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Gizzard shad are caught in nets as part of the harvest process and must be de-tangled from the netting.
A fishing story: Improving water quality in Lake Apopka, one fish at a time
By Ed Garland
The story of Lake Apopka is similar to that of the mythical Phoenix, one of decline followed by gradual rebirth. And a pesky, bottom-feeding fish called a gizzard shad.
Stretching across northwest Orange and southeast Lake counties, Lake Apopka is the expansive headwaters of the Ocklawaha Chain of Lakes. The state’s fourth-largest lake was once a world-class bass fishery but decades of degradation garnered Lake Apopka the dubious title of Florida’s most polluted large lake.
The culprits in Lake Apopka’s decline were familiar. Change came in the 1940s, when 20,000 acres of floodplain wetlands on the lake’s north shore were drained and converted to farming. The farms discharged phosphorus-rich water into Lake Apopka until the late 1990s. In addition, the lake received treated wastewater discharges from shoreline communities and discharges from citrus processing plants prior to the 1980s.
In the 1980s, the St. Johns River Water Management District embarked on a multi-pronged strategy to restore the pea-green lake, and its once world-class bass fishery.
The district’s long-term restoration strategies have focused on a phosphorus “diet and exercise” program. The diet includes efforts to reduce the amount of phosphorus reaching the lake from the lake’s watershed, including the former north shore farming area. Key to the diet has been the restoration of wetlands on the former farmed areas because this area’s phosphorus-rich soils, which once attracted farmers, if dry, would leach phosphorus to the lake.
The exercise program contains two innovative projects to remove excess phosphorus from the lake itself. A 760-acre man-made wetland filter, or “marsh flow-way,” uses wetland plants to filter algae and suspended sediments (and the associated phosphorus) from the lake’s water. This recirculating wetland has filtered the lake’s volume five times since it started operation in 2003.
A fisherman processes a day’s catch in his boat prior to offloading to use as bait in the U.S.’s Gulf Coast.
But back to our fishing story: In the early 1990s, district scientists began a more unorthodox exercise to remove nutrients. They reasoned that removing gizzard shad would help improve the water quality by removing the phosphorus contained in the fish’s bodies. Gizzard shad (or Dorosoma cepedianum), are native to Florida waters. In a healthy lake, gizzard shad may account for 5 to 20 percent of the fish population, but in nutrient-rich lakes, gizzard shad proliferate, reaching upwards of 90 percent of the fish population. Call them finned phosphorus factories that are easy to catch.
“Gizzard shad stir up sediments and cloud water as they graze on algae at the bottom of a lake,” says Dr. Dean Dobberfuhl, chief of the district’s Bureau of Water Resources. “Gizzard shad excrete nutrients in fertilizer form back into the water, perpetually recycling nutrients and fueling more algae growth, keeping the water murky green and limiting growth of desirable submerged plants that provide critical sport fish habitat. We’ve found that we can slow the cycle by harvesting tons of gizzard shad and the nutrients stored in their bodies.”
From October until late February or early March, commercial fishers fan out across the lake, harvesting the gizzard shad by the thousands with gill nets. Harvested rough fish are unloaded from boats at a temporarily constructed landing site on the district’s North Shore property. Each boat’s catch is weighed, iced and transferred to a refrigerated trailer truck for transport to a processing plant. The rough fish are sold as bait for crayfish and crab traps. The sale of the fish as bait offsets a portion of the harvest’s costs and reduces the district’s costs significantly.
“In terms of restoration costs, shad harvesting is very inexpensive compared to other options… It costs about $65 to remove a pound of phosphorus via shad harvesting, whereas more traditional treatments typically cost in the hundreds of dollars per pound.”
Dr. Dean Dobberfuhl, Water Resources bureau chief, SJRWMD
The district’s Dr. Dean Dobberfuhl, Water Resources bureau chief, is interviewed about the gizzard shad harvest and its benefits to Florida lakes.
“In terms of restoration costs, shad harvesting is very inexpensive compared to other options,” Dobberfuhl says. “It costs about $65 to remove a pound of phosphorus via shad harvesting, whereas more traditional treatments typically cost in the hundreds of dollars per pound.”
In pure numbers, it would seem removing gizzard shad based on the amount of phosphorus in their bodies — eight-tenths of a percent of their weight — would be a whopper of a story. But consider this: Apopka’s shad harvesting program has removed nearly 25 million pounds of gizzard shad from Lake Apopka since 1993. Combined with the rest of the diet and exercise program, phosphorus concentrations in the lake have been dropping for years and have been below the restoration target for a significant part of the past year.
And there’s another benefit as well: gizzard shad have a taste for zooplankton. Because zooplankton feed on algae, removing the fish may boost the zooplankton population, meaning more algae will likely be consumed. Zooplankton, in turn, are food for juvenile game fish species.
The shad are rinsed as they are unloaded from fishing boats.
“Our agency’s shad harvesting program exemplifies innovation and cost-effectiveness with regard to restoration of our water resources,” says St. Johns River Water Management District Executive Director Dr. Ann Shortelle. “As unorthodox as gizzard shad harvesting may seem, we are seeing measurable successes in the form of improved water quality.”
The entire harvesting process is strictly regulated to ensure game fish populations are not harmed. Prior to each harvest, the district obtains a permit from the Florida Fish and Wildlife Conservation Commission (FWC). The permit provides specific guidance on how to harvest shad while creating minimal impacts to sport fish. The gizzard shad harvest takes place only on weekdays to minimize interference with recreational sport fishing. The district and FWC monitor netting activities daily to ensure sport fish are unharmed. The district monitors all harvest activities, weight of rough fish (gizzard shad, tilapia and gar) numbers of fish caught other than rough fish, and water quality in the lake before, during and after the harvest.
In the proverbial big picture, intercepting these bottom-feeders in Lake Apopka and other lakes connected to the St. Johns River benefits water quality by exercising away existing nutrients. Combined with other nutrient diet and exercise projects, the district can continue its work to restore and protect water quality and aquatic habitats in Florida’s longest river.