Monitoring Ecosystem Dynamics in the Beaufort Sea using Stable Isotopes in Polar Bears (Ursus maritimus) and Ringed Seals (Pusa hispida)

• Author / Creator

  Boucher, Nicole

• Extensive declines in sea ice extent and thickness are occurring within the Arctic and are projected to continue in the future due to amplified polar warming. As a result, community composition and structure are changing within Arctic ecosystems. Animal diets are influenced by accessibility and availability of prey, and therefore, the diets of predators may provide insights into ecological shifts. To study ecosystem dynamics in the Beaufort Sea, I used polar bear (Ursus maritimus) and ringed seal (Pusa hispida) stable isotopes. I assessed whether sectioning guard hairs and claws of polar bears captured in 2007 to 2011 could be used to identify seasonal dietary trends, and evaluated whether variation in stable isotopes of polar bears could predict their space use patterns (i.e. coastal or pelagic) following an examination of home range fidelity. Sectioning of claws, but not guard hairs, identified seasonal dietary trends. Polar bears showed fidelity to their home ranges between years. Coastal polar bears were depleted in δ15N either due to feeding upon a δ15N depleted food web, relying upon more bowhead whale (Balaena mysticetus) carcasses from subsistence hunts, and/or experiencing less nutritional stress. Next, I examined temporal variation of polar bear stable isotopes, diet proportions and niche widths from 2004 to 2012 within the northern and southern Beaufort Sea subpopulations, in relation to sea ice dynamics, climate indices and biological factors. Ringed seal made up the highest proportion of the diet of polar bears in all ages, sexes, and subpopulations. However, dietary proportions varied between years. Stable isotopes of polar bears were affected by ringed seal ovulation rate, Arctic oscillation, sea ice dynamics and temperature, which influence availability of prey. Polar bears altered their foraging in response to prey availability, with larger niche widths in years of reduced ringed seal ovulation rates. As such, polar bear diets can reflect a measure of seal population dynamics which are currently understudied in the Beaufort Sea. Following examination of polar bear stable isotopes, I investigated spatial and temporal variation in ringed seal stable isotopes from 1964 to 2011 in relation to age, sex, sea ice dynamics, climate indices, temperature, and spatial distribution of the killed ringed seal in the longest study on ringed seal diet to date. Age and sex were not related to stable isotope value. Cyclonic circulation regimes were related to enriched δ13C, possibly due to changes to primary productivity. Depletion of δ15N occurred during warmer years, which may be due to ringed seals feeding at a lower trophic level. Both δ15N and δ13C were enriched in years with high seal population productivity. Increasing ringed seal niche width from the 1960s indicated ringed seal diet diversification, which may be a result of range expansions of sub-Arctic prey species. Overall, I found evidence suggesting that polar bear and ringed seal diets can be used to assess ecosystem dynamics, as their diets reflect prey availability and diversity. I found that abiotic variables that affect sea ice dynamics, such as temperature, were related to the diet of both species, reflecting the biological significance of sea ice to polar bears and ringed seals. My research highlights the importance of understanding how biotic and abiotic factors, as well as spatial distribution of the animal, influence diet when monitoring ecological changes. The results from this research may be applied to predict ecosystem changes in the future within the Arctic ecosystem.

• Subjects / Keywords

  • climate change
  • space use
  • Beaufort Sea
  • diet ecology
  • ringed seal
  • pusa hispida
  • polar bear
  • ursus maritimus
  • stable isotope

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-fyz9-x378

• License

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