Influence of sample degradation and tissue depth on blubber cortisol in beluga whales

Cortisol concentrations in a variety of biological tissues have been used to obtain short-term to long-term estimates of activation of the physiological stress response. In recent years, blubber has been demonstrated to be a good candidate tissue from which to extract steroid hormones, but no method for extracting cortisol from blubber of any marine mammal has been published and the effects of sample storage and variation in blubber depth on cortisol concentrations are unknown. The objectives of this study were to identify a method for extracting cortisol from blubber in beluga whales (Delphinapterus leucas) and to evaluate the concentration of hormones in relation to blubber depth and degradation from long-term storage using samples collected and archived over the past 30 years. Cortisol was extracted from blubber of beluga whales by modifying an existing progesterone-blubber extraction method. Cortisol concentrations were lower in degraded samples, but time in storage did not affect cortisol after controlling for sample quality. Cortisol concentrations increased with blubber depth, with highest concentrations in blubber closest to the muscle. These results show that although cortisol in blubber samples collected and archived prior to extraction may be degraded, high quality samples without visible degradation after long-term storage can still yield useful measures of cortisol. Additionally, sample depth should be controlled for during sample collection. These findings provide necessary information for developing accurate sampling protocols for extracting cortisol from blubber of marine mammals, including sampling by biopsy dart.