A seafood paradox: Will fish farming save or deplete our ocean fisheries?

February 17, 2001

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 will discuss the costs and benefits of fish farming at a symposium on aquaculture to be held on Sunday, Feb. 18, at 3 p.m. PT at the annual meeting of the American Association for the Advancement of Science (AAAS) in San Francisco.

Speakers at the session organized by Naylor will describe some of the negative environmental, economic and social consequences of aquaculture, and will outline 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 will explain how shrimp farms often replace wetlands and mangroves that serve as nurseries for native fish populations.

Nils Kautsky from the University of Stockholm in Sweden will show how a farm can affect surrounding areas by discarding excess fishmeal, transferring parasites to wild populations and introducing exotic fish into native ecosystems. Kautsky will demonstrate 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 will explain 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 points 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 will delineate 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!
Editors: This release was written by science writing intern Louisa Dalton. Senior Fellow Rosamond Naylor will moderate the symposium ``The Aquaculture Paradox: Does Fish Farming Supplement or Deplete World Fisheries?`` at the annual meeting of the American Association for the Advancement of Science on Sunday, Feb.18, from 3 to 6 p.m. PT at the Hilton San Francisco & Towers, 333 O`Farrell St., San Francisco, CA 94102. For more information, see the AAAS website at http://www.aaas.org/meetings.

Relevant Web URLs:

Stanford University

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