Shad swarmed back to the Susquehanna in record numbers this spring, and — for the first time in nearly a century — found almost the entire river open for their spawning run.

Maryland and Virginia officials also reported strong runs of shad, which have been the focus of major restoration efforts in the watershed.

On the Susquehanna, 131,000 American shad had moved through the fish lift at the Conowingo Dam by mid-May, and the spawning run was still in progress.

“We definitely have our new record solid in hand,” said Richard St. Pierre, Susquehanna River Coordinator for the U.S. Fish and Wildlife Service.

The previous best year — at least since shad restoration efforts began in the 1970s — was 103,000 for the entire spawning run. In one day alone this spring, 22,000 shad were lifted over the 100-foot-high Conowingo Dam, far eclipsing the previous one-day mark of 9,300.

The Conowingo is the southernmost of four large dams which had closed the Susquehanna to spawning runs for most of this century. In recent years, the utilities that own it and two upstream dams — Holtwood and Safe Harbor — have built expensive lifts to reopen the river to migratory fish. This year, the fourth dam was breached when a fish ladder opened at the York Haven dam just south of Harrisburg. By mid-May, 600 fish had already used it.

Completing that passage reopens almost the entire Susquehanna basin — historically the largest shad spawning area on the East Coast. Shad are an anadromous fish, which means they spend most of their lives along the Atlantic Coast, but return to their native rivers to spawn.

Shad restoration has been a goal of the Bay Program because the fish swim so far upstream to spawn that they uniquely tie the Chesapeake with its 64,000-square-mile watershed.

“Bringing shad and herring back to our rivers is one of the best ways to repay the farmers, the cities, the industries and others upstream for their efforts to reduce the oversupply of nutrients and sediments washing into the Chesapeake Bay,” said Bill Matuszeski, director of the EPA’s Chesapeake Bay Program office.

But the fish, once the most valuable commercial species in the Bay, declined dramatically in recent decades as the result of pollution, overfishing and obstructions that blocked access to spawning grounds. Maryland banned shad fishing in the Bay in 1980, and Virginia followed suit in 1994.

In recent years, major efforts have been aimed at stocking hatchery-reared fish in rivers — many of which had lost shad runs altogether — and building passages at dams so the returning fish could reach historic spawning grounds.

Early indications from all states show those efforts are paying off this year. But unlike the Susquehanna, where the number of returning shad can actually be counted as they go through mechanical lifts that carry the fish past large hydroelectric dams, biologists in Maryland and Virginia can only estimate what is happening.

In Maryland, where stocking programs in the Patuxent and Choptank rivers began only a few years ago, biologists report encouraging signs for both American shad and their smaller cousin, the hickory shad, which is also being stocked in the state.

Surveys have found scores of adult American shad, which take four to five years to mature, returning to the Patuxent to spawn, although stocking only began in 1994. Small numbers were also seen this year in the Choptank, where stocking began in 1996.

An early indication of future success may come from the hickory shad, which the state began stocking in both rivers in 1997. Hickory shad mature faster than American shad — in three years — and were reported swimming back to both rivers in droves.

“We’ve been seeing several hundred to thousands of hickory shad every time we go out to look” on the Choptank, said Steve Minkkinen, of the Maryland Department of Natural Resources. Ultimately, the goal is to establish self-supporting populations in both rivers and move stocking efforts to other tributaries.

Likewise, Virginia rivers have seen “a pretty good year,” said Tom Gunter, of the Virginia Department of Game and Inland Fisheries. Workers easily gathered enough American shad to collect 24.9 million eggs to rear in hatcheries, the second-best year ever. “Something’s happening,” Gunter said. “I think the effects of the moratorium here in Virginia are really starting to kick in.”

There was also good news for hickory shad. “One of the most impressive things were the hickory shad, both on the James and Rappahannock,” Gunter said. “It was a tremendous run.”