Do fish farms consume more fish than they produce?

Global production of farmed fish and shellfish has more than doubled during the past 15 years and currently accounts for more than a quarter of all fish directly consumed by humans. On balance, global aqua-culture production still adds to world fish supplies.

But some fish farms in the western world consume more fish than they produce claim some researchers. A new study shows that the situation is most extreme in Norway and the United Kingdom, although this may not be the case in many European and South American fish farms.

The new study undermines one of the arguments made by fish farmers, that they protect wild stocks already under pressure from global over-fishing. However, the fish produced are desirable, while some of the fish protein they are fed might otherwise be wasted "trash" fish.

Daniel Pauly of the University of British Columbia and colleagues found that farmed fish in Europe are on average much higher in the food chain than their wild counterparts.

Carnivorous fish such as catfish and salmon must be fed a proportion of fish protein and fish oil in order to grow and become nutritious food themselves.

Some acqua-culturists grind up herring to feed the salmon.

On average it takes 1.9 kilograms of wild fish to make one kilogram farmed, says Pauly.

Pauly and colleagues calculated the position in the food chain of global wild fish catches in 1998. In the 1998 study they found the average position had fallen between 1984 and 1998 because stocks of wild species like mackerel, cod and tuna are running low.

In their new study, the group found the food chain position of farmed fish rose during this period, because the industry is feeding them on larger wild fish.

Source: Daniel Pauly (University of British Columbia), Down with Fisheries, Up with Aquaculture: Implications of Global Trends in the Mean Trophic Level of Fish, conference presentation from the annual meeting of the American Association for the Advancement of Science, Feb. 18, 2001.

For AAAS conference summary http://www.aaas.org/meetings/2001/6164.00.htm

For more on Biodiversity http://www.ncpa.org/pi/enviro/envdex4b.html