Climate change is heating up the devil fish that own the Saint John River

In another spiraling nature scare to hell in Florida, scientists suspect global warming has allowed devil fish to run rampant and ravage the St. Johns River.

This summer, a team of state water and wildlife experts, with the help of a team of commercial fishermen, cast industrial nets in a central Florida section of the river at several miles south of Cocoa, called Lake Winder.

Of the estimated 40,000 pounds of many species transported for examination, only a small portion, less than 20%, was Florida: sea bass, crappie, edge, catfish, bowfin and others.

The rest were exotic: a type from South America widely known as armored catfish, some of which are also known as devilfish, and tilapia from Africa.

Since this exploratory outing, unanswered questions have arisen. Why are the invaders there, why do they far outnumber the natives, spoil the water quality and mow down essential aquatic plants in the river? Research plans are unfolding.

“We are in the early stages of investigating whether we can blame these exotic fish,” said Reid Hyle, freshwater fisheries biologist at the Florida Fish and Wildlife Research Institute.

These alien invaders have been established in parts of Florida for decades, but population numbers are unclear, Hyle said.

The St. Johns River Water Management District, a state agency responsible for the use and maintenance of surface and ground water from Orlando to Jacksonville, is also studying disturbance to fish populations.

Scientists know that armored catfish tear up river bottoms for nesting and that tilapia consume aquatic plants – behaviors that can upset water quality and ecosystem balance.

“A bigger issue that we suspect why they’re increasing over time is climate change,” said Erich Marzoff, district director for water and land resources. “We just don’t have the frequency of hard freezes that we’ve had for the past few decades.”

Florida’s well-documented rise in temperatures was particularly significant for the state’s warmer winters, which ushered in a northward migration of aquatic plants, including mangroves, and fish, including snook, which are not particularly cold hardy.

Central Florida is a tipping point between freezes that rarely occur in South Florida and still occur fairly often in North Florida.

Even in North Florida, however, tilapia and armored catfish are having a growing impact on the St. Johns River near Jacksonville.

These exotic fish are “contributing to the decimation of eelgrass that has been weakened by saltwater intrusion and more frequent hurricanes,” said Lisa Rinaman, head of the environmental group St. Johns Riverkeeper.

To some degree, the natives learned to enjoy or at least entertain themselves with the invaders, said Doug Sphar, a resident of Lake Poinsett, which is next to Lake Winder, and a longtime contributor to the environment. from Florida.

“Tilapia keeps alligators fat and happy,” Sphar said. “I see and hear them often take a big tilapia. They seem to play with them like a dog with a new chew toy. I also see alligators taking on armored catfish.

Hyle said a major cold snap in 2010 wiped out tilapia and armored catfish along the St. Johns River in central Florida.

“The kill was significant,” Hyle said. “It was amazing to come out on the St. Johns after that happened and say ‘wow, that’s how many of those things were here. “”

For tilapia and armored catfish, lethal water temperatures start in the low 50s. They are more suited to the tropical conditions where they come from – the waters of the Nile and Amazon river systems.

Fish are given many different common names by non-scientists. The armored catfish caught in Lake Winder is so called because of its impressive scales. Although they are cold wimps, they are otherwise tough as nails and can survive out of water for hours.

Two types of armored catfish have been carried and they are not closely related.

One was the brown hoplo which can grow to about 10 inches in length. They nest by chewing vegetation into frothy spit balls that cradle the eggs.

Largemouth bass and snook eat hoplos, which the Florida Fish and Wildlife Conservation Commissioner says are also “highly sought after as food by Floridians with cultural ties to Trinidad and parts of South America.” .

Of the more than 1,000 pounds of brown hoplos captured by researchers, they were quickly sold for $3.50 a pound.

The other armored catfish, a type often seen in ever-hot springs, such as Wekiwa and Blue in central Florida, is sometimes called a pleco, for plecostomus, a popular aquarium species.

They’re not actually a pleco, a rather small fish, Hyer said. They are a vermiculated catfish, he said, that can grow up to 20 inches and 3 pounds, which is why aquarists have thrown them into lakes and rivers.

In Texas and Mexico, the vermiculated sailfin catfish is sometimes referred to as devil fish.

The search party brought back 9,000 pounds of fish. There is no market for them. Some were transported to a landfill and others were washed into the river.

In public presentations of the Lake Winder findings, the Water District has included the popularly known name pleco and the attention-grabbing name devil fish.

Also according to the Lake Winder study, nearly 23,000 pounds of tilapia were sold at 58 cents per pound.

Evil fish drilled holes in river banks to nest. Tilapia dig potholes in the bottom of rivers, leaving what looks like a lunar landscape of craters.

Both nesting behaviors are thought to stir up sediment and dislodge aquatic plants.

The Florida Fish and Wildlife Conservation Commission, on its website, still describes devilfish or vermiculate catfish as “occasionally found in central Florida”.

“We really had no idea,” Marzoff said of the water district’s understanding of armored catfish populations in its flagship water body, the St. Johns River. “We suspected they were moving north and we didn’t have good recent data.”

Along with continued research into the damage caused by invading fish, the Water District is also considering a remedy like the one long implemented at Lake Apopka to get rid of a trash fish called gizzard shad that plays a role in increasing water pollution.

The Water District urges commercial crews to catch as many Apopka shad as possible, which are usually sold as crabbait to offset the cost of removing the fish.

A public-private partnership like this could help get rid of tilapia and armored catfish in the St. Johns River, Marzoff said. “We may not have to pay much.”

kspear@orlandosentinel.com