migrations be detected using claws?

  14. Claws – Growth Layers Photo: S. Carroll • Front flipper claws grow continuously • Keratin layers are deposited annually • Light growth: Summer / Fall • Dark growth: Winter / Spring • Distal wear after ~10 years • Carbon and nitrogen isotopes are incorporated into growing claws, representing diet at time of growth • Trophic history! • Can elucidate seasonal importance of prey and annual shifts

  15. Claws – How to… Trimmed of tissue and fur Cleaned of dirt, blood, and grime in ultrasonic water bath Cleaned of lipids using chloroform/methanol Photo: S. Carroll Light and dark bands identified Drilled each layer with Dremel tool Powder of each layer analyzed separately for 15N and 13C Photo: S. Carroll

  16. Trophic History from Claws – Ringed Seal Keratin enriched in 15N over prey by ~2.5‰ in 13C by ~3‰ RS-5-18-00 Female 5 years Harvested in Barrow N: 10.4 ± 1.2 C: -24.9 ± 0.7 N: 15.5 ± 1.0 C: -20.9 ± 0.4 TL

  17. Trophic History from Claws – Ringed Seal RS-2-00 Male 7 years Harvested in Barrow • 95-96 feeding on high TL • 97-98 feeding low TL

  18. Trophic History from Claws – Ringed Seal • 95-96 feeding on high TL • 97-98 feeding low TL • 00 feeding high TL RS-1-01 Female 21 years Harvested in Barrow

  19. Anything Unusual during these Years? 1997-98 1995-96 http://ingrid.ldeo.columbia.edu/%28/home/alexeyk/mydata/TSsvd.in%29readfile/.SST/.PDO/ Warm Cool

  20. What could it Mean? • Cold pool over shelf prohibitive to some fish species in “warm years” • Warm corridors form in “cold years”, providing abundant fish forage for seals

  21. Photo: NOAA

  22. Trophic History from Claws – Bearded Seal • 95-96 feeding on high TL • 97-98 feeding low TL • 00 feeding high TL BS-7-02 Female 28 years Harvested in Barrow

  23. Trophic History from Claws – Bearded Seal BS-1-01 Male 32 years Harvested in Barrow • Seasonal differences in TL • Migration

  24. Trophic History from Claws – Bearded Seal BS-6-02 Female 32 years Harvested in Barrow • Seasonal differences in TL • Migration

  25. Sea Ice Differences? Richter-Menge et al., 2008 • 95-96 and 00 – low ice years • 97-98 – high ice year • Possible impacts on benthic food chain

  26. Juveniles • 15N in utero likely resembles values of mother with no enrichment • Resources of mother and fetus at equilibrium during early term • As fetal demand increases, maternal proteins from tissue breakdown rather than diet? • Enrichment? • High trophic level in juveniles • Incorporate isotopic signature of mother from milk • Increased protein turnover and growth

  27. Summary • Claws capture trophic history of ice seals! • No seasonal migratory pattern (based on 13C) in ringed and bearded seals • Sporadic excursions • Little evidence of regular seasonal prey switching in ringed seals • But possibly related to PDO • Seasonal differences between high and low trophic level foraging in bearded seals • Possibly related to sea ice • Prefer high ice coverage • YOY seals show enriched 15N signature • In utero • Lactation / Weaning

  28. Thank You! Subsistence Hunters in Coastal Alaska Lori Quakenbush Taqulik Hepa Jill-Marie Seymour Greta Krafsur Anna Bryan Mark Nelson Christy Gleason

  29. Questions ? http://www.arved-fuchs.de/husavik/seals/Seals/geninformation.html

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