In the Field: Peconic ramp to give alewives a lift

takes Jennifer Smith In the Field logo.For a month or so this winter, Grangebel Park in Riverhead looked like Moses had stopped by to part the waters of the Peconic.

Usually the river here tumbles down over two waterfalls at an earthen dam just west of Peconic Avenue. But on a recent cold morning the southern passage over the dam lay open, drained dry and transformed for the benefit of alewives.

What was once a sheer 5-foot drop has been refashioned into a gently sloping artificial riverbed, 190 feet long and strewn with boulders and rocks. Fisheries managers call this a rock ramp - an engineered rapids designed to help these river herring scale low dams that would otherwise be insurmountable.

For centuries, alewives have swum from distant offshore feeding grounds into Peconic Bay and upstream to spawn. But starting in Colonial times they were thwarted by a series of dams on the river, including the one in Grangebel Park, which divides the freshwater and tidal sections of the river. Scientists believe such barriers have led to serious population declines across the Northeast.

"Alewives can only get up about six inches," said Laura Stephenson, the Peconic Estuary coordinator for the state Department of Environmental Conservation.

She pointed west, up the rock channel to a berm that held the water back during construction. "This is really just about a 7-degree angle heading upstream," Stephenson said. "When the downstream flow is coming down, these rocks will create eddies and resting pools for the fish."

The first of its kind on Long Island, the structure is a natural-looking alternative to metal fish ladders installed on steeper dams at Massapequa Lake and on the Carmans River at Southaven County Park. The rock ramp replaces a temporary metal ladder that for the past 10 years was placed on the southern spillway each spring.

The Grangebel Park ramp is the latest step in a 15-year-effort to reopen the upper Peconic to alewives. Stephenson said the structure will permanently restore access to 24 acres and 1.5 miles of historic habitat. American eels will also be able to use it to swim upstream.

The ramp was completed in time for this year's alewife migration, which biologists expect to begin later this month or in April. The $1-million project was paid for by federal and state wildlife agencies, conservation groups, Suffolk County and the Town of Riverhead.

Biologists and conservation advocates say helping these bony river herring will improve the overall ecology of the river.

The silvery, foot-long alewife is a critical food source for ospreys and heron, and for bigger fish such as striped bass and pickerel. "Just about everything eats alewives," said Charles Guthrie, regional fisheries manager for the DEC. More alewives means more food "for the predators, which are the game fish everybody wants to catch and eat."

The alewife migration is harder than it used to be. Since Colonial times, rivers across the Northeast have been dammed to power mills, create cranberry bogs and mark property lines. Scientists think loss of spawning habitat is one reason the coastal commercial alewife catch has plummeted. Landings are down from 8.9 million pounds in 1986 to 1.3 million in 2008, according to the National Marine Fisheries Service.

The restoration work at Grangebel Park started in 1995, when the DEC got a small federal grant to move the fish over the dam by hand. "We scooped them up, put them in a bucket of water and dumped them over the other side," said Byron Young, a former DEC official.

A group of devoted local volunteers soon joined in, led by the late Riverhead science teacher Robert Conklin. Money was raised for the temporary fish ladder in 2000, and plans for the permanent rock ramp began to take shape.

Next, the DEC plans to build more fish passages at three dams upstream that Stephenson said would open up another 182 acres of watery habitat.

"Restoration of alewives is really important coastwide," Guthrie said. "It's a lot of little projects adding up to a big project."