Improvements in water quality following biomanipulation of gizzard shad (Dorosoma cepedianum) in Lake Denham, Florida

Abstract We removed gizzard shad (GS; Dorosoma cepedianum) from Lake Denham, a 104 ha hypereutrophic lake in the Ocklawaha chain of lakes in central Florida, to evaluate biomanipulation for restoration of shallow hypereutrophic Florida lakes. A commercial haul seine removed GS in winters 1990, 1991, and 1992. The 3-year total removal was 51,738 kg wet weight or 498 kg/ha, which reduced the stock of harvestable adult GS to less than 3% of the initial level. Water quality in Lake Denham improved progressively during the biomanipulation, and some improvements persisted through 2007 despite removal of a fish barrier in 1993. From 1989 until 1993, mean annual Secchi disk visibility in Lake Denham increased from 23 to 57 cm, mean annual chlorophyll a decreased from 143 to 40 ug/L, and mean annual total phosphorus declined from 194 to 93 ug/L. Neither land use nor rainfall changed significantly during the experiment, and similar improvements were not evident in other basin lakes during the same period. These fin...