Periodicity of Habitation of a Stenothermal Spring Run in North-Central Florida by Blue Tilapia

Abstract

The blue tilapia Tilapia aurea, an exotic African cichlid, has attained nuisance abundances in many Florida lakes. The species congregates in stenothermal spring runs, making it vulnerable to control measures. To determine when control measures would be most effective, the relative abundance of blue tilapias in a spring run in north-central Florida was estimated at monthly intervals from October 1981 to April 1983 by means of gill nets and underwater counts along line transects. Relative abundance of blue tilapias in the run was inversely correlated with water temperature in Lake George, the water body into which the run flows. Many blue tilapias entered the run in late fall or early winter when water temperatures in Lake George fell below those in the run, and they emigrated in spring when Lake George became warmer than the run. Abundances in the run were highest in midwinter during or immediately after periods when lake water temperatures reached their lowest levels. The temperature differential between Lake George and the spring run was apparently the proximate directive factor governing movement of blue tilapias into the run, suggesting that only those blue tilapias that encountered the run's thermal plume in Lake George entered the run during winter. Control measures in the run would likely have little effect on the blue tilapia population of Lake George.