Biologists have yet to net a sturgeon on Maryland’s Nanticoke River, but evidence continues to mount that a number of the large fish have been hanging out in the Eastern Shore tributary.

A number of people in recent years have reported sturgeon jumping in the river, and in September one jumped into a boat with two anglers who helped return the 5.5-foot fish into the water.

Now, biologists say a receiver in the Nanticoke picked up a signal Sept. 8 from a female sturgeon which was caught off the Delaware Coast three years ago and tagged with a transmitter.

Biologists recently learned of the fish when they downloaded information from the receiver — something that has to be done by physically going to the location of the receiver. The sturgeon was 4.5 feet when it was tagged by biologists working with Delaware State University fisheries scientist Dewayne Fox three years ago. Genetic analysis of the fish showed it was from the Hudson River.

Biologists from the Maryland Department of Natural Resources and the U.S. Fish and Wildlife Service have been perplexed about why sturgeon have been showing up in the Nanticoke in recent years, but they so far have had no luck catching any of the fish.

The Nanticoke was the location of an experimental release of Atlantic sturgeon in 1996. That release used progeny of Hudson River fish that were reared in a hatchery in the Susquehanna River basin

Sturgeon are an anadromous fish, which spend most of their lives in the ocean but return to their native river to spawn when they mature, starting around age 15. But biologists think the sturgeon released in the Nanticoke, which were about a year old at the time, were too old to imprint on the river. Other anadromous fish imprint on rivers at a younger age, but no one is really certain when sturgeon imprint.

“There’s so much we don’t know about these fish,” said Steve Minkkinen, who heads the USF&WS Maryland Fishery Resources Office. “Until we handle some fish, we don’t have the slightest idea. Why are those fish going up there in the fall? Could there be fall spawning like they are saying happens in the James River? Or are they just going up there to hang out?”

They may get some answers in the future. More receivers were set to be installed in the Nanticoke and other areas of the Bay this fall that will help scientists track the movements of tagged fish, which may offer insights about their behavior.