Southeastern Fishes Council
Dedicated to the Conservation of Southeastern Fishes

Biologists Shock Fish To Estimate Population Levels
September 17, 2007

Release from:
Hannah Northey
The Daily News Record

ON THE SHENANDOAH RIVER Bob Owens has caught bass, perch, suckers and trout from the banks of the South Fork of the Shenandoah River for more than 50 years.

But these days, the Elkton native doesn't have much company on the winding riverbanks.

Fewer fishermen come to the South Fork, Owens says, because many of the fish have lesions or are sick. And no one he knows eats the fish, he said.

"People used to eat fish out of this river all their life, including myself," Owens said as he looked over the rippling waters. "But I don't keep anything out of the river anymore you don't know what the pollutants are."

For the past three years, mysterious fish kills in the Shenandoah, James, Cowpasture and Maury rivers have baffled biologists.

So it wasn't fishing that brought Owens out to the river on Thursday. It was curiosity.

Owens watched as more than 35 fish biologists from the Virginia Department of Game and Inland Fisheries used electric currents to stun and count fish along 60 miles of the river to estimate population, as well as the river's health.

"I've never seen anything like this before," Owens said.

A River's Health

From Tuesday to Thursday, VDGIF biologists counted, identified, weighed and measured fish in three sections of the South Fork of the Shenandoah in Warren, Page and Rockingham counties, said Steve Reeser, a VDGIF fisheries biologist.

Using a method called "electrofishing," 11 boats with two to three biologists each lined up on the river. Generators on the boat created an electric current that was channeled through electrodes on the front of the boat, Reeser said.

The current created a field that reached up to 8 or 9 feet below the boats, stunning fish that came into its path, he said. The shock immobilizes the fish and brings them close to the surface.

As the line of boats moved slowly down the stretch of river together, fish were scooped up and transported to 300-gallon tanks on the shore and in the boats.

The oxygenated tanks held the fish until biologists identified, weighed, and measured each one, Reeser said.

Owens, standing next to one of the tanks, took note of a 44-inch muskie that biologists had caught.

Like the other fish, Reeser said the muskie would be released back into the river after it was studied.

"That's the first muskie I've seen in this river," said Owens, rubbing his fingers along the fish's golden scales. "There's a stream-lined fish, buddy."

A Rare Technique

VDGIF is the only government agency nationwide using the technique, also called a "depletion estimate," on such a large scale, Reeser said.

Matt Henderson, a fisheries technician with the department, said he uses electrofishing to count fish populations about four times a year on rivers in his district. But that's a small operation compared to the population estimates the biologists conducted last week, he said.

Reeser said the idea developed in the 1990s, when he and other fish biologists came together to better manage smallmouth bass in state waterways.

The group, he said, decided in-depth population studies were needed to better understand the health of the rivers and their inhabitants.

Since then, biologists have used the technique on rivers throughout the state, including the South Fork in 2003.

Reeser said biologists look at past and present counts to better understand the river's health and how the fish kills have impacted the waterway over time.

"We're lucky to have that data to go back to and compare it with [past numbers]," he said. The comparison, he says, gives researchers "a better explanation of the impacts of the fish kills."