Decline of Big Fish Upsets Ocean Balance

More prey and fewer predators could throw the ecosystem out of balance

By 2050, small fish could dominate the oceans because of the rapid decline of larger, predator fish.

In a new report, the U.N. Food and Agriculture Organization finds that one-third of the world’s fisheries are overexploited, depleted or recovering and in urgent need of rebuilding. At a recent meeting of the American Association for the Advancement of Science meeting in Washington, University of British Columbia fisheries expert Villy Christensen predicted the eventual preponderance of small fish.

Twenty years ago, Christensen designed a computer tool called Ecopath to study complex marine ecosystems. Now Ecopath has 6,000 users in 155 countries.

Christensen used 200 marine models from the Ecopath database for the analysis released at the Washington meeting. “We are estimating that the predatory fish, the large fish that eat other fish, have declined by two-thirds in the 100 years and the decrease is accelerating. In the last 40 years alone, 54 percent of that decline occurred.”

Over the same 100-year period, Christensen says, prey fish like anchovies, herring and sardines have more than doubled. “We’ve never had numbers like that before. We expected it might be the case, now we have numbers documenting it. What has happened here really is that we’ve changed the wild ocean. We’ve removed the big fish.”