East Lyme - Typically, any travelers who back up near the stretch of Interstate 95 at Exit 74 are human, but this month the traffic jams involve fins, scales and an all-consuming instinct to mate and spawn.

In a culvert beneath that stretch of the busy highway flows Latimer Brook, which every spring attracts alewife migrating from Long Island Sound into the Niantic River, then into the brook.

Just beyond the culvert is a fish ladder, maintained by the state Department of Energy and Environmental Protection, that enables these river herring to swim around a dam to reach mating and spawning areas upstream. Dave Ellis, the fisheries technician who oversees crews that check the ladder daily in the spring and count the fish that pass through, said this year's alewife run at Latimer Brook has been something special.

"A couple of days last week they were stacked up from here down through the culvert to the pool just below it, waiting to get up the ladder," Ellis said, standing at the foot of the Alaskan steep pass ladder on Tuesday morning as assistants Kirk McPherson and Matt Shirley counted the lively little fish that had reached the trap at the top overnight. Once counted, the fish, measuring 14 to 16 inches with gray-green sides and silver bellies, were released to continue their journey.

"Some mornings we were here for a few hours, counting them by hand," Ellis said.

Due to warmer-than-normal water temperatures after the mild winter, this year's alewife run at Latimer Brook and other coastal streams began about three weeks earlier than normal, Ellis said. While the runs have been strong at several other streams, at Latimer the run already has surpassed previous totals for the entire six weeks that it normally lasts.

"Here we average about 2,500 fish for the whole season," Ellis said. "But this year we've already had 3,607. We've never seen this brook so full of fish."

Alewife, which along with blueback herring are collectively known as river herring, are important food for many land and aquatic animals, including striped bass, sea birds, otters and other mammals. But over-fishing in offshore waters, mainly for bait, along with dams on coastal streams that block access to ancestral spawning pools, have caused sharp decreases in alewife numbers and increases in calls by conservation groups for fisheries regulators to take strong action.

In some of the sampling he's done while the fish are being counted, Ellis has noted that nearly all the alewife that have come through the ladder thus far are males, perhaps headed to a giant bachelor party upstream before the females arrive to find mates and spawn.

"The males typically start the run, then before long it'll be more of a 50-50 mix of males and females," Ellis said.

Along the coast and inland, DEEP maintains about 10 other fish ladders where alewife are counted either by hand or machine as they migrate from marine to fresh waters.

One of the biggest runs statewide is at Bride Brook, also in East Lyme. There, about 40,000 alewife have tripped the fish counter thus far, Ellis said, compared to about 20,000 by this time in an average year. But because the total for the six-week run at Bride Brook usually ranges from 80,000 to 150,000 fish - last year's total was closer to 200,000 - it's too soon to say whether this will be a record year at Bride Brook, too.

The high numbers of fish using Latimer Brook is of special interest to members of the Niantic River Watershed Committee and to Judy Rondeau, the committee coordinator. As part of working to improve water quality in the river, the committee has decided to focus on Latimer Brook as a key source of runoff and other pollutants fouling the river. This spring, committee volunteers will begin a water quality monitoring project, collecting samples at seven sites on the brook throughout the coming year.

The fact that the brook is being so heavily trafficked by alewife gives the volunteers additional motivation for the project as a way not only to help the river, but also to make the brook better for an important but stressed species.

"We're trying to identify the problem areas we need to work on, and by improving those areas we'll be improving the water quality and improving the habitat," Rondeau said.

No commercial or recreational fishing of river herring has been allowed for several years in Connecticut and some other East Coast states, and many projects to restore populations by removing dams and building fish ladders have been undertaken.

Ellis said it's too soon to say whether the record numbers at Latimer Brook this year are a sign that restoration efforts are working. He said he can only speculate about the reasons for the phenomenon or whether this year's early season and high numbers will have any long-range benefits. Regardless, it's promising news.

"The benefit to them coming in early could be in predator avoidance, since the striped bass haven't moved in yet. The high numbers could be the result of several years of high success in spawning," he said. "But we're excited about it, obviously."

j.benson@theday.com