Our endangered Indian Ocean Humpback Dolphins
By Lloyd Edwards

1. News

It is not often that we spot these elusive Indo-Pacific humpback dolphins along the surf at the Alexandria Dunefields in Algoa Bay. What a great surprise to find a school of around 14 of them swimming along close inshore. They are not the easiest dolphins to photograph, as they spend most of the time submerged and rarely breach.

These dolphins get there name from the characteristic fatty hump on their backs, which gets progressively larger with age, especially males. Due to the low population estimates, low reproductive rate and high mortality, it is considered to be South Africa’s most endangered marine mammal. In 2018 it was up listed to “Endangered”. Its distribution runs along a narrow coastal strip from False Bay to the Bay of Bengal in India. Latest research points to there being an isolated population between Algoa Bay and False Bay. There is another population north of Durban. These animals have been very well studied in South Africa. It was only separated from Sousa chinensis and recognized as a separate species in 2014.

This has to be the easiest dolphin to identify but the most difficult to approach. They live very close to shore in the surf zone in water less than ten metres deep and often enter estuaries and harbours. They are slow moving and their long rostrum is the first part of the body to rise steeply out of the water, followed by the head. They have deep creases on their bodies, which become more exaggerated with age. In some of the largest adults, parts of the dorsal fin and hump become white with age, as do the tips of the rostrum and flukes. The dorsal fin has a distinct “scraggy” look about it and invariably has pieces missing, especially on the trailing edge. They are covered in scars, probably from entanglements in fishing lines, as they inhabit shallow water that is also utilized by anglers. Sharks must also leave their signatures. Their worst nightmare are the shark nets in Kwazulu Natal which have killed around 300 of these individuals. Why we still have these nets in place which kill hundreds of marine animals I will never know. Come on activists in KZN, step up to the challenge!

Maximum known body weight for males is 2,8m, while females reach 2,5m and weigh 280kg and 250kg respectively. Courtship and mating has been observed and studied here. Unlike Algoa Bay’s other dolphin species, pairs become isolated prior to mating. Partners swim alongside each other before breaching, and then dash off to repeat the process several times. After brief copulation they swim off, rubbing each other with their bodies. This would be repeated often. Calves are born after a gestation of a year, at one metre in length and weigh in at 14kg. Calving takes place throughout the year, but mostly between December and April. They are very pale at birth but darken with age. Individuals go through the whole cycle, as they lighten again with age when older animals get distinct grey patches. Calves start taking solid food from six months but can still be breastfed for many years. Both sexes can live for 40 years.

The best places to view them in Algoa Bay are between Happy Valley and the beacon at Cape Recife, around the harbour and at the mouth of the Swartkops River. They seem to prefer shallow water reef and sandy bottom fish and especially those that are estuarine dependent. In the stomach contents of two individuals stranded in Algoa Bay 20 fish remains, four squid and an octopus were found. They included 12 Blue Hottentot, four unidentified sea bream, one Cape stumpnose, one spotted grunter and a mackerel. Stomach contents from dolphins caught in shark nets reveal that they can prey on up to 60 different animals. As they often feed in dirty water by using sonar, they tend to eat more fish species that occur in these conditions.

Taken with a Nikon D810, ISO 220, f/8 and 1/1250th second. Calves are extremely difficult to photograph, ask me! Note the difference in colouration and skin textures of the cow and calf

Note the dolphin in the middle. The rostrum is the first part of the dolphin that breaks the surface.

The cliff in the background is aeolianite, sandstone derived from windblown sand.

The ageing process has already started in these two individuals which become even whiter with age.

It is always difficult to estimate the size of a school. Here there is evidence of at least 7. There are normally twice as many below the surface as above.