Shellfish farming.

摘要

Worldwide production of farmed shellfish is estimated at 12 million tonnes/year, compared with 26 million tonnes/year of fish and 2.1 million tonnes/year of crustaceans. This figure includes 4 million tonnes of oysters, 3.43 million tonnes of clams, 1.5 million tonnes of various species of mussels and 1.23 million tonnes of scallops. French shellfish farming output totals 192 000 tonnes/year, primarily oysters (115 000 tonnes) and mussels (74 000 tonnes). The French shell farming sector includes 3750 enterprises, employing 21 500 people in 10 407 full time equivalent jobs. The nature of shell farming means that molluscs are exposed to environmental changes and it is difficult to protect them against pollution or biotoxin-containing algae. Molluscs are very sensitive to the presence of micro-contaminants in water, which can, for example, cause reproductive or growth defects in shellfish. Because many species are eaten raw, increasing the level of risk to human health, it is important to establish sanitary monitoring systems in production areas and along the distribution chain. French oyster production is dominated by a single species, Crassostrea gigas or Japanese oyster. This lack of diversity is a weak point for the French sector, which has already seen the collapse of production based on the Portuguese oyster (Crassostrea angulata) and the flat oyster (Ostrea edulis) due to various diseases. Another problem with the oyster is the length of its breeding cycle, which ranges from 3-5 years depending on the shellfish density and plankton concentration. Oysters also have a low flesh yield (13%) which limits the possibility of producing processed products at acceptable prices. Shell farming suffers from competition for access to the water, including recreational users and fishermen. Levels of mechanization are low in the shell farming sector, but it is increasingly making use of new technologies such as genetic improvement and new sorting and packaging installations.