Numbers of endangered humpback dolphins (Sousa plumbea) in South Africa are half the figure previously estimated, and unless some drastic interventions are implemented, the picture will become even more bleak.
They are deemed to be the country’s most endangered resident marine mammal, facing a high risk of extinction.
This warning comes from scientists after 16 researchers working at 13 different locations on South Africa’s coast from Richards Bay to False Bay, collected and shared photographs of humpback dolphins’ dorsal fins, used to identify individual dolphins.
Designated the SouSA Consortium, the collaboration was established in May 2016 and findings led to previous estimates of 1 000 individual dolphins now assessed to be half that number.
Humpback dolphins are endangered because they are rare, they reproduce slowly and only occur in a narrow band of very shallow coastal waters, close to shore – an area that is fast being modified and degraded.
Tagging a shy and endangered species like humpback dolphins is not an option, so natural identification features are used to achieve the same objective. Many of the dorsal fins and humps have nicks and notches that make individuals identifiable, and some fins have a distinctive shape. Scars help too.
“We pooled all the photos taken between 2000 and 2016 with the aim of better understanding movement patterns at a national scale,” says marine biologist Shanan Atkins of the School of Animal, Plant and Environmental Science at the University of Witwatersrand.
“In these photographs, 247 distinctive individuals were identified, and 61 of them had been sighted at more than one location. We learnt that the dolphins frequently move distances of 150km and we documented journeys of up to 500km.
“Richards Bay had the highest humpback dolphin encounter rate of all the locations in SA.”
The researchers also make use of ‘citizen scientists’ who contribute by sharing photos of sightings and spreading the word of dolphin conservation.
Electronic aids such as hydrophones (underwater microphones) and live streaming webcams are also deployed to check dolphin movement and patterns. These attract international viewers who click an icon to record a dolphin sighting.
Atkins, who heads the Conserve Dolphins research project at Richards Bay, was highly influential in having the shark net that killed the most dolphins replaced by drumlines – essentially baited hooks.
The project is supported by the German Society for Conservation of Dolphins, the German Foundation for Ocean Conservation, the Endangered Wildlife Trust, Nerospec Networks and the KZN Sharks Board.
An acoustic project is currently being undertaken, with the aim of monitoring dolphins remotely, using their individual ‘signature whistle’ vocalisations.
Early evidence is that humpback dolphins have extremely high frequency whistles, much higher than their bottlenose cousins.
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