Researchers from Stellenbosch University (SU) recently spotted a newborn common dolphin calf with a pod of endangered humpback dolphins while busy with fieldwork near Mossel Bay.
This is according to Dr Tess Gridley, co-director of the Sea Search-Namibian Dolphin Project and research associate with the department of botany and zoology at SU. Researchers were surprised by this behaviour and questioned the calf’s survival prospects, according to Gridley.
“The common dolphin occurrence was quite interesting. We were out looking for humpback dolphins and we came across a group of humpback dolphins with a common dolphin swimming with them,” said Gridley.
Common dolphin calf spotted with humpback dolphins in Mossel Bay. PHOTO: Supplied/Guilherme Frainer
The sighting took place off the coast of Mossel Bay on 24 March during fieldwork conducted by Sasha Dines, a PhD student with the department of botany and zoology at SU.
“To see a common dolphin in the group was very unusual to us. We didn’t really believe what we were seeing,” said Gridley.
Possible explanations for the mingling
There are a few theories as to how the common dolphin calf ended up with the pod of humpback dolphins, according to Dines and Gridley.
“The calf could have been lost or orphaned by its mother and then adopted by the group of humpback dolphins,” said Dines.
Another theory is that the calf was kidnapped by the humpback dolphins. This behaviour has been observed among other dolphin species, according to Dines. However, the researchers saw no evidence of harassment that would indicate a kidnapping. They have also ruled out the possibility of the calf being a hybrid of the two species, she added.
Common dolphins can be identified by their slender snouts and the yellow stripes on the sides of their bodies. Humpback dolphins have a distinctive hump. PHOTO: Supplied/ Guilherme Frainer
“Behaviourally, they [common and humpback dolphins] are really different animals,” said Dr Simon Elwen, co-director of Sea Search-Namibian Dolphin Project and research associate with the department of botany and zoology at SU.
The team of researchers is worried about the survival prospects for the calf, according to Dines. “The main question raised is whether there is a lactating female in the group. The only way the baby would survive is if there’s an adult able to feed it. We didn’t see anything like that,” said Dines.
The common dolphin is usually found in deeper waters and much larger groups, making it unusual to find a common dolphin in the same area as humpback dolphins, according to Dr Tess Gridley, co-director of the Sea Search-Namibian Dolphin Project and research associate with the department of botany and zoology at SU. PHOTO: Supplied/Guilherme Frainer
Research that is making a splash
According to Dines, her research focuses on documenting the signature whistle used by humpback dolphins.
The whistle is a distinct, individually learnt sound that is used for identification among dolphins, according to Dines. The aim of the research is to monitor the health and movement of humpback dolphins using novel acoustic monitoring methods, she added.
“Humpback dolphins are the most endangered marine mammal in South Africa, with an estimated population of less than 500. They are a very shallow and coastal species, with low encounter rates in the ocean,” said Dines.
At the time of publication, the research team had not sighted the pod of humpback dolphins that included the common dolphin calf again.
INFOGRAPHIC: Kirsty Bucholz