Sounds of Stress: Assessment of Relationships between Ambient Noise, Vessel Traffic, and Gray whale Stress Hormone

Elevated noise from human activities in nature can impact animal behavior and physiology, with subsequent impacts on individual health and population dynamics. Baleen whale communication, navigation, habitat use, and ability to recognize and locate prey and predators may be impaired by anthropogenic activities that increase ocean noise within the whales' hearing frequency range. To understand the physiological impacts of noise disturbance on baleen whales, we investigated the adrenal stress response of gray whales ( Eschrichtius robustus ) to variable ambient noise levels through an assessment of fecal glucocorticoid metabolite concentrations. This analysis was conducted at the individual level, at multiple temporal scales (1-7 days), and accounted for factors that may confound glucocorticoid hormone concentrations: sex, age, nutritional status, and reproductive state. Data were collected along the Oregon coast, USA, from June to October of 2016-2018. Results indicate a significant positive correlation between underwater noise levels and vessel traffic. Vessel counts from the day prior to fecal sample collection and sex had significant positive relationships with glucocorticoid metabolite concentrations. This study increases knowledge of gray whale physiological response to variable ocean noise and may inform management decisions regarding regulations of anthropogenic noise activities and thresholds near critical whale habitats.