Stanford Report Online



Stanford Report, February 28, 2001
Fish farming may help feed a growing planet, but it depletes ocean populations

BY LOUISA DALTON

The world is dependent on fish farms. In fact, one out of every four fish consumed worldwide was raised on a farm. But the irony is that fish farming, or aquaculture, while helping to feed a growing human population, often comes at a surprising cost to wild fish populations.

"A lot of countries could use more protein, and aquaculture is a good way to get there," says Rosamond Naylor, an economist at the Stanford Institute for International Studies.

The problem, Naylor points out, is that farmed salmon, shrimp and other carnivorous species often take more out of the oceans than they keep in. That's because certain farmed fish are given processed feed made from wild catches of herring, mackerel, sardine and other ocean varieties. Naylor estimates that nearly two pounds of wild fish are required for every pound of farmed fish raised on processed meal.

On balance, aquaculture still adds to the world's supply of seafood, she says. Yet fish farming influences wild populations --- displacing natural breeding habitats, spreading disease and polluting the oceans in many ways that haven't been measured.

Naylor and other researchers from around the world discussed the costs and benefits of fish farming at a symposium on aquaculture Feb. 18, at the annual meeting of the American Association for the Advancement of Science (AAAS) in San Francisco.

Speakers at the session organized by Naylor described some of the negative environmental, economic and social consequences of aquaculture, and outlined specific solutions to counter those impacts.

Commercial fish farms are expanding rapidly, especially in Asia, taking up thousands of square miles of coastal land. Panelist Jason Clay of the World Wildlife Fund explained how shrimp farms often replace wetlands and mangroves that serve as nurseries for native fish populations.

Crustacean farming is one of the world’s fastest growing forms of aquaculture. These giant tiger prawns raised in the Phillipines were probably exported to the U.S., Japan or Europe. In 1997, fish farmers raised nearly 500,000 tons of giant tiger prawns worth $3.5 billion. courtesy: Jurgenne Primavera

Nils Kautsky from the University of Stockholm in Sweden showed how a farm can affect surrounding areas by discarding excess fishmeal, transferring parasites to wild populations and introducing exotic fish into native ecosystems. Kautsky demonstrated how the "footprint" of a farm -- its influence on the local environment -- can be up to 50,000 times larger than the physical farm itself.

AAAS panelist Jurgenne Primavera with the Southeast Asian Fisheries Development Center explained how the aquaculture industry affects not only ocean life but also humans. According to Primavera, shrimp farms frequently displace rice paddies, boat landings, houses -- even burial grounds. He pointed out that saltwater from inland shrimp ponds can seep into nearby soil and reduce rice yields.

But aquaculture needn't be so disruptive. Several AAAS participants delineated ways that the farming industry can trample less and produce more efficiently.

"There are now identifiable ways to improve shrimp aquaculture," says Naylor, including reducing food input and developing closed-water systems that prevent waste and parasites from escaping.

Farming more vegetarian fish and shellfish -- such as carp and mussels -- is one way to produce needed fish protein for people without depleting ocean populations, Naylor contends. Shellfish farming, in fact, purifies the water by filtering out algae and waste, she adds.

Naylor believes that aquaculture, when done correctly, can provide more benefit than harm, and that scientists and economists can offer critical improvements to a rapidly expanding industry. Commercial fish farms should take advantage of the new research on fish nutrition, she maintains.

In the meantime, Naylor encourages those at the fish market to watch what they eat. "People should be aware that they are not doing the environment a favor at all by eating farmed salmon," she says.

So, fish-buyer, tread lightly. Eat more shellfish!

Louisa Dalton is a science writing intern with the Stanford News Service.

Thailand is the world’s biggest shrimp producer. Shrimp ponds are usually constructed along the shore, destroying miles of coastal habitat for indigenous wild fish. courtesy: Nils Kautsky


Crustacean farming is one of the world’s fastest growing forms of aquaculture. These giant tiger prawns raised in the Phillipines were probably exported to the U.S., Japan or Europe. In 1997, fish farmers raised nearly 500,000 tons of giant tiger prawns worth $3.5 billion. courtesy: Jurgenne Primavera