East Lyme - Amid spring's flourish of new life, there's probably nothing in the state matching the primeval surge of small, sleek, silver-bellied fish out of the Atlantic Ocean into Long Island Sound and then into Bride Brook.

For David Ellis, the transformation of this small and otherwise unremarkable coastal stream into a herring highway to their ancestral spawning grounds at Bride Lake is his favorite seasonal cue.

"I don't think it's spring until the alewife come in," Ellis, research technician with the state Department of Environmental Protection, said Wednesday, after a morning of handling dozens of the lively little fish as part of ongoing research.

No one knows for sure, but the Bride Brook run is believed to be second only to the Connecticut River run in the numbers of alewife that use it, and their progeny have been transplanted by DEP staff to some 30 other streams and ponds around the state in a decade-long effort to bring back the once-mighty populations of river herring.

By the time the spring run ends in early June, some 65,000 to 120,000 alewife - one of two species of river herring, but the only one in Bride Brook - will have tripped the DEP's electronic fish counter at the site.

Early arrivals showed up on March 12, Ellis said, followed by successive waves by the hundreds each night that peaked last week and this week. On Wednesday morning, the fish counter showed 2,414 herring swam into the lake the previous night.

After spawning, adults will stay a week or two in the lake before heading back to the sea. Some of their offspring will stay in the fresh water to fatten on insects until the end of June, while others will wait until October to head for salt water.

"This year the herring run started one to two weeks early, and once it started, they really poured in quickly," Ellis said as two seasonal employees working with him set up buckets and nets and pulled on waders to prepare for the morning's work beside the rushing stream. "The floods (last month) sent a huge pulse of fresh water into the Sound, and it cued them to start coming."

Impressive as it is, the Bride Brook run isn't what it once was. Records from a scientist who collected data in the 1960s show 180,000 alewife would reach the lake each spring, Ellis said, and experts believe it was even higher for hundreds of years before that.

Declines more extreme than this have been seen throughout the coastal Atlantic states, where river herring runs once numbered fish in the millions, a worrisome trend Ellis and other wildlife officials throughout the East are hoping to reverse.

Completion of one herring restoration project will be celebrated Monday with a 2 p.m. ceremony at Rocky Neck State Park, where Bride Brook empties into the Sound.

Save the Sound/Connecticut Fund for the Environment, a nonprofit group, led a $510,000 project in partnership with the DEP and federal agencies to replace an unsafe, undersized culvert at the brook's mouth, making it easier for the thousands of alewife that use it each year to pass through. It will also improve water flows in a marsh the fish pass through on their way to the lake.

“Within the food web, herring are extremely important for the vitality of our fisheries, and for bird populations," said Christopher Cryder, habitat restoration director for Save the Sound. "There were other reasons (for restoring the culvert), but herring were probably the most important reason."

While rarer, top-of-the-food chain species like whales and wolves may capture much the public's attention when it comes to wildlife conservation efforts, river herring are the species at the bottom that, when abundant, make healthy ecosystems possible.

They are staples in the diets of many animals, including osprey, cormorants, otters and larger marine and freshwater fish. Herring also carry with them nutrients from salt water environments that improve the health of the fresh water lakes where they spawn.

"They're a keystone species for marine and freshwater systems, and for terrestrial species," Ellis said.

In 2002, the state banned all fishing of river herring and has renewed the ban every year since. Four other states have done the same. Before the ban, fishermen netted the fish mainly for lobster and fish bait.

In one dramatic example of their declining numbers, a fish counter on one Connecticut River dam recorded 630,000 river herring passing over in 1985. In 2009, just 39 fish were counted. But that, at least, was an increase over 2006, when the number was 21.

Some combination of factors is probably responsible for the decline, Ellis said. Possible explanations include increases in the populations of striped bass (herring make up a large part of their diet) and the proliferation of dams that block herring from getting to lakes and ponds to spawn (installation of fish ladders have helped).

Unmonitored offshore fishing of herring may also be a factor, as well as lakefront development that has compromised water quality where the herring spawn.

Bride Lake has been able to maintain its strong run, Ellis and Cryder noted, because there is no large dam blocking access to the lake, and about three-quarters of the lakefront is forest. State-prison buildings front the remaining portion. The town has a couple of groundwater wells near the lake, but is not drawing an amount that would make it less hospitable for the fish, Ellis said.

"The town is under heavy scrutiny to only draw a certain amount of water," he said.

The purpose of the field work on the herring, Ellis said, is to track any changes in the population as it responds to the various stresses and determine whether the fishery can reopen. The information is collected from six other sites with fish counters in addition to Bride Brook. Thus far, he added, the data don't support the reopening.

After setting up their equipment on the lakeside, Ellis and his two-man crew begin their work. One of the seasonal employees, Brandon Ritchie, wades through thigh-high water to corral some of the fish caught the night before into a net, then from the net to a pen. Then, scoop net by scoop net, a few herring at a time are transferred to a bucket on shore.

Ellis, holding gently but firmly, measures each fish, notes its sex and scrapes a few pearly scales from one side. These are passed on the knife blade to Andrews, the other seasonal employee, who puts them into a small envelope and marks them.

In all, Ellis and his crew collected data and scales on 100 Bride Brook fish Wednesday morning. Over the course of the run, this process is repeated four times, and the data shared with researchers and universities. During the winter, he and other DEP staff examine each set of scales under the microscope to determine the age of each sample, much like tree rings can be used to age a tree, and how many times each fish has spawned.

One key finding thus far, he said, is that herring are reaching sexual maturity at one or two years of age, instead of at three or four as had historically been the case. This indicates the way herring are adapting to the various stresses threatening them, by reproducing at a younger age.

"We're doing this because it tells you something about the population itself," Ellis said.

j.benson@theday.com