The state Department of Natural Resources, which has done some prying into the sex lives of the rockfish that roam Chesapeake Bay and its tributaries, never dreamed they would be reproducing in Piney Run Lake and Liberty Reservoir.
Not that the fish released into the lakes during the 1980s as part of DNR stocking programs were any less amorous than their Chesapeake counterparts. But rockfish -- or striped bass -- are anadromous. That means they live in saltwater bays or the ocean and go upstream to spawn, said Robert Bachman, director of DNR's freshwater fisheries division.
Biologists thought striped bass needed the turbulent waters of their spawning streams, which keep the eggs in suspension, for successful hatching.
"In 1987 we got reports of little striped bass in Liberty Reservoir. We thought, 'Oh, somebody's stocking the reservoir,' " Mr. Bachman said. "But no, they were reproducing."
Several years later, Mr. Bachman said, "We found out, sure enough, they're doing it in Piney Run as well."
The phenomenon is scientifically interesting because rockfish are not known to reproduce in reservoirs that lack the water turbulence to keep the eggs in suspension. The only similar documented natural rockfish hatchery is Lake Powell, on the border between Arizona and Utah.
The striped bass's talent for reproducing in unexpected waters also has practical implications for fisheries management, Mr. Bachman pointed out. The agency won't have to stock lakes where fish are reproducing naturally, but will have to use creel limits to regulate the population.
Biologist Ed Enamait, fisheries manager for the area that includes Piney Run and Liberty reservoirs, hypothesizes that "they're spawning successfully because at least a percentage of the Chesapeake Bay female striped bass emit eggs that are buoyant, that don't require turbulent [waters]."
Mr. Enamait said he initially thought the clarity of the bottom on Liberty Reservoir might have prevented the eggs from suffocating in silt, but changed his hypothesis after fingerlings also began to appear in Piney Run, where the bottom is less clear.
Mr. Enamait said he didn't get much audience response to a scientific paper on the phenomenon he presented at a conference last fall of the Southeastern Association of Fish and Wildlife Agencies. Representatives from other states may have been satisfied with existing stocking programs that give them easier fish population control than natural breeding, he said.
Some lakes are stocked with sterile fish for recreational fishing. The DNR has stocked Prettyboy, Triadelphia and Rocky Gorge reservoirs with sterile hybrid striped bass, which grow faster than purebred bass, Mr. Bachman said.
He said the agency used pure bass to stock Piney Run and Liberty because of concerns that hybrids might reach the bay and interfere with reproduction of the purebred fish.
The first rockfish were introduced to Piney Run in "a more-or-less unplanned, experimental stocking" in 1975, Mr. Enamait said. The biologist responsible for the area "had some fish left over from another stocking job and introduced them," he said.
At Liberty Reservoir, the stocking program began in 1981. Mr. Enamait noticed the first striped bass fingerlings in the lake five years later. It takes about five years for a female to lay viable eggs, he said.