Cuttlefish are related to slugs, snails, mussels and squid. They are not fish, but shallow water cephalopods and dwell on sandy or muddy substrates in coastal and marine waters. The common cuttlefish, is the largest British cuttlefish and has eight arms, two elongated tentacles and a mantle (a hood made of muscle and skin that covers the body). They also have a pair of flat, wide fins (like a skirt) that encompasses their entire mantle. Within their bodies, cuttlefish have an oval internal shell, the cuttlebone. These can often be found washed up on shore.

Behaviour

Cuttlefish are referred to as the “chameleons of the sea” due to their colour-changing abilities. They can change the colour of their mantel to match their surroundings and, in the case of males, to attract mates. They do this by using the pigment cells in their skin, called chromatophores. These cells can be used independently or together to produce different colors and patterns, which can also flash. Colours of cuttlefish include yellow, red, orange, black or brown. Like octopus, cuttlefish have an ink sac from which they can expel ink (called sepia), when in danger, or to confuse an enemy.

Cuttlefish spend most of their time hidden in sand. They typically spend the winter in deep water (100-200m) and move into shallower coastal waters to breed in the spring. They are not very sociable, but are active predators feeding on molluscs, fish, and crabs. They have a ‘beak-like’ jaw in the middle of their arms used to break open shells.

Mating for the common cuttlefish involves internal fertilization. The male deposits sperm into the female’s buccal membrane (close to the mouth). The female generally lays eggs, (between 150 and 1000), at depths around 30 or 40 m and attaches them, as clusters to various plants, or dead structures such as, drowned trees, cables or nets. The length of embryonic development is temperature dependent.

Size

• Mantle Length: 25-30cm (females), reaching up to 45cm (males)
• Weight:  2-4kg
• Average Lifespan: 1-2 years

Status

The common cuttlefish is not currently endangered. However, increased fishing by humans could become a threat. No conservation action has been targeted at this species.

Distribution

The common cuttlefish is generally found in the eastern North Atlantic, throughout the English Channel. Records exist along the east coast of Britain, the west and north coast of Scotland, including the Hebrides, but these are not as common as in the English Channel.

When to see

Spring and summer in shallow waters off selected parts of the Scottish coast, when the cuttlefish migrates to warmer waters to breed.

Facts

• The cuttlebone is used to regulate buoyancy, using chambers that may be filled with gas and/or water.
• Cuttlefish, like other cephalopods, have sophisticated eyes and although they cannot see colour, they can perceive the polarization of light, which enhances their perception of contrast. The cuttlefish pupil is a smoothly curving ‘W-shape’. Believe it or not, they can even see backwards!
• Cuttlefish have three hearts and blue-green blood. One heart is for the whole body, while the other hearts are for each set of gills. The blood is blue-green because it carries a copper-containing protein in its blood.
• Cuttlefish have one of the largest brains of any invertebrate. This, and their well-developed nervous system have proven that cuttlefish are highly intelligent and neurologically advanced. The cuttlefish brain can process input from senses like sight, smell, and even ‘sound’ in the form of pressure waves.