02.07.2018 – Dolphin diversity

Atlantic spotted dolphins (Stenella frontalis), Bottlenose dolphins (Tursiops truncatus) and Risso’s dolphins (Grampus griseus) were the species of cetaceans encountered out at sea on this busy summer day. The entertaining company of the spotted dolphins was frequently enjoyed on all tours today, both from the boat and in the water during this mornings snorkelling tour. The inquisitive and playful character of the spotted dolphins pretty much suits our conventional picture of dolphins. The Delphinid family, however, is an extremely diverse group of marine mammals many of which do not resemble our standardised picture of dolphins.

The Delphinidae family consists of 26 species that includes oceanic dolphins such as the Bottlenose dolphin or the Atlantic spotted dolphins, as well as species belonging to a group that are collectively referred to as “blackfish”. The term Blackfish was used by fishermen to describe the dark coloured, gregarious cetaceans that bear little resemblance to dolphins despite them being delphinids. This group includes the Short-finned pilot whales (Globicephala macrorhynchus), the False Killer Whales (Pseudorca crassidens) as well as the Orca (Orcinus orca), the largest known dolphin. In contrast to the fission-fusion societies of oceanic dolphins, blackfish are known to exist in well-structured groups and don`t have a beak. While the blackfish are clearly distinct from other dolphins, oceanic dolphins also show high variability in their phenotype. While most oceanic dolphin possess a prominent beak, others, like the Risso’s dolphin, do not.

Our sightings involved oceanic dolphins, that not only proved that dolphin species can vary in their phenotype but also in their behaviour. The small Atlantic spotted dolphin is notoriously curious and playful by nature, almost always approaching our vessels during our whale-watching tours. Bottlenose dolphins are much larger and move in smaller groups as do the Risso’s dolphins, who are distinguished by the white scarring on their bodies and their round foreheads. Bottlenose dolphins occasionally get curious but are generally less interactive than spotted dolphins. Risso’s rarely approach our boats although there have been reports of these animals riding the waves near the bow of vessels. Today they kept their distance, while the Bottlenose showed some interest and gently swam near our vessels.

 By Paula Thake

Sightings of the day

Ribeira Brava

09:00 Atlantic spotted dolphins, Bottlenose dolphins

13:30 Atlantic spotted dolphins, Bottlenose dolphins

Stenella

09:00 Atlantic spotted dolphins (snorkelling), Bottlenose dolphins

12:00 Atlantic spotted dolphins, Risso’s dolphins

15:30 Bottlenose dolphins