Environment

Weed-feasting carp released in South Florida canals

The South Florida Water Management District released about 8,300 grass-eating carp in a Homestead canal Monday to control invasive hydrilla. The sterile fish were farm-raised in Arkansas.
The South Florida Water Management District released about 8,300 grass-eating carp in a Homestead canal Monday to control invasive hydrilla. The sterile fish were farm-raised in Arkansas. South Florida Water Management District

Note to South Florida anglers: If you catch a foot-long, grass-eating carp in a local canal, please throw it back.

On Monday, the South Florida Water Management District released about 8,300 sterile carp — purchased from an Arkansas fish farm for $3.74 each — to help control hydrilla, a ropey, invasive water plant that can grow up to an inch a day, reach 20 feet and clog flood-preventing canals, smother native plants and tangle boat propellers.

The release in Homestead is the first to occur over the next month. By the end of January, about 24,000 carp will be munching away in man-made canals from Fort Lauderdale to Homestead.

The Asian carp, which grow to about 30 pounds and live a decade, are voracious eaters and bred to be sterile, explained Mike Bodle, an invasive species specialist overseeing the release for the district. Non-sterilized carp that escaped into the Mississippi River in the 1990s have spread to river systems in Ohio, Missouri, Illinois and Wisconsin, posing a major threat to the Great Lakes, where biologists fear they could critically damage habitat.

But for the last 20 years, South Florida water managers have successfully used sterilized carp as an alternative to treating hydrilla with weed-killing herbicides. About 10 carp can clear up to an acre of hydrilla, Bodle said.

“They love hydrilla,” he said. “If we give them a selection of weeds including hydrilla, they will actually eat the hydrilla first.”

Hydrilla, also called water thyme, was first imported to South Florida as an aquarium plant in the 1950s, according to the University of Florida’s Center for Invasive and Aquatic Plants. Like the python and iguana, it soon made its way into the wild and by the 1970s was filling freshwater canals, lakes and ponds.

“It’s one of these invaders that has no controls,” Bodle said.

Any fragment of a plant can take root, meaning it can be spread by boat propellers or simple current. The plant needs little light, so it can grow in deeper, murkier water than native plants, Bodle said.

“Where our natives wouldn’t do well, they do fine,” he said.

Water managers need to keep canals clear primarily for flooding. But in Homestead, the canals also feed the shallow aquifer where wellfields are located that provide water to the Florida Keys, Bodle said.

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