Going with the flow: Why fish passage matters

Other barriers to fish passage include dams to retain water upstream (e.g. habitat, mills, hydropower, etc.) and tide gates (built to keep salt water from entering freshwater sources while letting freshwater out to sea).

How fishways help fish passage: How fish ladders work in Canada

To circumvent barriers to fish movement, particularly low dams, fishways, or fish ladders, are installed to create optimum water flow. Of the more than 550 water-control structures that Ducks Unlimited Canada (DUC) manages in Atlantic Canada, about 150 are fish ladders.

Read more about our work to conserve and restore fish habitats.

There are two main types of technical fishways that DUC manages—pool and weir, and Denil—as well as nature-like fishways, explains DUC research biologist Nic McLellan.

“Our most common is called the pool and weir, and basically they contain a series of steps and resting pools.” Fish swim through a notch at each step into the next pool, where they can rest before moving through the next one as they travel upstream or downstream.

A Denil is a cement chute with plywood baffles to slow water down. “It actually creates reverse flows; it almost creates an escalator effect…creating back eddies, forcing the water back upstream,” McLellan explains.

Nature-like fishways use rocks and natural materials, rather than cement or plywood, to create steps and pools that mimic a natural stream channel. McLellan says, “Those are likely the best options, but we don’t have the capacity or space sometimes to do a nature-like, depending on the project and the location.”

DUC’s fishway research in Atlantic Canada

McLellan’s team has been studying fishways since 2013, under DUC’s Atlantic Fishway Initiative, and has become a leading expert in this field. So far, McLellan and his team have tagged and tracked more than 17,000 fish going through DUC fishways. While key species such as trout, American eel, Atlantic salmon and smelt all benefit from improved fishways, the team chose to focus on alewife, an anadromous river herring, because they are numerous and return from the ocean each spring to spawn in freshwater. They are highly “motivated” to move upstream, which is also important for assessing passage through fishways, McLellan says.

“We try to evaluate how well our fishways work to pass alewife in both directions, how long it takes them to get upstream (and down),” he says, explaining the fish have a “finite window” to reach their spawning grounds.

After spawning, the tagged fish move back downstream through fishways and depart into the Bay of Fundy. These migratory fish are recorded again when they return downstream after spawning and upon their return the following spring. “So we’re getting information on survival,” McLellan adds. Tagged fish have been recorded returning from the ocean and passing their fishways for up to seven years, meaning these fish are at least 10 or 11 years old.

“This year, we’ve expanded to include acoustic tags,” McLellan says. These tags get picked up by receivers placed in the river systems, the Bay of Fundy and beyond. They will provide new information about the fish’s time on the spawning grounds, where they overwinter at sea, as well as information on their migrations between the two areas.

Do fish ladders work? Real results from Atlantic Canada

The information gathered is used to improve fishway designs and implementation. For example, a pool and weir ladder the team was monitoring in Prince Edward Island for a couple of years wasn’t working well. So they built a nature-like fishway.

“So far it seems like it’s working much better,” McLellan says.

“Larger numbers of these migrating fish mean more nutrients being transported into freshwater habitats through spawning, defecation and fish carcasses (some fish will inevitably die), which is important for these ecosystems.”

Climate change, unsurprisingly, has entered fishway conversations. “New structures certainly have to meet new standards,” McLellan says, as heavy rains make rivers too fast, and long dry spells make them too shallow for fish to travel. “Last year was very dry, the water levels were so low, that we think some of the young of the year overwintered in the wetlands and lake systems rather than moving out into the ocean, because they just didn’t have [enough] water to get out.”

Fishways will need to continuously be adapted and re-designed to pass fish as river conditions change.

Why healthy fish populations support wetlands and waterfowl

Extreme weather, hydroelectricity projects, road construction—they all have the potential to negatively impact fish movement and water systems. Fishways help restore the balance by allowing fish to move more freely through habitats to complete their life cycle, from spawning to feeding, to dying and adding their nutrients to the water. This leads to larger and more abundant fish, and greater nutrition to support healthy wetlands for all the aquatic life—from invertebrates to waterfowl—that rely on them. The entire system benefits from well-built, well-maintained and easily passable fishways.