While American shad have been the target of major restoration efforts, scientists are mystified by the comeback of its close relative, the hickory shad, which has received little attention.

Although the Maryland Department of Natural Resources has stocked hickory shad in four rivers in recent years—the Patuxent, Choptank, Patapsco and Nanticoke—the slightly smaller relative of the American shad is strongly rebounding in Virginia rivers, the Potomac and the Susquehanna, where no restoration efforts were made.

Last year, a Virginia Department of Game and Inland Fisheries creel survey on the James River caught and released 8,300 American shad—but 56,000 hickory shad. On the Rappahannock, the survey found 550 hickories for every American shad.

Only a decade ago, hickory shad were in as poor of condition, or even worse, as American shad.

“There was talk that maybe they were actually extirpated,” said Greg Garman, director of the Center for Environmental Studies at Virginia Commonwealth University. “All of a sudden we’re up to our eyeballs with them.”

Some think the Baywide moratorium on commercial American shad fishing may have benefited hickories as well. Others doubt that, saying smaller hickories were not likely being caught in gear that targeted American shad.

“We can’t take any credit for that, at least not in any obvious way,” Garman said. “It’s exciting. It’s wonderful. But it’s a little bit frustrating because it says we maybe don’t understand as much about these populations as we think we do.”

Maryland’s hickory shad comeback has outpaced its American shad comeback as well. But it has stocked more than 65 million hatchery-reared hickory shad in the past decade—more than five times the number of American shad stocked in the state—in the hope of boosting a recreational fishery.

Steve Minkkinen, chief of hatchery programs for the Maryland Department of Natural Resources, said the hickory shad comeback is aided because they return to spawn at age 2 or 3, while American shad don’t return for four or five years.

But hickories are also rebounding in the upper Bay, the Susquehanna and the Potomac River, where none have been stocked.

Minkkinen said it was unlikely that fish stocked in Maryland rivers were responsible for rebuilding those populations. “They seem to show a lot of home river fidelity,” he said.

Hickory shad are poorly studied compared with American shad, and John Olney of the Virginia Institute of Marine Science speculated that some unknown environmental or climatological factors are benefiting hickories.

Scientists say they have also been harder to survey. “You don’t find their larvae and juveniles in abundance in our collections, even though the adults are increasing in abundance.” Olney said.

“Their life history is not well understood. So we have nothing to lend to that mystery.”