Vocal behavior of captive Atlantic bottlenose dolphins in a swim program

Dolphins emit distinct vocalizations in the contexts of stressful situations, such as when captured in nets. It has been assumed among animal rights groups that the presence of human swimmers causes stress in captive Atlantic bottlenose dolphins (Tursiops truncatus). Stress may be expressed in dolphin vocalizations and the associated visual behaviors before, during, and after swim sessions with humans. Thus, these behaviors were recorded to elucidate quantitative vocal patterns suggestive of conspecific stress. Significant differences among vocalization types within sample sessions were found only for whistles between During II and After sessions. Other comparisons indicated no significant differences for vocalization production frequencies between the presence or absence of human swimmers. Additionally, correlations found among the seven vocalization types and all five sample sessions indicated only that one variable, i.e. the presence or absence of human swimmers, was being measured in several different ways (by the different vocalization type production frequencies). Thus, conspecific stress, if indeed it can be measured by vocalization production frequency, does not appear to occur more often in the presence of human swimmers.