How to identify a cetacean?

You have just caught sight of a cetacean at sea, or of an animal stranded on a beach, and you would like to know which species it is? Identifying a cetacean is never straightforward: the sighting is often brief, partial (a blow, a back, a tail) and degraded by sea conditions. This guide sets out a step-by-step method for recognising the main cetaceans that can be observed in mainland France and in European waters. Worldwide, the reference list of the Society for Marine Mammalogy (SMM, Committee on Taxonomy), updated regularly, counts about 94 living cetacean species, divided into 15 mysticetes (baleen whales) and 79 odontocetes (toothed whales), among them the baiji (Lipotes vexillifer), listed by the IUCN as “Critically Endangered (Possibly Extinct)”. In practice, barely ten species account for most of what is encountered in our waters.

What to note before identifying

Before trying to put a name on an animal, take the time to observe several features and record them mentally (or on paper or a smartphone):

• The apparent size of the animal, compared with your boat, with buoys or with nearby birds.
• The shape and colour of the body: uniformly dark, contrasted, spotted, striped, white, grey, covered in scars…
• The shape of the blow: tall, low, vertical, angled, V-shaped, barely visible.
• The shape and position of the dorsal fin: tall, low, triangular, falcate, absent, set forward or set back.
• The behaviour: slow or fast swimming, breaching, bow-riding, tail lifted clear of the water, group size.
• The location and the depth: coastal, continental slope, open sea, warm or cold water.

👉 Tip: take a photograph, even a poor one, as soon as you can. An image allows specialists to confirm the identification and is often the only usable evidence. To go further into one particular feature, see our guide to identifying a cetacean from its blow and our page on cetacean morphometrics.

Step 1: mysticete or odontocete?

The first major distinction to make: are you looking at a baleen whale (mysticete) or a toothed whale (odontocete)? A few decisive clues:

Clue	Mysticete (baleen whale)	Odontocete (toothed whale)
Blowholes / blow	Two blowholes; tall blow, vertical or V-shaped	A single blowhole; more discreet blow, angled or barely visible
Size	Often > 10 metres	From 1.5 m (porpoise) to 18 or 20 m (sperm whale)
Head	Massive, fitted with baleen, with no prominent melon	Often a rounded melon and/or a pronounced rostrum
Behaviour	Usually solitary or in small groups	Often in groups, sometimes large ones
Swimming speed	Slow, calm at the surface	Often fast, with frequent breaching and bow-riding

👉 If you have seen a small, fast cetacean following your boat or breaching, you are almost certainly looking at an odontocete (dolphin, porpoise). If you have seen a large animal with a tall blow and a massive back, you are looking at a mysticete. To go further, see our guide to the difference between whale, sperm whale and dolphin.

Dolphin or porpoise? How to tell them apart

Along much of the French coastline, the English Channel, the North Sea and the Atlantic, the commonest small cetacean is not a dolphin but the harbour porpoise (Phocoena phocoena). Mistaking it for a dolphin is the most frequent error. Four criteria settle the question:

Criterion	Harbour porpoise	Dolphin (delphinids)
Size	Small, ~1.5 to 1.9 m (the smallest cetacean in Europe)	Generally larger (2 to 4 m)
Rostrum (beak)	Absent: rounded head, no pronounced beak	Clear, well-defined rostrum in most species
Dorsal fin	Low, triangular, broad-based, set mid-back	Usually tall and falcate (sickle-shaped)
Teeth	Spade-shaped (spatulate, “shovel-like”)	Conical and pointed

The shape of the teeth can only be seen on a stranded animal, but the absence of a beak and the low, triangular dorsal fin are generally enough to recognise a porpoise at sea. Discreet and undemonstrative, it “rolls” slowly at the surface and rarely breaches.

Step 2: the dorsal fin, your best ally

The dorsal fin is one of the most discriminating features. Its shape, its position and its height often settle the choice between several species.

• No visible dorsal fin → right whale, grey whale, beluga, narwhal (and the sperm whale, whose “dorsal fin” is reduced to a hump followed by ridges).
• A simple rounded hump followed by “knuckle” ridges → sperm whale.
• A very tall, straight, tapering dorsal fin (up to 1.80 m) → male killer whale. This is the tallest dorsal fin of any cetacean: vertical, almost straight, and not at all triangular.
• A low, triangular, broad-based dorsal fin → harbour porpoise. Not to be confused with the upright fin of the killer whale.
• A tall, falcate dorsal fin (sickle-shaped) → common bottlenose dolphin, common dolphin, striped dolphin, Risso’s dolphin.
• A low, broad-based dorsal fin set well forward on the body → pilot whale (falcate in young animals and females, thickening and becoming rounded in old males).
• A very small dorsal fin, set clearly far back → blue whale, fin whale, common minke whale.
• A small, set-back dorsal fin on a tapered body with a “beak” → beaked whale (see below).
• A medium dorsal fin set towards the rear of the body, with long white flippers → humpback whale.

Step 3: recognising the blow

The blow, or spout, is often the first thing visible during a sighting. Its shape and its height are valuable signatures. One caution, however: the height depends on the weather and on the force of the exhalation.

• A vertical blow, a dense column, very tall (commonly ~9 m, exceptionally up to ~12 m) and visible for kilometres → blue whale. This is the tallest blow of any cetacean.
• A vertical columnar blow, more modest (~4 to 6 m) → fin whale. Contrary to what is often read, it is markedly lower than that of the blue whale, which helps to separate these two easily confused species.
• A broad V-shaped blow (~5 m, two widely spaced blowholes) → right whale.
• A vertical, bushy blow, up to ~3 m → humpback whale.
• A low blow angled forward and to the left (~3 m) → sperm whale (a single blowhole set to the left).
• A virtually invisible blow → dolphins, porpoises, killer whales and beaked whales (rarely perceptible).

Step 4: the tail flukes

When the animal dives and lifts its tail clear of the water (a behaviour known as fluking), the flukes yield very valuable information:

• Black flukes with unique white markings → humpback whale (each tail is as individual as a fingerprint, the basis of photo-identification).
• Broad, uniform blue-grey flukes → blue whale.
• Triangular, grey, slimmer flukes (rarely lifted) → fin whale.
• Dark triangular flukes, raised vertically to ~90° → sperm whale (the emblematic silhouette before a long dive).
• Flukes not lifted clear of the water → dolphins and porpoises, which do not “fluke”.

Step 5: behaviour and habitat

Certain behaviours and certain sighting areas strongly point the identification one way:

• An animal riding the bow wave → common bottlenose dolphin, common dolphin, striped dolphin.
• An animal breaching, rolling over or slapping the surface with its long flippers → humpback whale.
• An animal raising its head vertically out of the water (spyhopping) → a frequent behaviour in Risso’s dolphin, which combines it with breaching and lobtailing. It raises its head upwards, not its tail: confusion with a “headstand” (head down) is common but mistaken.
• An animal “doing a headstand” (head down, feeding on the bottom) → more likely the grey whale, for which this headstanding is a benthic feeding strategy; it is not a trait of Risso’s dolphin.
• An animal diving with its tail raised vertically → sperm whale.
• A small, discreet cetacean with no beak, a low triangular dorsal fin and little breaching → harbour porpoise (the English Channel, the Atlantic).
• A white animal swimming in a group in cold water → beluga (very rare in western Europe).

Beaked whales (ziphiids): the most difficult group

Beaked whales (ziphiids) are among the cetaceans hardest to identify at sea. In the north-western Mediterranean (the Pelagos Sanctuary), the only regular ziphiid is Cuvier’s beaked whale (Ziphius cavirostris). In the Bay of Biscay and the north-east Atlantic, Sowerby’s beaked whale (Mesoplodon bidens) and the northern bottlenose whale (Hyperoodon ampullatus) may also be encountered, two Atlantic species virtually absent from the Mediterranean. A few useful clues:

• A tapered, torpedo-shaped body, with a small “beak” of varying distinctness.
• A small, set-back dorsal fin, two-thirds of the way along the body.
• A discreet blow, often barely visible.
• Long, deep dives: Cuvier’s beaked whale holds two distinct mammalian records, a depth reaching ~2,992 m (Schorr et al. 2014, PLOS ONE) and a breath-hold duration of up to ~3 h 42 min (222 minutes) (Quick et al. 2020).
• Most often alone or in small groups (2 to 7 individuals), with bodies marked by scars (cookiecutter shark bites, tooth rakes between males).

Identification to species level is generally a matter for specialists and often rests on good photographs. See our resources on cetacean diving records and the profile of the sperm whale, another deep diver.

A quick decision tree

Here is a mental shortcut for placing a sighting quickly:

• A small animal (< 4 m), in a group, breaching or riding the bow wave → dolphin (depending on colour: common, striped, common bottlenose).
• A small, discreet animal with no beak, a low triangular dorsal fin, coastal → harbour porpoise.
• A medium-sized animal (~3 to 4 m), very pale grey to white, covered in scars, with a tall dorsal fin → Risso’s dolphin.
• A strongly contrasted black and white animal, with a very tall, upright dorsal fin (male: up to 1.80 m) → killer whale.
• A uniformly black animal, with a bulbous melon and a low, broad-based dorsal fin set forward → pilot whale.
• An entirely white animal, with no dorsal fin, in cold water → beluga.
• A tapered body with a small beak, a small set-back dorsal fin, discreet → beaked whale (ziphiid).
• A very large animal with a very tall blow (~9 to 12 m) and a tiny, set-back dorsal fin → blue whale; a lower blow (~4 to 6 m) → fin whale.
• A large animal with a humped back, a medium dorsal fin and long white flippers → humpback whale.
• A large animal with a blow angled forward and to the left, diving with the tail vertical → sperm whale.

The species most often seen in France

The species you are most likely to come across differ from one area to another:

• The north-western Mediterranean (the Pelagos Sanctuary): fin whale, sperm whale, striped dolphin, common bottlenose dolphin, Risso’s dolphin, long-finned pilot whale, Cuvier’s beaked whale.
• The Bay of Biscay: common dolphin, common bottlenose dolphin, harbour porpoise, striped dolphin, pilot whale, fin whale, beaked whales.
• The English Channel and the North Sea: harbour porpoise (by far the commonest), common bottlenose dolphin, occasional Risso’s dolphin.
• The French overseas territories (the Antilles, Polynesia, Réunion, Mayotte): humpback whale (on migration), sperm whale, spotted dolphin, spinner dolphin, and many others.

To decide where and when to watch, see our cetacean watching hotspots and our pages on annual migrations and cetacean conservation (IUCN status).

A special case: a stranded cetacean

If you find a stranded cetacean, do not try to identify it or handle it on your own: alert the Réseau National Échouages (RNE) immediately, which will send trained correspondents to carry out the examination and the precise identification. Note the size, the colour and the location, and take photographs while you wait for them.

👉 More information: What to do if you find a stranded cetacean and The RNE in France.

Frequently asked questions

How can a dolphin be told from a porpoise?

The harbour porpoise is smaller (~1.5 to 1.9 m), has no pronounced beak and carries a low, triangular, broad-based dorsal fin. The dolphin is generally larger, with a clear rostrum and a tall, falcate dorsal fin. On a stranded animal, the teeth settle it: spatulate (“shovel-like”) in the porpoise, conical in the dolphin.

Which species has the tallest dorsal fin?

The male killer whale: its dorsal fin, straight and tapering, reaches up to 1.80 m, the tallest of any cetacean. It is upright, almost vertical, and not triangular with a broad base like the much lower fin of the porpoise.

How can a blue whale be told from a fin whale by its blow?

The blue whale produces a dense columnar blow, very tall (up to ~9 to 12 m) and visible for kilometres. The fin whale also sends up a vertical column, but a markedly lower one (~4 to 6 m). This difference in height is one of the few useful clues for separating the two species at a distance.

How many cetacean species are there worldwide?

The reference list of the Society for Marine Mammalogy, updated regularly, counts about 94 living species, of which 15 are mysticetes (baleen whales) and 79 odontocetes (toothed whales), with the baiji (Lipotes vexillifer) included in that total but listed as “Possibly Extinct”. The classification is changing: Rice’s whale (Balaenoptera ricei) of the Gulf of Mexico was only described as a valid species in 2021, and the Bryde/Rice complex (Balaenoptera edeni, with the subspecies edeni and brydei) remains debated.

Further reading

• Our guide to the difference between whale, sperm whale and dolphin.
• The interactive cetacean phylogeny and cetacean evolution, to place each species in the tree of life.
• The glossary of cetology terms and our cetacean FAQ.
• Our species profiles: sperm whale and Risso’s dolphin.