Researchers at the University of Maine have discovered the first population of endangered shortnose sturgeon in the Penobscot River in nearly 30 years, offering scientists hope that habitat conditions in the river are improving.

During the past week, a research team has pulled 23 shortnose sturgeon from several spots in the Penobscot near Winterport. Discovery of so many fish likely rules out any chance that the sturgeon had strayed into the Penobscot from other rivers, researchers said Wednesday.

“It means there is hope for recovery of a species in our system and one that represents a really unique component of our ecology,” said Michael Kinnison, co-leader of the project and a professor of biological sciences at the University of Maine in Orono. “It is part of our history.”

A cousin of the much larger and better known Atlantic sturgeon, shortnose sturgeon are reclusive bottom dwellers that spend most of their lives in their home rivers. They can live 30 years or longer and weigh up to 25 pounds. Atlantic sturgeon, by comparison, can grow to a length of 8 feet and weigh 300 pounds or more. Sturgeon are primitive creatures with bodies that haven’t changed much since the days of the dinosaurs. These “living fossils” have a series of bony plates that run the length of their bodies, a forked tail and a mouth on the underside of the head to enable bottom feeding.

The federal government designated shortnose sturgeon as “endangered” in 1967, several years before the Endangered Species Act became official. The Atlantic sturgeon is listed as a “species of special concern.” Dams, polluted rivers and overfishing – in part for their prized caviar – are often blamed for the collapse of the sturgeon population in Maine and elsewhere.

The last documented case of a shortnose sturgeon in the Penobscot was in 1978 despite several extensive scientific surveys in the decades since. The fish are known to inhabit other Maine rivers, including the Kennebec and Androscoggin.

UM graduate student Stephen Fernandes and several others were primarily gill-netting for Atlantic sturgeon near Winterport as part of his work with Kinnison and the other project co-director, Gayle Zydlewski, a professor of marine sciences at the university.

So Fernandes said he was elated to see the first shortnose sturgeon netted on June 14. The group caught another 10 shortnoses during the next six days and then a dozen more on Wednesday alone.

“I was as excited as all can be. It was crazy,” Fernandes, a master’s student in ecology and environmental science, said Wednesday in an interview. “We had already been fishing the nets for a while and hadn’t caught anything.”

Fernandes implanted special transmitters into five of the fish, which will allow researchers to track their movements up and down the Penobscot. Kinnison said he hopes that the tracking devices will lead the team to more shortnose sturgeon, which will help with population studies.

Kinnison acknowledged that there are many unknowns about the sturgeon’s sudden reappearance. Sturgeon can be difficult to find, meaning the fish could have been in the river all along but simply evaded detection.

They are also not likely to be caught by anglers, and even if they were, the fish could be misidentified or simply tossed back as an odd catch, he said.

Kinnison also said that habitat conditions for both the shortnose and Atlantic sturgeon have improved in the Penobscot in recent decades, thanks largely to the removal of several lower dams and efforts to clean up pollution.

The campaign to remove three more dams on the river – known as the Penobscot River Restoration Agreement – should open up even more river to sturgeon as well as other species, including the endangered Atlantic salmon.

“As long as we don’t degrade the river appreciably … there is a good chance these fish can hold on,” Kinnison said.

The UM study on sturgeon is funded by a grant from the National Oceanic and Atmospheric Administration’s Fisheries Service. Joseph Zydlewski with the U.S. Geological Survey’s Cooperative Fish and Wildlife Research Unit also is assisting with the project.

“It is really great news that shortnose sturgeon have been confirmed in the Penobscot,” Thomas Squiers, director of the Resource Management Stock Enhancement Division of the Maine Department of Marine Resources, said in a statement. “The next step will be to locate where these fish are spawning, and to confirm the presence of eggs and larvae.”