Cows under water
Pallavi Agarwal | Highlands TodayAVON PARK - Kelle Sullivan pulled out a long, wiry hydrilla stem from the shoreline of Lake Glenada as waves lapped in the breeze, showing a glimpse of green vegetation under the water.
Published: February 8, 2013
Published: February 8, 2013
If left unchecked, this highly invasive, non-native plant, which brings shudders to some people who have to deal with it, can literally choke up a lake.
From the lake bottom where it grows, hydrilla proliferates to the surface, forming dense mats that clog waterways, chokes beneficial native plants and makes recreational activities challenging or impossible, explained the Florida Fish & Wildlife Commission biologist.
Thursday morning as ducks waded around in the peaceful Avon Park lake, fringed by cat-tails, Sullivan waited for a consignment of hydrilla fighters – silvery fish with a voracious appetite for the exotic plant.
FWC was going to put a 1,000 of the fish, called grass carp, into Lake Huntley in Lake Placid and 300 into Lake Glenada Thursday.
"The stocking rate is two fish per acre," Sullivan said.
She likens the grass carp to cows under water. They nibble up all the hydrilla, thus helping to control it.
Healthy lakes require native aquatic vegetation, Sullivan explained.
"When the right kind and correct quantity of plants are part of the natural system in local lakes, the water is clear, the shoreline is stabilized and fish and wildlife populations are balanced," she added.
Lakes Glenada and Huntley are a handful of public water bodies in the county that have grass carp.
Two years ago, FWC stocked Lake Glenada with some grass carp after applying herbicide to first knock off the hydrilla so the fish could contain it from growing back, but the carp was not enough.
"Last year the hydrilla kept coming back along the shoreline," Sullivan said.
The carp that is used is a functionally sterile kind, called triploid. They can't reproduce, have a life span of 10 to 15 years but are really effective for hydrilla control for six to 10 years.
Permits are also issued to private groups that want to stock the triploid grass carp to control the invasive plant, from apartment complex ponds to canals such as like in the Spring Lake Improvement District, which has had grass carp since the 1990s.
Sullivan said 187 water bodies in Highlands County have permits to stock the fish, and that includes the "less than five" public lakes that have the carp.
She said the grass carp work best and are the most cost-effective when used in conjunction with a herbicide treatment.
And the "lawn mowers with fins," as they are sometimes described, don't work everywhere.
As research has gotten better, Sullivan said, experts now know where the grass carp works and where it does not.
Using these fishes, which are native to China, for aquatic weed control is nothing new.
A 1987 article from the Orlando Sentinel discusses how FWC – when it used to be known as Florida Game and Fresh Water Fish Commission -- planned to begin stocking Lake Yale in Eustis with 4,000 grass carp to prevent a reinfestation of hydrilla.
Sometimes, the grass carp did the job.
Sometimes, an overabundance of the fish that didn't get enough hydrilla to subsist on, instead nibbled up or destroyed the good vegetation, too.
That's what happened when too much grass carp was introduced to Lake Jackson in 1996.
They stripped the lake of anything green, even when they didn't want to eat the plants such as the cat-tails.
"They are like cows under water in a pasture," Sullivan said. "If you have too many cows in a pasture, you are left with very little grass."
Grass carp also are instinctively drawn to flowing water and will just float away if they are not stocked in a contained body of water, without any inflows and outlows. Like salmon, they fawn upstream, Sullivan added.
Many years ago, researchers thought Lake Istokpoga was too big for the grass carp to escape. Turns out, because of their propensity to flowing water they ended up in Arbuckle Creek or in Lake Okeechobee.
Today, Sullivan would like to consider restocking Istokpoga.
"The research then was not as extensive," she said.
Spring Lake Improvement District's Manager Joe DeCerbo said the grass carp have worked well for them. About three or four months ago they restocked their canals and ponds with about 1,500 of the fishes.
To say they are voracious eaters may be an understatement. When Spring Lake first got its juvenile carp they were about 8 to 10 inches long.
"Right now they look like logs," DeCerbo said. "It's unbelievable. Some of them have got so big they look like alligators."
The gators are also their big enemy and the fish may end up being food in a gator-infested place.
DeCerbo estimates that about 20 percent of their grass carp have been consumed by gators.
If you have questions or concerns about the grass carp treatment, call FWC Regional Biologist Kelle Sullivan at (863) 534-7074.