If things were this bad in the late 1770s, George Washington’s starving Continental Army might never have made it out of Valley Forge.

The shad, according to one account, came charging up the Schuylkill River to spawn and ran headlong into soldiers who leapt into the water, herded them into nets and wolfed them down.

Now the shad are depleted to the point of collapse. The population is so low that the federal Mid-Atlantic Fishery Management Council last week imposed the first-ever cap on the domestic commercial catch of shad and river herring — which Washington’s army also ate during the war against the British.

The move is the latest action by a fishery-management group to try to shore up species that have been nearly exhausted by overfishing and poor water quality. The harvest of menhaden, considered the most important fish in the sea because it provides food for many animals and helps filter pollution, was recently cut by the Atlantic States Marine Fisheries Commission because of its low stocks.

On shad and herring, the federal council took action after the states’ commission “evaluated the health of these fish in rivers and oceans . . . and both species were determined to be at near-historic low levels,” said Kate Taylor, senior fishery management planning coordinator for the commission.

Most states along the Atlantic Coast already enforce moratoriums for shad and herring fishing in their waters, which extend three miles offshore. But beyond that, in federal waters, a fleet of trawlers fishing for mackerel hauls in more than 900 metric tons of shad and herring per year as bycatch.

The fleet, under the new guidelines imposed by the federal council, will be limited to 236 metric tons of bycatch, far less than the industry proposed but far more than the limit pushed by conservationists.

The cap, which goes into effect next year, is “a really important first,” said Joseph Gordon, manager of U.S. oceans in the northeast for the Pew Charitable Trusts. “River herring and shad used to be the largest fisheries on the coast, forage fish that others eat. Most of their population has declined 90 percent.”

Rather than closing off parts of the ocean to fishing, the federal council gave the industry discretion to figure out how to avoid picking up shad and herring. That’s important to an industry that wants to preserve its mackerel catch, worth $3 million annually overseas.

“I think the industry agrees that they need to avoid these species,” said Jason T. Didden, a fishery management specialist for the council. “If they can figure that out, and they likely are in the best position to do that . . . then they will be able to still catch the full mackerel quota while assisting in the conservation of river herrings and shads.”

Independent observers already are stationed on the mackerel trawlers — most of which are based in Massachusetts but fish as far south as North Carolina — to monitor the shad and herring catch for the federal government. To beef up enforcement, dockside observers will also weigh bycatch when the boats arrive in port.

The Mid-Atlantic council was careful to call the fisheries depleted, not overfished, Didden said. The disappearance of shad could also be due to the huge dams blocking their spawning migration in rivers such as the Susquehanna.

Shad, which start life in fresh water and swim the ocean for years before returning to their birthplace to spawn, are often pushed off course by the powerful water flows from dams or sliced by the structures’ turbines. And they can be disoriented by elevators designed to help them over the dams by funneling them through gates and lifting them in buckets over walls.

The Susquehanna alone has four hydroelectric dams — Conowingo, York Haven, Holtwood and Safe Harbor. Three allow only small percentages of the shad to pass.

Shad have a rich, if disputed, history in the story of America’s founding. Some historians believe American and Hickory shad are among the reasons that the United States stands today. In 1778, after the Continental Army stumbled out of Delaware, cold and nearly starved, it started making its way up the Schuylkill.

While shad are tough little fish that fight until the end, they were no match for hungry soldiers, according to Harry Emerson Wildes, author of the book “Valley Forge.”

“Countless thousands of fat shad, swimming up the Schuylkill to spawn, filled the river,” Wildes wrote. By his account, soldiers lined the banks and a cavalry unit rushed in, beat the water and drove the shad into nets.

“So thick were the shad that, when the fish were cornered in the nets, a pole could not be thrust into the water without striking fish,” according to the account, provided by the Shad Journal, an online publication of the Shad Foundation.

The writer John McPhee disputes such accounts in his book “The Founding Fish,” saying what happened on the river was no miracle. George Washington was a commercial fisherman who no doubt knew a shad run was coming. That is probably why the general led his troops to that site, McPhee argues.

Whatever happened, the enormous shad runs are gone. In 1956, the stocks were estimated at nearly 12 million pounds for shad and 70 million for herring. Now, both are fewer than 5 million pounds, according to the National Marine Fisheries Service.

“These fish are in need of conservation management,” Gordon said. “They’re disappearing up and down the coast. Absolutely I think they can be restored at much higher levels than they are now.”