Carbon and Nitrogen Isotope Concentrations in Polar Bear Hair and Prey from the Alaska Beaufort and Chukchi Seas, 1978-2019

Guard hair was sampled by pulling 10-20 hairs from one of the upper forearms of polar bears captured on the sea ice or on land in the Chukchi Sea in Alaska and Russia 1987-1989, on the sea ice of northwest Alaska from Shishmaref to Cape Lisburne 2008-2017, and on land and sea ice off the northern coast of Alaska between Utqiagvik and the Canadian border 1983-1989 and 2004-2017. Bears were located by helicopter and immobilized with a dart containing zolazepam-tiletamine (Telazol®). Capture and handling followed protocols approved by under U.S. Fish and Wildlife Service research permit MA 046081 and the U.S. Fish and Wildlife Service Alaska Regional Office Animal Care and Use Committee. All bears captured in the Alaska Chukchi Sea were captured during the spring (mid-March through mid-May). Bears were captured in the spring in the Alaska southern Beaufort Sea during all years and in the fall (Aug-Oct) for some years in the 1980s and in 2007-2009. Muscle and blubber samples were collected from marine mammal species that were potential prey of polar bears, including ringed seals, bearded seals, bowhead whales, gray whales, Pacific walrus, beluga whales, spotted seal and ribbon seal in the Alaska Beaufort and Chukchi Seas. Samples were collected from Native-harvested animals near coastal communities identified in the data set and from carcasses left by polar bears that were encountered during annual polar bear capture efforts in the Alaska Beaufort and Chukchi Seas. The source of samples, including location, date sampled, animal age (if known) and who collected are provided in the tables.

Polar bear hair was stored frozen and dry in whirlpaks or envelopes until analyzed. Hair was cleaned by soaking in three successive beakers containing 2:1 v/v chloroform:methanol (i.e. progressively cleaner with respect to organic contaminants) and air dried overnight. Single, whole dried hair was packaged into 4 x 6 mm silver capsules for mass spectrometry because polar bear guard hairs have a high tensile strength that precluded the typical use of tin capsules. Prey muscle was freeze dried, lyophilized, and sub-samples analyzed for elemental and isotopic compositions with no pre-treatments (i.e. 'bulk'). The high C:N ratio of blubber precluded accurate conventional analysis by continuous flow isotope ratio mass spectrometry (CF-IRMS). Therefore, we first freeze-dried prey blubber samples. Blubber was then sub-sampled and massed to fit inside of a 10 x 50 mm cellulose extraction thimble (Whatman). Packed thimbles were then extracted by Soxhlet distillation for 5 hours using a 2:1 chloroform:methanol solvent mixture. The lipid residue plus solvent was retained, evaporated at room temperature under a light vacuum for approximately 3 days, and analyzed for weight % carbon and d13C. Likewise, the structural protein (e.g. collagen residue contained in the extraction thimbles) was retained, massed, lyophilized, and analyzed for elemental and isotopic compositions. Elemental and isotopic compositions of prey were measured via CF-IRMS at three laboratories that used the same standards. All polar bear hair and most prey sample measurements were conducted at the U.S. Geological Survey Stable Isotope Laboratory (Denver, CO, USA; see Rode et al. 2016). The prey data set includes a column identifying the laboratory that conducted the analyses.