dc.description.abstract
Public concern about the welfare of dolphins and other cetaceans, both in human care and in the wild, is increasing. Yet, assessing their wellbeing remains a challenge, especially through non-invasive and scientifically robust methods. This study explored the potential of two hormones naturally present in dolphin skin-cortisol, related to stress, and oxytocin, linked to social bonding and wellbeing-as physiological indicators of welfare. Using skin samples from five bottlenose dolphins monitored over several months, we validated laboratory methods for measuring these hormones and examined how their levels varied in response to real-life events. Epidermal cortisol levels were lower after mild weight loss and diazepam administration and varied seasonally. Oxytocin levels tended to decrease during periods with more negative welfare indicators and during park closures related to the COVID-19 pandemic and tended to increase with higher visitor presence and diazepam administration. These results suggest that both hormones reflect relevant changes in the animals' environment and health, although interpreting oxytocin remains challenging. Our findings highlight the promise of skin-based hormonal markers to monitor dolphin welfare over time. With further validation, this approach could improve how we assess and promote cetacean wellbeing, contributing to better care, management, and conservation strategies. 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.
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