By John Holyoke, Bangor Daily News
BANGOR, Maine — University of Maine researchers went to the Penobscot River with new optimism this spring, as they hoped to find evidence that endangered shortnose sturgeon had spawned in the river. Documentation of that would be the first since two dams were removed from the river in recent years.
That wasn’t the case, but the team did receive some good news: Two shortnose sturgeon were captured at the Milford Dam fish lift, marking the first time since those dams were removed that sturgeon have accessed the entire range of their original native habitat.
“We knew that, historically, they made it up that far in the river,” said Gayle Zydlewski, a UMaine associate professor in the School of Marine Sciences, who has been a member of the research team for the past 10 years.
But the team had no evidence that sturgeon had moved that far upriver, graduate student Catherine Johnston explained.
In October, the research team learned that three tagged female sturgeon that could be detected by acoustic receivers in the river had moved upriver to a spot about 6 miles downstream from Milford. The hope was that the fish were searching out spawning territory, and Johnston spent time mapping the river to find probable spawning habitat.
This spring, egg-collecting mats and larvae traps were deployed in the river in hopes of collecting evidence of spawning activity.
That didn’t happen, but the upstream move by at least two fish was encouraging, Johnston said.
“The Milford fish lift is at River Kilometer 62, and the farthest upstream that we had seen any fish travel last fall was River Kilometer 52, 10 kilometers farther [downstream],” Johnston said. “The dam removal [as part of the Penobscot River Restoration Project] restored 14 kilometers of habitat, so now we can say that shortnose sturgeon have explored the entirety of that. That was exciting.”
Johnston, who defends her master’s thesis Thursday and is seeking full-time employment, will likely step away from the project soon. She has been studying sturgeon along with the rest of the team since 2014. She said the fact that sturgeon made it to Milford was gratifying.
Sturgeon are bottom-dwellers that are not especially strong swimmers and sometimes struggle to fight their way upstream through rapids.
“I was very impressed that sturgeon were able to swim over the Great Works rapids, because if you’ve seen [those rapids] from shore or gone over them in a canoe, they’re kind of intense,” Johnston said. “It was kind of cool that they were able to swim upstream through those rapids. We can’t say at what level of river discharge those two individuals made it over those rapids. That’s something that potentially future tagging efforts could help us identify, if there are other individuals going up there.”
At the present time, more than 30 Penobscot River sturgeon have active acoustic tags — Zydlewski said the team is seeking funding for more of the tags so they can gather more data on fish movements.
In past research, the team has identified more than 1,000 sturgeon wintering in the river.
The radio receivers that were in the river over the winter were retrieved in the spring, and data could be retrieved from them at that point.
“Over the winter, that was the anticipation — of waiting to get that data,” Zydlewski said. “When we did [and learned fish hadn’t moved upstream to spawn] it was a bit of a disappointment.”
The discovery of sturgeon in the fish lift at Milford “changes the complexion a little bit,” she added.
Zydlewski said that based on the researchers’ understanding of the optimal water temperature and time of year during the spawning season on other rivers, it didn’t appear the sturgeon that made it to Milford were intent on spawning. Instead, they might have been exploring.
“Based on what they see on the Kennebec [River], based on when these fish went into the fish lift, the conditions don’t seem to be appropriate for spawning,” Zydlewski said. “However, we don’t know how long they were up there before they went into the lift.”
Only future study will help determine that.
And while Johnston will be moving on, she’s confident a lucky graduate student eventually will get to pop the cork on a champagne bottle bought several years ago, scheduled to be opened only when evidence of spawning activity is discovered.
“Someone, someday,” Johnston said. “But it was worth celebrating [the two fish that made it to Milford, too].”
This story appears through a partnership with the Bangor Daily News.