A fishy tale indeed

Nutria. Fire ants. Kudzu. Since they first arrived on South American and Asian cargo ships, all these invasive species have displaced native animals and plants and become the bane of backyards throughout bayou country. This summer, the Louisiana Department of Wildlife and Fisheries (LDWF) has quietly fought a valiant battle to save Port Sulphur waterways from the latest exotic intruder: African tilapia.

While the panneed version may not appear too intimating on a dinner plate, the prolific live fish is a formidable opponent with the potential to wreak long-lasting ecological havoc. “There are instances where tilapia have taken over the native fish population,” explains LDWF Biologist Program Manager Mark McElroy. “They can survive in poor water quality situations, have high salt tolerances, protect their young and have a high reproductive cycle in the summer. So it’s troublesome to get rid of them.” And with the potential of a hurricane or large rain to disperse the fish, rapid response is the only way to stop the small population from growing exponentially.

So when LDWF detected thousands of tilapia an eight-foot-by-one-mile wide area of ditches and ponds near Port Sulphur, its staff wasted no time in hauling out the big guns. The agency collaborated with scientists from the Department of Natural Resources, Department of Environmental Quality, Department of Agriculture and Forestry, Plaquemines Parish government, Barataria Terrebonne National Estuary Program, U.S. Fish and Wildlife Service, U.S. Army Corps of Engineers, Louisiana State University, Nicholls State University, Tulane University and the University of New Orleans.

The consortium decided upon a direct and drastic approach. During June and July, LDWF released rotenone, a naturally-derived fish-killing agent, into the water. Since the drug doesn’t discriminate, all fish in the area were sacrificed. Fortunately, the rotenone-tainted fish were non-toxic to birds and other scavengers because the agent is formulated to disrupt the function of gill capillaries.

“From the outset, we knew our efforts to completely eradicate the established tilapia populations using chemical alone was at best somewhere between 90 and 99 percent,” McElroy says. “We believe we are very close to 99 percent. Now it is up to the native fish species we are stocking and the elements to carry the ball to reach our ultimate goal of 100 percent.”

Toward that end, LDWF has reintroduced bowfin, mud catfish, spotted gar, alligator gar, largemouth bass, green sunfish and other native fish species. In addition, scientists from local universities will monitor the area with fish sampling and water quality for at least two years.

“This research will ultimately reveal how successful the rapid response efforts were in this instance, and may provide insight into how we can improve future responses to aquatic invasive species introductions,” McElroy explains.

LDWF has also collected clues about how the native African fish found its way to American waters. So far, the agency is not ready to reveal the suspected source of the outbreak. Still, McElroy cautions, “People have to be more careful about bringing in fish or plants from other places. There are too many invasive species.”

For more information on the fishing closure and tilapia, visit the LDWF web file.

Click here for this week’s Creature Feature.

Click here for this week’s City Lynx.