Two scientists have slammed the Norwegian salmon farm off Gansbaai as "an ecological disaster". Michael Scholl, who is researching Great White sharks at Gansbaai through the University of Cape Town, and Nicholas Pade of the University of Aberdeen, have produced a paper highly critical of the salmon farming venture.

Scholl, from Switzerland, said on Monday that fish farming was highly controversial in Europe.

"Many Europeans say you shouldn't buy farmed salmon because of the associated environmental problems," he said.

"In Norway, which has a lot of salmon farms, they are getting very strict with lots of laws and regulations. Now, because the regulations (in Norway) are so strict, they probably want to come to South Africa."

Salmon are alien to South Africa. They are farmed in pens anchored to the seabed and are fed a protein-rich diet of fish and fish oil. Producing a kilogram of farmed salmon requires two to five kilograms of wild fish.

Scholl's paper quotes the World Wide Fund for Nature, which said in 2002: "Without reform, this fast-growing industry could be consuming all the world's fish oil and half of its fish meat by 2010, up from 70% of fish oil and 34% of fish meal now."

The salmon's faeces and uneaten food would pollute the surrounding water, lead to eutrophication of the seabed, algal blooms that could be toxic and a lowering of oxygen levels, Scholl said.

Salmon farming was "a hotbed for disease" because the fish were crowded together. These diseases could be transmitted to wild marine creatures, including perlemoen and crayfish. Antibiotics, widely used in fish farming, would find their way into the sea.

Marine animals like sharks, dolphins, whales and seals ran the risk of becoming entangled in the nets in which the salmon were "penned", the paper said.

"Great White sharks will be attracted to the salmon pens. These sharks may break or damage the nets, get entangled or be killed by fish farmers."

A study in British Columbia found that over four years 431 seals, 38 otters, 29 sea lions, a porpoise and several seabirds had been killed at salmon farms.

Grant Pitcher, of Marine and Coastal Management (MCM), said the salmon farming company had conducted an environmental impact assessment and had held public hearings.

The parliamentary portfolio committee on the environment had given the farm the go-ahead and MCM had issued a licence. It had also given the company a permit, renewable each year, with strict conditions.

The company was not available for comment.