Sunday, August 09, 2009

Indo-Pacific Humpback Dolphins

Indo-Pacific Humpback Dolphins are characterised by a robust and medium sized body with a short, slightly recurved and triangular-shaped dorsal fin. Individuals from the western part of the species' range have a prominent dorsal ridge forming part the base of the dorsal fin. However, this ridge is not present in Australian animals.

Colouration is uniformly grey, with flanks shading to off-white. Age related changes include a loss of grey colour (shading to white or pinkish) and increased ventral spotting in older animals.

In Australian waters, male Indo-Pacific Humpback Dolphins are recorded to attain lengths of 2.62 m, while females have measured up to 2.6 m. The age and length at physical maturity of South African animals are 13-14 years and 2.58-2.74 m respectively. The maximum lengths and weights recorded in South African animals are 2.7 m and 260 kg for males, and 2.4 m and 170 kg for females.

Adult Indo-Pacific Humpback Dolphins may be found singly or in pairs, while immature individuals tend to associate with groups containing more than one adult. Group size is generally four to seven, but may be as large as 25. Larger Indo-Pacific Humpback Dolphin groups are comprised of all age classes, with adults representing between one half and two thirds of the group.

Goodwin indicated that humpback dolphins show strict female philopatry (stay in the area they were born). However Atkins and Atkins were less certain about the state of philopatry in Richards Bay, KwaZulu-Natal, South Africa, but stated that a small proportion of the animals could be considered resident.


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