Species – Pembrokeshire’s Big 5

There are five cetacean species commonly found in the Irish Sea:

Common dolphin, Bottlenose dolphin, Harbour porpoise, Risso’s dolphin and Minke whales.


Whales, dolphins and porpoises belong to a single group of marine mammals called the cetaceans (order Cetacea). Cetaceans evolved from their land mammal ancestors around 55 – 60 million years ago. There are around 83 species of whale, dolphin and porpoise in the world, but new species are still being discovered.

Cetaceans are divided into two groups


Otherwise known as the toothed cetaceans, this group contains the majority (70 species) of whale, dolphin and porpoise. These cetaceans have teeth and a single blowhole. They also use echolocation to find food and navigate.


Also known as the baleen cetaceans. This group contains about 13 species. Instead of teeth, these cetaceans have baleen plates growing from their upper jaw which sieve prey such as small schooling fish and plankton from the water. Baleen is made from keratin, the same substance as human hair and fingernails. Mysticetes have two blowholes and are not known to echolocate.

You can read more about Pembrokeshire’s Big 5 species found in the Irish Sea below…

Harbour Porpoise

Phocoena phocoena Identification at a glance No beak – rounded head Up to 1.8 m long Small, triangular dorsal fin with straight back edge, i.e., not hooked or ‘falcate’ (the shape of the dorsal fin does vary slightly between individuals, with some having a subtly more curved trailing edge, but the dorsal fin is much… Continue reading Harbour Porpoise

Bottlenose Dolphin

Bottlenose Dolphin Tursiops truncatus Bottlenose dolphins are between 2.4 m and 3.8 m long and 260 kg to 500 kg in weight. They have: A short stubby beak Large hooked or ‘falcate’ dorsal fin Dark grey back and sides,  pale belly Robust head and body shape Pale lower jaw/ dark upper jaw (compare with: white beaked… Continue reading Bottlenose Dolphin

Risso’s Dolphin

Risso’s Dolphin Grampus griseus  This species grows to 3.9 m long, and has: No beak and a broad head A tall, often raked, hooked dorsal fin Colouration is variable. Dark to pale Scarring visible on the sides of many adults and occasionally juveniles Long flippers Risso’s dolphin is widely distributed throughout the world’s temperate and… Continue reading Risso’s Dolphin