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Cortisol levels in blubber sets a low stress benchmark for wild beluga population Lisa L. Loseto, Kerri Pleskach, Carie Hoover,ab Gregg T. Tomy, Jean-Pierre Desforges, Thor. Halldorson, Peter S. Ross

1. The Arctic is experiencing change driven by both climate change and anthropogenic change. How these changes will either directly or indirectly effect or impact the Eastern Beaufort Sea Beluga whales remains unknown, however developing a means to monitor or assess stress will provide a benchmark and guidance for conservation and management.

2. In this study we examined a common measure of physiological stress, cortisol, in blood and blubber to evaluate its use as an indicator of stress. We assessed levels of cortisol and compared them to circulating levels of organic contaminants. We then used findings to make recommendations towards the use of cortisol a long term monitoring indicator of stress in beluga.

3. Cortisol levels ranged among tissues with levels in blood being the highest likely reflecting acute stress (e.g. being chased during the hunt). Higher cortisol levels in the inner blubber suggest this tissue more closely reflects circulating levels relative to the middle and outer blubber. Overall cortisol levels in harvested beluga were similar to captive belugas at a ‘resting’ state indicating Eastern Beaufort Sea beluga whales are under low stress.

4. Cortisol levels in outer blubber tissue (near skin) will make for an ideal indicator for monitoring chronic stress. . The lack of relationship between levels of cortisol and contaminants, a known physiological stressor, suggests current contaminant burden in beluga may not be having a significant impact on overall stress.

Arctic beluga whales are facing profound changes in their habitat, with impacts expected at the individual and population level. Detecting and monitoring exposure and response to environmental stressors is necessary for beluga conservation and management of human activities.

Cortisol has proven a useful tool to assess stress on wildlife. Cortisol was measured in three blubber layers and blood in subsistence-hunted Eastern Beaufort Sea beluga whales from the summers of 2007 to 2010. Within blubber, levels of cortisol were highest in the inner blubber layer likely reflecting circulating levels of cortisol and the acute stress experienced during the hunt and capture of the beluga. Cortisol levels were similar to resting levels in captive belugas suggesting overall low levels of stress in this population of wild beluga.

We did not find relationships between cortisol and biochemical factors such as organic contaminants suggesting cortisol levels are not significantly influenced by present contaminant concentrations. Our findings support the use of middle and outer blubber tissues to measure indicators of chronic stress that are less subject to the influence of acute stress.

Read the full paper in Arctic Science: Cortisol levels in beluga whales (Delphinapterus leucas): Setting a benchmark for Marine Protected Area monitoring

Corresponding author: Lisa Loseto, lisa.loseto@dfo-mpo.gc.ca

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