A 2-part study (multiple mark-recapture and telemetry) was used to estimate the size of the shortnose sturgeon (Acipenser brevirostrum) population and their habitat use in the Ogeechee River, Georgia. The mark-recapture study was conducted from July 1993 to December 1994 and used the modified Schnabel model for estimating population size. Sixty-two shortnose sturgeon were marked; 17 were recaptured at least once. Seventy-eight percent of the marked fish were older juveniles and adults [>56.0 cm fork length (FL)]. Estimated population size was 266 (95% CL 236-300) in 1993 and 72 (95% CL 57-91) in 1994. CPUE declined 6-fold from 1993 to 1994. The telemetry study was conducted from June 1994 to June 1995. Radio and ultrasonic transmitters were used to monitor the movements of 20 adults and 1 juvenile shortnose sturgeon. Tagged fish never left the river system and used specific regions of the river during summer, fall/spring, and winter. During the summer, when water temperature was >27.0 C, fish were found frequently aggregated in deep holes (>4.5 m) at tidal freshwater locations [>44.0 river kilometer (rkm)]. During spring and fall, when water temperature was <27.0 C and >16.0 C, respectively, shortnose sturgeon moved into mesohaline areas (26.2-36.6 rkm); during winter when water temperatures dropped below 16.0 C, sturgeon moved farther downriver to polyhaline regions (19.2-30.5 rkm). Shortnose sturgeon were more dispersed and their movement increased when water temperatures were <27.0 C. This behavior altered the catchability of these fish and may have influenced our population estimates.
