Anatomy of Florida Fish Kill
So, what happened, and could it happen to a lake near you? Unfortunately, it seems like a case of nature taking its course and, yes, it happens throughout the state each summer. In this case, it appears that heavy rainfalls flushed organic matter into the lake and the organic matter began to decompose, resulting in a low-dissolved-oxygen (DO) fish kill. As in most such cases, the die-off did not kill all of the fish, and when the water cleared and the sun came out, oxygen levels recovered and biologists observed numerous surviving fish.
This type of fish kill is pretty much a natural occurrence. They are especially prevalent in summer when a number of factors can come together to deplete the oxygen that is dissolved in the water. Fish absorb this oxygen from the water using their gills.
Aquatic plants produce most of the oxygen in lakes through photosynthesis, which occurs when green (chlorophyll) cells convert light into energy. However, at night or when there is inadequate light, plants use oxygen and give off carbon dioxide. Additional oxygen enters the water from the atmosphere by diffusion. In addition to fish using oxygen and plants removing it at night, a major demand on oxygen comes from decomposition of dead plant and animal tissue (organic matter).
Biologists visited daily for several weeks, documenting the number of dead fish and concluded that few adult game fish survived. However, they observed some schools of fingerling bass and bream from the spring spawn and a few bass on beds.
“We know there was over 19 inches of rain in the area from January to April, and the lake got its share of rain and runoff,” said Chris Paxton, the FWC’s freshwater fisheries administrator for northwest Florida. He said the FWC was in constant contact with the Florida Department of Health and the Department of Environmental Protection and that FWC staff accompanied investigators from the Department of Agriculture to inspect the lake during the fish kill. There was no visual evidence of chemical pollution, toxic algal blooms or signs of disease among the dead fish.
“This is something all of us, including the residents around the lake and our own fisheries management staff, wish never happened but in time the lake will recover,” Paxton said. Once oxygen levels build back up, the FWC will restock the lake with fingerling sport fish.
The good news is there is no evidence of any form of contamination that would prevent the lake from recovering. In addition, reduced competition often allows young sport fish to grow rapidly after kills of this type.
To learn more about fish kills and what you can do to help prevent them, visit MyFWC.com/Contact. Although most summer fish kills relate to natural processes, the FWC requests your support in reporting fish kills to the FWC Fish Kill Hotline at 800-636-0511 or at the above link.
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