Page 271 - Environment: The Science Behind the Stories

Aquaculture is the fastest-growing type of food produc-
tion; global output has doubled in just the last decade. Most
widespread in Asia, aquaculture today produces $125 billion
worth of food and provides over three-quarters of the fresh-
water fish and two-thirds of the shellfish that we eat.

Aquaculture brings benefits

When conducted on a small scale by families or villages, as in
China and much of the developing world, aquaculture helps
ensure people a reliable protein source. Such small-scale aqua-
culture can be sustainable, and its compatibility with other activ-
ities can make it an excellent path toward sustainable agriculture Figure 10.14 Transgenic salmon (top) grow considerably
in general (pp. 287–288). For instance, uneaten fish scraps make larger than wild salmon of the same species.
excellent fertilizers for crops, and food waste can be fed to fish.
At larger scales, aquaculture can help improve a region’s or
nation’s food security by increasing supplies of fish available. disease to them. Researchers have concluded that in some
Aquaculture on any scale helps reduce fishing pressure circumstances, escaped transgenic salmon may increase the
on overharvested and declining wild stocks. Reducing fish- extinction risk for native populations of their species, in
ing pressure also lessens bycatch (p. 457; the unintended part because larger male fish (such as those carrying a gene
catch of nontarget organisms) that results from commer- for rapid and excessive growth) have better odds of mating
cial fishing. Furthermore, aquaculture consumes fewer fos- successfully.
sil fuels and provides a safer work environment than does
commercial fishing. Fish farming can also be remarkably
energy-efficient, producing as much as 10 times more fish Preserving Crop Diversity
per unit area than is harvested from waters of the conti-
nental shelf and up to 1000 times more than from the open Whether one is considering salmon in the Pacific Northwest
ocean. or maize in Mexico, the prospect of genetically modified
organisms crossbreeding with wild relatives and influencing
Aquaculture has negative impacts the genetic makeup of the population raises a host of compli-
cated issues. With cropland agriculture, our modern industrial
Along with its benefits, aquaculture has disadvantages. monocultures of genetically similar plants essentially place
Dense concentrations of farmed animals can increase disease, all our eggs in one basket, such that any single catastrophe
which reduces food security, necessitates antibiotic treat- might potentially wipe out entire crops. Our wide adoption of
ment, and results in expense. A virus outbreak wiped out half industrial agriculture has also reduced the diversity of crops,
a billion dollars of shrimp in Ecuador in 1999, for instance. and today we as a global society rely on a much smaller num-
Aquaculture can also produce remarkable amounts of waste, ber of plant types than in decades and centuries past. This
both from the farmed organisms and from the feed that goes is partly why so many people grew concerned about genes
uneaten and decomposes in the water. Like feedlot livestock, from transgenic corn moving into local Mexican landraces
commercially farmed fish often are fed grain, which affects of maize.
food supplies for people and is energy-inefficient. In other
cases, farmed fish are fed fish meal made from wild ocean Crop diversity provides insurance
fish such as herring and anchovies, whose harvest may place against failure
additional stress on wild fish populations. For all these rea-
sons, industrial-scale aquaculture can leave a large ecological Preserving the integrity of diverse native crop variants gives
footprint. us a bulwark against the potential failure of our homoge-
If farmed aquatic organisms escape into ecosystems nized commercial crops. The wild relatives of crop plants
where they are not native (as several carp species have done and their locally adapted landraces contain a diversity of
in U.S. waters), they may spread disease to native stocks or genes that we may someday need to introduce into our com-
may outcompete native organisms for food or habitat. These mercial crops (through crossbreeding or genetic engineer-
possibilities raise special concern when the farmed animals ing) to confer resistance to disease or pests or to meet other
are genetically modified. Genetic engineering of Atlantic unforeseen challenges.
and Pacific salmon produces transgenic fish that grow to Because accidental interbreeding can diminish the
several times the normal size for their species (Figure 10.14), diversity of local variants, many scientists argue that we
and the USDA may approve the first GM salmon for sale need to protect landraces in areas like southern Mexico that
and consumption soon. Such GM fish could help reduce remain important repositories of crop biodiversity. For this
fishing pressures on wild stocks, but they might also—if reason, the Mexican government helped create the Sierra de
they are released or if they escape into the wild—outcom- Manantlan Biosphere Reserve around an area harboring the
270 pete their wild cousins, interbreed with them, or spread world’s only population of the plant thought to be the direct

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