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DORSET WILDLIFE TRUST: Amazing animals and why they wash ashore
1:00pm Tuesday 11th March 2014 in News
Any beach walker or budgie owner will be familiar with the white cuttlebones that strew our shores and help pet birds maintain healthy beaks, writes Julie Hatcher.
But how much do you know about the amazing animals they come from and why they wash ashore in such large numbers?
Cuttlefish are a real favourite of scuba divers. Close relatives of octopus and squid, they are not fish at all but cephalopods – a type of mollusc.
Coming from the same family as snails they have a shell – but not on the outside. The cuttlebone is a modified shell that has evolved to be worn on the inside.
The cuttle’s internal shell has a surprising role – rather than providing protection as in snails it provides buoyancy and depending on how much gas is put in or taken out it allows the animal to move up or down without the effort of swimming.
Cuttlefish are remarkably intelligent and expressive and often entertain divers with their communication skills.
Their ability to change the colour, pattern and texture of their skin is also used for camouflage.
When hiding on fine, white sand for example, they can make their skin smooth and pale while on seaweed-covered rocks they can become dark and knobbly.
There are several species of cuttlefish found in UK waters but by far the most common is Sepia officianalis. The name sepia was also used for the ink they produce which was once used by artists.
Ink is one of the cuttlefish’s defence mechanisms and is squirted into the water to distract predators.
Common cuttlefish grow up to 30cm long and move into coastal waters in late spring to breed, the females laying clusters of black, grape-like eggs attached to seaweeds, ropes and fishing pots.
Females only breed once and stop feeding after producing their eggs. They die soon afterwards, leaving only their cuttlebone behind to wash up on beaches all around the country.
To help maintain cuttlefish populations, Dorset fishermen are asked to keep their pots and traps in the sea until September, to allow attached eggs to hatch. However, divers are concerned that encounters with cuttlefish are not as common as they once were. For details on cuttlefish fisheries go to dorsetwildlifetrust.org.uk/ greatdorsetseafood
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