This despite the fact that the salmon are continuously monitored. Underwater cameras and divers are constantly on the lookout for small holes in the nets of the aluminium cages that lie 35 meters (115 feet) under the surface.

The escapes are "a crime against the environment", Peter Gullestad, the head of the Norwegian Directorate of Fisheries, told AFP, adding: "Norway is facing its biggest ecological challenge."

The fish that escape from Norway's 1,000 fish farms, located in fjords and rivers along the 21,347 kilometers (13,264 miles) of coastline, threaten the maritime ecosystem.

"Salmon lice is the biggest threat" to stocks of wild salmon in the long term, explained Espen Farstad, a spokesman for the Norwegian hunting and fishing association NJFF.

The lice, which live in salt water and are known by the Latin name Lepeophtheirus salmonis, bite the salmon until they bleed, feeding off of the fish's mucus and causing the least resistant fish to die.

Most susceptible are young wild salmon swimming in the fjords and rivers before they head off to the open sea, as their immune systems are not yet fully developed.

The lice is a problem at all salmon farms around the world. In Norway, it poses a particular problem since fish is the country's second-largest natural resource export after oil and gas.

Also, as farmed salmon increasingly mix with wild salmon, the genetic composition of the latter changes.

"In the future, the entire genetic system of the wild fauna could be modified," Farstad warned.

"We are doing everything we can to prevent salmon from escaping from their cages and infecting the nearby rivers," insisted Bernt Wictor Haugen, a fish farmer in the Finnmark region in Norway's far north.

The industry is using frogmen, anti-lice baths, antibiotics, vaccines, and any other methods available to help fish farms and commercial fishing co-exist in harmony.

But for environmental organisations, not enough is being done.

"The fish farmers are not taking the problem seriously enough. The farms at fault should be punished," said Maren Esmark of the Norwegian branch of WWF.

She wants authorities to introduce severe sanctions on the fish farms. The complaints filed to the police are seldom followed up, according to Gullestad.

The fisheries ministry meanwhile says that the fish farm escapes are a top priority, as Norway has a reputation as a world leader to defend.

In 2006, fish farm exports totalled 18.7 billion kroner (2.2 billion euros, 2.9 billion dollars), up 24 percent from a year earlier, according to the Norwegian fisheries export committee EFF.

The increase is due primarily to rising demand for salmon and the arrival of cod and halibut farms.

Norway is Europe main's supplier of fish, both farmed and wild, with a market share of 62 percent in 2006.

And last year, fish farm exports for the first time exceeded exports from the traditional fishing sector, reaching 17 billion kronor.

In July, a special committee was set up by the fisheries ministry to improve security at the fish farms.

"Now all fish farm equipment has to be certified by the committee. A very strict inspection takes place once a year," said Rune Bildeng, an advisor to the fisheries ministry.

In order to meet the new demands, Norway's fish farms are slowly being turned into ultra-modern fortresses, resembling less and less the traditional fish farms.

"But a well-monitored salmon will always be better on the plate," insisted fish farmer Bernt Wictor Haugen.

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