Humpback dolphin

Sousa chinensis, S. plumbea, S. teuszii, S. sahulensis

Humpback dolphins are found in relatively shallow nearshore waters throughout their range which includes most of the coastlines in Australia, Africa and Asia. Their dependence on nearshore habitats brings them into contact with many types of human activities, putting them at risk from fisheries entanglement, boat traffic, pollution, and habitat loss. However, this habitat selection also makes them easy to observe from shore. There are four recognized species of humpback dolphins with very little overlap between their ranges: the, Indo-Pacific humpback dolphin (Sousa chinensis), the Indian Ocean humpback dolphin (S. plumbea) the Atlantic humpback dolphin (S. teuszi) and the Australian humpback dolphin (S. sahulensis)¹. Because they tend to be relatively shy, and less active than the bottlenose dolphins with which they often share territory, this species is not often the primary target of dolphin watching tours. However, they can be encountered in nearshore waters, and in some areas, like Hong Kong, and the Musandam Peninsula of Oman, they are the stars of the show.

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Humpback dolphin species' global distribution. Adapted by Nina Lisowski from Würsig,B., Thewissen, J.G.M. and Kovacs, K.M. Editors (2018) "Encyclopedia of Marine Mammals", 3rd ed. Academic Press, Elsevier: San Diego. CA. Copyright Elsevier: http://www.elsevier.com

The 3 characteristic rostral ridges on a Brydes whale Plettenberg Bay Gwenyth Penry

Indian Ocean humpback dolphins (Sousa plumbea) off the coast of Pemba, Tanzania. Photo courtesy of Gill Braulik.

Adult Indo-Pacific humpback dolphin and calf in Sarawak, Malaysia. Photo courtesy of Cindy Peter, Sarawak dolphin project

Distribution

Humpback dolphins are limited in their range from the West coast of Africa in the West to the coast of China and the east coast of Australia in the East and are always found in shallow nearshore waters. The four different species have distinct geographic ranges as follows:

Atlantic humpback dolphins are native to: Angola, Benin, Cameroon, Congo (Republic); Congo (Democratic Republic); Côte d'Ivoire, Equatorial Guinea ; Gabon ; The Gambia; Ghana; Guinea; Guinea Bissau; Liberia; Mauritania; Nigeria; Senegal; Sierra Leone, Togo; Western Sahara

Indian Ocean humpback dolphins are native to: Bahrain; Bangladesh; Comoros; Djibouti; Egypt, Eritrea; India; Iran; Iraq; Israel; Kenya; Kuwait; Madagascar; Mayotte; Mozambique; Myanmar; Oman; Pakistan; Qatar; Saudi Arabia; Somalia; South Africa; Sri Lanka; Sudan; Tanzania; UAE; Yemen.

Indo-Pacific humpback dolphins are native to: Bangladesh; Brunei Darrusalam; Cambodia; India; Indonesia; Malaysia; Myanmar( Burma); People’s Republic of China; Philippines; Singapore; Taiwan (Republic of China); Thailand; Vietnam

Australian humpback dolphins are native to: Australia and Papua New Guinea

Biology and Ecology

Feeding

Humpback dolphins seem to be fairly adaptable in their diet, with studies from South Africa, Hong Kong, Australia and Oman revealing a variety of fish species, and sometimes crustaceans, squids, octopus and cuttlefish in the stomachs of by-caught or stranded animals^2-6. Humpback dolphins use a variety of feeding techniques, including partially stranding themselves on shore while chasing fish⁷. In some locations, humpback dolphins are also known to follow fishing trawlers in order to opportunistically feed on discarded and escaped fish⁸.

Social structure, Reproduction and growth

Humpback dolphins usually occur in small groups of 2-6 individuals, but larger aggregations of up to 30 or 50 individuals have been recorded from Oman^9,10, and Malaysia¹¹, and over 100 individuals from Bangladesh⁸. Males often show scarring consistent with aggression within their own species – such as tooth rakes on their dorsal fins¹². The species also appears to interact with other dolphin species in its range, with a number o documented cases of both benign and aggressive interactions between bottlenose dolphins and humpback dolphins¹⁰, and the apparent incorporation of an Irrawaddy dolphin into humpback dolphin groups in two different sites in Malaysian Borneo^13,14. Females of all four species are thought to reach sexual maturity at 9-10 years. In Hong Kong and South Africa, calves are predominantly born in the spring and summer, but little is known about the seasonality of reproduction or other life history characteristics of Australian or Atlantic humpback dolphins^7,15.

Research, threats and conservation

As with many other species of whales and dolphins, individual humpback dolphins can be recognised from the unique patterns of scarring and pigmentation on their dorsal fins. Researchers build up catalogues of known individuals and track them over time. Because almost all humpback dolphin populations have fairly stable nearshore home ranges, they provide excellent subjects for long-term monitoring, including studies of social structure, reproductive parameters, residency and range^16,17. Because their nearshore habitat also brings them into contact with human activity, they are also the focus of studies that try to assess the potential impact of coastal development and other threats on dolphin populations¹⁸. For more information about methods used to study whales and dolphins click here.

Natural Predators

Humpback dolphins’ main natural predators are sharks, with one photo-identification study in Australia revealing that 46% of sampled humpback dolphins had scarring associated with shark attacks¹⁹. Great white, tiger, and bull sharks are thought to be the species most likely to pose a risk to (young) dolphins.⁷

Human induced threats

Humpback dolphins throughout Africa, Australia and Asia often live in close proximity to densely populated urban areas. In developed areas, like Hong Kong, their habitat is continually affected by coastal construction and high volumes of vessel traffic. In developing countries, their distribution often overlaps with areas where fishing effort is exponentially increasing^7,20. As with almost all species of whales and dolphins, accidental entanglement in fishing gear – or bycatch- is the leading source of human-induced mortality for humpback dolphins²¹, but coastal development¹⁸, pollution^22-24, and in some areas, such as West Africa, direct hunting²⁵ also pose serious threats.

Conservation status

The IUCN Red List status of all four species of humpback dolphins has recently been re-assessed, resulting in the current designations: (1) Atlantic humpback dolphin - critically endangered,^25,26; (2) Indian ocean humpback dolphin -endangered,^27,28; (3) Indo-Pacific humpback dolphin- vulnerable^8,29; and (4) Australian humpback dolphin - vulnerable^30,31. Of all four species, Atlantic humpback dolphins are considered the most severely at risk of extinction, and are listed on Appendix I of the Convention on Migratory Species (CMS). The IWC also considers this species of the utmost priority for conservation action³².

Humpback dolphins and dolphin watching

Please see the IWC Whalewatching Handbook

References

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