South Africa's most endangered dolphin needs your help!

March 02, 2017 Meredith Thornton & Sandra Hoerbst

At the Dyer Island Conservation Trust we are lucky to have one of South Africa’s lesser-known species of dolphin occurring right here in the Greater Dyer Island Area.  This is a shy and somewhat elusive species called the Indian Ocean humpback dolphin.  Their species, or Latin, name is Sousa plumbea and they are officially classified as endangered in South African waters.

There are probably less than 10 000 in the world and most likely only a few hundred left in South Africa!  This very small population size means that they are South Africa’s most endangered dolphin and are thus in need of increased protection and continued monitoring.  They live close inshore, usually in waters less than 20m deep, and are often found around river mouths, like the Uilkraal estuary.

Humpback dolphins are very easy to recognise – they surface by first sticking their rostrum/snout right out of the water, and then when they dive forward you can see a fleshy hump on their back.  Males are larger than females and can grow to about 2.8 m in length.  Their colouring is generally grey with a paler belly that is sometimes spotted.  When they breach many times then this belly becomes pink with the increased blood supply.  As animals become older their dorsal hump and fin can show lots of white scarring, so they usually appear light grey when they are old.  The scarring probably occurs from biting one another and from failed shark attacks.

Unfortunately for humpback dolphins they use exactly the same areas of the coast that humans do, so besides for shark predation, threats are usually as a result of man’s activities.  Power boats and jetskis disturb their behaviour, shark nets put up to protect bathers indiscriminately catch dolphins too and because they like estuarine areas they are especially vulnerable to exposure to pesticides and other pollutants that make their way from agricultural areas down the river system and into the sea – often being accumulated in the prey that humpback dolphins consume.  This can kill newborn calves when they feed on polluted milk from their mothers and it can weaken an adult dolphin’s defence against diseases.

Our ecotourism partner, Dyer Island Cruises runs an ecotour and whale-watching vessel, going out to sea almost every day.  They have a guiding biologist on board who collects environmental data, like water temperature, salinity and weather conditions as well as sightings and photographic data whenever possible.  They have recorded a substantial number of sightings in this area and, because there are far fewer sightings west of here, it is believed that the Greater Dyer Island Area is an important one for this species.

To date we have identified 28 different humpback dolphins from the Dyer Island area and, together with the Mammal Research Institute and Sea Search, we are embarking on an intensive research project to collect data to understand more about their distribution, ecology and population size.  The plan is for these data to aid conservationists and environmental managers to make decisions on marine spatial planning and shark nets that will protect humpback dolphins in the long term.

Photo-identification and behavioural data will continue to be collected from the commercial trips, as well as during dedicated research surveys. The photo-identification data are being used to establish a catalogue of Indian Ocean humpback dolphins for this region, and to estimate their local abundance. Very exciting is a recent collaboration between all researchers in South Africa, who are collecting data on humpback dolphins, called the ‘Sousa Project’, whereby all data from the South African coast have been combined to find out more about the national population size and movements of these animals.  There are also plans afoot to establish collaboration with Mozambique, because animals do not recognise international borders – so these dolphins must be protected and studied in neighbouring countries too.

We urgently need help with the financial aspect of this project, so if you are able to contribute please do so by contacting office@dict.org.za. Your help is greatly needed and donations will be used to buy essential camera equipment for collecting photo ID data.  Remember that Your Choice Makes A Difference!