The behaviour and ecology of short-beaked common dolphins (Delphinus delphis) along the east coast of Coromandel Peninsula, North Island, New Zealand : with a note on their interactions with humans : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Science at Massey University
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Date
2001
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Massey University
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Abstract
This thesis provides new insights into the behavioural ecology of free-ranging short-beaked common dolphins (Delphinus delphis), in New Zealand. A preliminary assessment of common dolphin-human interactions was also carried out as part of this 3-yr field study (1998-2001). 166 surveys were conducted in the greater Mercury Bay area, on the east coast of Coromandel Peninsula, North Island, New Zealand. These led to 105 focal group follows, with a total of 118.2 h spent following common dolphins. Seasonal movements of common dolphins were uncovered, and are apparently tied to fluctuations in sea surface temperature. Common dolphins appear to live in a fission-fusion society. Groups frequently merged and split again. The merging of groups was often accompanied by either sexual, or feeding activity. 408 individual dolphins were identified from photographs of their dorsal fins. No evidence of long-term associations between individuals was found. Resightings of identifiable dolphins indicate movement of individuals between Mercury Bay and the Hauraki Gulf, as well as between Mercury Bay and Whakatane. This study provides the first activity budget for common dolphins in the wild. Common dolphins spent 55.6% of their time traveling, 20.4% milling, 16.2% feeding, 7.1% socialising, and 0.7% resting. This proportion did not change significantly by season, or from year to year. Common dolphins were found to feed on at least six different fish species. A number of different feeding strategies were employed to capture these fish. Some of these techniques had previously been observed in bottlenose dolphins and orca, but have never before been described for common dolphins. The results of this study suggest that common dolphins can potentially be negatively affected by interactions with humans. Boat traffic appears to disturb some dolphin groups, especially those containing few individuals. However, commercial tourism appeared to have little impact on the dolphins, at this study site. Few attempts at swimming with common dolphins resulted in a sustained interaction, but unsuccessful attempts did not elicit an obvious negative response. Fishing poses the greatest threat of physical injury and possible mortality to common dolphins. Several key issues were identified, and their value in managing human-dolphin interactions is discussed.
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Delphinus delphis, Common dolphin, Dolphin-human interactions, Dolphin ecology, Dolphin behaviour, Dolphin feeding