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Implementing a Statewide Protocol for Monitoring Freshwater Fish Health

The Florida Fish and Wildlife Conservation Commission (FWC) values the health of Florida’s freshwater ecosystems and sportfishes and agency staff recently addressed concerns about fish health in response to stakeholder concerns. These stakeholders commonly attribute aquatic plant management and herbicide use to the degradation of Florida’s water quality and the apparent increase in fish disease. Until recently, freshwater fisheries biologists lacked data to evaluate these concerns and determine the appropriate course of action. In response, the FWC’s Freshwater Fisheries Research and Management divisions implemented standardized protocols to record fish health abnormalities into the established freshwater fish long-term monitoring program.

Map with triangles mostly in middle of state with a couple spread throughout the bottom and one in Panhandle area

Figure 1: Distribution map of lakes sampled for comparisons between percent fish health abnormalities and water quality, herbicide use, watershed use and fisheries community metrics.

Abnormalities were recorded into five categories while in the field. The “FLOPS” model was developed to standardize fish coding across the state:

F = fin rot/erosion
L = lesion (including, but not limited to, sores, ulcers, tumors)
O = other (wounds created by anglers, natural predators, or spawning stress)
P = parasitic infections
S = skeletal malformation

Abnormalities were noted in Spring 2020 and Spring 2021 at 64 and 68 lakes across the state of Florida, respectively. On average across both years, 6% of largemouth bass exhibited abnormalities, of which lesions (2.5%) were most prevalent during both years. In 2020, 18,519 bass were examined and 1,088 (5.9%) coded with some abnormality, while in 2021, 18,918 were examined and 1,072 (5.7%) were coded. Parasites (code P) were recorded most often in 2020 while lesions (code L) were the most recorded abnormality in 2021.

The percent of abnormalities was then compared to 39 variables from categories including herbicide use, water quality metrics, watershed land use, and fish community composition. A few specific variables were the percent of urban land use by watershed, total pounds of applied active ingredient herbicide (i.e. glyphosate, diquat, 2,4-D) per surface acre, and total lake productivity or trophic state. FWC biologists found no evidence to support a link between any variables and the prevalence of abnormalities in bass.

This initial study demonstrated no relationships between the percentage of largemouth bass with abnormalities and a variety of physical, chemical, and biological lake characteristics. Continued data collection will support future analyses of trends in the prevalence of abnormalities in largemouth bass and other freshwater species of sport fish. Future management efforts will focus on providing current, relevant information to citizen stakeholders on different abnormalities and their effects on the status of Florida’s freshwater.

Chart with circles (plots) mostly along the 0 value of the y-axis

Figure 2: Example of scatterplot of metric (total pounds of active ingredient standardized by lake acres) and proportion of observed abnormalities of largemouth bass by waterbody.