Recruitment Trends of Atlantic Sturgeon in the Altamaha River, Georgia: Are We on the Road to Recovery?

Atlantic sturgeon once supported a lucrative commercial fishery throughout the US eastern seaboard; however, decades of overharvest and habitat alteration have decimated most populations. In response, the Atlantic States Marine Fisheries Commission closed this fishery in 1998, and today, this species is being considered for federal listing under the Endangered Species Act. Unfortunately, the effects of the fishery closure are unclear because of a lack of quantified data on current abundance and population trends.  Recent studies have shown, however, that mark-recapture estimates of age-1 cohorts may provide a quantified measure of recruitment that can forecast long-term population trends.  The objectives of this study were 1) to assess recruitment of age-1 Atlantic sturgeon in the Altamaha River and 2) to determine which environmental factors are most influential in determining year class strength of Atlantic sturgeon. From 2004-2010, we conducted mark-recapture estimation of age-1 Atlantic sturgeon cohorts within the Altamaha River using the Huggins closed-capture model in Program Mark. Over the seven years of the study, age-1 population estimates varied from a low of 433 in 2006 to a high of 6225 in 2010. The seven consecutive years of cohort abundance estimates were then used to create a recruitment model to evaluate effects of different environmental variables on annual recruitment. Our results showed that the primary factor influencing recruitment of Atlantic sturgeon is the length of time following the fishery closure.  These finding provide the first quantified evidence that the 1998 fishery moratorium has aided in the recovery of the species. Though our results are promising, additional years of recruitment data are needed to confirm a positive trend in recruitment, and hence, recovery of the Altamaha population.  Similar efforts also are needed on other rivers to evaluate population trends and key recruitment variables in other parts of the range.