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Stinky fish kill not a danger

A Hillsborough county scientist says a fish kill was caused by the drought, coupled with last month's heavy rainfall.


© St. Petersburg Times, published April 27, 2001

A Hillsborough county scientist says a fish kill was caused by the drought, coupled with last month's heavy rainfall.

CITRUS PARK -- Residents of Fawn Ridge are accustomed to seeing a variety of birds darting around a retention pond on Sheldon Road. But they're not used to seeing buzzards circling that normally tranquil scene.

Last weekend, however, Geoff Patton who lives on Colorado Place, counted 18 of the big birds feasting on a smorgasbord of dead fish. And they weren't alone. Other birds were also feeding on the carcasses of dead fish that had washed up or were floating in the retention pond across from the western entrance to Citrus Park Mall.

Patton, who works in bio-medical research at the University of South Florida, said he was frustrated by what he called the lack of immediate response by the county.

"I'm concerned there is not a better way to get a prompt response that would be timely if it had been a toxic event," Patton said. "There were no numbers I could find."

A flurry of telephone calls eventually linked Patton with the Hillsborough County Environmental Protection Commission and Eric Lesnett, an environmental scientist in the water monitoring section.

After checking out the fish kill Monday morning Lesnett determined it was most likely caused by the drought, coupled with last month's heavy rainfall.

"It stinks to high heaven," Lesnett said, but "it's not dangerous to the birds."

Lesnett said the fish "died from a shortage of oxygen. It's not like they were tainted with a chemical."

During a drought, everything from leaf litter to fertilizer collects, then when it finally does rain, the debris is washed into retention ponds. As micro-organisms in the water break down the runoff the oxygen level in the water decreases, killing the fish.

Shawn College, president of the Fawn Ridge Homeowners Association, theorized that herbicides applied monthly to control exotic weeds in the pond might have been a contributing factor.

"That, coupled with drought and warmer temperatures makes it more likely for fish kills to occur if the pond maintenance company is not careful," College said.

While this type of fish kill is not dangerous to birds, it is dangerous to ducks and other water fowl because of a bacteria that lives in the gullet of most fish, Lesnett said.

The bacteria is transmitted when the fish dies and contaminates nearby vegetation. Water fowl consume the vegetation and contract a disease similar to food poisoning. Though harmless to humans it eventually kills the animals, Lesnett said.

"When you see them staggering, wobbling, that's a paralysis of the central nervous system," Lesnett said.

That's why it is so important to remove the fish carcasses as soon as possible, said Lesnett who predicted the pond would eventually return to normal, especially after "we get three feet of water with the rainy season."

Lesnett said the problem could also be alleviated by installing a fountain to circulate the water and increase the oxygen level.

The county has counted more than 20 fish kills since early January, almost all have been caused by low oxygen levels or cold water. Wildlife officials said it is not unusual for fish to frequently die in retention ponds because the water and nutrient levels fluctuate so frequently.

"This whole event underscores man's joking attempt to try to manage an ecosystem," Patton said. "We can't even manage a small retention pond over a couple of acres."

- Jackie Ripley can be reached at (813) 226-3468.

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