UMass research casts doubt on fish ladders
The fish ladder below the Turners Falls Dam brings fish from below the dam to the impound above the dam when it is operational.
Thousands of fish ladders have been constructed in the U.S. since the 1700s — many using tax dollars — but few people have assessed whether the passages built to help fish travel over dams actually work.
It turns out that New England fish ladders are, for the most part, failing to get fish up and over dams to their spawning grounds, sometimes letting no fish pass at all, according to new research out of the University of Massachusetts Amherst. This inefficiency is contributing to the dwindling stock of some of the area’s most economically important species — Atlantic salmon, shad and river herring — according to the study, which was recently published in the journal of the Society of Conservation Biology, Conservation Letters.
The study, by a UMass assistant professor of environmental conservation and six other researchers as far away as Abu Dhabi, adds to a handful of other investigations conducted on fishway effectiveness, a tiny field of research that cites the inability of the man-made passages to get the job done.
Supporters of the research say the paper shows the importance of studying the effectiveness of fishways in a system of dams, instead of one by one, to better understand and improve their effectiveness. When studied from this vantage point, fishways appear to be ineffective. They call for more fishway research to increase the passageways’ efficiency.
Although a few researchers sound the alarm on fishways, the ladders continue to be constructed. A $1 million ladder is planned this spring to aid fish over a dam on the Manhan River in Easthampton, for example.
“We’ve treated fishways like a panacea — put it in and you’ll achieve results,” said Adrian Jordaan, one of the researchers on the paper and a UMass assistant professor of fish population, ecology and conservation. “I’d say the results are mixed, but with most species they don’t work well.”
Researchers surveyed 20 dams, some large, some small, most with fishways on the Connecticut, Merrimack and Susquehanna rivers. They found migration over these dams is falling far short of stated goals.
For example, the number of American shad that pass over the dams is hovering around 2 percent of the target on the Merrimack River and close to 0 percent of the target on the Connecticut and Susquehanna rivers. Sturgeon aren’t getting through passages on the three rivers at all. These salt-water fish want to get upstream to spawn.
There are about eight main-stem fishways on dams in Massachusetts, including ones on the Connecticut River in Holyoke and Turners Falls, but the number of passages established on the thousands of small tributary dams in the state is unclear because maintenance on some of the structures has fallen by the wayside.
Systemwide, in this study, fewer than 3 percent of anadromous fish — those that are born in fresh water, spend most of their lives in salt water and return to fresh water to spawn — make it upriver from the dam farthest downstream past the uppermost main-stem dam.
The study has its critics who accuse researchers of cherry picking data, Jordaan says. He’s heard from people who maintain the assertion that shad aren’t making it over the dams in good numbers is misleading. They point to 2012 as being a good year for shad passage, saying that on the Connecticut River 500,000 shad made it over dams, although the target number was 1 million.
Turners Falls lacking
Jordaan said while this is true, looking at one year doesn’t tell the whole story and the team he was on looked at decades worth of data.
Ted Castro-Santos, a researcher at the Silvio O. Conte Anadromous Fish Lab in Montague City, said there has been little data on how well individual fish passages actually work around the world. Still he said, “Absolutely, low-passage performance is a problem, absolutely, it’s widespread. But there are several examples of very successful fishways out there.”
One of those is at Vernon, Vt.
“We build them and then we don’t evaluate them,” said Castro-Santos. “Of the tens of thousands of fishways that have been built, only a tiny proportion have been evaluated.”
He admitted that the Turners Falls Fish Ladder has serious flaws, with less than 10 percent of the shad that enter the system at Cabot Station actually passing the dam. By studying and modifying the passageway out of the power canal, scientists have been able to increase passage 12-fold since 2008.
“At Turners Falls, they have to pass two dams and a power canal — three barriers — so it’s a problem,” Castro-Santos said. Only 25,000 shad passed at Turners Falls last year, out of half a million that got beyond the lift at Holyoke. The Cabot ladder is a particular problem, he said.
Other critics, such as Frank Heller head of Katahdin Energy Works, a Maine alternative energy firm, say the study doesn’t take into account the most recent dam research or the importance of dams in saving water for droughts, preserving wetlands and filtering pollution from downstream waters.
“Designing better fishways has come a long way, and I tend to look at how they do it (in) Europe and (at) the newer naturalistic paths,” says Heller, citing the effectiveness of Dutch fish siphon fishways and tailoring passages to particular species. “It is possible to have a dam and an effective fish pathway; and it is possible to bring back some species like shad.”
But the state’s Fish and Wildlife Service acknowledges fishways aren’t living up to their promise. According to Curtis Orvis, a fish ladder engineer with the state fish and wildlife department’s Springfield office, in general, fishways are about 28 percent effective.
Orvis said the best way to improve fish ladders is for the scientific community to focus on conducting more data-driven research.
“All our research, or a large part of it, to date has just been too empirical, just by the seat of the pants, try this, try that,” Orvis said. “We’re only at the tip of the iceberg as to how much research we need.
“The problem is, we have a zero budget for this,” Orvis added. “They’ve been trying to get money, but there is no money set aside for fish passage research.”
What’s wrong with fishways
There are several types of fishways: pool and weir, rock-ramp, baffle, elevator and vertical slot. Once installed, one fishway has to work for a variety of fish, which hurts their effectiveness. What works for a sturgeon may not work for an eel or a herring.
Jordaan said it’s not clear why fishways aren’t better at moving fish over dams, hence the need for more research. It could be fishways are being poorly designed. Predators may be staking out entrance points where fish gather to go up and over dams. Or fish may not be interested in entering concrete passageways, a foreign-looking path to many aquatic animals.
The sheer number of dams and fishways, however, is playing a role in the decline of migratory fish populations, Jordaan said. The removal of smaller dams on tributary streams like the Green River could significantly help some fish populations rebound. Jordaan said his research suggests that with each dam a fish has to pass, the number of fish that get through decreases until the diminished group makes it to the main-stem dam and few get across.
“It shows that after you pass the first, you’re already down to a really low percentage,” Jordaan said.
Other federal agencies have noted the unhealthy effects of dams on fish populations. A U.S. Food and Drug Administration report on the genetic engineering of Atlantic salmon notes, for example, the salmon are extinct in 84 percent of the rivers in New England that historically supported them. They’re in “critical” condition in the remaining 16 percent of rivers. This decrease is most likely due to dam building, but overfishing, pollution and climate change played a role, too, the FDA states in “An overview of Atlantic salmon, its natural history, aquaculture, and genetic engineering.”
Preliminary results of a U.S. Fish and Wildlife study of the fishway at Cabot Station raise concerns about the ability of shad and other species to navigate the cumbersome passages at Turners Falls, Connecticut River Coordinator Kenneth Sprankle told a Federal Energy Regulatory Commission meeting last week.
After swimming 150 miles upstream to the Holyoke fish lift and then navigating their way another 35 miles farther to Turners Falls, they have to choose climbing the 66-step Cabot Station ladder at Montague City to enter the power canal or the relatively calm, dry main river channel for two miles to climb the 42-step spillway ladder to reach the base of the dam. Either way, they then have to climb another seven pools of the gatehouse ladder to continue their upstream migration.
“They first proceed, fairly rapidly, from one barrier to the next,” Sprankle said. “And once they reach a dam ... there are delays associated with that. Particularly with shad, the concern is that they have a limited amount of energy and they won’t have enough energy to get back out to the ocean.”
Counts at the Holyoke Gas & Electric Barrett Fishway show a similarly dramatic decrease in fish populations. In 1985, for example, 632,255 blue back herring passed through the fishway, but in 2010 only 76 made a successful trip over the dam. For Atlantic salmon the number of fish making it over the dam has decreased to 41 from a high of 368 in 1992.
But Paul Ducheney, hydroelectric superintendent at Holyoke Gas & Electric, said the lift-style fishway, which was built in 1955, is not a factor in the declining population.
Although the number of certain species of fish passing the Holyoke Dam has declined over the years, it is important to note that the timeline of population abundance demonstrates that “the Holyoke Dam and the associated fish passage facilities (first put into operation in 1955) are not a causative factor, as counts increased in years between 1976 up to a peak in 1985,” Ducheney said in a statement. “Additionally, certain subject matter experts point to other factors, beyond the river, that are more likely the cause of declines in counts at the Holyoke Dam, including the fact that currently the largest proportion of fishing mortality of river herring appears to occur as bycatch in coastal fisheries.”
Not all fishways are failing. On the West Coast, massive fishways over hydropower dams have had good records of fish passage. And in New England, rock-ramp or natural-looking fishways are among the most successful fish passages, according to a 2008 study by the National Marine Fisheries Service Office of Habitat Conservation, which in the first paragraph of the report, notes that researchers had little data with which to work. They were only able to find two studies of nature-like fishways in the Northeast — one in Plymouth and another in Guilford, Conn. The studies focused on alewife. Passage was modest, at about 41 percent in Guilford, to good at 94 percent in Plymouth.
“Fish are believed to find natural substrates more acceptable than concrete channels or channels with baffles in structural fishways,” the study, “Design and Evaluation of Nature-Like Fishways for Passage of Northeastern Diadromous Fishes,” concluded.
Jordaan also noted that tiny coastal ponds with fishways designed to provide access to alewives and some blue back herrings have been relatively successful.
“If you’re looking at one species, in one situation, you can find some pretty good evidence for success,” he said.
Like a growing number of conservationists, Jordaan and Orvis, the fish ladder engineer out of Springfield, said the best fishway is no fishway — that is to say, complete dam removal.
“That’s the ultimate fish passage,” Orvis said. “Always, our first preference is to take the dam out, but that’s just not going to happen in some places where they’ve been there a long time and are part of the infrastructure, where the dam may be critical to our power grid.”
Because many dams can’t be removed, Jordaan said, it is important to design more effective fish passages and to have a national conversation about balancing conservation with energy needs. The community needs to take a systemwide approach to improving fish passage instead of studying each dam on its own.
“What kind of future do we want?” Jordaan said. “What infrastructure do we want? What kind of restoration do we want? These are the big questions that are not part of the public discourse. ... Fishways have always been seen as a solution, but we never took a hard look at them. But that’s a hard way to look at something we’ve put so much time and effort into.”