Humpback dolphins of G ansbaai

Humpback Dolphins of Gansbaai

The Indian Ocean humpback dolphin (Sousa plumbea) has only been recognised as a distinct species a few years ago. Little is known by researchers, and even less by the public, about these often shy and elusive dolphins. Their name originates from a prominent hump below the rather small dorsal fin and therefore makes them easy to identify from other dolphins found along the South African coast.

CONSERVATION PROFILE

Humpback dolphins are a medium sized dolphin and known to inhabit only a narrow coastal band with water less than 25 meters deep. They are often found traveling in small groups of less than 10 individuals. Their distribution stretches from the Bay of Bengal to False Bay in South Africa. Within South Africa their home range is limited to shallow, nearshore environments, over relatively short along-shore ranges of approximately 120km from Kosi Bay in the east and False Bay in the west. They are often encountered in protected bays, near estuaries and sometimes rocky reefs.

Coastal areas are facing ever increasing anthropogenic impacts which are threatening coastally dependant animals such as humpback dolphins. The species is listed internationally (IUCN – Red List) as ‘Endangered’. Although South Africa’s Indian Ocean humpback dolphins are protected under the Marine Living Resources Act (Act 18 of 1998), their preference for shallow and nearshore areas means they are living in some of the world’s most intensively used, modified and polluted waters.

Pollution in estuaries and nearshore waters is a major concern for the Indian Ocean humpback dolphin. Persistent organic pollutants accumulate in the blubber of marine mammals as they consume fish and can cause cancer, immune, reproductive dysfunction, and birth defects. Off South Africa, humpback dolphins have been found to contain the highest levels of such pollutants when compared to other dolphin species. Additionally, the ingestion of and entanglement in plastic pollution is a growing concern for marine mammals like humpback dolphins and often has fatal consequences.

To aid in conservation efforts for the humpback dolphins the Dyer Island Conservation Trust has collected data on the species since 2003 using the daily observational platform of Dyer Island Cruises, an award-winning responsible tourism company in Gansbaai (South Africa). The latest photo identification (ID) catalogue was created in 2014 to contribute to the long dataset collected on the species in this area previously and has been updated on a regular basis ever since. The photo ID catalogue of the greater Dyer Island area has contributed to projects at a national scale within the SouSA Consortium.

Through this nationwide collaboration between scientists contributing photo ID catalogues, research published in 2017 has identified 247 uniquely and well-marked humpback dolphins along the South African coast. From this, scientists were able to produce a first national abundance estimate for the population that was way below the previously estimated 1000, with numbers closer to 500 individuals.

The humpback dolphins in the greater Dyer Island area have been mostly seen at Uilenkraalsmond, a natural estuary that is seasonally open. However, there have also been occasional sightings in Pearly Beach, as well as on the coast towards Danger Point and even closer to Dyer Island. Through the national collaboration and comparison of the ID

‘Coastal areas are facing ever increasing anthropogenic impacts which are threatening coastally dependant animals such as humpback dolphins... ’

CONSERVATION PROFILE

photographs we discovered that the dolphins from the greater Dyer Island area travel all the way to False Bay and are therefore the most westerly seen individuals of the species range. Over the years we have not only taken ID photographs but also observed and recorded their occurrence and behaviour. Humpback dolphins have been seen swimming with the seasonally visiting southern right whales, playing with Cape fur seals as well as teaming up and chasing a great white shark.

Here we introduce you to four of our humpback dolphins that for many years have visited the bay on a regular basis. Oupa #013 Captain Hook #003 OUPA (#013) is a well-known Indian-Ocean humpback dolphin to our bay. We first photographed him in September 2014, the year we started the new humpback dolphin catalogue. Ever since he has been snapped by the camera on board the whale watching boat of Dyer Island Cruises regularly. Since 2014 we have encountered him on at least 44 occasions.

On most encounters, we have seen him individually from close to Danger Point to Pearly Beach and even along the De Clyde, a reef system, going from the mainland towards

Dyer Island.

Image credit - W Gilmore

CAPTAIN HOOK (#003) is one of our well-known females and her name came about because of her hook like dorsal fin. Since we started taking photographs of her in 2014, she was seen with her calf named BigZ. However, since June 2018, she has been sighted alone again, and separated from her young one. She always shows relaxed and calm behaviour around our whale watching vessel. We are curious how long it will take to encounter her again with a new calf.

FINGERS (#001) is one of the dolphins that have been known to us for a long time and is seen on a regular basis is. The sex of this dolphin is unknown, but it is suspected that it is a male. Fingers is seen in the bay throughout the year, around the Uilenkraalsmond estuary, and has been at least 65 encounters have been documented since 2014.

NEWTON (#029) is one of the more adventurous individuals we encounter in the greater Dyer Island area. This dolphin is never shy of the boat and always comes closer to have a look at us and the vessel. Newton has also been observed swimming with a pod of bottlenose dolphins and playing with Cape fur seals on various occasions. Newton was last encountered in our area on the 17th of March, just before lockdown. ic Name: Megaptera

Fingers #001

Image credit - Sandra Hörbst

Newton #029

Experience The Wonder Of The Humpback Dolphins And The Rest Of The Marine Big Five With Dyer Island Cruises

The Dyer Island ecosystem off the coast of Gansbaai is unique in the world, home to the Marine Big Five™ - Sharks, Whales, Dolphins, the Cape fur seal, and the endangered African Penguin. It is here that the team of Marine Dynamics/Dyer Island Cruises operate with due care for the species they share with guests every day. Join them on an unforgettable and educational marine safari.

The many sheltered areas of the bay provide the breeding ground for the Southern Right Whales that migrate here from the subAntarctic islands between June to December each year. Out of this traditional whale season, you may also see Humpback whales that migrate along the coastline. In the early half of the year you may see the shy Bryde’s whale. Gansbaai is world renowned for the iconic great 84 responsible traveller white sharks that visit the bay. This is one of the most accessible populations in the world as the sharks are often found just metres from shore or hunting around the 60 000 strong seal colony on Geyser Rock, opposite Dyer Island.

You may also be lucky to see the bronze whaler sharks with their shimmering gold colour that enthrals nature lovers. We have three dolphin species that move through these waters – the Common dolphin, the Bottlenose, and the Humpback dolphin. The African penguin breeds on Dyer Island and is sometimes seen in groups swimming at sea. Sadly, the species is classified as endangered with an estimated 13 300 breeding pairs left in South Africa.

CONTACT: MARINE DYNAMICS www.dyerislandcruises .co.za whales@marinedynamicstravel.com ph: +27 (0) 82 801 8014 By joining this tour, you can be assured that YOUR CHOICE MAKES A DIFFERENCE for conservation and the community.