Indo-Pacific Hump-backed Dolphins
From the NUS Dolphin Study Group
Etienne Douaze <firstname.lastname@example.org>
Permission obtained on 30 July 1998, Email message.
- Indo-Pacific Hump-backed Dolphin
- Atlantic Hump-backed Dolphin
Species of this genus were once classified as Sotalia, but they
have recently been separated into a separate genus. Species in the eastern
hemisphere were placed under Sousa, while species in the western
hemisphere were put in Sotalia. There is significant debate about
speciation in this genus. The species are commonly known as hump-backed dolphins,
since they have a protrusion that supports the dorsal fin. All hump-backed
dolphins share certain characteristics. Adults are between seven and nine
feet and weigh less than 150 kg, depending on the population. They have
sloping foreheads and long, narrow beaks.
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Indo-Pacific Hump-backed Dolphin
The Indo-Pacific hump-backed dolphin is not relatively well known.
It is found along the coasts of the Indian Ocean and the East Indies, mostly
in estuaries. It moves in a leisurely manner and is relatively tame. There
is a great deal of disagreement about the taxonomy of the stocks of this
species. Three general forms have been identified: a spotted form in the
region of South Africa, called by some S. lentiginosa, a solid gray
form in the Persian Gulf, called S. plumbea, and a brilliant white form
near the China Seas and Sarawak, called S. chinensis. Since the
divisions between these stocks are not clear, they are all lumped into a
single species. Feeding habits and behavior are not well known, although
bottlenose dolphins and hump-backed dolphins have been seen playing together.
The social organization is not understood. Groups contain up to 25
individuals, and appear to be somewhat flexible, with relationships between
(Click for larger version)
Atlantic Hump-backed Dolphin
As a rather isolated species, the Atlantic hump-backed dolphin is not well
known. It is found along the western coast of Africa, from Cameroon north to
Senegal and Mauritania. The range may extend as far south as Angola and as
far north as 20° N. Within these areas, it makes use of coastal,
estuarine, and possibly riverine habitats. The mangrove areas in the south
appear to be an important habitat for this species. The taxonomic distinction
between this species and the Indo-Pacific hump-backed dolphin is not entirely
clear, as they are almost identical. They are termed separate species because
the populations appear to be completely isolated, but there are also some
craniological differences, such as the number of teeth. All individuals
are slaty gray on all sides and slightly paler on the ventral areas.
The forehead is smoothly curved, and the beak is long and narrow. Whether
females have humps in addition to males is uncertain, as few specimens have
been collected. Currently the only major threat to this species is that
the mangrove habitats along the coast are threatened. However, because the
Atlantic hump-backed dolphin lives along the coasts of some lesser
developed countries where there is a high degree of protein deficiency, the
potential for greater threats to their survival is present.
Baker, Mary L. Whales, Dolphins, and Porpoises of the World. New York: Doubleday & Company, Inc., 1987.
Carwardine, Mark. Eyewitness Handbooks: Whales, Dolphins, and Porpoises. New York: Dorling Kindersley Ltd., 1995.
Ellis, Richard. Dolphins and Porpoises. New York: Alfred & Knopf, Inc., 1982.
Klinowska, Margaret. Dolphins, Porpoises, and Whales of the World: The IUCN Red Data Book. Gland, Switzerland: World Conservation Union, 1991.