Manatees face new challenge in Florida from harassing, non-native armored catfish
Watching manatees gather in the crystalline waters of Blue Spring is one of Central Florida's outdoor treasures.
Increasingly, however, it's been a bit of a creep show: manatees are being sucked on by dark, plated, spiny and air-breathing invaders.
Rather than gorging on blood or flesh, the fish are eating algae growing on manatees, but that still freaks out and endangers the big animals, which is a key reason for the start of another season of hunting and killing the sailfin suckermouth catfish.
"You can see a manatee with 20, 30 or 40 catfish on it at the worst," said Melissa Gibbs, a mostly serene biology professor at Stetson University, who has mastered wreaking devastation on the exotic fish with a 7-foot, three-pronged, barb-tipped spear.
Gibbs explained that manatees seek winter refuge at Blue Spring near DeLand, escaping the colder St. Johns River.
There is no food for them in the spring and its stream that flows a third of a mile to the St. Johns River.
By staying calm and conserving energy, the animals can remain in spring waters for long periods before having to slip into the perilously chilly river to forage.
"The catfish aren't physically, directly damaging manatees," Gibbs said. "They annoy the heck out of them. And if manatees are twitching and moving around, they are burning calories."
"The harassment by the catfish indirectly affects the manatees that are then more prone to cold stress," Gibbs said.
Having studied the exotic fish for two decades, she thinks their numbers and the threat they pose are greater than ever.
One remedy being applied vigorously by Gibbs and others are early-morning hunts taking place now that the manatee winter season at Blue Spring is over.
Wielding her weapon, Gibbs brings a hunter's focus and, perhaps most importantly for someone with a doctoral degree in neurobiology, research-supported clarity for wanting them gone.
From the vantage point of a canoe or boardwalk, Blue Spring and its stream convey iconic Florida scenery. The water is transparent, showcasing manatees and a variety of fish.
But with a mask and snorkel, the underwater environment is surprisingly active, spacious and sort of cinematic.
Schools of juvenile tarpon rip to and fro with seriousness, manatees become comic blimps and fallen tree limbs provide visual mazes.
Also apparent is that sailfin suckermouth catfish are aquatic rats swimming amok.
Gibbs said they first appeared in Florida in the 1950s associated with fish farming in the Tampa Bay area.
Since then, they have spread elsewhere in the state, an invasion likely assisted by releases of aquarium fish.
In Florida's fresh waters, sailfin suckermouth catfish are mostly unstoppable.
Monica Ross, a senior scientist at Clearwater Marine Aquarium Research Institute and a manatee specialist, said she has observed the catfish at many other springs during the past winter, which had no cold snaps that might have suppressed their numbers.
And in Blue Spring waters, the poop of catfish, weighted with sand that the fish also ingest, is potent in contributing to the further formation of a plague of algae.
The fish feces contains digested algae that acts as fertilizer and live algae ready for explosive reproduction.
"You have a little nutrient bomb that lands on the bottom of the spring run," Gibbs said.
That's another reason to get rid of fish that don't give up easily.
They are shielded with boney plates, and often are called armored catfish, and can breathe air. When in distress, they turn their top and side fins into unyielding and formidable spines.
"I sometimes say facetiously they are evil and must be destroyed," Gibbs said. "But we know we can't destroy them."
At best, Gibbs and other catfish hunters can hope to reduce the population briefly and perhaps alter their behavior, making them more timid about leaving the St. Johns River to venture into Blue Spring.
Opening day of the catfish hunting season—which is limited to park officials and biologists—was last week at sunrise.
Blue Spring State Park manager Michael Watkins conducted a pre-hunt briefing on safety and on protocols for observing and staying away from inquisitive manatees.
The team's routine is to be out of the water before many park visitors arrive. They stalk the fish in a zone of the spring run that is off limits to boats and swimmers.
The harvest of catfish was steady, slowed only by the hunters having to swim back and forth to an unmanned canoe loaded with bins for the carcasses.
The fish each weighed 2 to 3 pounds and sometimes more.
In less than an hour, the four hunters had taken 125 of the fish, which are widely considered to be inedible, and they soon became a pile of organic fertilizer in a citrus grove.
In the past 10 years, Gibbs and others have removed more than 7,000 of them.
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