North Stonington - With a slow, careful plod, Kasey Pregler and Matt Traceski dragged a seine net through the swampy, waist-high waters of Shunock Brook and Lower Hewitt Pond Wednesday, employing this ancient tool in pursuit of modern scientific understanding of a small but significant fish.

"Prey species are important, too," said Pregler, a graduate student in ecology and evolutionary biology at the University of Connecticut. "It's important to manage these prey species, or else you won't have the larger fish you want to fish for."

Bridle shiners, pinky-sized, pearly green minnows, inhabit muddy underwater jungles where lily pads, cattails and sedge grasses grow, largely overlooked by most people but considered worthy of attention by fisheries biologists concerned about their well-being. Though they were once common throughout Connecticut, the state now lists them as a "species of special concern," and other states designate the shiners as "endangered," "threatened" or "regionally rare."

Over the last few years, though, experts including Jason Vokoun, associate professor in the UConn Department of Natural Resources, and Neal Hagstrom, senior fisheries biologist with the state Department of Energy and Environmental Protection, have been questioning whether the shiners' status as a declining species is merely an artifact of what turned out to be an inappropriate use of high-tech gear. That's where Pregler, Traceski and the seine net, equipment used in Biblical times, by native Americans and in cultures worldwide for aeons, come in.

"Science is always fixing itself," said Hagstrom, who is overseeing Pregler and Traceski's work as DEEP seasonal research assistants on the seining project, as he stood on the banks of the brook. "That's the self-correcting nature of science."

From the 1930s through the 1950s, he explained, field researchers seined shiners in 58 streams, ponds and lakes statewide. In the 1980s, scientists returned to these sites to reassess the species, this time using electrofishing gear instead of the slower, simpler seining process. The device, which involves sending an electrical charge into the water that temporarily stuns fish so they can be easily scooped up, measured and counted, worked well on larger species. When Hagstrom in the 1980s used to track bridle shiners, he found them in only eight of the 58 original sites, and other researchers had similar findings.

Then in 2011, Timothy Jensen, then a UConn Natural Resources graduate student, began working with Vokoun and the DEEP on a study of the Shunock River, where Hagstrom had recently found bridle shiners while looking for another species, banded sunfish. Jensen described the habitats being used by the shiners in the Shunock, a waterway protected by Avalonia Land Conservancy and town-owned open space properties. Toward the end of the study, Vokoun explained in an email message, he and Jensen became concerned that electrofishing had exaggerated the shiners' decline, because when Jensen seined the brook, he captured many more of the minnows. The finding led them and Hagstrom to question if the same would be true of other waterways.

"How can we conserve biodiversity if we don't even know where the species are and are not?" Vokoun asked.

After Jensen's study, Vokoun began working with Pregler to compare results from electrofishing to seining in the Shunock and Natchaug rivers. Seining, it turned out, "worked almost twice as good at detecting these tiny minnows," Vokoun said.

In the muddy, highly tannic habitats where shiners live, Hagstrom explained, the electrical charges from the electrofishing gear don't work well. In addition, because the gear is expensive and cumbersome, often carried in backpacks into the sites, researchers were either unable or unwilling to take it into some of the swampy, difficult-to-access areas where shiners thrive. But with seine nets, buckets and waders, researchers are more likely to venture there.

Now this summer, Pregler and Traceski, an Enfield resident studying wildlife ecology at the University of Maine, are paying multiple visits to seine all 58 lakes, ponds and streams where shiners where once found, plus another 50 or so waterways where sampling had not been done previously. The project is being funded by a $16,000 grant from voluntary contributions from state residents through the income tax wildlife checkoff program.

"We've been all over the state, probably to 80 or 100 sites so far this summer," said Pregler, a Meriden resident. Thus far, she added, they're finding shiners in at least half of the 58 sites where they were found historically, as well as in many of the new sites. Overall, she added, there is still evidence of some decline of the species, and that lakes and ponds are harboring more of the little fish than streams. While much of the research in her field involves studying species declines and other environmental problems, this project gives Pregler and her colleagues a refreshing opportunity to demonstrate at least one instance where environmental conditions might not be as bad as once thought.

"We're hoping this is just a detection issue," she said. "You can miss these fish really easily."

In southeastern Connecticut, the pair have seined Wyassup Lake and Whitford Pond in North Stonington, Long Pond in Ledyard, Rogers Lake in Old Lyme and Pattagansett Lake in East Lyme, among other locations. On Wednesday, after a few hours at Shunock Brook, they would wade into the waters of Anguilla Brook in Stonington and Great Brook in Groton.

A single seine haul, she explained, is measured in increments of about 35 to 40 meters - roughly 40 yards. After each drag, the two painstakingly sort through the back pocket of the net where the fish collect to pick out pond weeds, sticks and dead leaves. The minnows are then placed in a bucket to be individually counted and measured before being returned to the brook.

"We've got a bridle at 42 millimeters," said Pregler, gently holding the small, squirmy creature between her thumb and forefinger against the measuring stick, as Traceski jotted the numbers in a notebook. "Here's another bridle at 27 millimeters."

In addition to the counting and measuring, the team is also collecting small tissue samples from the shiners for genetic analysis that will be done by Michael Hessenauer, a UConn Natural Resources doctoral candidate. Comparing the genetics of populations from different locations, Vokoun said, can provide valuable insight into whether dams and culverts have caused populations to lose a healthy level of diversity. It will also help identify the healthiest populations that would be the best candidates to repopulate waterways where they've disappeared. With the combination of the genetic information and the seining data, restoration efforts can better focused and, ultimately, more effective.

The Shunock, Hagstrom explained, as the "control site" for the study, is being sampled multiple times at multiple locations and times of day along its meandering path to get the best overall picture of species abundance there.

"We can gauge everything else against this site," he said.

On Wednesday, the final seine haul of the morning, at the place where the Shunock opens into lower Hewitt Pond, netted the jackpot - 45 bridle shiners compared to single numbers in the previous hauls.

"That was a really good one," said Pregler. "There was one bridle that was 60 millimeters."

j.benson@theday.com