Altogether, about 240 different freshwater and saltwater species are now being farmed around the world, and industry growth has averaged about 10 percent a year since 1970. The things that constrain aquaculture, however, are similar to those that limit land- based farming— lack of suitable land or coastline for ponds, polluted water, environmental regulation, land- tenure issues, sea- level rise, and the availability of feed supplies. It takes roughly five tons of wild- caught fish to make fishmeal to feed a single ton of farmed fish, so fish farming can be even more destructive of marine fish stocks than actual fishing.
Consequently, more and more farmed fish, like chickens, pigs, or feedlot cattle, are fed on grain. This competes with other uses for the grain, including human food, and imposes greater stress on the agricultural landscapes called on to grow it. In other words, farming fish also degrades the land. At the same time, the quality of water needed to grow fish or prawns in is declining disastrously in many countries, as these countries dump toxic industrial wastes, pesticides, oil, hormones, heavy metals, nutrients, and sewage into their waterways.
Fish obligingly concentrate these poisons in their meat and pass them on to the humans who eat them. Aquaculture itself produces pollution— in the form of nutrients and the antibiotics and fungicides needed to keep farmed fish healthy; the growing reluctance of local authorities to permit fish farms in areas with sensitive waterways is yet another brake on the industry’s future growth.
A scientifically controversial option is to seek to replenish wild fisheries by breeding and rearing hatchlings artificially and then releasing them to sea. This has long been done with salmon, and recent breakthroughs in raising tuna, abalone, and other species from the egg make this form of extensive “ocean ranching” more than just a possibility as a way to sustain dwindling wild populations; however, the effect of this reseeding on natural populations, the wider marine environment, and other species is unknown.
An important development is that the world harvest of aquatic plants has, for the first time, reached 15 million tonnes (16.5 million U.S. tons). This is far short of the 2.5 billion tonnes (2.8 billion U.S. tons) of grain we grow on land, but it is a vital signpost to the farming of sea plants as a major future source of food and feed, which has been neglected in most countries for too long. Sea plants, like fish, depend on good water quality, however.
On the intensive farming front, fish are extremely efficient at turning grain into meat— far more so than livestock or even poultry, which implies that if grain supplies are scarce, fish may well be more efficient to produce than pigs or cattle, provided clean water is available. Integrated systems such as aquaponics— the raising of fish and vegetables together in water tanks, with the fish fertilizing the plants and the plants cleaning the water— appear promising. Nonetheless, although she is positive about the potential for aquaculture to expand in the future, Meryl Williams questions whether the global industry will be able to grow fast enough to supply the unfulfilled demand for marine protein, should wild harvests continue to stagnate or decline.
The Plunder of the Nature and Defenseless Environment
