French oyster farmers have seen between 40 and 100 percent of their oysters aged one to two years wiped out in recent weeks, far higher than the normal mortality rate in the summer months, a top industry expert said.
The phenomenon is affecting all the oyster-producing regions of France, although the worst hit is the Thau saltwater lake, near the southwest city of Montpellier.
"I bought around 200,000 spat (oyster larvae). They can all be thrown away," Olivier Gonzalez, an oyster farmer at Bouzigues, bordering Thau, told AFP.
"We are facing a major problem, with 40 to 100 percent of young oysters dying, depending on the beds. We will know with the coming high tides if the adults are also affected," Martial Monnier, director general of the national shellfish industry board said.
"We always have a higher mortality rate of young oysters in the summer, but only up to a maximum 30 percent. We haven't seen anything like this since the crisis in the 1970s" which decimated the native flat oysters, now largely replaced by the Pacific oysters, originally from Japan.
Agriculture and Fisheries Minister Michel Barner on Friday urged research scientists at France's marine research institute to mobilise all its resources to try to establish why the oysters are dying off in such high numbers.
Rising water temperatures because of climate change since 1995 are believed to have rendered oysters more vulnerable, but experts do not believe that sea temperatures are dangerously high.
It is possible the oysters have been killed by temporary stress because of the sudden changes in temperature in June and oyster farmers will be able to replenish their stocks, although this will involve new investment, Monnier explained.
But in the worst case scenario, the oysters have been affected by a mystery pathogen as in the crisis in the 1970s. The virus could take one or two years to identify, he said.
For now, the mature ready-to-eat specimens that will go on sale at the end of the year are not affected. The problem will essentially affect the coming seasons in 2009, 2010 and 2011.
France is the biggest oyster producer in Europe and fourth in the world after China, Japan and South Korea. Its 15,000 to 20,000 oyster farmers produce around 130,000 tons of oysters per year.
