Shellfish and Shore Gathering

Limpets, mussels, clams, razor clams, percebes and the rules that keep you alive

6 minIntermediateUpdated 2026-10-23 Shellfish and Shore Gathering

You will learn

Find and gather five common shore foods at low water
Read a tide table to work the lowest tides of the month
Refuse a harvest when biotoxin, sewage or closure rules say no

⚠️ Shellfish biotoxins cannot be cooked, frozen or washed out. Check official closure notices, IPMA in Portugal, on the day you gather, and never gather bivalves if you cannot check.

⚠️ Never gather near sewage outfalls, harbours or river mouths, and wait at least 48 hours after heavy rain.

⚠️ A rising tide cuts off rock platforms. Know your exit, set an alarm for low water and never gather alone on exposed rock. Percebes gathering kills people every year, leave it to professionals.

The five that feed you

Limpets grip bare rock and come off with one sharp sideways knock of a blunt knife, never a slow prise. Mussels grow in beds on mid shore rocks and pull off in clumps; take only the larger ones, cut the beard away and discard any that stay open when tapped. Clams and cockles live in sand and mud, found by raking the top few centimetres. Razor clams give themselves away with a keyhole shape in wet sand and rise when you drop salt into the hole. Percebes, goose barnacles, cling to surf hammered rock and are genuinely dangerous to gather. Leave them to licensed professionals.

💡 Any bivalve that stays open when tapped, or is cracked, goes back on the rocks.

Working the tide table

Shore gathering happens in the two hours around low water, and the lowest lows are the spring tides a day or two after a new or full moon. Get a local tide table, note the predicted height in metres, and go on the days showing the smallest numbers. Arrive an hour and a half before low water, work outward as the sea retreats, and turn back the moment the water stops falling. Always know your exit. People drown gathering shellfish every year because a rising tide cut off a rock platform behind them while they were looking down at their bucket.

💡 Set a phone alarm for low water so you start walking back, not further out.

Biotoxins and red tides

This is the non negotiable part. Filter feeding bivalves concentrate algal toxins that cooking does not destroy and that you cannot see, smell or taste. Paralytic shellfish poisoning can stop your breathing within a couple of hours; amnesic and diarrhetic types cause lasting harm. During a bloom, sometimes visible as a red or brown tide, authorities close areas by name and species. In Portugal, IPMA publishes bivalve closure notices by coastal zone and species, updated weekly, and those notices are legally binding. Check them the same day you gather. If you cannot check, do not gather bivalves, and never eat a bivalve given to you without knowing where it came from.

💡 IPMA closure notice first, bucket second. Cooking does not remove these toxins.

Sewage, closures and depuration

Never gather within sight of an outfall pipe, a marina, a harbour mouth or a river carrying town drainage, and never after heavy rain, which flushes untreated sewage and farm runoff to the coast. A 48 hour wait after heavy rain is the common working rule. Commercial shellfish from class B waters are purified in tanks of clean circulating seawater, a process called depuration, for 42 hours or more. You cannot reliably copy that at home with a bucket, so gather only from clean open coast classified for direct harvest, and cook everything thoroughly. Depuration removes bacteria, not algal biotoxins and not heavy metals.

💡 After heavy rain, give the coast 48 hours before gathering anything that filters water.

Take little, leave the bed working

Shore gathering is legal in many places with a licence, a daily weight limit, minimum sizes and a closed season, and completely prohibited in reserves. Portuguese shore gathering is licensed through DGRM, with species limits by weight per person per day. Beyond the law, work the bed lightly: take only larger animals, never strip a patch bare, turn every rock back the exact way it was lying, and move on after a few minutes in one spot. A turned rock left upside down kills everything under it. Rinse the catch in clean seawater, keep it cold and cook it the same day.

💡 Turn every rock back. It is somebody's roof.

Check yourself

Algal biotoxins in shellfish are removed by

Cooking, freezing and soaking do not destroy paralytic, amnesic or diarrhetic shellfish toxins. Only official closure notices protect you.

In Portugal, bivalve harvesting closures are published by

IPMA issues weekly biotoxin and closure notices by coastal zone and species, and they are legally binding.

The lowest tides of the month happen

Spring tides follow new and full moons, giving the lowest low water and access to ground exposed only a few days a month.

A mussel that stays open when tapped should be

A bivalve that will not close is dead or dying, and dead shellfish spoil rapidly and cause illness.

Try it for real: One safe low water walk

Find the next spring low tide for your coast and note the predicted height
Check your national shellfish authority for closures covering that stretch, IPMA in Portugal
Confirm whether a licence, daily limit and minimum size apply where you live
Walk the shore at low water and identify limpets, mussels and one clam species without taking any
Plan your exit route and time, then repeat the walk gathering only if everything above is clear