The Gulf sturgeon (Acipenser oxyrinchus desotoi) is a threatened anadromous species in the Gulf of Mexico. Nineteen subadult Gulf sturgeon were equipped with ultrasonic transmitters (34-40 kHz) in the Choctawhatchee River and Bay during fall 1996 and 1997 before their entry into marine habitat. The movement and habitat use of Gulf sturgeon in the estuarine/marine environment was determined from November through April 1996-1999. A total of 344 sonic contacts were made in this study. We documented fish location using a GPS and recorded water depth, temperature, salinity, substrate type, and distance from shore. Subadult Gulf sturgeon migration from the freshwater riverine system to the marine system was influenced by an increase in river flow and a decrease in water temperature. Fish moved throughout Choctawhatchee Bay, but mostly used shoreline areas. The use of 5 geographic areas by 95% of telemetered Gulf sturgeon may be linked to food availability. Gulf sturgeon overwintered for 5-6 months from November through April in Choctawhatchee Bay, Santa Rosa Sound, and Pensacola Bay. After overwintering in Choctawhatchee Bay, telemetered subadults returned back to the Choctawhatchee River in late April through May when mean water temperatures ranged from 18 to 25 C. Several telemetered fish were relocated in the Muddy Lake area of the river and remained there for several days before downstream or upstream migration.