Today we had the chance to encounter all three our ‘resident’ species of dolphins: Common, Bottlenose and Risso’s Dolphins.
A mother and calf Bottlenose Dolphin (Tursiops truncatus) porpoise next to Terra Azul boat. The mother’s ribs are clearly visible: this might denote a strong blubber reduction as consequence of the huge effort of feeding herself and her dependent calf.
While Bottlenose Dolphins (Tursiops truncatus) were mainly feeding in the morning, in the afternoon the group was socializing near a large pod of about seventy Risso’s Dolphins (Grampus griseus). The two species often interact in São Miguel waters and this generally means that they can bite each other, and even hybridize! (you can learn more about this phenomena in our previous post here). However, these dolphins have totally different dentition, and rake marks – that’s how bite scars are called – can be discriminated.
Bottlenose Dolphins (Tursiops truncatus) have several conical teeth on both upper and lower jaws.
Risso’s Dolphins (Grampus griseus) have ‘only’ four to eight large teeth on the lower jaw. These teeth fit in sockets in the upper jaw gum when the dolphin closes its mouth, similarly to what happens in adult Sperm Whales (Physeter macrocephalus).
In the picture below you can see an example of Risso’s Dolphin that had a really close encounter with a Bottlenose Dolphin! 😉
An adult Risso’s Dolphin (Grampus griseus) surfaces close to Terra Azul boat. The rake mark on the top of its fin is likely the result of a Bottlenose Dolphin’s (Tursiops truncatus) bite. The other wider and ‘double lined’ marks are from co-specifics. In Risso’s dolphin scars never re-pigment and cause old individuals to become totally white.
Rake marks can tell a lot about the social life of cetaceans! 🙂