– Sturgeon were the United States’ vanishing dinosaurs, armor-plated beasts that crowded rivers until mankind’s craving for caviar pushed them to the edge of extinction.

More than a century later, some populations of the bottom feeding fish are showing signs of recovery.

Increased numbers are appearing in the cold streams of Maine, the lakes of Michigan and Wisconsin and the coffee-colored waters of Florida’s Suwannee River. A 14-foot Atlantic sturgeon — as long as a Volkswagen Beetle — was recently spotted in New York’s Hudson River.

“It’s really been a dramatic reversal of fortune,” said Greg Garman, a Virginia Commonwealth University ecologist. “We didn’t think they were there, frankly. Now, they’re almost every place we’re looking.”

Following the late 1800s caviar rush, the nine sturgeon species and subspecies in the U.S. were plagued by pollution, dams and overfishing. Steep declines in many populations weren’t apparent until the 1990s.

“In the past three decades, sturgeon have been among the most studied species in North America as a result of their threatened or endangered status,” said James Crossman, president of the North American Sturgeon and Paddlefish Society, a conservation group.

Scientists have been finding sturgeon in places where they were thought to be long gone. They credit cleaner water, dam removals and fishing bans. Still, the U.S. sturgeon population is only a tiny fraction of what it was — and the health of each species and regional populations vary widely.

While some white sturgeon on the Pacific Coast are abundant enough to support limited fishing, Alabama sturgeon are so rare that none have been caught for years.

Dams still keep some populations low by blocking spawning routes. And the fish face newer threats such as rising water temperatures.

It will take decades to measure a population’s recovery, experts say. Sturgeon can live longer than humans and spawn infrequently, often requiring half a century to bounce back from overfishing.

Environmentalists warn that conservation efforts are still needed. “They’ve survived relatively unchanged for 200 million years,” said Jeff Miller, a senior conservation advocate at the Center for Biological Diversity, which is planning a lawsuit seeking federal safeguards for sturgeon in the Great Lakes and Mississippi River watersheds. “If they’re going to survive us, they’re going to need additional protection.”

Sturgeon swam with the dinosaurs. Bony plates line their bodies. Their toothless mouths vacuum up anything from worms to mussels.

Their meat fed American Indians, the starving settlers of Jamestown and the Lewis and Clark expedition. Then came caviar. The Russian delicacy of salt-cured sturgeon eggs became a fad for Europe’s new middle class — and that took a heavy toll on American sturgeon.

“People just massacred them, just like we massacred the buffalo,” said author Inga Saffron. “The difference being they were catching the sturgeon as they were migrating to spawn. Not only did they kill the fish, they killed future generations ”

But eventually fishing bans took effect and environmental laws became stronger. Among the species showing improvement is Atlantic sturgeon. The population around the Chesapeake Bay was feared to be extinct in the mid-1990s. Now, thousands are believed to be there, scientists said. “This could be a kind of a comeback generation,” said Matthew Balazik, a sturgeon research ecologist.

The shortnose sturgeon also shows signs of bouncing back. In Maine, scientists captured about 75 this decade on the Saco River, where they were previously never seen.

Lake sturgeon and Gulf sturgeon are also slowly recovering,

Not every river is seeing improvement. Dewayne Fox, a fisheries professor at Delaware State University, said the Delaware River’s population remains low, possibly because of collisions with cargo vessels or dredging on spawning grounds.

Decimated by dams, only one Alabama sturgeon has been caught since 2007, but DNA tests of river water confirm some are still there.

“They’re hanging on,” said biologist Steve Rider. “But they’re barely hanging on.”