Kristy Beard's Master's Thesis
Citation: Beard, K. (2008) Use of Bubble Emissions by Bottlenose (Tursiops truncatus) and Atlantic Spotted Dolphins (Stenella frontalis) Relative to Age and Sex
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In marine mammals, communication is a combination of acoustic, visual, and tactile signals, which may be used singly or concurrently to modify the intended message(s). While most cetacean species have been reported using visual signals as communicative displays, and visual communication is believed to be important to cetaceans, current literature reveals less research on visual communication in dolphins than on acoustic communication. For years, cetaceans have been documented to produce bubbles in a variety of forms from the blowhole. In dolphins, streams of bubbles have been documented synchronously with and without whistles, but bubble streams are a rare event. The function of bubble streams is not known, and there is debate as to whether their presence with whistles is representative of the entire whistle repertoire, or if bubbles are instead used as visual cues that accompany certain whistles in certain contexts. Bubble production in dolphins may be affected by factors such as sex, age, group type, and whether the dolphins are wild or in human care. In this study, it was hypothesized that calves and juveniles would produce bubble streams more often than sub-adults and adults, and that females would produce more bubble streams than males. Underwater data were collected from bottlenose dolphins (Tursiops truncatus) at Dolphin Encounters in Nassau, The Bahamas, and from Atlantic spotted dolphins (Stenella frontalis) around Bimini, The Bahamas. The Poisson regression model of general loglinear analysis was used to determine if there were significant interactions between sex and age class at both research sites. If there was no significant interaction, the Poisson regression was used to determine the main effects of sex and age class on the number of bubble streams produced. In Bimini, 12 of the 32 dolphins of known identity were recorded on video producing bubble streams. Of these 12 animals, females produced significantly more bubble streams (n = 84; 83%) than males produced (n = 17; 17%), (p < .001). There was a significant difference in the number of bubble streams produced by dolphins in each age class (p < .001). Adults produced 2% of these bubble streams, sub-adults 54%, juveniles 44%, calves and neonates 0%. At Dolphin Encounters, seven of the 20 dolphins were recorded on video producing bubble streams. Females produced significantly more bubble streams (n = 46; 82%) than males produced (n = 10; 18%), (p < .001). There was a significant difference in the number of bubble streams produced by dolphins in each age class (p < .001). Adults produced 59% of the bubble streams, sub-adults 21%, juveniles 13%, calves and neonates 7%. In both locations, females produced the majority of bubble streams; calves and neonates produced the least amount of bubble streams. The significant difference in bubble production between sexes and age classes indicates that bubble streams may not function the same for all dolphins or in all situations.