Subsurface and nighttime behaviour of pantropical spotted dolphins in Hawai'i

Robin W. Baird, Allan D. Ligon, Sascha K. Hooker, and Antoinette M. Gorgone. 2001.

Canadian Journal of Zoology 79: 988-996

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Pantropical spotted dolphins are found in both pelagic waters and around oceanic islands. A variety of differences exist between populations in these types of areas, including average group sizes, the extent of movements, and the frequency of multi- species associations. Diving and night-time behaviour of pantropical spotted dolphins were studied near the islands of Maui and Lana'i, Hawaii in 1999. Suction-cup attached time-depth recorder/VHF radio tags were deployed on six dolphins for a total of 29 hours. Rates of movements of tagged dolphins were substantially lower than reported in pelagic waters. Average diving depths and durations were shallower and shorter than reported for other similar-sized odontocetes but were similar to those reported in a study of pantropical spotted dolphins in the pelagic waters of the eastern tropical Pacific. Dives (defined as > 5 m deep) at night were deeper (mean = 12.8 m, SD = 2.1, n = 2 individuals, maximum 213 m) than during the day (mean = 57.0 m, SD = 23.5, n = 4 individuals, maximum 122 m), and swim velocity also increased after dark. These results, together with the series of deep dives recorded immediately after sunset, suggest that spotted dolphins around Hawaii feed primarily at night on organisms associated with the deep scattering layer, as it rises up to the surface after dark.

Image of tagged spotted dolphin

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