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Les écluses à poissons - rock pooling in France

Les écluses à poissons - rock pooling in France

Situated just off the Atlantic coast, the islands of Oléron, Ré and Noirmoutier all have something unique - les écluses à poissons or fish locks. Chris Luck investigates this traditional method of catching fish dating back to the Middle Ages which has provided both local food and economic benefits.

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Wherever the coast was rocky and there were ample available stones, ancient communities constructed fish locks or fish traps on the shoreline between the high and the low tidal lines.

The huge stones that make the walls are stacked in a manner that can withstand the onslaught of the continual tides and frequent Atlantic storms. They form a horseshoe shape or ribs with the open ends towards the shore. Although their main role is in catching fish they also serve as breakwaters, mitigating the marine erosion of the cliffs and beaches. On the sides nearest the sea there are more enclosures with openings or sluices to allow the water to flow out as the tide recedes. These are fixed with grills to prevent fish over a certain size from escaping allowing the fishermen to pick up the trapped fish. Grills are usually made from metal these days but traditionally would have been wooden posts and poles made into a lattice creating a simple but very effective system.

Historically it is very difficult to determine the exact origins but they are mentioned in documents as early as 1017 for les pêcheries de Ré and there is evidence they were in use on Oléron during the same period. The first time we see them shown on maps is in 1627 when Claude Chastillon, architect, engineer and surveyor in the service of King Henry IV of France, published a map showing them on the forefront at Chardonnière, Trois-Pierres and Chassiron. Even though they were portrayed in a somewhat fanciful manner the fact remains that this symbolic representation shows that they were important in the landscape. With Jean-Baptiste Colbert and the ‘Grande Ordonnance de la Marine’ in 1681 we find les écluses à poissons are clearly defined in Maritime law. “The parks will be constructed of rows of stones in a semi-circle, and raised to the height of four feet or less using no lime, cement or masonry. They will have in the end of the sea side of an opening two feet wide which will be closed with a grid of wood with mesh holes.”

There isn’t space here to cover all the historical events concerning these interesting structures but we know that there were several hundred of them in use on the islands by the middle of the 19th century. Today Oléron has only 17 locks and 12 on Ré. In addition to the two wars, the decline and erosion of the locks has been the result of changing lifestyles. The locks were essentially maintained by peasants for whom it provided a source of additional income. As more and more people looked to the mainland for employment and had more time and money for leisure activities, the requirement for regular maintenance lacked importance in their lives. There are now asssociations working to restore and reinstate some of them but they are vast structures with heavy stones that require considerable time and labour.

From a naturalists’ point of view these unique structures have created special habitats. In 2008 the écluse at Chassiron, occupying the area to the west of the lighthouse at St Denis d’Oléron, was made the subject of a scientific study monitoring the rock formation and marine species associated with it. This included a prohibition of pêche à pied - literally fishing by foot for fish or crustaceans when the tide recedes - making it a temporary protected zone under an arrêté préfectoral which is renewable. 

Earlier this year, along with a small group of people, I had the pleasure of spending a weekend there organised by Vienne Nature and IODDE, (Île d’Oléron Développement Durable Environnement), where we benefited from the expertise of Jean-Baptiste Bonnin. As many creatures will only be found by carefully raising large rocks, he was keen to impress the need for great care when carefully putting the rocks back without crushing anything while making sure the same surfaces are exposed as before.

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Crabs are easy, something everyone can find and a good place to start. The photos show a few of the 17 species of crab that it’s possible to discover as well as a couple of other interesting creatures that are easy to find at low tide.

One of the crabs that can be found is Hemigrapsus sanguineus, the Brush-clawed shore or Asian shore crab, which probably arrived in ships’ ballast tanks from China and has been present since around 2001, yet another example of an introduced invasive species that is a cause for concern.

Le Crabe de rocher, Eriphia verrucosa, Warty or Yellow crab, declined rapidly in the 1970s due to over fishing and more or less disappeared totally from the French Atlantic coastline. Following a restriction on capture being only for personal or family consumption with commercialisation illegal, they have made a return with the islands being their northern limit. The water depth and protection afforded by the fish locks is particularly suited to this species. They are a ferocious crab with powerful pincers and need to be handled with care using gloves.

 Eriphia-verrucosa--warty-crab-or-yellow-crab.jpg

 

L’etrille, Necora puber, Velvet Swimming Crab, is also known as the Devil crab or Witch crab due to its red eyes and general appearance. It has a wide distribution in north-west Europe and is appreciated for its fine taste. As the name implies it has a distinctly velvety texture to the touch and is a fast swimmer using its rear paddle-shaped feet.

Necora-puber-Velvet-Swimming-Crab.jpg

Le Crabe Marbré, Pachygrapsus marmoratus, Marbled crab, can be found on all of the suitable coasts of France, but in the UK is considered to be non-native with only a few recorded. They are small square crabs, up to 5cm across with three ‘teeth’ on each side of the front margin. Colour varies from deep purple on a whitish background to almost completely black with a marbled, yellowish-brown pattern. They are a crab that inhabits the intertidal zones, avoiding deep water, and will often climb high on to exposed rock surfaces.

Pachygrapsus-marmoratus--Marbled-Crab.jpg

Le Crabe enrage, Carcinus maenas, Common shore crab, is native to Europe but has become an invasive species in many parts of the world. It’s likely to be the crab that most people will commonly find in rock pools. The male illustrated is showing its hinged abdominal casing opened to expose its sex organs.

Carcinus-maenas-Common-shore-crab-male.jpg

Other easy-to-spot creatures include sea slugs, particularly le Lièvre noir de mer, Aplysia fasciata, Mottled sea hare or Sooty sea hare. These can be found on both the Mediterranean and Atlantic coasts of France and are abundant in the locks, making the most of the large numbers of scattered rocks. Here they mate and lay their long strings of eggs on the undersides of the rocks, resembling cream or pink spaghetti. This was a first for me and I was interested to handle them and feel the internal shell that covers their backs. They swim in open water using relatively slow beats of their two ‘parapodia’ (wide lateral membranes covering the top of the body at rest).

Etoile de mer glaciaire, Marthasterias glacialis, Prickly starfish, is widespread on the Atlantic coastline of France, including the Channel, where they live on rocky bottoms. These can grow to a remarkable 80cm across and live to a depth of 180m. Their colour is variable: whitish, bluish, pink, purple, greenish-grey or brown, and they are not looked upon with great favour by the people that work the oyster and mussel beds due to their voracious appetite for molluscs and shellfish. They have the ability to regenerate their limbs should they loose one or more of them.

Starfish.jpg

 

Pêche à pied

rock-pools-franceOr fishing by foot for crustaceans on the unprotected locks is regulated by arrêté ministériel according to EU rules for the minimum size of the different species that can be taken to maintain sustainable populations. There is also a limit of 5kg a day for personal/family use only with no resale or other commercialisation without a professional licence.

Always know the times of the tide, be aware of when it’s coming in to avoid being cut off and wear proper sensible footwear, wellies or old trainers, NEVER go barefoot.

 

 

© All rights reserved. Originally published in Living Magazine December 14