BANGOR -- University of Maine researchers are turning to sonar as they try to estimate the burgeoning population of shortnose sturgeon that is spending the winter in 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 2½ years ago that researchers documented the first populations on the Penobscot in nearly three decades.

Sonar images reveal dozens of shortnose sturgeons crowded together on the river bottom. Analysts hope to use the information to get an idea of how many of the prehistoric-looking fish are wintering in the Penobscot.

File photo
A shortnose sturgeon.