Once, sturgeon were so abundant in the rivers of the Midwest that bartenders in turn-of-the century taverns used to give away the sturgeon’s salty caviar to boost beer sales.

Today, a few thousand sturgeon swim in the Mississippi and Missouri rivers. Most are aging adults with one or two more chances to spawn.

In less than a century, Americans have driven a fish that swam among the dinosaurs to the brink of extinction.

The same factors that have decimated U.S. fish stocks and the jobs it supported—overharvesting, dam building and pollution—have nearly wiped out European, Black Sea, Caspian and Chinese sturgeon as well.

Only one of 27 species of sturgeon worldwide—the white sturgeon in the Pacific—is holding on, according to scientists. Most sturgeon species are declining, and some are essentially extinct because population levels are simply too low to support reproduction.

Eight sturgeon species are found in North America, including the Atlantic sturgeon that once filled the Chesapeake Bay but is now rarely seen and cannot be legally caught for about 40 years.

Five of North America’s species or subspecies are considered endangered by the federal government, including gulf sturgeon, pallid sturgeon, Kootenai River white sturgeon, and the Alabama sturgeon. Only white sturgeon, shovelnose sturgeon and lake sturgeon can be legally caught, and only in some states.

Several of the most valuable sturgeon species are found in the rivers draining into the Caspian Sea, which borders Russia, Kazakhstan, Turkmenistan, Iran and Azerbaijan. More than 100 rivers drain into the inland sea, including the Volga, which supplies about 75 percent of Caspian’s sturgeon. Overall, the region supplies 90 percent of the world’s sturgeon and caviar, including the famed beluga caviar.

Sturgeon are also found in China, Japan, Siberia and Europe’s Atlantic drainage.

Caspian sturgeon populations were already falling when the Berlin Wall came down in the early 1990s. The fall of communism eliminated any real limits on sturgeon fishing—only Iran has the resources to monitor fish stocks and enforce limits, according to experts.

As a result, 10 illegal fish are taken for every legal fish caught in the Caspian and its tributaries.

“Back in the old Soviet days, there was a lot stricter control over how many sturgeon could be caught every year,” said Sunny Wu, a spokeswoman for SeaWeb, a conservation group. “Once the Soviet Union collapsed, that sort of management vaporized.”

Russian scientists recently reported that beluga sturgeon populations have fallen 90 percent over the past two decades.

Covered with plates that resemble armor and a long snout, a sturgeon is well-equipped for the life on bottom of muddy, swift-flowing rivers like the Mississippi and the Volga. Some sturgeon species live to be more than 100 years old, grow up to 15 feet long and weigh more than a ton.

But a sturgeon does not reach sexual maturity until late in life and may only produce eggs once every three or four years. That makes it hard for the prehistoric fish to quickly rebuild populations.

All sturgeon must return to fresh water to spawn on the cobble that covers some river bottoms. That makes the sturgeon easy to catch. And, the value of sturgeon roe—more than $100 an ounce—makes the fish a highly prized catch.

But, overharvesting is just one of the problems facing the sturgeon.

“We wish it was as simple as closing down fisheries, but that by itself does not seem to do very much,” said Dick St. Pierre, a sturgeon expert with the U.S. Fish and Wildlife Service.

Dam construction dramatically reduced the quantity and quality of spawning and rearing habitats. For example, scientists estimate that 85 percent of the spawning habitat found in the Volga River is blocked by dams.

What’s more, water pollution from factories and wastewater treatment plants has also lowered dissolved oxygen levels.

“Sturgeon are probably the most oxygen-loving fish in the Chesapeake Bay,” said Dave Secor, a biologist at the University of Maryland’s Center for Environmental Science who has studied Atlantic sturgeon. When it comes to dissolved oxygen, sturgeon “are more like a coldwater species like cutthroat trout” than species typically found in an estuary, he said.

Two years after officials upgraded wastewater treatment plants along the Hudson River, sturgeon populations increased dramatically, Secor said.

Sturgeon populations have fallen so low that all sturgeon species are now considered “Appendix 2” species under the Convention on International Trade in Endangered Species, Wu said. That means that U.N. officials in Geneva can set limits on how many of the sturgeon can be legally bought and sold on international markets.

But, U.N. officials and environmentalists disagree on whether some sturgeon populations are increasing or decreasing. For example, the United Nations says Beluga sturgeon populations increased 25 percent between 2001 and 2002, but scientists with the Pew Institute on Ocean Science say they fell 39 percent.

The poaching of sturgeon makes those limits meaningless, experts say. “Simply put, trade in sturgeon is still outpacing recovery efforts,” Wu said.

SeaWeb, the Wildlife Conservation Society and the Natural Resources Defense Council have petitioned the U.S. Fish & Wildlife Service to list the beluga sturgeon as an endangered species, which could result in beluga caviar being banned in U.S. markets.

They are pushing farm-raised caviar as an alternative to the roe harvested from wild fish. And, they’ve enlisted hundreds of famous chefs to support their cause.

“Limiting the poaching would be the first step,” St. Pierre said.