Florida population

Exotic blue tilapia make up 86% of the total fish mass at Silver Springs


A recent count of the famous Florida fish Sources of money revealed alarming results: Blue tilapia, an invasive fish, now accounts for 86% of the biomass, or weight, of the total fish population in the springs.

What was considered a “tilapia explosion” by the Howard T. Odum Florida Springs Institute (FSI) coincides with declining native fish populations, general decline in spring health, and continued calls to cross the dam. Rodman / Kirkpatrick near Palatka.

“He’s a rebel invader,” said ISF director Robert Knight. “Once they got in, I don’t know if anyone managed to control them.”

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FSI is an independent nonprofit organization founded in 2010 by Knight, which has researched the Florida sources, which number more than 1,000, since his doctoral research on Silver Springs in the 1970s.

Decline in native fish populations

In the counts taken in 2004, 2009 and 2013, tilapia were present, but their populations were not significant. According to the FSI’s first tally, taken in 2019, blue tilapia made up 25% of the weight of living fish in Silver Springs. They were also 26% in 2020, but the numbers jumped to 86% in a count in July.

In a press release on the results, Knight said tilapia competed with native mullet and gizzard shad for food, as well as bass and sunfish for nesting areas.

Paula Russo, Florida State Parks Foundation Grants and Programs Administrator, top right, was all smiles on August 26 as the fish passed under the Chief Potackee-Betty Mae Tiger Jumper, the world's first glass-bottom boat fully accessible to join the Silver Fleet from Springs State Park.

Native fish species were only 41% of their population size before the Rodman / Kirkpatrick Dam was completed in 1968 when populations collapsed.

Fish populations declined 78% in 1979 and 92% in 2004. Although the overall biomass is increasing again, it is largely due to non-native tilapia.

Between the 1950s and 2004, the populations of the largemouth bass and crappie declined 67% in Silver Springs, and they are still down 48%.

More dramatically, the number of catfish has fallen by 91% since 1954, and the striped mullet, essential for consuming algae, has fallen by 77%.

Who released the tilapia?

Knight suspects that tilapia, native to the Middle East and parts of Africa, were allowed to enter the St. Johns River system, which is home to many invasive species, through the dam lock.

“We also saw another exotic that had an explosion years ago, but nothing like this tilapia explosion,” Knight said. “It was an armored catfish, and it’s a South American fish that infiltrated all of North Florida.”

Both are tropical fish attracted to springs due to the heat of the water in winter.

Blue Tilapia with Mullet on the Silver River.  This photo was taken during the Florida Springs Institute's Silver River Fish Count on July 19.

Knight says the health of the Florida sources has declined at an accelerating rate. Silver and Rainbow Springs are both polluted with nitrates, which cause algae blooms and alter the types of vegetation in the area.

“The tilapia explosion is linked to the pollution of Silver Springs,” he said. “I think it might end eventually, but they react to a damaged system. This is what happens when you damage a complex ecosystem. You get invasive species.

A damaged ecosystem

Knight remembers riding the iconic glass bottom boats of Silver Springs with his grandparents 68 years ago when he was just 5 and the fish were the big draw.

While tourists may not notice the lack of diversity in fish species, the ecosystem will.

“Fish have a purpose,” Knight said. “The fish are not just there for decoration.

He explained that the best consumers control the ecosystem by preying on the lower consumers, who control herbivores and cascading down the food chain. Mules, which are still present to some extent, do a good job of reducing algae populations, but tilapia do not.

A kayaker heads to the springs on August 16 as Captain Mark Miller guides a glass bottom boat along the Silver River.

“What happened with Silver Springs was that there was a large population of catfish, and the catfish are literally bottom eaters. They eat everything. They’re gone, ”Knight said. “Gars have almost disappeared from Silver Springs based on the past three years. The gar count was insignificant last year, and they’ve always been part of the food chain here.”

Violation of the Rodman / Kirkpatrick Dam would bring back catfish and other large predatory fish like striped bass to compete with tilapia and potentially control their population, according to the FSI press release.

“The whole system is changing, and what we see when we measure the productivity of the Silver River, we see a decline in the productivity of the river,” Knight said, referring to the total production of organic matter in the system. is producing.

Tilapia do not help maximize ecosystem productivity, he added. He expects the system to support the fish only temporarily before the population collapses, as the armored catfish did.

How to restore Silver Springs

Whether the population is naturally controlled or not doesn’t change three needs of Silver Springs for Knight.

First and foremost, he says, he needs his return, which has been altered by the pumping of groundwater and an increasing number of wells. Second, nitrogen pollution from fertilizers and septic tanks needs to be addressed. Third, the dam must be removed.

“To restore Silver Springs to its former beauty and glory, you are going to have to address these three issues,” he concluded.

The rupture of the dam has been expected for 50 years in Knight’s mind, and many activists and organizations, such as Free the Ocklawaha, also pleaded for its removal.

“The economics have been studied, the alternatives have been studied, the environmental impacts have been studied,” Knight said. “It’s just a matter of having the political will to confront a fairly small group of supporters of maintaining the dam, because it’s not in the public interest.

Knight, who says he spends his retirement fighting for the springs, also hopes to build the Silver Springs Environmental Center in Silver Springs State Park, pending funding.

The center would conduct research on artesian springs and the Florida aquifer, which supplies the region with groundwater, as well as a hub for spring awareness and education.

Contact reporter Danielle Johnson at [email protected]


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