France: A new farming activity calls for thorough groundwork

by Thomas Jensen
Oyster sorting

Turkish delegation travels to France to study shellfish cultivation

This article was featured in Eurofish Magazine 1 2023.

Turkey is surrounded by four seas, the Black Sea, the Sea of Marmara, the Aegean Sea, and the Mediterranean. This abundance of water has given rise to a capture fisheries industry and a thriving finfish farming sector. However, Turkish production of mussels is modest and of oysters is non-existent, according to data from FAO.

The Ministry of Agriculture and Forestry would like to increase production and export of these two shellfish varieties and through its representatives to the Eurofish governing council suggested a trip to France to study the shellfish farming sector there.

Brittany dominates farmed shellfish ­production in France

Over three days in October, the Turkish delegates accompanied by representatives from Eurofish visited four farms in Brittany, the hub of French mussel and oyster production. The oyster farm Celine Maisons in Saint-Méloir-des-Ondes has operations in France (one site) and in Ireland (seven sites). The Irish connection goes back 20 years when concessions were easily available while getting a new concession in France was difficult. All the grading, packaging, and marketing of the oysters whether they originate in Ireland or in France is done at the French site. Total production is 2,000 tonnes of oyster of which 80% comes from Ireland. The entire production is exported—half to the EU and half to China. This level of production places Celine Maisons among France’s biggest producers; average production at a French farm is 100-200 tonnes, says Mr Boutrais, the former owner of Celine Maisons. Most shellfish farms in France are family owned and after a career in management Mr Boutrais joined the family business and then bought the farm running it for three decades. He had also managed an oyster hatchery and so had a complete idea of the production process and the market.


Two kinds of oysters are produced by the company—the Japanese or Pacific oyster (Crassostrea gigas) and the European flat oyster ­(Ostrea edulis). Both species are produced in France, while the Pacific oyster alone is produced in Ireland. The area where the oysters are produced is well known for its dramatic tides. In the area of the production the water moves 3 km in and out between tides while further along the coast it moves 6 km in and out. This movement of the water makes the area particularly suited to shellfish production as it forces the shellfish to open and close strengthening and growing the muscles. The bay is home to oyster and mussel production, 6,000 tonnes of gigas, 1,000 tonnes of flat oysters and 10-12,000 tonnes of mussels. Gigas takes three years to reach market size, while the flat oyster takes four, and mussels take 1.5-2 years. Shellfish absorb two different kinds of food, says Mr Boutrais. They consume minerals like calcium which is important for the proper growth of the shell and phytoplankton which they need to for energy. Within the mussel the phytoplankton is converted to glycogen so that when ones eats a mussel half the nutrition is glycogen and the other half is protein. The movement of the tides supplies the shellfish with the nutrients they need. But because the difference between high and low tide is so vast, farmers can only visit their concessions at low tide. In contrast, further south along the coast, the difference between high and low tides is not as big allowing farmers to access their concessions at any time.

The presence of natural gigas stocks hinders farming

Centuries ago some 20,000 tonnes of flat oyster were harvested from the bay and exported across Europe. Today, however, total flat oyster production in France is 1,000 tonnes, all of which is produced in the area. Disease was responsible for the collapse in output and the decimation of flat oyster stocks encouraged farmers to import gigas, because it had a long history of being consumed in Asia, was known to grow rapidly, and could adapt to different water temperatures. The problem was that gigas in the wild grew very fast and spread across large areas so that it started competing with the farmed oysters for feed. In addition, in the summer when the naturally occurring gigas reproduce, the larvae settle on the shells of the farmed gigas making them more difficult to harvest, grade, and market. The challenges posed by the naturally occurring gigas pushed farmers to Ireland where there was no natural stock of gigas, because only sterile (triploid) oysters could be cultivated there.

This is why, when starting oyster production, Mr Boutrais explains, it is important to have legislation in place that ensures only sterile oysters may be used for the production. It is impossible to farm oysters in a place where there is natural reproduction. Triploid oysters offer other advantages too. Natural oysters reproduce in summer and put all their energy into gametogenesis. The flesh becomes milky, and they taste terrible. Since triploids are sterile they maintain the same quality throughout the year, the growth rate is faster, and the environment is protected. However, triploids can only be produced in a hatchery, which means a country starting oyster production will, at least initially, have to import the spat. Later it can collaborate with another country that has developed the technology to produce triploids and establish its own laboratory. There should also be a legal framework to manage the industry. In France, for example, the state owns the concession which it then leases to the farmer. Foreign investment is prohibited, the farmer must be French, and must have the educational qualifications needed to produce shellfish. Finally, the farmer must be personally involved in the production, it cannot be left to others. Other countries manage their industry differently, but these are issues that a country should consider when it introduces shellfish farming.

Oyster density is reduced manually as the animals grow

Shellfish farming techniques vary greatly depending on the conditions at sea and on the level of innovation. According to
Mr Boutrais, it is the New Zealand industry that is the most inventive having designed a shellfish bag that turns around on its own with the tides and does not have to be rotated manually. The bags must be rotated periodically to prevent them from being colonised by predators and to expose both sides evenly to the light. Growing oysters involves adjusting the density in the bag as they grow. When they are first introduced into the bag they are 6 mm in length and weigh 1 g. A bag initially contains 5,000 of these juvenile oysters. As they grow a proportion is transferred to other bags to reduce the density. In France the most popular size of oyster is 65 to 85 g. This category is the target of production and the number of oysters in a bag needs to be monitored throughout the production. Once a year the oysters are thinned out to ensure that the target size is achieved. In France oysters are classified into 7 categories and the most popular category is no. 3. In the EU oysters are graded by weight. The success of French oysters on export markets is explained by their quality. The government monitors daily the water where they are grown and closes the area if contaminants such as toxic phytoplankton, chemical pollution, or human pollution are discovered in the water. Farmers are responsible for depuration and for ensuring there is no salmonella in the depuration water and that E-coli levels are below the legal threshold. The legal and infrastructural framework that enables this system of controls should be in place when starting to farm shellfish.

The information from Mr Boutrais was very useful to the Turkish delegation. His experience and the points he mentioned including the use of triploids, the need for regular testing of the water by officials, farming techniques, management of the industry, and identification of the market and the consumers were well received and will be included in the discussions in the ministry.