KINGS BLUFF - The turbulent rush of water flowing across the dam drowned out all other sounds. A tree hung precariously in the balance on the lip of the dam.

Sooner or later, the rising water of the Cape Fear River would free it from its resting place, sending it down the face of the man-made waterfall and into the final stretch of free-flowing water heading for the Atlantic Ocean.

But, while objects float downstream, some species of fish swim upriver, against the current.

A pair of fishermen had tied their fiberglass boat against the wall of Lock No. 1. They wore orange life vests, and like other anglers in nearby boats, they kept a wary eye on the snagged tree while fishing for shad with light spinning tackle.

Unlike most of the other fishermen who were catching shad for sport or for their meat and roe, these two anglers were catching them in the interest of science.

"We're collecting American shad to place transmitters inside them," said Joe Smith, 30, a Zoology Department graduate student at N.C. State. "We want to track their movements upriver as they make their spawning runs. We're trying using transmitters to tell us if the fish are getting into spawning habitat above the three locks and dams."

Smith's partner, field technician Matt Lubejko, 22, said they were fishing with shad darts, small jigs designed specifically for catching shad. He said they had also been given six live shad caught by the N.C. Wildlife Resources Commission's fishery biologists during a general electrofishing survey for multiple fish species.

"The shad we catch on hook-and-line undergo less stress than those caught by electrofishing," Lubejko said. "We will tag a total of 20 shad with VEMCO V9 transmitters."

Lubejko held a shad while Smith readied one of the sonic transmitters. Smith put the device into a length of clear plastic tubing and inserted a piece of an old fishing rod into the other end. He put the tubing holding the transmitter into the mouth of the shad and pushed the fishing rod, inserting the transmitter into the upper stomach of the fish in the manner of a hypodermic needle injection. The tubing was then extracted.

American shad once ran as far upriver as Erwin. That was before the three locks and dams were built for navigation purposes along the river in the early 1900s. Some fish still make it upriver through the locks because the locks are operated to assist their movements during the spring when the fish enter the river. But the farther upriver, the fewer fish manage to make the journey through the locks.

"We fish at Lock and Dam No. 1 because it's a known place where the fish congregate," Smith said. "It's the first place they're stopped by a dam. One thing being discussed is removing Lock and Dam No. 2, so we were interested in understanding more about their migration. Where would they spawn and where would they go if we got them up above the locks and dams?"

Smith said the historical spawning grounds are in the Erwin area. Last year, the team transported sonic-tagged fish above Lock and Dam No. 3. Some shad survived, but the striped bass had a lower survival rate.

Each sonic tag emits a unique code. While there is a mobile receiver on their boat, Lubejko and Smith received most of the transmitter information from sonic-tagged fish via stationary receivers placed in the river. One stationary receiver was placed near each of the three locks and dams, and several were placed upstream of Lock and Dam No. 3.

"Shad survive a long time with the transmitters in place," Smith said. "They don't feed on their spawning runs, so they don't regurgitate the tags. A lot of them die off and don't make repeat spawns, so the tags only need around four months of battery life."

Asked why shad strike small jigs if they do not feed during their spawning cycle, Lubejko said he wasn't certain.

"It's probably an impulse strike," he said.