Tracking Epidermal Cortisol and Oxytocin in Managed Bottlenose Dolphins as Potential Non-Invasive Physiological Welfare Indicators

Growing concern over cetacean welfare has highlighted the need for rigorous, science-based assessment methods. Within this context, epidermal cortisol (ECC) and oxytocin (EOC) concentrations have emerged as potentially valuable physiological indicators. In this study, we first validated the analytical measurement of ECC and EOC in bottlenose dolphins (Tursiops truncatus) using AlphaLISA assays. Subsequently, weekly ECC and EOC levels were measured over an extended period in five managed dolphins and analyzed alongside aggregated environmental and welfare-related variables, using various time lags to account for delays between physiological activity and hormone deposition in the epidermis. ECC was negatively associated with mild weight loss and diazepam administration, exhibiting seasonal variability. In contrast, EOC was negatively associated with negative welfare indicators and COVID-19 park closures but positively associated with diazepam administration and peak visitor seasons, also showing seasonal variability. However, the interpretation of EOC remains complex due to a limited understanding of the cetacean oxytocin system and its dual role in positive and negative affective states. Overall, ECC and EOC show promise as non-invasive biomarkers for monitoring long-term welfare changes in cetaceans, although further research is necessary to validate these biomarkers across broader populations and contexts and to clarify their temporal dynamics in the epidermis.