Wearing waders, rubber gloves and boots, state researchers slogged into Carmans River and used electrical shocks to catch and tag fish so they could track marine life.

The Department of Environmental Conservation's effort to count, measure and weigh marine life in the river last month led to the activity along the waterway.

Some DEC workers carried nets, others clutched buckets, while a few used the shocker devices.

The electrical shockers, which look like metal detectors with a rounded disc at the end resembling a strainer, charge water within a 5- to 6-foot area with 400 volts of electricity, stunning trout and eel and making them easier to catch.

Electro fishing uses low-doses of electricity so fish can be collected and processed. While a few dozen fish did not survive, the DEC said the shocks are less invasive and harmful than using nets to sweep an area.

"Once they're in the field, they're completely stunned," said Chart Guthrie, regional fisheries manager for the DEC. "They can't move."

On this warm April day, DEC specialists, researchers and students were going to walk an 800-foot stretch of the river three times, each time shocking fish, removing them and measuring them to help determine population levels.

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The state stocks trout in the area and usually tags about 10 percent of those.

But the program is expanding to acoustically tag eel and brook trout to see how they move about the river, Guthrie said.

Seven sites along the river in Brookhaven from the Wertheim National Wildlife Refuge to the Long Island Expressway are equipped with antennas. Each time a tagged fish passes, the time and place is noted.

"We're interested in fish passage," said Kellie McCartin, a graduate student at Stony Brook University who was working with the DEC to collect the fish and eels.

As the DEC team started its day, members focused on the grassy shoreline and rocky areas that are home to eels. Those caught were to be taken down river, past a stepped fish ladder that allows fish to move upstream.

It's known that baby eels can climb the gate but it's not so clear when it comes to adult eels. And they tend to be territorial, choosing to return to the same place, Guthrie said.

"Eels will come back to their rock," said Kathleen Marean, a seasonal technician at DEC. Tagging them means "we'll know if they come back," she said.

As the DEC team moved downstream, the water deepened. A trout hot spot was found, with electricity stunning up to 10 at a time. They were collected and brought upstream to be tested and then deposited outside their 800-foot work area.

How fish move about the river, if they leave the tagging area or are caught, will be part of the study, as will how they react to the fish ladder.

"We can see how many times the fish tried to get up [the ladder] and if they actually made it up," McCartin said.

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In all, teams spent three days combing 2,000 feet of the river in April, counting their catch. A similar population count is planned for August to compare fish stocks along the river, Guthrie said.

"The idea," Guthrie said, "is to learn more about the fish that aren't there anymore."