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Shellfish guide, identification, sustainability, how to prepare and cook them


Coastal and estuary

Shellfish are molluscs such as oysters, clams, mussels and cockles, crustaceans like crabs, lobsters and shrimps and also echinoderms such as sea urchins.

Shellfish can cause severe allergic reactions in some people (anaphylaxis). In these severe cases, it is advised they carry an epi-pen (epinephrine auto-injector) at all times.

As a rule, never collect molluscs after rainfall. This is because they are filter feeders so land run-off can contain all sorts of chemicals and toxins.
Shellfish are generally collected when there is an ‘r’ in the month, so from September to April. From May to August, shellfish tend to breed so they are best left to it. Oysters for example go very pappy when breeding so their flavour and texture is not good. Also, in the summer months, the sea warms up and there is the possibility of ‘red tide’ when algae blooms can occur. The algae produces a toxin called okadaic acid that can cause diarrhetic shellfish poisoning which can cause diarrhoea and vomiting for a few days.

Dog whelk
Dog whelks are carnivorous and like to feed on mussels – if you find a mussel with a hole in its shell, it has been eaten by a dog whelk. They use their razor-like tongue to drill through shells. This is pretty gruesome, mussels get their own back by spinning out their byssus threads onto the dog whelk. The dog whelk is unaware of this so once they have finished eating and they try and slither off to find more food, they realize they are stuck fast and die of hunger. Dog whelks are cooked the same way as periwinkles and have a liver-like flavour.

Periwinkles can be easily found on rocks near rock pools. These are herbivores and graze on seaweeds. Both periwinkles and dog whelks have a ‘door’ (operculum) which they close to protect themselves and also to prevent the snail from drying out. Pick periwinkles sporadically and from a clean source. To cook them, I like to make a court bouillon to simmer them in – a court bouillon is a light stock made from carrot, celery, herbs, water and wine. They cook quickly, roughly 10 minutes. Once they are done, use a pin to pick off the operculum and dip them in melted butter to eat.

Oysters are best eaten in the winter because when they are spawning in the summer months, their meat becomes soft and pappy. Oysters are so popular throughout the world, there are oyster farms that grow them (ostreaculture). To harvest wild oysters, they can be found attached to rocks but also in similar places to where cockles are found. Pick only what you plan on eating, give them a good wash and scrub their shells, then prize open their shells ideally with an oyster knife – BE CAREFUL NOT TO SLICE OPEN YOUR HAND!!! Once you’ve opened the shell, loosen the meat and either eat it raw, with a squeeze of lemon juice or vinegar and diced shallots, cook them by pan frying, adding to soups, stews, etc. or deep fried as “Po’ boys”. I prefer them simply pan fried as they are delicious and sweet – as good as cockles or scallops. If you are hoping for a pearl in your oyster shell, you are unlikely to find one as pearls come from a different family of oyster (pteriidae family) which live in deep oceans. Make sure you gather your oysters (and all your shellfish) from a clean source – food poisoning from shellfish is pretty horrible!

Native oysters are also called common oysters and have a shell with concentric growth rings, which is grey, rough and scaly. The inside of the shell is smooth and white. Pacific oysters are more irregularly shaped than the flat native oysters, and the edges of the shell have distinctive wavy, large frills. In some areas this species has escaped being farmed and has become an invasive species, sometimes being sold as 'rock oysters'. Pacific oysters were introduced in the 60's and 70's to be farmed and at the time weren't a threat but as the seas have warmed, they have multiplied to the extent of overcrowding and damaging other marine life. They can grow into reef-like structures where they grow on top of one another.

Limpets are often overlooked and overcooked! If you want to eat limpets, first knock them off the rock in one swift move. If they are stuck fast, don’t continue to hit, just move on. If you have damaged their shell, then it is best to harvest them as they will be vulnerable to predators, etc. Once you have mastered removing a limpet from the rock it is attached to, then locate the head by pressing the foot (main body part) gently. You’ll see the head with little horns like a snail popping out. Now push the foot towards the head to release the stomach/guts, then the foot should come away fairly easily from the shell. Rinse the foot in a pool and return to the shell ready to cook. Add a tiny amount of garlicky butter and grill it in its shell for about a minute. Limpets are enjoyed in Madeira and they even have a festival for them. They serve them in a variety of ways including pickled with chilli and bay leaves.

Clams differ in looks from cockles as the ridges on a cockle shell run to the hinge, where clam shell ridges run across the shell. Clams prefer sandier sediment than cockles. A tasty morsel, clam chowder is a great dish to try if you are new to them, simply steaming with Asian flavours such as lemongrass and ginger or pan frying until they open and lightly frying the meat in a little butter.

Cockles live in sandy muddy areas so often found along estuaries. At low tides they are easiest to find. I like to look for an occasional ‘squirt’ of water from the mud. They tend to be pointing hinge down, opening up so finding a shell on its side is mostly fruitless. Make sure the diameter across the shell is more than 2cm – if it is less, then put the cockle back. As they live in sediment, they need purging to remove any grainy bits from their shells so I put them in a bowl of fresh water with a good amount of table salt and leave them over night. Once purged, cook them by heating under the grill, pan frying, adding them to a dish such as chowder and the heat will cook the meat and cause the hinged shell to open. As with mussels, if the shell is open when collecting then leave it and if it doesn’t open after cooking then discard it.

Pick mussels when there is an ‘r’ in the month, avoid after rainfall and try and go for large ones with as few barnacles on them as possible. This should save time on preparation and will help make the dish less gritty. Pick mussels off the rocks sporadically rather than all in one place. Try and remove their ‘beards’. The ‘beard’ is a collection of byssus threads that the mussel squirts out in liquid form to attach itself to rocks, acting like an anchor. Pick only what you will eat and make your dish the same day or the next at the latest. I don’t bother purging the mussels but if you want your meal to be completely grit-free, scrape and scrub every mussel and pop them in a bowl of water so they are totally submerged and add salt so they think they are back in the sea. Add oatmeal or bread if you want but it isn’t necessary. If there are any mussels that are open at this stage, chuck them (if they are open a slight bit, these will be fine – they are just filtering). Once the mussels are cooked using whichever method, if there are any that are closed, chuck them – never try and force a mussel open as they are most likely dead.
To cook them, either grill them, pop them whole on a barbeque, pan fry in butter or oil with shallots to then make moules mariniѐres with cream, thyme, white wine and garlic…

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