Habitat use and movements associated with changes in dissolved oxygen (DO) levels and hydrology for 20 radio-tagged largemouth bass {Micropterus salmoides) were studied in the Kissimmee River, Florida, in 1992 and 1993. River channel littoral vegetation, smartweed (Polygonum hydropiperoides) and spatterdock {Nuphar luteum), were habitat types bass most commonly used. Bass maintained home areas in remnant channels and the C-38 canal that had DO >2 ppm throughout the year. During summer when DO dropped slowly over several weeks, bass were frequently located in waters with DO between 1 and 2 ppm. Daily movements, which averaged <100 m in more than half of the location samples, were greatest when previous location DOs were <1 ppm during summer and <2 ppm during fall. Daily movements >1 km from June through October were coincidental to acute decreases in DO <2 ppm at previous location sites. Although bass were occasionally located in waters with DO <1 ppm during summer, they usually died or moved out of these low DO areas. Northern remnant river channels and northern sections of the C-38 canal in impounded river pools consistently maintained higher DO levels (>2 ppm) than southern areas. Bass were tracked to these northern areas during periods of stressful DO. During periods of increased flow and high water, bass moved into smartweed, spatterdock, and submerged willow (Salix spp.) along channel margins, and inundated floodplain with terrestrial grasses, where flow averaged <6 cm/sec. Bass returned to previously established home areas after DO increased above lethal concentrations or as flood plain waters receded. Improvements in DO availability and reestablishment of complex floodplain habitat, which are dependent on reintroduction of historic flow regimes and amelioration of river channel habitat, are keys for restoration of the Kissimmee River's fisheries.
