The small size and fast movements of many small delphinids present challenges when studying their ecology, behavior, and communication. Yet their relative abundance and large group sizes often result in large overlaps with human activities (e.g., fishing, noise), the impacts of which are poorly understood. Pantropical spotted dolphins are globally distributed throughout the tropics, yet little acoustic or behavioral data exist for this species. In Hawaiian waters three island-associated populations and an offshore population are recognized, with varying degrees of overlap with fisheries and Naval activities. The goal of this study was to characterize the daytime dive behavior and whistle repertoire of pantropical spotted dolphins using digital acoustic behavior tags (DTAGs). Five tags were applied across two groups off the west coast of Hawai’i Island, for over 14 hours of total recording time. Results show repeated, relatively shallow, short dives and few foraging buzzes during daytime hours. This supports previous data suggesting that pantropical spotted dolphins are likely foraging primarily at night, but occasional shallow foraging bouts may also occur during the daytime. Seven spectral and temporal characteristics were measured from the fundamental frequency of each whistle, resulting in relatively few (ten) whistle categories, which differed significantly in duration and start, end, minimum and maximum frequencies. Production of at least one whistle category could be attributed to a specific tagged animal, suggesting that this species may produce signature whistles. The overall whistle spectral and temporal characteristics were similar to far-field array-recordings, reflecting the compatibility of these two methods for whistle classification. The results on individual acoustic behavior are valuable for developing detection/classification algorithms and density estimates. Overall, this work represents one of the first successful DTAG studies of small, wild odontocetes, and shows promise for future tag-based examinations of smaller odontocete species.
Silva, Tammy L., T. A. Mooney, L. S. Sayigh, P. L. Tyack, R. W. Baird. 2015. Whistle characteristics and daytime dive behavior of pantropical spotted dolphins (Stenella attenuata) in Hawaii. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.