The Pacific walrus (Odobenus rosmarus divergens) is an iconic Arctic marine mammal that Alaska Natives rely on as a food, economic, and cultural resource. A decrease in critical sea ice habitat and uncertain population numbers have led to walruses being listed as a candidate for the Endangered Species Act. However, there is no clear understanding of how walruses might be affected by climate change.
The first objective of this study was to describe how bone steroid hormone concentrations relate to commonly used blubber and serum steroid hormone concentrations. Tissues were collected from individual adult walruses harvested by Native Alaskan subsistence hunters during 2014 and 2015. Steroid hormones (cortisol, estradiol, progesterone, and testosterone) were measured and compared among tissues. Bone and blubber steroid hormone concentrations were similar with the exception of testosterone. Male progesterone concentrations were significantly correlated between bone and blubber. These results show that bone serves as a long-term reservoir of steroid hormone concentrations compared with circulating serum concentrations, and progesterone measured in blubber can be compared with bone progesterone.
The second objective of this study was to understand the physiological resiliency of walruses to the current warming in the Arctic. I measured steroid hormone concentrations in walrus bone collected from archaeological (>200 calendar years before present (BP)), historical (200 – 20 BP), and modern (2014 – 2015) time periods, with an analysis of finer decadal (1830s – 2010s) patterns. Walrus bone cortisol concentrations were similar among all time periods indicating no increase in the stress response of walruses to current sea ice conditions in the Arctic. Estradiol, progesterone, and testosterone were significantly correlated with walrus population estimates. Data from the current decade (2010 – 2015) indicate that the current walrus population has lower reproductive hormone concentrations compared with walruses during times of rapid population increase.
Overall, these data provide walrus management with insights into the physiological resiliency of walruses in response to arctic warming, and validated bone as a valuable tissue for monitoring long-term physiological changes in the walrus population.