Looking upstream to the return of migratory fish

As trees and flowers emerge from winter, several species of silvery fish abandon life in the open ocean to return to the Chesapeake Bay.

Jim Thompson is there to greet them.

In his role as fish passage coordinator for the Maryland Department of Natural Resources, Thompson oversees efforts to restore habitat to anadromous fish—those that return to their freshwater birthplace after reaching adulthood in salty ocean waters.

“Spring is definitely our busy time of year,” said Thompson.

The first of the anadromous fish to return is the alewife herring, relatively small at a maximum of 15 inches. Then hickory shad, American shad and blueback herring take turns fighting against currents to reach their spawning grounds. Males and females will cast tens of thousands of eggs and sperm simultaneously into the water.

“The theory is they’re getting into the freshwater streams, away from some of these saltwater predators that would eat their young,” Thompson said. “It’s a life cycle designed to increase their survival.”

Nevertheless, shad and river herring are important food sources for striped bass and bluefish in the Chesapeake Bay, in addition to animals like dolphins and tuna in the open ocean.

“It’s the perfect [forage fish] because it’s skinny and it doesn’t have sharp spines on it like a white perch would, so it slides down your belly,” Thompson said.

“Of course they’re in big schools too so once you find them you get a bunch of them.”

A history of herring

The largest and most notorious of the shad and river herring that visit the Chesapeake is the American shad, which was once the most valuable commercial finfish fishery in the region.

But, there simply aren’t as many left.

“In George Washington’s days they were really commercially valuable because they were so tasty,” Thompson said. “People would go all winter long with not much food and then these fish would run up in the spring and they’d catch them and salt them.”

Even George Washington himself supplemented his income with the shad harvest on the Potomac River. However, overharvesting and loss of habitat took their toll, and Maryland and Virginia closed their commercial fisheries in the 1980s and 90s.

“Around the 1800s and 1900s, people built dams to run mills, and that blocked off that historic habitat for this fish, and that’s one reason these fish have declined.”

In 1987, the Chesapeake Bay Program began a fish passage effort spanning Virginia, Maryland and Pennsylvania to rebuild migratory fish populations. The states eventually staffed their own coordinators to maintain the effort. From 1989 to 2011, 2,510 stream miles were restored as fish habitat. The 2014 Chesapeake Watershed Agreement calls for an additional 1,000 miles to be restored by 2025. As of 2017 that goal had already been exceeded, with 1,236 miles opened up to migrating fish, mostly in Pennsylvania and Virginia.

Bloede Dam in Patapsco Valley State Park, seen in 2016, is the focus of a dam removal project. Removal will allow much more fish to migrate beyond the site than the fish ladder that is currently in place. (Photo by Leslie Boorhem-Stephenson/Chesapeake Bay Program)

Removing threats to public safety

In recent years, Thompson said an emphasis on installing fish ladders has shifted to dam removal.

“[Ladders] do work, they do pass fish, but they’re not as efficient as taking out a dam.” Thompson said. “It also addresses public safety. We’ve had some dams where people have drowned below them. They’re liabilities. Many dams are no longer being used, so it just makes sense to take them out now.”

One defunct dam, Bloede Dam in Maryland’s Patapsco Valley State Park, has caused nine deaths since the mid-1980s. The dam was built as a hydroelectric generator in 1907 but was shut down in 1932 because its turbines kept filling with sediment.

“Bloede Dam has been a long project coming,” Thompson said.

The Bloede Dam removal project requires relocating a sewer line that runs through the dam. And Thompson says an earlier part of the process involved cutting down trees on an impoundment of sediment that has been trapped behind the dam since Hurricane Agnes ravaged the region in 1971.

“That sediment is there unnaturally,” Thompson said.

The sediment behind Bloede isn’t contaminated with pollutants, and won’t have a significant impact on the Chesapeake Bay ecosystem.

When the dam is removed and the sediment is released, it will have adverse impacts on fish for a couple of years. But the payoff is worth the risk. Removing Bloede will open up eleven miles of historic spawning habitat for river herring, American shad and the American eel, which is also facing declining populations. Species like freshwater mussels will also benefit, along with eels and other fish that serve as their larval hosts, transporting the immature shellfish to new habitat upstream.

American shad larvae start to hatch at Van Dyke Research Station for Anadromous Fishes in Port Royal, Pa. The eggs were collected from the Potomac River in Virginia. (Photo by Will Parson/Chesapeake Bay Program)

A decade of progress

About once a week starting in January, Thompson will don waders, jump into fast-moving water and clear tree limbs and other debris from fish ladders that mimic the strong current of streams, attracting fish and leading them upstream past dams.

Clearing the ladders also benefits local species like yellow perch, which are the first to appear around late February.

From March to June, Thompson conducts sampling to determine where fish end up spawning in a given year.

“In the summer and the winter, you kind of speculate where you think they may be and where the habitat is, but you don’t really know until the fish are here,” he said. “One year you might see them in one spot but then the next year they won’t be there.”

The Chesapeake Bay Program uses the presence or absence of shad and other species as part of measuring progress toward its fish passage goal. Across the watershed, the data paint a mixed picture of recovery. American shad have surpassed target levels in the Potomac and Rappahannock Rivers but are largely absent from the James River and the Susquehanna—the Chesapeake’s largest tributary. As of 2014 the species was at 44 percent of population targets overall, up from just 11 percent in the year 2000.

Shad hatcheries in Maryland, Virginia, Pennsylvania, Delaware, and the Pamunkey and Mattaponi tribal governments aid the recovery by releasing millions of fish larvae in major tributaries every year. In Washington, D.C., the Schools in Schools program brings shad fry into classrooms for students to raise as they learn about the fish’s life cycle.

And larger dams, like Conowingo Dam on the Susquehanna River, operate mechanical lifts that carry massive bucket loads of fish upstream.

But some studies suggest that unintentional catches of shad and river herring by offshore fisheries is limiting the potential of recovery efforts.

Starting in June, when the blueback herring are the last to leave, Thompson spends the offseason working with partners to coordinate future potential fish passage projects. He said many dams are on private property, and it can sometimes be difficult to convince landowners to undertake a project.

“These dams are expensive to maintain, and if they can’t afford to maintain it and they’re not using it, [landowners] could get some grant money through my program and through some federal programs to remove that dam and restore passage for fish,” Thompson said. “And they could have some spawning fish above their property that they could catch recreationally.”