About the Dolphins

Quick Facts ● The Straight Talk ● The Science

Quick Facts

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Indian Ocean humpback dolphins are endangered.

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These dolphins are elusive and not well known.

The Straight Talk

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They are fast disappearing throughout their range.

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They can be found along the rim of the western Indian Ocean, the Arabian/Persian Gulf, the Red Sea and some islands - but only in very shallow, coastal waters <25m deep.

The Science

Their numbers are declining

For the detailed science, visit the IUCN's Red List entry for Indian Ocean humpback dolphins.

IUCN Red List

Endangered

Using the IUCN’s Red List assessment criteria, Indian Ocean humpback dolphins Sousa plumbea qualify as Endangered based on the criteria: A2cd+3cd+4cd. This means that, over 3 generations, their population size is suspected to have declined by more than 50% for three reasons: they are being exploited, they occur in fewer places than they did historically and the quality of their habitat has declined.

These dolphins are very specific about the habitats they prefer and they have a particularly restricted distribution. Both of these characteristics are known to increase the risk of extinction. They are limited to very shallow coastal waters, usually within 2 km of shore - the same places that most small-scale fishers set their gillnets and this puts them at high risk of entanglement and death. Unsustainable mortality rates have been reported from several areas and are suspected in many others. In addition to this, the coastal habitat that we share with them is increasingly being lost, degraded and polluted. Coastlines are being developed and industrialised by Blue Economies with spreading urbanisation, extensive land reclamation and the rapid expansion of ports and shipping. Even remote coastal areas are becoming degraded, polluted, and noisy habitats.

©C McFarlane

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Humpback dolphins occur in 23 countries, 15 of which are rated as lower-income with few resources for marine research or conservation.

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The dolphins and their habitat are impacted by human activities in the
sea, on land and in freshwater.

Threats

Gillnets

Because humpback dolphins are restricted to shallow coastal habitats, they live in some of the world’s most intensively utilised, fished, shipped, modified and polluted waters. The primary threat to the Indian Ocean humpback dolphin throughout its range is incidental mortality in gillnets (‘bycatch’), including shark control nets in South Africa. It has been impossible to evaluate the magnitude of the threat of bycatch in gillnets in most areas. However, everywhere that it has been evaluated, the bycatch rate appears to be high, unsustainable and causing rapid local population declines.

Ports and associated activities and infrastructure

There are also very few areas where this dolphin’s habitat has not been altered by humans. Around the western Indian Ocean rim and adjacent gulfs and seas, large and small ports are being developed incredibly rapidly, often in the estuaries and protected bays that best suit humpback dolphins. Harbour construction, maintenance and operations include disruptive activities such as construction blasting, land reclamation, dredging and boat traffic. In addition, these ports attract other industries, like manufacturing, and result in expanded human settlements. Many of the large urban centres and ports release a toxic cocktail of untreated human and industrial waste into coastal waters.

Chemical contaminants

Living so close to shore, humpback dolphins are exposed to various contaminants and many of these contaminants accumulate in the dolphin’s layer of blubber. Where studies have been conducted, humpback dolphins’ levels of accumulated contaminants (e.g. DDTs, flame retardants, PBDEs) appears to be very high compared to other, more oceanic marine mammals. Such chemicals affect dolphin health and reproduction. These impacts are likely contributing to local declines in the number of dolphins. It is important to note that just because humpback dolphins may persist in these degraded habitats does not mean that habitat degradation does not adversely affect their health.

Other threats

There are other threats that appear somewhat less serious (possibly because of lack of information) or only affect a certain portion of the species’ range. These include underwater noise, climate change, boat traffic/harassment, direct killing, and oil spills and exploration (including inshore seismic surveys). All together, these impacts threaten the dolphins’ survival in ways that are challenging to measure but are likely to be impactful.

Conservation

Very few people have even heard of humpback dolphins which makes it particularly difficult to conserve them. However, the situation is far from hopeless and conservationists have various tools in their toolboxes.

International treaties can be useful conservation tools. For example, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is an international agreement between many governments that prohibits trade of certain wildlife species. Humpback dolphins are listed on Appendix I, subject to the strongest restriction in international trade. The Convention on the Conservation of Migratory Species of Wild Animals (CMS) strives to protect species that migrate or move predictably across borders. The humpback dolphin is listed on Appendix II and a process has begun for the species to be assessed against the criteria for Appendix I.

Within nations, a useful conservation strategy is delimiting Marine Protected Areas (MPAs). For example, South Africa recently declared many new MPAs, including uThukela MPA where there is a higher density of humpback dolphins than surrounding areas. There are also other types of useful legislation, such as the South Africa’s National Environmental Management: Biodiversity Act No. 10 of 2004 which protects all marine mammals in the country.

Another conservation strategy is finding alternative livelihoods. Dolphins used to be hunted in Menai Bay in the south of Unguja Island, Tanzania. In the 1990s, the hunt was replaced by swim-with-the-dolphin tourism. Similarly, in southwest Madagascar, there has been some success engaging communities that hunt marine mammals with the establishment of community-based, nature-oriented tourism, local protection and enforcement, and social outreach campaigns.

It remains a high priority to improve our understanding of what needs to occur to safeguard populations.

Biology

A humpback dolphin can be recognised by the dorsal ridge (which in some animals forms a pronounced hump) and small dorsal fin. They have a characteristic way of surfacing - breaking the water’s surface with their long thin rostrum/nose, which is followed by the head and then arching back.

The Indian Ocean humpback dolphin Sousa plumbea is one of 4 species of Sousa and can be found in coastal waters from False Bay, South Africa, in the west, through the coastal waters of east Africa, the horn of Africa, and the Middle East to approximately the southern tip of India and Sri Lanka, including the Seas and Gulfs in the Middle East, and several offshore islands, such as western Madagascar, Socotra, Mayotte, Pemba, and Zanzibar. Within this range, they inhabit a very narrow strip of shallow coastal waters, less than 25m deep. However, their distribution is not continuous - there are gaps where the continental shelf is narrow (as well as areas have not been surveyed).

View Map

Scientific surveys have shown that most humpback dolphin populations are small: always fewer than 1,000 individuals and generally fewer than 100, often in discrete or semi-isolated areas. Globally, an educated estimation suggests that abundance is probably no higher than a few ten thousand.

Humpback dolphin’s conservation biology indicates that they occur in restricted habitats and are distributed discontinuously; they are slow to mature and reproduce and they are not abundant anywhere in the range.

Humpback dolphin calves are born at about 1m in length, usually in the summer. Females give birth to a single calf, after a gestation period of about 1 year, at about 5-year intervals. Both sexes reach maturity at about 8 years of age. In South Africa, females do not grow much bigger than 2.4m whereas males do not grow much bigger than 2.7m. At the other end of their range, specimens from India and Pakistan appear to grow exceptionally large. Humpback dolphins can live to ages of over 40 years.