Researchers use sonar to reveal a growing population of shortnose sturgeon wintering in the river.
BANGOR — University of Maine researchers are turning to sonar as they try to estimate the burgeoning population of shortnose sturgeon spending the winter in the murky bottom of the Penobscot River.
Once abundant in rivers from Florida to the St. John in Canada, the mysterious and reclusive shortnose sturgeon is under federal protection as an endangered species. It was only 2 years ago that researchers documented the first populations in the Penobscot in nearly three decades.
Sonar images reveal dozens of shortnose sturgeon, identifiable as long white splotches, crowded together along the bottom of the 20-foot-deep river.
“When people have done this and gotten good video, they say they look like cordwood just stacked one on top of another,” said Gayle Zydlewski, a professor at the university’s School of Marine Sciences.
Analysts hope to use the information to get an idea of how many of the fish are wintering in the Penobscot.
The shortnose sturgeon is a living fossil that apparently was around during the latter days of the dinosaurs 70 million years ago. Armorlike plates run the length of its body, which can exceed 3 feet. It has the undermouth barbels of a catfish, but a tailfin more akin to a shark’s.
Acting on a hunch about where the secretive fish might be found, the researchers managed to snag 57 of them in a single gill netting this fall. The sturgeon were tagged and released.
Shortnose sturgeon are smaller than Atlantic sturgeon, which can grow to 10 feet long. Both types have been harvested since Colonial times for their meat and eggs, which are prized as caviar. But pollution and dams that disrupt spawning have reduced their numbers.
