Recent declines in Arctic sea ice and previously unrecorded sea ice minima have led to concerns regarding the future health of ice-dependent pinniped populations. Pacific walruses (Odobenus rosmarus divergens) rely heavily on sea ice as a platform for giving birth, molting, and resting between foraging bouts, making this species particularly vulnerable to warming climates and reduced sea ice coverage.
This study uses stable isotopes of carbon and nitrogen (δ13C and δ15N) in walrus bones, as well as trace element analyses of walrus teeth, to investigate changes in diet and feeding location across three time periods (prehistoric, historic, and modern). Samples were obtained from walrus remains collected in association with archaeological digs, housed in museum collections, and from Native subsistence harvests in Alaska.
Major climatic anomalies, including the Roman Warm (2200 – 1900 BP, calibrated years before present), the Medieval Warm (1100 – 800 BP), and the Little Ice Age (450 – 150 BP) are encompassed by the prehistoric samples, while historic and modern samples span ~100 years and a series of major regime shifts in the North Pacific and Bering Sea. Preliminary stable isotope values differed significantly among all three eras (δ13C: P < 0.001; δ15N: P < 0.001), and analyses of eight fine-scale time periods revealed significant changes in both δ13C and δ15N within the prehistoric and historic eras. Analysis of trace elements allows for differentiation among observed changes in stable isotope ratios caused by trophic shifts and those caused by geographic movements. We used an Agilent 7500ce Inductively Coupled Mass spectrometer to measure concentrations of barium, cadmium, cesium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, strontium, and zinc in walrus teeth.
This study is first of its kind and provides novel insight into the impacts of climate change on walrus foraging.