A researcher holds an endangered shortnose sturgeon caught in a net in the Saco River in April in Biddeford, Maine. Sturgeon had been disappearing because of humans’ craving for their eggs. Recently they have been reappearing. (Robert F. Bukaty/AP)

Sturgeon were like vanishing dinosaurs, armor-plated beasts that crowded rivers until humans’ craving for eating caviar (fish eggs) pushed them to the edge of extinction.

But more than a century later, some U.S. populations of the massive bottom-feedingfish are showing signs of recovery.

Increased numbers are appearing in the cold streams of Maine, the lakes of Michigan and Wisconsin and Florida’s Suwannee River. A 14-foot Atlantic sturgeon was recently spotted in New York’s Hudson River. The Chesapeake Bay-area population was feared to be extinct in the mid-1990s. Now thousands of them are believed to be there.

Scientists are seeing increased numbers of them in some rivers because of cleaner water, dam removals and fishing bans. These discoveries provide some hope for a fish that is among the world’s most threatened.

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

Sturgeon swam with the dinosaurs. Bony plates line their bodies. Whisker-like fibers hang from their chins. Their toothless mouths telescope out and vacuum up anything from worms to mussels. Their meat fed Native Americans, 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.

Matthew Balazik, a sturgeon research ecologist with Virginia Commonwealth University, holds a baby Atlantic sturgeon in December. The fish was caught from Virginia’s James River. (Ben Finley/AP)

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

“However, 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.

But the U. S. sturgeon population is a tiny fraction of what it once was — and the health of each species and regional populations varies widely.

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

It will take decades to measure a population’s recovery, experts say. Sturgeon sometimes live longer than humans. Environmentalists warn that more conservation efforts are still needed.

Last fall, Matthew Balazik, a sturgeon research ecologist at VCU and the U.S. Army Corps of Engineers, netted more than 200 baby Atlantic sturgeon in the James River — the first seen there in years. “This could be a kind of a comeback generation,” Balazik said.

— Associated Press