Cortisol levels in beluga whales (Delphinapterus leucas): Setting a benchmark for Marine Protected Area monitoring

Abstract

22 Beluga whales (Delphinapterus leucas) are facing profound changes in their habitat, with 23 impacts expected at the individual and population level. Detecting and monitoring exposure and 24 response to environmental stressors is necessary for beluga conservation and management of 25 human activities. Cortisol has proven a useful tool to assess stress on wildlife. Cortisol was 26 measured in three blubber layers and plasma in subsistence hunted beluga whales from the 27 summers of 2007 to 2010 using an HPLC/MS/MS. We assessed the effect of biological and 28 biochemical factors. Cortisol ranged from ND to 17.8 ng/g in blubber and 2.5 to 61.2 ng/mL in 29 plasma. Concentrations were highest in the inner blubber layer likely reflecting circulating 30 levels. All tissues were significantly higher in 2008 for reasons that remain unclear. Cortisol 31 levels were on par with resting levels in captive belugas. Best fit models for cortisol revealed age 32 to be an important determinant along with length and blubber thickness. Lack of relationships 33 with biochemical factors such as organic contaminants suggest current cortisol levels are not 34 significantly influenced by present contaminant concentrations. Our findings support the use of 35 middle and outer blubber tissues for an integrated measure of chronic stress that are less subject 36 to the influence of acute stress. 37 38 39