Abundance of endangered shortnose sturgeon (Acipenser brevirostrum) in the Altamaha river in Georgia

Abstract

Anthropogenic perturbations during the 19th and 20th centuries resulted in major declines in abundance of populations of shortnose sturgeon (Acipenser brevirostrum). Despite the designation of this species as endangered, most populations are still not recovering. Abundance monitoring is needed to identify fluctuations in recruitment and survival; however, river-specific assessments are deficient throughout the range of this species. During the summer of 2011, we used anchored nets to fish a closed population of shortnose sturgeon in the Altamaha River in Georgia. Markrecapture tagging resulted in the capture of 288 shortnose sturgeon (272 fish with unique marks and 16 fish recaptured) over 11 weekly sampling occasions. Estimates of the abundance of shortnose sturgeon were derived by using Huggins closed-capture models. The preferred model incorporated effects of temporal variation on weekly capture probability and estimated an abundance of 2218 individuals (95% confidence interval [CI]: 1424–3350), including 725 (95% CI: 455–1192) juveniles and 1493 (95% CI: 954–2409) adults. Point estimates of group abundance indicate that the population is dominated by adults, although dynamic shifts in size structure following periods of high recruitment have been reported to occur. This study continued previous mark-recapture efforts in this river system, and its results offer further evidence that the Altamaha River supports the largest population of shortnose sturgeon south of Chesapeake Bay.