WILTON — Wilton may be getting some unusual springtime visitors this year. At least that’s what Jon Vander Weff is hoping.

Weff is a fish biologist with Save the Sound and he’s got a fish trap in the Norwalk River where he’s hoping to humanely catch an alewife or two.

“The alewife is incredibly important. It’s a keystone species that keeps the ecosystem intact,” Vander Weff said.

The alewife is considered a river herring, he explained, similar to the American shad. It is an anadromous fish, meaning it lives in salt water and migrates into fresh water to spawn, just as salmon do. As an adult it lives in the northwestern Atlantic Ocean.

“This time of year, the fish move from the Sound to lakes and ponds for spawning,” Vander Weff said. His trap is in the river at Merwin Meadows, just below the Dana Dam. If he can prove the fish is here, it would strengthen the argument for removing the dam.

“The Norwalk River had 20 dams at one time,” said Jeff Yates, explaining they were built during the Industrial Revolution. Yates is with Trout Unlimited, which supports the project and the dam removal.

In the flood of 1955 many failed and were not rebuilt. Eventually the river had just four dams, none of which had any economic or industrial value. “But they are expensive to remove so they have just been sitting there for 100 years,” he said.

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The Flock Process Dam in Norwalk — the southernmost on the river — was removed in 2018. Next on the way north is the Dana Dam. After that is the Cannondale Dam, which was partially breached in 2018 after it started to fail. The northernmost dam is the Factory Pond Dam at the Gilbert & Bennet site in Redding.

“We are looking for sea-run fish passage,” Yates said. “We know the fish will return after the dams are removed.” Alewives have been spotted in the river north of where the Flock dam was.

The health of the oceans is connected to what happens in waterways further inland.

The alewife, which grows to about 10 inches, Vander Weff explained, is a food source for tuna, striped bass and bluefish, “all the sport fish people like to catch, as well as commercial fishing.” It is also eaten by wildlife around the river, such as raccoons, river otters, mink and great blue herons.

“It’s incredibly important to give evidence showing a direct correlation of the stressed bass decline to the stressed alewife decline. They are very important fish,” he said.

The alewife population has declined drastically since the development and industrialization of the watershed, Vander Weff said.

“More dams, culverts and road crossings have hurt spawning as well as over-harvesting,” he said. “Pollution has degraded the water quality and that limits the amount the fish can grow.” So, too, do algae blooms which create nutrients that take oxygen out of the water.

Wilton is not the only location where Vander Weff has a trap. He’s got one in the West River in New Haven, Fenger Brook in New London, Haley’s Brook in Groton and two in Whitford Brook in Stonington and Ledyard.

While nothing has shown up in the Wilton trap as of yet, Vander Weff has found alewife, American shad, yellow perch, largemouth bass, and two types of sunfish — pumpkinseed and bluegills — at the other sites. In past years he has also caught sea lamprey, another anadromous species.

The traps are checked daily by Vander Weff and a team of volunteers — Dean Keister and Lawry Frank of Wilton and Milton Buchta and Ken Werner of Norwalk. The trap is non-lethal and any fish caught are released upstream. There is a moratorium on taking alewives, so Vander Weff assured he is not keeping any. He has a state permit for the traps.

Dam removal

Trout Unlimited has raised $400,000 for egineering and permitting for the removal of the Dana Dam, but the actual work will cost about $1.5 million.

The Factory Pond Dam in Redding is an even bigger project, Yates said, because of sediment behind it contaminated with pollutants such as lead, arsenic and mercury.

“Any dam is going to fail at some time in the future,” Yates said. “At some point that dam will break and send contaminated sediment downstream.”

From an ecological standpoint, the dams are a barrier to fish swimming upstream and they change the water temperature, which is harmful to cold water species.

Before the dams were built, fish like alewives would make their way along the river to natural ponds and those created by beaver dams. There are still beaver and beaver dams in the river from Georgetown to Route 35 in Ridgefield, but there are two dams remaining between them and the fish that would spawn there.