Fear of mercury may be what keeps some Americans from eating fish, but the real danger is that people could run out of fish to eat at all, conservation groups say.

Numerous popular and once prolific U.S. fish species have been reduced to 1% to 10% of their original populations, according to Oceana, an international ocean protection organization.

With the global market for fish growing and improved technology to find what fish are left, "there's basically no place left for a fish to hide," says Michael Hirshfield, Oceana's chief scientist.

Overfished species

* Orange roughy: Lives 100 years or more - so the fillet in your freezer might be from a fish older than your grandmother. Slow growing, it shows dramatic population declines in some areas.

* Atlantic cod: Scientists agree that humans are now fishing the last 10% of this population.

* Sturgeons: The sturgeon of the Caspian Sea, a traditional source of caviar, are nearing extinction.

* Sharks: As many as 50% of all sharks are accidentally caught by drift gillnets or longlines. They mature slowly and give birth to a few young at a time, so most do not reproduce quickly enough to keep up with demand for their meat and fins.

* Bluefin tuna: Bluefin tuna provide the world's most valuable sushi. The Atlantic population has declined by nearly 90% since the 1970s.

Source: Oceana

Things started to go downhill for U.S. fish populations in 1976 with the passage of the Magnuson Act, which was meant to protect fisheries (ocean regions where fish are raised and caught). But it had the paradoxical effect of harming them, says Bill Hogarth, director of the National Oceanic and Atmospheric Administration's Fisheries Service.

The law was the fruit of concerns that foreign-based fleets were sucking fish out of the sea that rightfully should have gone to U.S. fishermen. To protect those fish, the United States extended its jurisdictional limits to 200 miles from the coast.

But the U.S. fishing fleet simply wasn't big enough to fish that large an area, so the second part of the law assisted the industry by providing government-subsidized, low-cost loans for boats and gear.

The number of fishing vessels bloomed, says Barton Thompson of the Stanford Institute for the Environment. "We did a good job of (helping the fishing industry) — in fact, we did too good a job."

As fish became harder to find, fishermen began to take advantage of technological advances, including sonar, sea-floor mapping and global positioning satellite data.

Today, endangered fish include yellowtail flounder, Atlantic halibut, speckled hind (grouper), red snapper, Warsaw grouper and Atlantic cod. The flounder is at the top of that government list because only 1% of original stocks remain. The halibut is close behind at 2%.

Fishing fleets were built up beyond the capacity of the seas to provide that much fish, Thompson says. But scaling back means taking away people's livelihoods, he adds.

"This is not a story of evil, money-grubbing people going out and destroying a resource. Those fishermen have boats they have to pay off and families they have to feed."