The great British shark hunt

You don't have to leave these shores to find relatives of the great white. An afternoon's beachcombing will throw up fascinating finds - and could even save some species from the jaws of extinction.

Fancy taking part in a shark hunt this month? To get involved with sharks, you might think you need to have scuba-diving skills and to travel towards the tropics. But Britain has its own - admittedly fairly modest - sharks in the form of dogfish, skates and rays.

And to find out where they are and what they're doing, you don't even need to enter the water. Instead, Britain's biggest-ever shark hunt is harnessing our age-old passion for beachcombing. Simply by wandering up and down the strand and poking about in the weeds with a stick, you can contribute more to shark knowledge than any amount of time eyeballing a great white from a cage. It's called the Great Eggcase Hunt.

Unlike tropical sharks, which give birth to live young, British dogfish and rays lay eggs. These are very distinctive, being shaped roughly like a parcel of ravioli with horns on the four corners. They are known as mermaid's purses. The dogfish purse has long twirling tendrils that anchor the egg to seaweed.

The shape of the horns helps to identify the fish that laid them. Skate eggs, which can be as big as an A4 bag, have short, stumpy horns like a bull. The cuckoo ray has beautiful long horns, which look like the handles of a barrow from the side. By far the most common one, with medium-sized horns, belongs to the thornback ray, Britain's shy, retiring and completely harmless version of the manta ray.

Once the baby fish has chewed its way out, the empty case floats to the surface and sooner or later it is cast ashore by the tide. Once on land, the sun dries the case to a blackened, feather-light crisp, which can be blown along by the wind. The best places to find them are beaches backed by an obstacle, such as a cliff or bank of dunes. If soaked in a bucket overnight the cases regain their olive-green colour and pasta-like consistency.

The Great Eggcase Hunt is being organised by the Shark Trust, which looks after the interests of sharks and their relatives in Britain and across the world.

Ali Hood, a marine biologist who acts as the trust's conservation director, has co-ordinated eggcase hunts on about 600 beaches from Cornwall to Shetland.

"We have family groups who regularly patrol beaches at home or on holiday, as well as schools and marine centres around the country," Hood says. Children are particularly good at spotting them. Once you "get your eye in", you tend to find more and more. Some spectacular hauls of mermaid's purses have turned up, especially after a storm.

One of the most exciting was a cache of huge brown eggcases, as though a sinking ship had disgorged a cargo of big brown envelopes. They were found by a party of schoolchildren in Orkney who were taking part in the Hunt as part of an outward-bound project.

The extraordinary objects were laid by the so-called common skate - now, unfortunately, very uncommon. "The skate has been lost from 90 per cent of its range," Hood says. "Frankly, we've eaten them all. This is a magnificent animal, which grows to three metres long and weighs up to 300lb. Large numbers of eggcases almost certainly point to a nursery near by. If so, this is a completely new and exciting discovery."

Such spectacular finds are exceptional, but even the odd eggcase of a relatively common fish like the thornback ray helps to refine what is known about it. "We don't know how far the cases can float," Hood says, "but by talking to fishermen we can tie up finds with local catches."

Hood emphasises that even if you fail to find a single case, it's still worth reporting that fact. It is as important to know where British sharks don't occur as where they do.

"You don't have to go scuba diving to get involved with sharks," she says. "The Eggcase Hunt allows anybody to go to the beach and walk into a conservation expedition." This is where beachcombing turns into serious biology. The Great Eggcase Hunt is one of many events in the annual Marine Week, which is organised by the Wildlife Trusts and is running to 14 August. Other activities around the country include watching for dolphins and the exciting basking shark, which appears along the coast in late summer to suck up the plankton into its vast gaping jaws. County wildlife trusts have also organised rockpool rambles, strandline walks and even "snorkelling safaris".

To take part in the Great Eggcase Hunt, contact the Shark Trust at enquiries@ sharktrust.org.for a free eggcase identification chart and records form. Also, you can visit the site at www.sharktrust.org/eggcase. For details of other Marine Week events, see www.wildlifetrusts.org

All washed up

DRIFTWOOD

Wood that has been in the sea for a long time is usually riddled with worm holes. The big ones were gnawed by the shipworm, the curse of Nelson's navy. Break them open and the burrows should be lined with chalk secreted by the worm as a home comfort.

SEA WASH BALL

Spongy balls that look like a bit like weathered bubble-wrap are the dried-up eggs laid by whelks. The whelk provides its offspring with baby food as well as an incentive to be quick: the first one out of the egg gets to eat the others.

CUTTLEBONE

The favourite of caged budgies the world over, this is the mortal remains of a cuttlefish, which is a relative of the squid. It's the bit that keeps the body buoyant and horizontal, like a fish's swim-bladder. On its own, it floats, and so ends up on the beach. Disappointing as a Frisbee.

HORNWRACK

What look like a scrap of papery brown seaweed is in fact the remains of an animal. When alive, these were bryozoans, or sea-mats - masses of tiny creatures using their tentacles to scrounge whatever they can pick up from the sea.

SEA BEANS

Grow your own palm. Sea-borne beans and nuts wash up on British shores from as far away as the Caribbean. Most common on the west coast, they have been kept and worn as good-luck charms. Sometimes they are even alive and fertile.

BY-THE-WIND SAILOR

What looks like twisted pieces of plastic are the remains of a jellyfish relative known as the by-the-wind sailor. They ride the wind like little sailing ships until they fetch up with a bump on Britain's shores. When freshly beached and still alive, they are a beautiful iridescent blue colour. Most common on western coasts in late summer.

MERMAID'S PURSES

Blackened objects like ravioli cases with horns in the four corners are the (usually) empty eggcases of rays or dogfish, brought ashore by the tide and further dispersed by the wind. There are about 14 different kinds, the most common being laid by the thornback ray. Soak them in seawater for 24 hours and they revert to their original olive-brown colour. Lots of mermaid's purses indicate a nearby fish nursery.

FOR EGGCASE HUNTING:

* Get the Shark Trust's identification guide

* Wrap up warm and wear wellies or stout boots

* Children under the age of 12 should be accompanied by an adult

* Check the time of the tide

* Use a stick to poke around in strandline debris

* Bring a basket or bucket