Maryland’s Conowingo Dam. (Linda Davidson/The Washington Post)

Wildlife advocates say the numbers of American shad journeying from the Atlantic Ocean to spawning grounds in the Susquehanna River each year could climb to 2 million over the next 50 years as a result of a deal struck this week with the owner of Conowingo Dam.

In an agreement with the U.S. Fish and Wildlife Service, ­Chicago-based Exelon Corp. agreed to do more to help shad and river herring migrate over the dam straddling the river between Harford and Cecil counties in Maryland. The company will increase the capacity of a fish lift that carries them 100 feet from the dam’s bottom to its top and also will trap fish and drive them upstream by truck.

The agreement is part of Exelon’s efforts to renew its federal license governing dam operations for the next 50 years and comes after years of discussion about how to help the fish migration.

Fish and Wildlife Service officials called the plan a once-in-a-generation chance to help more migratory fish bypass the Conowingo and a series of other dams.

“We’re anticipating the fish populations will grow over time, and the needs for fish passage will grow,” said Sheila Eyler, a project leader with the service’s Mid-
Atlantic Fish and Wildlife Conservation Office. But apart from the federal licensing process, “we don’t have a mechanism to come to a dam owner and ask them to do something.”

The numbers of shad, herring and other fish that successfully bypass the Conowingo and other dams along a 60-mile stretch of the river are at their lowest since the 1980s.

Hundreds of thousands of shad and herring passed the Conowingo as recently as 2000, but those numbers have dwindled to less than 15,000 shad the past two years and less than 1,000 herring each year since 2003.

The numbers fall further beyond each of three dams between the Conowingo and the spawning grounds near Harrisburg, Pa., Eyler said. Officials estimate only 30 to 40 percent of the migratory fish are able to successfully pass the Conowingo, and other dams have similarly poor passage rates.

Researchers say 43 American shad completed the journey from the Atlantic to the Susquehanna spawning grounds last year.

The goal is to get 2 million shad and 5 million herring beyond all the dams.

“We’re very far off from where we need to be,” Eyler said. “We have a long way to go.”

Migratory fish such as shad and herring once were abundant in the Susquehanna and other rivers along the East Coast, spawning as far upstream as New York portions of the river before overfishing and dam construction devastated the populations. Construction of the Conowingo was completed in 1928.

As the dams’ toll on the fish populations became apparent, fish elevators — such as fish “ladders” that aid jumping salmon along the Pacific coast — were built as a remedy.

There are two fish lifts at the Conowingo. Currents created at the mouths of the elevators encourage fish to swim into basins that are then lifted upward into the reservoir behind the dam.

One lift built in 1991 carries fish up and over the dam. An older lift on the west side of the dam does not carry fish to the top but reaches a parking lot on the Harford County side. For now, if it is used, it is only to gather fish to use in research.

The newer lift was built amid pressure from wildlife and conservation advocates the last time the Conowingo was applying for a license from the Federal Energy Regulatory Commission in 1980. That license expired last year, opening the door for a similar effort on behalf of the fish.

Exelon officials submitted an application for a new 50-year license late last year. But instead of going through a legal battle with the Fish and Wildlife Service over fish passage, the company opted to voluntarily withdraw the application and work toward an out-of-court settlement, Exelon spokeswoman Deena O’Brien said.

“We decided this is probably the best of both worlds,” O’Brien said, with wildlife advocates getting their say and Exelon getting a relatively quick resolution.

The company agreed to install larger basins that can carry more fish and to carry two of the basins at a time, instead of just one. The elevator’s hoppers currently are overloaded by other species of fish that are more plentiful and can reproduce anywhere, leaving little room for shad and herring.

Migrating fish carried by the smaller lift will be gathered and driven upstream to help boost the population of fish that grow up to return to the Susquehanna.

Exelon officials did not respond to a question about exactly how much the effort would cost, but O’Brien said in a statement that the company plans to invest millions of dollars.

Conservationists said they are pleased with the agreement.

“For the shad, the stakes are high,” said Ann Swanson, executive director of the Chesapeake Bay Commission. “I applaud [Exelon] for agreeing to try. Energy is important, and so are fish.”

No quick rebound in the shad and herring populations is expected, though. It takes five years for shad to reach maturity and return to the spawning grounds.

It also will be at least a few years before Exelon’s efforts begin. Its licensing application is being delayed while a study explores the Conowingo’s ability to trap sediment flowing downstream. The Conowingo has long helped keep Chesapeake Bay waters clear and clean by trapping nutrients and sediment, but it has reached its capacity for collecting those materials.

Eyler said that could mean nothing will change for the shad and herring until 2019 or later. But Fish and Wildlife Service officials nonetheless called the agreement a victory.

“We think it’s going to be really good for the fish,” Eyler said. “We think it’s going to be really meaningful over 50 years.”

— Baltimore Sun