Fishmeal industry figures are all at sea

Sir, You report the UN Food and Agriculture Organisation (FAO) recommendation that there should be a big increase in fish farming to meet the rising global demand for seafood, and the assertions by Willie Mackenzie, of Greenpeace, that "it just doesn't make sense to catch fish to feed to fish - you use four to five times the weight".

Mr Mackenzie's figures are out of date and inaccurate, and misinform the debate. The part of worldwide aquaculture that is fed on compounded feeds uses only half a tonne of wild caught feed fish for every tonne of farmed fish and shrimp produced.

Also, today, about 25 per cent of the raw materials used to produce fishmeal and fish oil are the trimmings (head, tails, offal, etc) from food fish processing, which the fishmeal industry is recycling into fishmeal and oil and would otherwise have to be disposed of at high environmental cost. The amount of fishmeal and oil used in aquaculture diets varies by species, with the highest users being salmon and shrimp, and the lowest including tilapia and catfish. But even the highest do not approach Mr Mackenzie's "four or five times the weight" of feed fish used to produce each tonne of farmed fish.

Up-to-date calculations show that the amount of feed fish required to produce one tonne of farmed salmon is 1.7 tonnes, and that for shrimp is about 0.9 tonnes, and that both are falling. Most of the other main fed aquaculture species use even less, hence the global average of 0.5 tonnes.

There is also an impression that the growth of aquaculture has resulted in more and more fish being caught to keep up with this growth. However, as is made clear in the FAO report, what has actually happened is that fishmeal, which used to go to the pig and poultry industries, now goes to aquaculture. The weight of fish now being taken from the wild to produce fishmeal and fish oil has, in fact, decreased over the past decade, as more is now going for direct human consumption.