For the first time in U.S., and probably global, history a fish identified as endangered has been shown to have recovered -- and in the Hudson River, which flows through one of the world's largest population centers, New York City.

The population of shortnose sturgeon, which lives in large rivers and estuaries along the Atlantic coast of North America, has increased by more than 400 percent in the Hudson River since the 1970s, report Mark Bain, associate professor of natural resources at Cornell, and his colleagues in the online publication PLoS ONE. However, the shortnose sturgeon is still endangered in other rivers, Bain said, and will not necessarily be removed from the endangered species list by the U.S. government.

In the past 100 years, 27 species of fish have died out in North America and four have become extinct. The U.S. government currently protects 149 fish species and subspecies and a total of 1,311 species under the U.S. Endangered Species Act.

"Endangered and threatened U.S. fish outnumber mammals, reptiles, birds, etcetera," said Bain. Since 1966 when the federal government started identifying threatened species, only 16, including the American alligator, American peregrine falcon and brown pelican, have recovered. "Recovery is very rare," said Bain, who has been monitoring the shortnose sturgeon's population since the mid-1990s and has access to data on the populations since the 1970s.

"The nature of this species, its habitat and evidence for a large and secure population are an example of successful protected species management," said Bain. "Scientists and legislators have called for changes in the U.S. Endangered Species Act; the act is being debated in Congress and has been characterized as failing to recover species."

However, he said, recovery of the shortnose sturgeon suggests the combination of species and habitat protection with patience can successfully recover threatened species, even next to one of the busiest cities in the world.

The study will appear in the Jan. 24 edition of PLoS ONE, an international, peer-reviewed, open-access, online publication from the Public Library of Science.