Tracking epidermal cortisol and oxytocin in managed killer whales as potential non-invasive physiological welfare indicators

Growing public concern regarding cetacean welfare has emphasized the need for developing robust, science-based tools for welfare assessment applicable across diverse species and settings. Within this context, in a broader effort to advance the validation of novel physiological indicators for monitoring cetacean welfare, this study optimized a non-invasive epidermal sampling method in killer whales (Orcinus orca; N = 5) and validated AlphaLISA immunoassays for quantifying epidermal cortisol (ECC) and oxytocin (EOC) concentrations. Analysis of body location as a potential confounding factor revealed notable intra-individual variability and lateral asymmetry in hormone concentrations, highlighting the importance of standardized sampling procedures. Significant associations emerged between both hormones and negative welfare indicators, while EOC was also linked to positive behavioral engagement and body weight variation. When considered alongside previous findings, ECC may represent a reliable and feasible biomarker for assessing retrospective, intermediate-term welfare changes in killer whales, particularly when embedded within a broader, multifactorial framework that integrates complementary indicators. By contrast, EOC remains less reliable at this stage, largely due to the limited understanding of the oxytocinergic system and its involvement in both positive and negative affective states. Future research involving larger populations, detailed welfare assessments, and improved understanding of epidermal hormone incorporation dynamics will enhance the practical utility of ECC and EOC as welfare biomarkers in cetaceans.