While on a recent cruise, I spotted one of the many cruise liners we have been entertaining, steaming into Algoa Bay past Cape Recife. I thought it would be a good idea to welcome them into our stunning bay. While cruising alongside them, our head guide, Purity Khosa, shouted from the roof of “My Bru” that there was a feeding frenzy going on on the other side of the liner. We called the liner up on the marine radio and told them to inform their guests of the turmoil that was unfolding 100 metres off their starboard bow. We followed the action for as much time as our permit conditions allowed and were treated to some amazing spectacles, wow! At one stage while they were on the move, the school was 3000 strong.
As their name implies, these dolphins are relatively abundant and have a worldwide distribution in tropical and temperate waters. As usual, with geographically isolated populations, there is uncertainty about the number of species, sub-species and forms that exist. At least 20 different species have been proposed over the years. Local forms could have evolved independently in different locations from nearby oceanic populations.
They are easily identified by the hourglass or figure of eight pattern on their flanks, which is orange brown at the front and yellowish grey at the back. Their appearance in the bay is usually given away by the clouds of following Cape gannets and other seabirds. When they approach closer, your breath gets taken away by their sheer energy in motion and the noise this creates. Generally further than four km from shore, we have on occasions seen them feeding in shallow water just off Summerstrand. They travel in close proximity to one another at speeds of up to 35km/h for extended periods, many animals breaching simultaneously. More than any other species, they will actively follow and interact with our boats for long distances, even if this means leaving the rest of the school for a while. Once you have been in a large school of common dolphins you will take the experience to your grave! They average between one and three thousand although while filming with the BBC far south of Bird Island, we came across an estimated 10 000 individuals.
They are smaller than our other dolphin species. Males are slightly larger than females and can attain two and a half metres and weigh 110kg. Distribution is from St Helena Bay all the way to Richard’s Bay. Although that are present through the year, large numbers start arriving in Algoa Bay in April which is when vast schools of pelagic bait fish start moving past. They will also follow the “sardine run” as it moves up the coast towards Transkei and KZN.
Besides African penguins, these are the only other predators in our area that manage to get the bait balls stationary and closer to the surface. This allows many others species to feed including Bryde’s and Minke whales, SA fur seals, Cape gannets, Cape cormorants and other seabirds, sharks and game fish. Besides sardines they also feed on anchovies, mackerel, saury, elf and bottom dwelling hake. In Algoa Bay squid that comes here to breed forms a major part of their diet.
The calving season is spread over several months but reaches a peak in summer. Calves are born at a metre after a gestation of 11 months. They are suckled for six months at which time they are around 1, 5 metres. The mothers use the highly nutritious fish associated with the sardine run to wean their calves. We know this as stranded animals have had both fish and breast milk in their stomachs. Both sexes can live for 40 years.
They are very vocal animals and quite easy to record and film even off a moving vessel. A wide repertoire of squeaks, whistles and clicks are produced. While travelling they seem to coordinate these short duration sounds with breathing and breaching.
These schools seldom mix with other species of dolphin which is probably due to the continuous high speed at which they move. We have however often seen solitary individuals in the company of slower moving bottlenose dolphins. This is not a once off sighting and these individuals stay with their adopted schools for up to ten years.
This species is susceptible to mass strandings and a few have been observed on the sandy beach between Sunday’s River and Woody Cape. In excess of 2000 have been caught in the shark nets of KZN since the 1960s. They are also caught in fishing gear and especially purse seine nets. Luckily the population is healthy and in excess of 20 000. They are preyed upon by large sharks and killer whales. They accumulate high concentrations of industrial and agricultural pollutants which are passed onto calves by their mothers and may lead to death, especially in the first born.
Read more about the Algoa Bay Marine Protected Area in Addo Elephant National Park here.