The real price of cheap salmon
More and more of the fish we eat is being produced on commercial farms – but at what cost?
How important is fish farming?
Very. Although it’s an ancient business – the Chinese were farming fish in 3500BC – the rise of aquaculture has been one of the biggest revolutions in food supply over the past half century. In 1970, global output was less than 2.5 million tonnes; in 2018, that figure exceeded 80 million tonnes, according to UN data. In 2016, the UN’s Food and Agriculture Organisation said that the world’s population was for the first time consuming more farmed fish than wild-caught fish; shellfish, salmon, trout and carp are the most common types of fish to be reared on farms. Today, farms containing millions of fish apiece can be found the world over. China, India, Vietnam, Egypt, Norway and Chile are among the world’s biggest aquaculture producers. Some 90% of farmed fish are in Asia.
What are aquaculture’s benefits?
It has made fish – a low-fat, high-quality protein, and an important source of omega-3 fatty acids, vitamins and minerals – more affordable for consumers around the world, democratising the consumption of what used to be luxuries, and easing the pressure on hard-pressed wild stocks. Aquaculture also has many clear environmental benefits: compared with other ways of growing animal protein, it uses little or no land, and has low greenhouse emissions. And while the world has traditionally had a lamentable record of regulating wild fishing, fish farming generally occurs within the boundaries of governments, meaning it should, in theory, be much easier to ensure that good practices are upheld.
Salmon.
sea before reaching a harvestable size of 3-4kg. Last year, Scotland’s 200-odd fish farms produced a record 203,881 tonnes of salmon, or about 51 million smolts (for reference, the total population of all wild Atlantic salmon is 3.3 million). The industry also employs 1,651 people in areas where good jobs are scarce.
What are its environmental effects?
Scottish salmon is marketed as highquality and sustainable – and, by international standards, it is. But the industry – which is nearly all foreign-owned – has a heavy environmental footprint. Food, pesticides and faeces from the huge numbers of fish pollute the seabed. Conditions such as amoebic gill disease, as well as fungi and parasites, kill about nine million fish a year, or 20% of the total. Fish also escape in large numbers when pens are damaged: 136,470 salmon are recorded to have escaped from Scottish farms so far this year. The males usually die off, but the females’ eggs are fertilised by wild males, fouling up the gene pool. Farmed variants are designed to grow fast, and don’t have the capacity to live in the wild, managing the long sea and river migrations needed to spawn. A salmon with a farmed parent or grandparent is much less likely to survive. But the worst single problem, say conservationists, is that fish farms are factories for sea lice.
Why are sea lice such a problem?
These small crustaceans live in small numbers on salmon in the wild. However, in pens with hundreds of thousands of salmon, their effects are devastating. They eat the skin, head and neck, causing injury and infection. “They will completely skin a fish’s head and then it will die of exposure,” says Mark Kurlansky in his new book, Clear evidence exists that farms spread salmon lice to wild salmon (and to sea trout), lowering their populations. Chemical pesticides kill the lice, but affect other crustaceans, too. Biological solutions – smaller fish such as lumpsucker and wrasse that feed on lice – have been used with some success (though that has led to overfishing of both species).