Understanding oxygen management in grey seal blubber

The ability to undergo dramatic changes in body mass and condition is vital for grey seal survival. Biomedical studies suggest that oxygen availability in fat tissue is affected by tissue expansion during obesity and is a potential health concern. However, whether and how blubber remains normoxic under radical adiposity changes is unknown. Grey seals have a similar fat percentage to obese humans; therefore, we hypothesise that oxygen availability in blubber will be affected by increasing tissue depths and adiposity. For the first time, we measured oxygen saturation (SpO2) and partial pressure of oxygen (pO2) on the dorsal flank´s blubber of sedated and anaesthetised juvenile grey seals (n=12). Blood oxygen saturation, heart rate and breathing rate were monitored throughout sampling. Oxygen saturation and blood flow were recorded using non-invasive Near Infrared Spectroscopy (NIRS) to assess oxygen supply. Simultaneously, dissolved oxygen availability was measured in the same blubber region at different depths, with a non-consuming, temperature compensated optical oxygen probe (NX-LAS-8/OT/E, Oxford optronix). In four cases, two probes were inserted simultaneously 33±3 mm apart to examine inter-site variability. To investigate the influence of adiposity, we estimated fatness by photogrammetry and measured blubber depth using ultrasound. Furthermore, four animals were resampled after weight increases of 6 to 25 Kg. Preliminary results suggest substantial decreases in blood SpO2 correspond with a lagged decrease in blubber pO2. Large inter-individual differences have been recorded, however values are similar to those reported in human studies. Surprisingly, pO2 varies irrespectively of blubber depth or adiposity. Further statistical analysis will better evaluate adiposity effects and vascularity. Our data suggest that blubber is well is not hypoxic, despite its large volume and radical changes in size. Further work on freely diving animals needs to be undertaken to explore changes in oxygenation and potential hypoxia during large changes in oxygen availability