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

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Abstract:

Pantropical spotted dolphins (Stenella attenuata) 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, extent of movements, and frequency of multi-species associations. Diving and nighttime behaviour of pantropical spotted dolphins were studied near the islands of Maui and Lana'i, Hawai'i, in 1999. Suction-cup-attached time–depth recorder/VHF-radio tags were deployed on six dolphins for a total of 29 h. 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 = 57.0 m, SD = 23.5 m, n = 2 individuals, maximum depth 213 m) than during the day (mean = 12.8 m, SD = 2.1 m, n = 4 individuals, maximum depth 122 m), and swim velocity also increased after dark. These results, together with the series of deep dives recorded immediately after sunset, suggest that pantropical spotted dolphins around Hawai'i feed primarily at night on organisms associated with the deep-scattering layer as it rises up to the surface after dark.

Les Dauphins tachetés pantropicaux (Stenella attenuata) fréquentent aussi bien les eaux des zones pélagiques que les eaux qui bordent les îles océaniques. Il existe un certain nombre de différences entre les populations de ces types de milieux, notamment dans le nombre moyen de dauphins par groupe, l'importance des déplacements et la fréquence des associations multispécifiques. Les plongées et les comportements nocturnes des Dauphins tachetés pantropicaux ont été étudiés au large des îles Maui et Lana'i, à Hawai'i, en 1999. Des chronobathymètres/marqueurs radio VHF ont été attachés à six dauphins au moyen de ventouses pendant 29 h au total. Les taux de déplacement des dauphins marqués sont considérablement plus faibles que ceux signalés dans les eaux pélagiques. La profondeur et la durée moyennes des plongées sont moins élevées que celles enregistrées chez des odontocètes de même taille, mais sont semblables à celles observées au cours d'une étude sur les Dauphins tachetés pantropicaux dans les zones pélagiques du Pacifique tropical oriental. Les plongées (de plus de 5 m) sont plus profondes (en moyenne = 57,0 m, écart type = 23,5 m, n = 2 individus, profondeur maximale de 213 m) la nuit que le jour (en moyenne = 12,8 m, écart type = 2,1 m, n = 4 individus, profondeur maximale de 122 m) et la vitesse de la nage augmente également à l'obscurité. Ces résultats, ajoutés à l'observation de plongées profondes immédiatement après le coucher du soleil, indiquent que les Dauphins tachetés pantropicaux se nourrissent surtout la nuit d'organismes associés à la couche diffusante profonde, pendant sa remontée vers la surface la nuit.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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