What is a

‘Cetacean’ is the collective name for all whales, dolphins and porpoise which form the taxonomic order of Cetacea. Despite spending the entirety of their lives in the water, they are mammals like us. Meaning that they are warm blooded, give birth to live young, nurse their young, have traces of hair, and must come to the surface to breathe air through their lungs.

It is believed that modern cetaceans evolved from a common terrestrial ancestor, and that their closest living relative today is the hippo.
They are highly evolved, intelligent and sentient animals, who exist in highly organised and culturally diverse societies. Modern whales may be divided into two subgroups; Odontocetes (toothed whales) and Mysticetes (baleen whales).

What are Mysticetes?

Mysticetes are a sub-order of Cetacea known as baleen whales. Instead of using teeth to feed like odontocetes, they use a highly specialised filter feeding apparatus known as baleen which is a keratinized structure like our hair and fingernails. The exact method by which baleen is used differs between species (gulp-feeding with balaenopterids, skim-feeding with balaenids, and bottom-feeding with eschrichtiids). It hangs down in two rows, one from each side of the roof of the mouth of the whale.

The longest sides of the plates are smooth and situated along the outer edge of the mouth, whereas the inner sides are frayed into bristles. Other differences from odontocetes include a paired blowhole, symmetrical skull, and absence of ribs articulating with the sternum.

Many species undertake very long migrations and some like the humpback whale, are known for their complex songs.


Odontocetes are a sub-order of Cetacea, referred to as toothed whales. They include dolphins, porpoise, killer whales, beaked whales, belugas and narwhals, and all other species possessing teeth as opposed to baleen. They vastly range in size from the vaquita (~1.4m) to the sperm whale (12-16m). Common characteristics of odontocetes include; a single blowhole, asymmetrical skulk, three sternum bones and the use of echolocation to navigate and to hunt.

They live in highly complex social structures and have been known to exhibit diverse species specific cultures and behaviour.

10 Dolphin Facts

Humans can still breathe while we are asleep, as our respiratory system is involuntary. However, cetaceans have a voluntary respiratory system and have to consciously decide to surface to breathe. Bottlenose dolphins are believed to shut down half of their brain while ‘sleeping’, along with the opposite eye. The other half stays awake at a low level of alertness, to watch for predators, obstacles and also to signal when to surface to breathe. After a period of time this process will be reversed, resting the active side of the brain and waking the rested half. Other mechanisms help cetaceans to hold their breath longer before needing to surface to breathe. Their lungs are proportionally larger than humans, so they can take in more air and exchange more with each inhalation and exhalation, and their red blood cells carry more oxygen. They reduce the number of breaths they take during these sleeping/rest periods.

Also, they have a higher tolerance for carbon dioxide (CO2), and so their brains do not trigger a breathing response until their CO2 levels are much higher than what humans could tolerate. All of these mechanisms are adaptations to living in a marine environment.

Harbour porpoise, common dolphin, bottlenose dolphin, minke whale, humpback whale and fin whales are some of the most common species reported to our sighting scheme.

There have been 8 species of dolphin found in Irish waters.

For reasons not fully understood, bottlenose dolphins such as Fungi are sometimes encountered living on their own and are termed ‘social-solitary dolphins’. Cases of social solitary dolphins have been reported from all over the world and span several decades. The vast majority are bottlenose dolphins, but many other species have been reported. There are other solitary bottlenose dolphins in Ireland including Dusty in Clare and the Aran Islands and Nimmo in Galway city. More information on social solitary dolphins can be found here

In the wild, dolphins can be very long lived, and their lifespan varies between species. Orcas are on average believed to live for up to 50-80 years old. The oldest documented living orca was J2 aka ‘Granny’, a 103 year old female of the Southern Resident pod.

The largest species of dolphin is the orca/killer whale. Despite their common name of ‘killer whale’, they are in fact members of the dolphin family.

They don’t need to drink the way we do as their main prey (fish) has a high water content, so they gain water from their food.

A calf will nurse for up to two years after birth and may stay with its mother anywhere from three to four years after that.

Cetaceans evolved from land mammals, and many features characteristic of mammals (such as the presence of hair) were lost in the evolutionary process. All modern cetaceans now lack hair on their body overall however, some species retain a few hairs on their face and in other species hairs are found on neonates.

Yes, they have acute eyesight both in and out of the water and their eyes are capable of functioning independently. In situations where vision is not sufficient i.e. at great depths of distance, they can use echolocation to sense their environment.

10 Whale Facts

Ireland’s smallest and most frequently observed rorqual whale, the minke, is also Ireland’s most odoriferous, hence their nickname, the stinky minke. They do tend to fart a lot on or near the surface.

The humpback whale breaches (leaps) out of the water more than any other Irish whale. In 2010 whilst filming humpbacks off Hook Head, Co. Wexford for the “Wild Journeys” series on RTE, we filmed one breach continually for over 35 minutes…..a sight we’ll never forget.

Fin whales are regularly recorded feeding along the Irish South coast in late autumn and early winter, and one of their favourite techniques is lunge feeding, during which they almost dislocate their lower jaws which creates sufficient drag to stop them abruptly on a bait ball. This event has been described by whale biologists as the planet’s single biggest bio-mechanical event.

Our largest whale, the mighty blue whale, feed on some of the smallest creatures in the ocean, namely krill, which are about the size of your thumbnail.

The Cuvier’s beaked whale is one of the deep diving specialists in the beaked whale family, which are found in deep Atlantic gully systems off the Irish Continental shelf edge. The most recent scientific literature confirms they are the deepest of all the divers, reaching depths of almost 10,000 feet (3,000 meters)…..it’s no wonder we rarely get to see them!

The killer whale (Orca) despite its name is not a whale. The central position of their very tall dorsal fin (males) means they are in the dolphin family. They are therefore Ireland’s and the planet’s largest dolphin.

Ireland’s largest toothed whale (odontocete) is the sperm whale. This is the species of Moby Dick fame. The original version of this classic movie was filmed in Youghal, Co. Cork in 1955 with the American actor Gregory Peck playing the deranged Captain Ahab.

On IWDG’s 25th anniversary we got a nice surprise, when footage secured of a whale at the mouth of Carlingford Lough, Co. Louth/Down, was confirmed to be of a Bowhead whale. The arrival of this Arctic vagrant increased to 25 the number of cetacean species recorded in Irish waters.

On 30th July 2015 a beluga whale was photographed close to shore off Dunseverick, Co. Antrim. While not a new species for Ireland, this was the first Irish sighting of the mysterious white whale supported by photographic evidence. Other rare Arctic vagrants in recent years include the Bowhead whale and bearded seals. What’s happening to Arctic ecosystems?

Irish inshore waters along our south, southwest and west coast provide some of the best land and boat based whale watching potential in the North Atlantic. So why not grab your binoculars and head up to a local cliff top on a calm day, to see how many of the above species you can find….Oh and please report your sighting to IWDG on www.iwdg.ie

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