By Todd Gutner, WBZ-TV

BOSTON (CBS) – They call it “electrofishing,” and it’s helping tell us about the health of the Charles River. It’s part of a state project to re-introduce the fish called the American Shad into the river, but you might be surprised to see how they’re finding out if it’s working.

“We’re supplying current to the water,” says Matt Ayer from the state’s Division of Marine Fisheries. Along with Doug Smithwood and Joe McKeon from the U.S. Fish and Wildlife Service, they’re on a Charles River fishing expedition for science and nature.

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Using a specially equipped boat, they send a mild “zap” into the water. “Electricity just stuns the fish. We’re able to scoop them up. If they’re what we want to sample we take them back to the lab and if we want to release them, we’ll let them go and they swim off,” says Ayer.

WBZ-TV’s Todd Gutner reports

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They’re looking for adult shad, a species that was once plentiful in the Charles, and was an important food for native Americans and European settlers. However, because of pollution and the damming of the river, the shad disappeared. But now they’re stocking the Charles with shad “fry,” pumping them into the river by the millions. When the fish become juveniles they swim out to the ocean to mature.

The shad project has been going on for about five years, and this summer is the first time they can begin to measure the results. That’s because the first batch should be returning to the river as adults to spawn. So the electrofishing boat trolls.

“We’re seeing small numbers of adult shad,” says Ayer. And since they mark the fry before they’re released, “We’ve actually been able to find those marks on some of the adult shad that are most likely five-year-olds from our 2006 stock,” he adds. Not enough to declare victory, but enough to offer a sign of success, and a sign that the river is clean enough that the long gone shad can once again thrive there. “I tend to be an optimist, so I like to hope that we will see shad in great numbers here in the Charles eventually.

Why spend money on this project? Well if the shad take hold they’ll add to the biodiversity of the Charles. They’re also great for sport fishing, and since they’re very sensitive to pollution, they can act as a marker for water quality.

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Visit the website of the Mass. Division of Marine Fisheries