Abundance and Size Structure Of Shortnose Sturgeon Acipenser Brevirostrum In The Altamaha River, Georgia

Endangered Shortnose Sturgeon Acipenser brevirostrum inhabit large tidal rivers along the Atlantic coastline of North America, from the St. John River, Canada, to the St. Johns River, Florida. Currently, long-term assessments of southern populations are completely lacking. To address this information gap, the objectives of our study were to assess recent changes in 1) abundance and 2) age-structure of Shortnose Sturgeon in the Altamaha River, Georgia. During the summers of 2004-2010 we conducted an intensive mark-recapture population assessment in the lower Altamaha River using anchored entanglement gear. Over the 7-yr study, we captured a total of 1,737 Shortnose Sturgeon, (72 recaptures). Using the Huggins closed-capture model in Program Mark, we estimated that annual abundance varied from a high of 5,551 in 2006 to a low of 1206 in 2009. Much of the annual variation in abundance was caused by fluctuations in annual recruitment, which ranged from a low of 62 in 2009 to a high of 3,467 in 2006. The results of our study suggest that variable recruitment in conjunction with the accelerated life cycle of southern populations may explain why total abundance in southern rivers is typically much lower than those typically reported in northern systems.