ORONO, Maine — Ever since an angler targeting striped bass caught a shortnose sturgeon in the Penobscot River 10 years ago, scientists have been studying the fish, tracking their numbers and movement as a restoration project changed the character of the river.

In October, for the first time, that University of Maine team documented fish — three tagged females that can be tracked by acoustic receivers — that had moved into a stretch of the river above the former Veazie Dam.

And while those researchers have been tracking sturgeon movement for nine years, that slight upstream move — perhaps the precursor to spring spawning activity — is being heralded as a major step in the recovery of the species, which is listed under the federal Endangered Species Act.

The slight upstream migration into freshwater could mark the next step toward sturgeon actually spawning in the river, researchers say.

“For us, we think it’s very encouraging that we’re seeing fish start to explore regions of the river past the [former] dam, up to the portions that we think spawning might happen,” said Michael Kinnison, a professor in the University of Maine school of biology and ecology. “Those are the sort of forays that fish could take this time of year that could lead to [spawning].”

Since 2004, Joe Zydlewski of the U.S. Geological Survey, who also serves as assistant unit leader at the Maine Cooperative Fish and Wildlife Research Unit, has been helping scientists track a variety of fish in the river. Funding for the project has been provided by National Oceanic and Atmospheric Administration Fisheries, and the collaboration includes the Penobscot River Restoration Trust, The Nature Conservancy and others.

The network of acoustic receivers he has helped install in the river allow fish that have been fitted with a tag to be tracked as they swim past those receivers. Among the species that have been fitted with tags: Atlantic and shortnose sturgeon, Atlantic salmon, striped bass, sea lamprey and American eels.

“I think one of the things we’ve been doing over the last years is uncovering the complexities of movements of [shortnose sturgeon],” Zydlewski said. “You think that the fish are here, so you assume they’re completing their life cycle here.”

That’s not necessarily the case, as Zydlewski’s wife, Gayle Zydlewski, an associate professor in the UMaine School of Marine Sciences, can tell you.

Since 2006, she has studied sturgeon in the Penobscot with a series of graduate students. After discovering the presence of sturgeon in 2005, researchers sought to catch and tag fish, then figure out how many sturgeon might be living in the river.

They’ve identified a population of about 1,000 fish that spend their winters here, and have seen their wintering area change from year to year.

But those fish haven’t been spending their entire lives in the Penobscot.

“In the early days, we were putting tags [on fish] and expecting them to stay in the Penobscot,” Gayle Zydlewski said. “And then they started turning up in the Kennebec.”

One possible reason: The spawning habitat in the Penobscot, especially before two dams were removed as part of the Penobscot River Restoration Project, was not as attractive as the spawning habitat in the Kennebec.

“We’ve been trying to follow a fish [by monitoring tagged fish] in the Penobscot for 10 years,” Kinnison said.

That monitoring has been unsuccessful.

Graduate student Catherine Johnston, who has been working on the project since the spring of 2014, is the latest grad student to handle those monitoring chores. Among other tasks, Johnston spends a couple nights a week in May and June tending nets designed to catch eggs and larvae that spawning sturgeon would leave behind … if they’re spawning in the river.

All of those researchers have come up empty: No evidence of spawning sturgeon has been found.

“I’m only maybe the fifth grad student who’s done that — look for eggs and larvae and not [find] them,” Johnston said. “We know that it’s a worthy cause, but it’s a lot of hours fishing on a boat, at night, because we think that would be the most likely time to have success if there were larvae in the river.”

Gayle Zydlewski is optimistic that eventually, the crew will find that evidence. She has even planned ahead.

“About three [grad] students ago, a bottle of champagne was bought. It’s sitting in [an office] waiting to be popped,” she said.

The latest discovery is important for a few reasons. First, only one out of every 50 sturgeon living in the river is tagged. The presence of three fish above the former Veazie Dam site could mean that 100 or more sturgeon have actually staged upriver.

“That’s the sort of number that you think about if spawning’s going to happen,” Kinnison said. “You could have fairly dramatic changes to the system pretty quick.”

Second, though Johnston is still researching possible spawning sites in that area, the scientists think it’s likely that there’s much better spawning habitat in that stretch of the river than there is below Veazie.

“In order for the population to persist, you need two types of habitat,” Kinnison said. “You need the spawning habitat, which is where they need to put their eggs … but what they really need, too, is when those eggs hatch, they need juvenile habitat.”

Optimal juvenile habitat exists in a place where the fish can settle down before they reach saltwater, Kinnison said, and with head-of-tide in the Penobscot at the Veazie Dam site, areas above that former dam are likely the most attractive to spawning sturgeon.

Come May, Johnston and others will be back on the river, looking for evidence of that spawning. The bottle of champagne has been waiting for years to celebrate just such a discovery.

And Kinnison said the relatively short movement of the tagged fish will help fuel the research crew when they head onto the water in 2016.

“It’s a lot easier to have hope now that we know that there are fish up there,” he said. “It’s going to provide some new energy for the field work [next] year.”

John Holyoke

John Holyoke has been enjoying himself in Maine's great outdoors since he was a kid. He spent 28 years working for the BDN, including 19 years as the paper's outdoors columnist or outdoors editor. While...