The Largest Bottlenose Dolphin Groups on the Planet are found in Algoa Bay
By Lloyd Edwards

1. News

According to Dr Thibaut Boveroux, Algoa Bay boasts the largest reported groups of Indo-Pacific bottlenose dolphins ( Tursiops aduncas ) found anywhere on the planet! Our observations over the last 25 years concur with this. The paper was published in the Marine Mammal Science Journal of the Society for Marine Mammalogy in 2018, although the research was conducted prior to the commencement of Ship to Ship Fuel Transfers (Bunkering) in Algoa Bay in 2016. Thibaut spent many hours on Raggy Charters cruises in Algoa Bay during his research.

This paper was a follow up to the one by Reisinger and Karczmarski in 2010, who estimated that the Indo-Pacific bottlenose population for Algoa Bay was 28 482. It was due to these findings that Raggy Charters launched Algoa Bay as “The Bottlenose Dolphin Capital of the World” in 2016.

So how can Algoa Bay harbour such a huge population of apex predators and why are the groups so large? Then the question must surely be asked as to what effects Ship to Ship fuel transfers (Bunkering) and other anthropogenic factors could have on these animals? Any adverse effect on our marine environment will have a negative effect on tourism and especially marine tourism in Port Elizabeth, the mainstay industry of the Metro.

Scientific research and our own observations indicate that the season of the year did not seem to play a role in the group size. The animals behavior also did not seem to play a role.

A distinct advantage to a large group size would be to increase the protection against predators, like large sharks or killer whales. It would also reduce the amount of time spent on predator vigilance and allow more time for feeding, mating and socialising. Living in these large groups will increase the chances of detecting a predator or minimise the chances of an individual being targeted.

These groups may also improve the effectiveness of cooperative hunting, as many sets of eyes and individuals echo locating, will increase the chances of detecting prey. The downside to this is that there will be more competition among individuals for limited resources, if this was the case.

It can be deduced that Algoa Bay must have abundant resources in order to support such a large population. Dolphins are not the only apex predators, there are many others, namely Bryde’s and Minke whales, common and humpback dolphins, SA fur seals, African penguins, Cape gannets, a myriad of other seabirds, sharks and game fish. This reflects the capacity of our incredible marine ecosystem to support all of this!

This large group size could also offer advantages to new born and young dolphins, who are the most vulnerable to predation. While calves are born throughout the year, the peak always seems to be in mid and late summer. We have seems so many of late. These groups may also offer protection against the aggressive sexual advances by the males towards receptive females (see a previous post in this regard).

The largest groups of dolphins are found close to the shore along our 90km coastline in the bay and especially off the Alexandria Dunefields on the section of coast from Sunday’s River to Woody Cape. Research conducted by another old associate of Raggy Charters, Dr Matt Dicken, showed a partial overlap in the spatial distribution of large dolphin schools (600) and white sharks in this area. The shallow bottom is sandy however, and this makes it much easier for the dolphins to observe the sharks than if they were swimming over a varied substrate.

It has been suggested that Algoa Bay is a nursery area for white sharks, and going from our recent sighting of up up to 20 white sharks per cruise, this definitely seems to be the case! Although our shark diving operation at Bird Island shows the main season for sharks is from April to November, there is not any change in dolphin group size during this period.

A comparison of shark bites from dolphins around the world is interesting. In Shark Bay Australia, 74% of dolphins have shark wounds compared to a 37% in Moreton Bay further to the west. Compare this to 31% in California and only 10 to 20% in Algoa Bay. As shark predation on dolphins is very rarely observed, the frequency of these wounds has been used as an indirect measure of the threat posed. The problem is that these wounds are a result of failed predation attempts, while the actual rate of attacks will be much higher.

A downside to living in large groups is the possible transfer of pathogens and ectoparasites (outside of the body) between individuals. This may lead to affecting many animals of one kind at the same time. We often notice lesions and other growths on their skin, sometimes only when viewing our images on the desktop. There is also more competition amongst males for females and a higher chance of being detected by predators.

Calling Cetacean and especially Dolphins Scientists!

Raggy Charters would like to offer assistance to dolphin scientists to work on these animals in Algoa Bay, as further research may provide important information of the health of our marine ecosystems. We assume that they are healthy enough, given that there would have to be abundant and rich enough resources in order to sustain such a large population of apex predators. This research could also reflect how animals respond and adapt to a change in their environment. As mentioned, this could be brought about by Ship to Ship fuel transfers and the inevitable spills of both the crude oil and other toxins. Who knows what other anthropological factors will have an influence on Algoa Bay, like the shoddy transfer of Manganese ore in our ports.

Who is watching who?
An Indo-Pacific bottlenose dolphin which was part of a school of around 400 breaches clear of the water next to Raggy Charters catamaran "My China". Taken with a Nikon D810 full frame, ISO 280, 70mm zoom, f/10 and 1/1600th second.

This image in a sequence of 4 is a fraction of a second later. The most important thing is to get the boat into the correct position to compose the shot. Good and experienced skippers are the key.

Most of the guests on "My China" have their cameras in hand and ready to catch the moment. Compared to other vessels along our coast ours are very spacious. Some carry twice the amount of pagers sitting cinema style. Not the greatest for viewing.

St Croix Island is located just to the right of this image, while Hougham Park is behind. The port at Coega is to the left.

A few individuals from the school of 400 broke away and approached our catamaran. Permit conditions state that we must run parallel to the dolphins. If they approach us closer than 50 metres we must hold our course and allow the dolphins to control the close encounter.

The launch of the "Bottlenose Dolphin Capital of the World" in 2016. The Minister of Tourism, Head of Eastern Cape Parks and CEO of Nelson Mandela Tourism joined us on this memorable occasion.