River Monsters

Louisiana Department of Wildlife and Fisheries responded to a call at a Jefferson Parish drainage canal on May 5. A fisherman had snagged an alligator but was unable to free the animal. Upon arrival, agents discovered the fisherman had actually caught a crocodile. Since Audubon Zoo experts identified the croc as the type produced by the pet trade, agents imagined the animal either escaped or was deliberately released.

But it is far from the only invasive river monster lurking in South Louisiana waters.

The same day, LDWF closed commercial and recreational fishing in an area south of Port Sulphur in Plaquemines Parish following the discovery of tilapia in public waterways.

While the diminutive fish is surely less of a threat to humans than a saber-toothed reptile, LDWF Biologist Program Manager Mark McElroy says the fish’s affect on the environment is equally dangerous. The threat of tilapia pose comes as a surprise to many Louisianans, who have welcomed the fish—particularly if topped with mango salsa or paneed with white wine and lemon.

“There are instances where tilapia have taken over the native fish population,” he says. “They can survive in poor water quality water situations, have high salt tolerances, protect their young and have a high reproductive cycle in the summer. So, it is 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.

Fortunately, the tilapia are currently contained in an area roughly eight-feet long by one-mile wide. So, why not hold a tilapia rodeo or allow commercial and sport fisherman access to the area and promote the fish as the state’s specialite de la maison? “This fish is a mouthbreeder and can carry up to 150 young in its mouth. If a fisherman catches one and carries it to an ice chest, there’s the possibility of distributing the young in the water to multiply. That’s why we call it ‘the beast.’”

Next week, the agency is planning the staged application of rotenone, a naturally derived fish-killing agent. “As soon as it goes in the water, “ McElroy explains, “the fish will begin piping [coming to the surface]. The tilapia are more hardy and the last to come up. So, it will take about 15 minutes.”

Because rotenone will kill all the fish in the area, McElroy says, “It’s going to stink. It’s going to be a mess for about three to four days until the fish break down.” While there are no plans to clean up the fish kill, LDWF will discourage birds from feeding on the fish and spreading fish progeny in flight. If another animal does happen eat the rotenone-killed fish, McElroy assures the animal will remain safe from poisoning because the agent is formulated to work in gill capillaries. LDWF will monitor the area and re-apply rotenone sporadically for estimated three weeks until all signs of tilapia have vanished.

Over the past few weeks, LDWF has 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 wlf.louisiana.gov/tilapia.

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