A slow walk along the tide line

There is a particular kind of quiet that arrives about an hour after high water, when the strandline is fresh and nothing has been picked over yet. Beachcombing is simply the habit of walking that line slowly, reading it like a page. On a good day you might pass a mermaid's purse, a tangle of fishing line, three shades of sea glass and a piece of driftwood worn to the smoothness of bone — and you have to decide, at each one, whether it comes home with you. The rule of thumb that serves most coastal walkers well is this: take only what is small, common and clearly abandoned. Leave the rest for the shore, and for the next person along.

Small, common finds worth pocketing

Some things genuinely do no harm to collect, provided you take a modest amount and not a carrier bag full.

• Sea glass. Decades of tumbling turn broken bottles into frosted pebbles. White, green and brown are everywhere; blue, red and cobalt are rarer. Take a few, not a jarful, especially on beaches known for their glass.
• Common empty shells. Mussels, limpets, slipper limpets, oysters, razor shells. Only take shells that are empty and dry — a shell with a creature inside is a home, not a souvenir.
• Mermaid's purses. The empty egg cases of rays, skates and dogfish. Once blown clear of the water and dried, they are safe to take and rather lovely to identify.
• Small pieces of sea-worn pottery from ordinary Victorian dumps — the plain, unmarked stuff that has already been broken for a century.
• Litter. The best find of all. Every crisp packet, balloon, bottle top or length of fishing line you carry off is a piece of plastic the tide will not return.

Driftwood is doing a job

Driftwood looks like debris; ecologically it is infrastructure. Rotting timber on the strandline feeds sandhoppers, woodlice and tiny beetles, which in turn feed the wading birds and pipits that work the same strip of beach. Larger logs shelter insects, give birds somewhere to perch and roost, and help hold sand in place along the top of the shore. On shingle beaches, driftwood is one of the few things holding a fragile habitat together.

There is a practical argument too. Salt-soaked wood burns badly and gives off corrosive and toxic fumes when it goes on a fire or in a woodburner, so it is not even good fuel. Photograph it, admire it, and leave it where it landed.

Live creatures and the rockpool rule

Everything alive goes back. That includes the obvious — crabs, anemones, starfish, small fish — and the things people forget are alive, such as limpets clamped to rock and barnacles crusted on a stone. A limpet grinds its own exact shape into the rock over years and returns to the same scar; prising one off usually kills it.

If you lift a stone to look underneath, put it back the same way up, in the same place. If you fill a bucket, keep it shaded, change the water, and tip everything back within half an hour. And if you come across a stranded jellyfish, a seal pup or a live stranded whale or dolphin, keep your distance and call the coastguard or a marine rescue charity — do not try to move or push it back yourself.

Anything historic, anything mysterious

Some finds are not yours to keep. Objects from wreck sites are protected by law, and it is an offence to remove anything from a protected wreck without a licence. In practice, that means leaving things alone whenever you are not sure.

• Ship's fittings, coins, cannon, anchors, marked pottery or anything with a date on it. Note roughly where you found it and take a photograph instead.
• Possible ordnance. Anything rusty, cylindrical or bomb-shaped — including flares and smoke canisters. Never touch it, never put it in a rucksack. Mark the spot, keep others away, and dial 999 and ask for the coastguard.
• Bones, including whale vertebrae and large skulls. Report them to a local museum or the county archaeologist, who can record them properly.
• Anything on a Site of Special Scientific Interest, nature reserve or National Nature Reserve where signage asks you to leave everything in place. The signs are there for a reason.

Habits that keep the strandline healthy

A few small routines make beachcombing better for you and for the shore.

• Walk on a falling tide, and check the tide tables before you set out. The best strandline is often the one you can leave easily.
• Between March and July, keep to the lower shore, as the dunes and shingle above are being used by nesting ringed plovers and oystercatchers. Keep dogs close and under control.
• Wear boots with grip, carry gloves, and take a bag for litter plus a separate one for finds.
• Fill any hole you dig, and leave stones and seaweed where you found them. A turned-over beach is a damaged beach.
• If you are not sure whether something is common or rare, take a photograph and leave it. A picture lasts; a shell does not.

The pleasure of the tide line is that it is never the same twice. If everyone takes only the small, the common and the already-broken, there will always be something left for the next walker along — and for the birds, the beetles and the sandhoppers that got there first.