After last years' sharp and unexplained declines, the number of American shad returning to the Susquehanna River to spawn appears to have rebounded this spring.

In mid-May, after three weeks of operation, the fish lifts at the Conowingo Dam had collected 13,800 migrating shad - more than all of last spring. The spawning season was expected to continue until early June.

"We're doing really well, with plenty of time to go," said Richard St. Pierre, Susquehanna River Coordinator for the U.S. Fish and Wildlife Service.

Last spring, only 13,500 shad were captured at Conowingo, down from 25,700 in 1992, and 27,200 in 1991.

Last year's drop was perplexing because the number of spawning shad declined about 50 percent all along the East Coast for reasons that remain unexplained.

The drop caused a particular concern on the Susquehanna. Last year, the utilities that own three hydroelectric dams upstream of Conowingo agreed to construct fish lifts at their facilities. But the agreement between the dam owners and government resource agencies contained a clause allowing construction to be delayed if the population dropped sharply for unknown reasons the year construction was to begin, which was 1994.

"That question is now put aside," St. Pierre said. "We're in fine shape. The only thing that could have really hurt us was if we had yet another decline this year."

A $12 million fish lift was completed at the 100-foot-high Conowingo Dam - the closest dam to the Bay - in 1991. When passages are completed at the three upstream dams, hundreds of miles of spawning habitat will be available to shad.

Shad are an anadromous species, living most of their lives off the coast but returning to fresh water rivers to spawn. The Susquehanna was once the largest spawning territory for the shad on the East Coast, but the river was closed to migratory fish early this century when dams were constructed.

Dams that block spawning grounds, fishing pressure, and pollution have been blamed for a sharp drop in shad populations in recent decades. Populations have fallen so much in the Bay that Maryland and Virginia have banned shad fishing.

Restoration efforts in the Susquehanna began in the mid-1970s when a shad hatchery was built on the Juniata River, the Susquehanna's largest tributary. Since then, returning shad trapped at the Conowingo Dam have been placed in trucks and hauled north beyond the other dams and released near Harrisburg so they can spawn - a practice which is credited with dramatically increasing the Susquehanna's shad population in recent years.

When the fish passages at upstream dams are completed, the Conowingo fish lift will move the shad directly over the dam and into the reservoir behind it, ending the need for trucks.

Despite this year's rebound, St. Pierre said construction will probably still be delayed a year because of design problems for the fish lift at Holtwood Dam, the first dam beyond Conowingo.

As a result, construction probably will not start until next year instead of this fall, and will probably be completed in 1997 instead of 1996, St. Pierre said. The agreement allows fish passages at the Holtwood and Safe Harbor dams to be completed as late as 1997.

The passage at the third dam - York Haven - is to be completed within three years of the other two passages.

St. Pierre credited cool water temperatures with boosting this year's spawning run. "Most of the weather that we've had is great for continuing the run," he said. "It's been cool at night and warming into the 70s in the day. That's holding the water temperature down."

Last year's lift operation started late because of high spring flows and were cut short by hotter than normal temperatures in May, he said. Those climatic conditions further compounded the impact of a sharp drop off in spawning shad that affected the entire East Coast. Biologists believe some unexplained factor kept most of the migrating shad out to sea.

But the number of shad that had returned by mid-May seems to indicate that most of the fish that remained at sea did not die, which had been a major concern, St. Pierre said. Still, he added, it was too soon to tell whether shad numbers were rebounding all along the coast.

Nonetheless, St. Pierre was optimistic that the number of returning shad would increase sharply in the next few years. Susquehanna shad have had good spawns during the past three years and those fish are beginning to mature, he said. Even though the number of spawning shad dropped by half last year, those that did return produced large numbers of young, he said.

"I think we're just starting to get into our stride now in terms of getting some substantial natural production out of these fish," St. Pierre said.