Its numbers had also been hurt by cities dumping raw sewage into rivers, which made oxygen levels in the water drop.
"By the 1900s it was rare to see shortnose sturgeon," Bain said, and by the 1950s "they had declined to such low levels they were barely ever seen."
The fish's recovery seems to be due to its protection as an endangered species as well as modern sewage treatment required under the 1977 Clean Water Act, Bain says.
Sturgeon are long-lived—they can live as long as people—and reproduce slowly, so their recovery took decades.
The lesson of this study, Bain said, is that "we're likely to need a lot of time and patience" in helping endangered species.
Ray of Hope
Most species on the endangered list are removed either because they go extinct or by a technicality: getting reclassified as another nonendangered species.
But a few species have recovered enough to make it off the list, such as peregrine falcons and the western Great Lakes population of gray wolves.
(Related news: "Wolves to Be Hunted if Removed From U.S. Endangered List" [February 5, 2007].)
"It can be difficult to ask people to make space for a species when they do not see the immediate payoffs" of conservation efforts, said David Lusseau, an ecologist at Dalhousie University in Canada.
But this new study "provides a ray of hope in the gloom of endangered wildlife management," Lusseau said.
"It offers us a great lesson: Long-term investment in species recovery can pay off."
Free Email News Updates
Best Online Newsletter, 2006 Codie Awards
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES