Metabolic Rate, Body Composition, and Blood Biochemistry Data from Polar Bears (Ursus maritimus) on Land, Western Hudson Bay, Canada, 2019-2022

To measure the specific activity of deuterium oxide and oxygen-18 in serum samples, we immobilized 20 polar bears on land in Wapusk National Park, Manitoba, Canada. Following immobilization, we inserted either an external jugular or cephalic catheter to facilitate blood sampling and administration of isotopes. We took a blood sample at the time of the initial capture to serve as a baseline measure of oxygen-18 (18O) and deuterated water (2H). The bear was then injected intravenously with a precisely weighed dose containing 0.26 – 0.47 g/kg of 98.4% enriched 18O (Isoflex USA, San Francisco, CA) and 0.06 – 0.10 g/kg of 99.8% enriched 2H (Sigma Aldrich, Inc., St. Louis, MO) with NaCl added to make it 0.9% isotonic and sterilized using a 0.2 μ Millipore filter (Corning, Inc., Corning, NY) (Table S3). On injection, the syringe was back washed with blood three times to ensure all the DLW had been injected into the bear. The bear was kept immobilized for 2 hours after the injection of DLW to allow isotope equilibration (Farley and Robbins 1994, Pagano et al. 2017). We collected serial blood samples 30, 60, 90, and 120 minutes after dosing to evaluate equilibration curves (Speakman 1997). We recaptured bears 19 – 23 days later to obtain a blood sample to measure final enrichment. At recapture, similar to the initial capture, following immobilization, we inserted either an external jugular or cephalic catheter to facilitate blood sampling and administration of isotopes. An initial blood sample was collected to measure final enrichment after which bears were dosed with 0.10 – 0.11 g/kg of 99.8% enriched 2H (Sigma Aldrich, Inc.) made isotonic with 0.9% NaCl and sterilized using a 0.2 μ Millipore filter. On injection, the syringe was back washed with blood three times to ensure all the 2H had been injected into the bear and serial blood samples were collected 30, 60, 90, and 120 minutes after dosing. Blood was collected in 10 ml glass evacuated tubes without anticoagulants (Serum Vacutainer, Becton Dickinson, Franklin Lakes, NJ or Monoject noncoated tubes, Cardinal Health, Dublin, OH) and centrifuged to separate serum from red blood cells. Serum was stored frozen in 2 ml cryogenic vials (Corning, Inc.) at -80°C until analysis. Water was extracted from each serum sample by vacuum sublimation. Specific activity of 18O and 2H were determined by wavelength-scanned cavity ring-down spectroscopy (Metabolic Solutions, Inc., Nashua, NH).

To obtain blood urea nitrogen and creatinine concentrations, serum samples from each capture and recapture were analyzed using an Abaxis Vetscan VS2 chemistry analyzer (Abaxis, Inc., Union City, CA).

To obtain serum progesterone levels, serum samples from the 8 adult female polar bears from each capture and recapture were analyzed by radioimmunoassay (ImmuChem™ Progesterone 125I, MP Biomedicals, LLC, Santa Ana, CA) by either the Endocrine Service Laboratory at the University of Saskatchewan (Saskatoon, SK) (2021 samples) or the Endocrinology Laboratory at the Animal Health Diagnostic Center (Cornell University, Ithaca, NY) (2019 and 2022 samples).

Age was determined by counts of cementum annuli from an extracted vestigial premolar.

To measure respiratory exchange ratio of bears we collected breath samples from 20 polar bears on land in Wapusk National Park, Manitoba, Canada. We placed a mask (Smiths Medical Inc., Dublin, OH) over the snout of each bear. The mask was attached to a two-way valve with ports for inhalation and exhalation (Hans Rudolph Inc., Shawnee, KS), which allowed the bear to inhale fresh air while exhaling into a 25-liter Douglas bag (Harvard Apparatus, Holliston, MA). Volumes of oxygen consumption (VO2) and carbon dioxide emission (VCO2) were measured from breath samples using an O2 and CO2 analyzer (FOXBOX; Sable Systems International, Las Vegas, NV). We zeroed the CO2 sensor with nitrogen gas and spanned the CO2 sensor with a known concentration of CO2 gas and the O2 sensor with ambient air using Drierite (W. A. Hammond Drierite, Xenia, OH) to remove moisture. We flowed the breath samples through the sensors at 200 ml/min, preceded and followed by baselines of ambient air. We corrected VCO2 measures due to the gas permeability of Douglas bags by adding 0.006 per hour between the time of collection and analysis.

We measured total body mass at each capture using an electronic load cell suspended from an aluminum tripod.