Powell's Creek was smooth as glass, but that was about to change as fisheries biologists dipped electroshocking gear off the end of a boat and sent a low-frequency charge into the stream.

Suddenly, stunned fish began popping to the surface of the creek, which is part of the James River National Wildlife Refuge. They included blue catfish, channel catfish, largemouth bass, killifish, pumpkin seed, gizzard shad, blue gill and others.

By tweaking the device to send out a certain number of pulses per second, the biologists suddenly brought only catfish to the surface.

In some places, that results in "an insane number of fish," Bob Greenlee, a fisheries scientist with the Virginia Department of Game and Inland Fisheries told a group of scientists and fishery managers who had come for a firsthand look at the number of blue catfish in the river. The group, all members of the Bay Program's Sustainable Fisheries Goal Implementation Team, are grappling with whether to recommend actions that could stem the spread of blue catfish, a nonnative species that is now found in all of Virginia's Bay tributaries and some of Maryland's.

Some scientists worry that the "insane" numbers of the predatory catfish could harm populations of other species, but the blue cats, which reach sizes greater than 100 pounds, have become popular with anglers seeking trophy fish.

This June day on Powell's Creek, the numbers were not insane. Nonetheless, scores of catfish - overwhelmingly blue catfish - were soon flopping to the surface. Most were less than a foot long, though a healthy number were 2 feet or more. One tipped the scales at 42 pounds; another weighed in at 22 pounds.

"That was a moderate level of sampling," said Greg Garman, director of the Virginia Commonwealth University Center for Environmental Studies. "It can be an order of magnitude greater than what we saw."

The goal team, which met formally after the trip, is reviewing whether it should recommend that the blue catfish be considered an invasive species that is known or likely to cause "negative impacts that do not provide an equivalent or greater benefit to society."

But at this point, it's unclear the extent to which blue catfish cause negative impacts. Because of their huge numbers - in some areas surveys have estimated they account for about three-quarters of all fish biomass - there's concern that they may be reducing populations of other species, including largemouth bass, channel catfish, white catfish and freshwater mussels. Of particular concern is their potential impact on American shad, which has been the focus of major restoration efforts and for which there are fishing moratoriums in the Bay.

Their numbers can create other problems as well. Many blue catfish become entangled in gill nets targeting other species, causing problems for other fisheries such as striped bass.

In some areas where blue catfish have been introduced, there have been impacts on native species, said Mary Fabrizio, a fisheries scientist with the Virginia Institute of Marine Science. But in the Bay region, the extent of blue catfish predation on other species has not been well studied; most available information is anecdotal.

"Once the blue catfish was introduced into the Rappahannock, James and York rivers, there was a decline in the numbers of white catfish," she told the goal team. "However, we do not know whether there is a cause-and-effect relationship."

Preliminary stomach analysis of blue catfish from the Potomac River by Maryland scientists show that while shad are not the major source of food for blue catfish, significant numbers might still be consumed.

Besides the Potomac, blue catfish are known to be in the Upper Bay and mouth of the Susquehanna, Patuxent and Nanticoke rivers in Maryland. Maryland's Department of Natural Resources has expressed concern that the fish could reach other rivers, or be intentionally introduced in them by anglers.

"The weight of evidence suggests they are likely to cause ecological harm," said Tom O'Connell, Maryland DNR fisheries director.

Bill Goldsborough, a senior fisheries scientist with the Chesapeake Bay Foundation, said that when populations of a species are at low levels, as is the case with shad, "even a slight increase in mortality in a given tributary" could be important.

But in Virginia, particularly on the James, blue catfish support a major trophy fishery - recently, a state-record 109-pound fish was caught - and recreational anglers who attended the meeting argued that blue catfish have become a valuable species that drives millions of dollars in economic activity.

Jeff Parks, an angler who fishes for blue catfish on the James five to six times a month, said, "People come from all over to fish here. It's a sport fish, and it brings in all sorts of money."

Some also suggested that the blue catfish, which Virginia fisheries biologists introduced into the state in the 1980s, was being singled out because it was a relatively new arrival compared to other nonnative species that populate the region's waterways, such as largemouth bass, channel catfish, bluegills and brown trout.

"People are talking about their effects on largemouth bass. Largemouth bass are also nonnative. Why should largemouth bass be considered superior?" asked Andrew Chase, an angler who fishes the James. "They are equally nonnative."

Early documents that had suggested the goal team might consider eradicating or reducing blue catfish populations to the lowest level practicable had raised alarm among many recreational anglers and become a hot topic on fishing blogs. Goal team members reported being inundated by hundreds of e-mails on the topic.

At the meeting, members sought to calm those fears, noting that the eradication of blue catfish was impossible, and even seeking sharp population reductions was likely impractical. More likely actions, team members indicated, would be efforts to keep catfish from entering new tributaries, or trying to control populations in certain areas if a valuable resource was considered to be at risk. No time frame was set for making a recommendation.

Peyton Robertson, chair of the goal implementation team and director of the National Oceanic and Atmospheric Administration's Chesapeake Bay Office, said his office would support more research about the blue catfish population size and range around the Bay and to better assess whether they are having a significant impact. In the meantime, he said the office may work with others to develop a public education campaign about issues related to blue catfish around the Bay.

"We think the responsible thing to do is raise awareness that there is a potential issue and use the best information we have to establish some clear next steps," he said.