for National Geographic News
A fondness for cod and chips, widely regarded as Britain's national dish, is set to fuel a big increase in fish farming in northwest Scotland.
But environmentalists claim pollution from cod farms could endanger already depleted Atlantic salmon and sea trout populations.
The warning follows recent research showing that cultivated cod discharge 50 percent more waste into coastal waters than farmed salmon.
After decades of over-fishing, cod fishing quotas in Europe have been slashed in a bid to conserve the species. The aquaculture industry now hopes to capitalize on Britain's appetite for the fish. And by putting farmed cod on the menu, it says pressure will be taken off rock-bottom wild stocks.
Opponents of the industry, including anglers and environmental groups, see things rather differently. Already concerned about the ecological impact of salmon farming in northwest Scotland, they claim intensive production of cod and other new species will add to pollution in sea lochs.
Both the Scottish Government and European Commission are committed to significantly increased levels of fish farming.
Scottish targets for the industry, revealed earlier this year, include 2,000 extra jobs and doubling the value of annual exports from £200 million (U.S. $330 million) to £400 million ($660 million). The EC has announced plans to create 10,000 more jobs, mainly in areas where commercial fishing is in decline. It wants farmed fish production to grow by four percent each year.
This will mean an influx of cod, haddock, and other cultivated fish to European waters. Nutreco, the Dutch food group, predicts annual cod output will rise to around 700,000 tonnes by 2015. In Scotland, where cod farming is still in its infancy, the target is 25,000 to 30,000 tonnes within the next decade.
But recently published figures suggest farmed cod generate considerably more waste than Atlantic salmon, the species that dominates aquaculture in Scotland.
Government scientists from Scotland's Fisheries Research Services found cod discharge 72.3 kilograms (159.4 pounds) of nutrient nitrogen into the surrounding environment per tonne of production. The figure for turbot is even higher, at 86.9 kilograms (191.6 pounds) per tonne. This compares with 48.2 kilograms (106.3 pounds) per tonne for salmon.
"Cages containing these fish discharge waste directly into the sea as sewage or uneaten feed," said Don Staniford from the Salmon Farm Protest Group, an environmental campaigning organization. "Nitrogen and phosphorous contained in this waste can lead to toxic algal blooms."
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