BANGOR, Maine — Weeks of mild, dry weather that led to prime conditions may be the cause of a historically high early return of Atlantic salmon on the Penobscot River.
As of 3 p.m. Wednesday, 255 adult salmon had been captured at the Veazie Dam fish trap, the first barrier to upstream passage on the river. That count surpasses the previous record for the date of 139 salmon, set in 2008. A year ago 109 fish had reached the trap as of the same date.
The Veazie fish trap started up in 1978. Last year a seasonal total of 1,958 salmon returned to the trap. In 2008, 2,115 fish were trapped. The single highest seasonal return since 1978 took place in 1986, when 4,137 salmon reached the trap.
Norm Dube, a fishery biologist for the Department of Marine Resources’ Bureau of Sea-Run Fisheries and Habitat, said he’s unsure of the exact reason for the drastic change, but he has some ideas.
“My gut feeling is that it’s low discharge [over and through the Veazie Dam], so that the fish are able to find the fishway much sooner than normal,” Dube said.
Dube explained that as salmon work their way upriver, they follow the flow and look for attractive places to swim. The bubbles and current that exist below a dam attract the fish.
During high water periods, water spills over the top of the dam, and there is turbulence across the breadth of the river. Now, with flash boards up on the Veazie side of the river, returning salmon are essentially handed a road map of current and turbulence that leads them back to the lone attractant.
“There’s no spill going over there. You just have the tailrace of Station A [on the Veazie side of the river] and the fishway entrance,” Dube explained. “And the largest turbine discharge is right by the fishway entrance, so it [attracts] fish right up in there.”
In 2009 the National Oceanic and Atmospheric Administration moved to list Penobscot River Atlantic salmon as endangered under the federal Endangered Species Act. Before the decision’s approval by the federal government last June, the state canceled the catch-and-release fishing season for salmon just days before it was scheduled to open in early May. There is no season this year either, and won’t be another until the salmon are taken off the endangered list.
Many of the salmon that are captured are taken to Craig Brook National Fish Hatchery in Orland, where they serve as brood stock for the restoration effort.
Others are released above the dam, where they can continue their upstream trek.
Just finding the fishway passage can be a challenge for the salmon, Dube said.
“Typically during the month of May you have spill over the entire dam and you’ve got multiple attraction points,” Dube said. “To find a 2-foot slot in the fishway, it takes awhile for them to do that.”
Oliver Cox, the Bureau of Sea-Run Fisheries and Habitat biologist who oversees the trap-tending crew, said that when staffers opened the trap on May 3, there were plenty of fish waiting.
“We had some fairly warm water temperatures right when we opened the trap,” Cox said. “Our first tend was 24 fish. That’s huge for that tend, and that’s an indication that there were fish in the river earlier, and they were just kind of waiting for the door to open.”
Cox said the early returns are encouraging, but don’t necessarily mean the entire season will be a success.
“Everybody is, I’d say, cautiously optimistic, because it could just be that the run has shifted earlier, and the science kind of points to that,” Cox said.
Another potential factor: Beginning in 2007, fisheries personnel began stocking smolts — young salmon that will eventually migrate into saltwater — lower in the river than they had been in the past.
In 2007, 147,619 smolts were stocked below the Great Works Dam in Old Town. In 2008, another 147,789 smolts were stocked below that dam. Fins were clipped on those fish so that biologists could identify them upon their return. Cox said another 500,000 smolts are stocked in the Penobscot River drainage every year.
By Wednesday, Cox said 40 of the 255 returning salmon, or 15.7 percent, were smolts originally stocked below Great Works Dam.
“It’s way too early to tell if [the record trap count is due to] increased ocean survival of those smolts that were stocked a couple of years ago,” Dube said.
With low discharge and mild weather come other concerns, the biologists caution.
“We’re kind of concerned, with low discharge and no rain in the forecast for the next week or so — 90 degrees [on Tuesday] — that things could get a little hairy for the salmon and could even shut the run off for awhile,” Dube said.
Dube said that when the water reaches about 77 degrees Fahrenheit fish look for cooler spots in the river and will hold in spring holes or cold-water seeps.
But on Wednesday, after yet another hot day, the Penobscot’s water temperature had risen to about 72 degrees, Cox said. Since last Thursday, the Penobscot has warmed by 14 degrees.
Last year, due to cool, wet weather in June, the river didn’t reach its peak temperature of 73 degrees until late in July or early in August, Cox said.
Cox and Dube both agreed that regular periods of moderate rain would help conditions remain attractive for salmon.
“I was sitting outside yesterday and it was 90 degrees,” Cox said on Tuesday. “I wouldn’t mind a little bit of rain to cool the water temperatures. We’re like farmers. We’re wishing for that one inch of rain a week.”