Feasibility of heart rate variability analysis for welfare assessment in dolphins: a preliminary report

Monitoring stress and emotional states in dolphins is an important step toward improving animal welfare in managed care. Established physiological approaches, such as measuring cortisol from blood or fecal samples, have provided valuable information for stress assessment. Suction-based devices have also enabled cardiac monitoring, contributing to our understanding of diving physiology and circulatory control. Each of these methods offers unique strengths, but they may not always be suited for real-time or continuous monitoring during routine conditions. In this study, we propose a framework in which heart rate variability (HRV) serves as a non-invasive indicator of autonomic activity, stress, and emotional states. As an initial step, we tested the feasibility of attaching a commercially available belt-type heart rate monitor to dolphins. The device was fitted safely and generally tolerated, although subtle behavioral resistance was observed in some cases. In principle, this HRV-based framework is not limited to the belt-type device tested here and could be adapted to other attachment methods, provided stable cardiac signals are obtained. Continuous cardiac signal acquisition and HRV analysis are ongoing, but these preliminary results represent a first step toward introducing HRV-based welfare assessment in cetaceans. Future directions include refining attachment methods and implementing staged habituation to achieve stable signal acquisition, followed by HRV analysis combined with behavioral observation. This framework has the potential to extend beyond dolphins to other marine mammals such as pinnipeds and sirenians, thereby contributing to the establishment of practical, non-invasive welfare assessment standards for zoos and aquaria.