The small fish begin surfacing first, flopping on the top of the Sunflower River as the 1,000-volt charge from eight electrodes reaches them near the bank of the river.
Gradually, larger fish start surfacing, and Emily Cotton of the Mississippi Department of Environmental Quality moves quickly to scoop them up in her net so they can be transported to MDEQ laboratories for testing.
Cotton, a regional biologist for MDEQ, traveled to the Delta Wednesday afternoon along with MDEQ Environmental Scientists Al Gibson and Doug Upton as part of an effort to monitor levels of DDT and toxaphene in wild fish populations.
DDT and toxaphene are both pesticides that were banned decades ago, but residue continues to runoff into Delta streams and lakes where it can be consumed by fish.
Gibson said Wednesday's fishing trip on an MDEQ "shock boat" will provide follow-up information for a study conducted last year that indicated high levels of those chemicals in some Delta fish populations.
"Here we are looking for remnants of DDT and toxaphene," Gibson said. "So, we're looking for species that people want to eat and are common."
Based on information from last year's study, the MDEQ issued an advisory on June 26 warning that many bottom-feeding fish in Delta lakes and streams may be contaminated with DDT and toxaphene. The report recommends that residents not consume more than two meals per month of carp, buffalo, gar and those catfish longer than 22 inches.
The advisory does not apply to other species in Delta lakes and streams or to farm-raised catfish.
Upton said that using the shock technique to stun fish makes gathering samples much easier, but it has one drawback.
"It spoils you from the conventional methods."
He said after the fish are shocked and pulled from the water, they are put on ice so they can be transported. He said those that are not picked up come to in a few seconds and are not harmed.
"After we catch them, they'll be sorted according to species and size," Upton said. "Then, they are fileted to take the edible meat out."
He said meat from three to five fish of the same species and size is ground together to form a composite that is tested for concentration of chemicals.
The researchers are hoping to compile four to six composite samples from their Wednesday trip.
MDEQ Lab Director Henry Folmar said the fish composites from the Delta will be evaluated during the next few months at either Mississippi State University or the department's Jackson facilities.
Information from the tests will be used to issue an update to the June advisory sometime next year.
Folmar said that in addition to monitoring existing test sites like the Sunflower River, the MDEQ is also beginning to sample new places in order to identify safe rivers and lakes.
