Rock Creek Fish Head Home Again
Saturday, March 31, 2007
Bill Yeaman spotted the first ones Monday: a school of six silver-sided alewives, swimming in place in the greenish current of Rock Creek.
The fish seemed unexcited. The man was electrified.
"It was just -- boy, I don't know -- it's hard to explain the feeling. But, just, jubilation," said Yeaman, a National Park Service ranger. "That all the hard work that all these people were doing had paid off."
Yeaman was at Peirce Mill in Northwest Washington, where since 1904 a dam had blocked the path of fish returning from the Atlantic Ocean to spawn. But over the past three years, environmental engineers found ways around, over or through eight obstacles that prevented fish from passing.
This week, when Yeaman spotted those fish on the other side of the dam -- which can now be circumvented via a fish "ladder" -- it was a signal that one of Washington's oldest spring rituals was on its way back.
"I was witnessing something that hadn't happened for over 100 years," Yeaman said yesterday, standing at the side of the creek. "That's pretty amazing."
For centuries, this region's spring was punctuated by a series of massive migrations of fish -- shad, herring, striped bass -- that crowded the area's rivers and provided a bounty for local fishermen. Even in shallow Rock Creek, biologists say, hundreds of thousands of alewives and blueback herring, a nearly identical cousin, swam upstream in an attempt to return to their birthplaces.
But then, people blocked the way. They built fords, using rocks or concrete to make the creek bottom passable for vehicles. They laid sewer pipes from bank to bank. And they built the Peirce Mill dam, as the tale is told, to provide some scenery for customers at a tearoom in the old mill building.
The waterfall created by the dam is about 12 feet tall -- beyond insurmountable for a foot-long alewife. After a journey from the ocean, through the Chesapeake Bay, up the Potomac River and about 4.5 miles up the creek, the fish would leave their eggs next to the dam.
Upstream, miles of suitable spawning ground were permanently off-limits.
"That was the ultimate obstacle," said Jon Siemien, the head of fisheries research for the D.C. Department of the Environment.
For years, scientists had been looking for a way to remove or circumvent these blockages. Then, finally, help came from an unlikely source: the Woodrow Wilson Bridge Project. That $2.4 billion construction project included some Potomac River dredging, which damaged habitat there. As a kind of environmental community service, the project was required to help improve habitats in Potomac tributaries.
In 2003, bridge project engineers started to remove Rock Creek's fish barriers. To allow the fish to pass over a still-used sewage pipe, for instance, the engineers arranged large rocks in the stream, creating what looks like a natural set of rapids. It's really a carefully planned flow constrictor, designed to make the water pool and rise until it covers the old barrier.
"It's not like we just throw some rocks in a stream and hope for the best," Patrick DiNicola, environmental mitigation manager for the bridge project, said yesterday as he looked at the stream -- babbling precisely as it should have been. "But that's what it looks like."
At Peirce Mill, however, going over wasn't an option. Planners had to go around, building a concrete fish ladder that allows the migratory fish to climb one tier at a time. The ladder is a series of small steps, each with a spot for fish to rest before going on to the next.
This was the last piece of the $2 million-plus restoration. About 28 new miles of the stream are now open, extending all the way to Lake Needwood near Rockville.
D.C. scientists had been preparing for this moment for several years, capturing alewives and blueback herring below Peirce Mill, and bringing them upstream in a truck. The hope was that their offspring would seek to return to the same spot.
For now, it seems that not all the fish have gotten the message. Yesterday, D.C. biologists were using an electroshocking machine to capture fish below the dam and found that many had already spawned, without exploring further upstream. The alewives' spawning ritual usually involves a female scattering her eggs on the creek bottom, while a gaggle of males follow behind trying to fertilize them.
"They're all spawned out," said fisheries biologist Luke Lyon, holding a foot-long female. She was now as skinny as the males, Lyon said. If she were still carrying eggs, "she'd have a big fat belly."
But scientists said perhaps 100 alewives have actually made the journey up the fish ladder so far. Scientists say they expect a few hundred more, plus blueback herring, when their run begins in early May. They expect that the populations of the two fish will grow in the coming years, because they now have more good habitat in which to spawn. They might also provide targets for area fishermen -- although in the District, fishing for these species is prohibited between Porter Street NW and the Maryland line.
After this year's spawn, the scientists said, many of the adult alewives will head downstream again, returning to the ocean. After a few days, their eggs will hatch into larvae that, if they're not eaten along the way, will grow up, leave and someday return.
"They'll become imprinted to the area," Siemien said. "And then, in another two to four years, these spawn will come back here and make the same trip."
Staff writer John Kelly and staff researcher Meg Smith contributed to this report.