Fish-Farming: Needed to Feed the World?

By Nick Cunningham

Last week I wrote about Callum Roberts "The Ocean of Life," an interesting book on some of the big problems facing ocean ecosystems. I didn't intend to revisit it, but I came across a really fascinating section on fish farming that I think is worth its own post.

typical aquaculture 'raceway' in Korea (photo: NOAA)

As Roberts notes, global (wild) fish catches peaked in 1988 and have begun to decline, after thousands of years of rising. This is due to a variety of reasons - overfishing, pollution, climate change, invasive species - but the picture looks pretty bleak. Many fisheries are on the edge of collapse, including in both developed and developing countries. The collapse of the cod fishery near Nova Scotia is one infamous example.

So, in order to feed the 1 billion people around the world that rely upon fish for their main source of protein, a number that is rising everyday, one alternative is to breed and raise fish in farm-like conditions.

Known as aquaculture, farming fish is a bit like industrialized agriculture. It involves fish "pens" in which the fish are caged along the coast of the ocean, an estuary, or river. Since the ecosystem would not naturally support such high numbers of fish in such a small space, these fish must be fed. This is analogous to packing cows into a small space, and feeding them so that they get really fat really quickly. Since many of the farmed fish species are predatory fish, not vegetarians, they are fed sources of protein that are perfectly edible to humans, like anchovies or herring. As a result, it takes "several pounds of wild-caught fish to produce just one pound of farmed fish." Not a particularly efficient use of resources.

The impacts on the local ecosystem can be pretty ugly as well. With such a high density of fish, waste is a huge problem. Nitrogen and phosphorus from fish waste create algal blooms, depleting the waters of oxygen and contributing to dead zones.

When cows are packed into tight quarters they may develop diseases and require a heavy dose of antibiotics. Similarly, chemicals are sprayed in the waters of fish farms to rid the pens of diseases, devastating the marine ecology in and around the farm.

Photo: USGCRP

Roberts provides a cringing description of massive fish farms in China, in which fish pens are located next to each other as far as the eye can see. The waters smell putrid, and are dangerously contaminated (including from other industrial pollution), but 4 out of 5 fish eaten by the average Chinese person comes from a fish farm. China is also a major exporter of farm-raised fish.

Unfortunately, companies running fish-farming operations often clear vital ecosystems in order to raise fish. The expansion of the Thai shrimp industry provides a cautionary tale of the dangers of intensification. In the 1970s and 1980s, increases in shrimp farm productivity brought huge profits to farmers as international demand for shrimp soared. Mangrove forests were converted to shrimp farms and total mangrove area in Thailand decreased from 3,679 km2 in 1961 to 1,685 km2 in 1996. Mangroves provide critical ecosystem services - like erosion prevention, storm surge protection, and flood control. Clearing mangroves for aquaculture is not the direction want to be heading in.

With all of these nasty problems with aquaculture, it would seem obvious that we need to quickly move away from such an approach of sourcing our food. However, that would be pretty simplistic.

Just like the debate with intensification of agriculture, intensifying fish production does have benefits. With agriculture, packing animals into a small space relieves a huge amount of pressure on global forests. In Brazil, the largest source of deforestation is due to the conversion of forests for cattle pasture. Global beef demand is rising so quickly that land is more valuable for meat production than it is as forest. So, by intensifying cattle operations, there is an environmental benefit in land use.

So it is with aquaculture. Intensifying fish production can relieve pressure on other fisheries, including endangered species.

Moreover, with so many mouths to feed, maybe it is inevitable that we need to intensify fishing.

But, as Roberts notes, there are "better and worse ways of doing it." Choosing areas that don't jeopardize wetlands or mangroves is smart. Operating at less density may reduce the impact on local ecosystems. Finding alternative sources of food for feed, rather than other fish, would also be an improvement.

It's not easy. But, ultimately, aquaculture is here to stay.