Evidence of Metapopulation Dynamics in Shortnose Sturgeon in the Southern Part of Their Range

Abstract

The shortnose sturgeon Acipenser brevirostrum is one of the most endangered members of the sturgeon family because of overexploitation, depressed population levels, and a shrinking range. The lack of historical data on shortnose sturgeon populations has led to an increase in sturgeon research over the last three decades; however, most recent studies have not focused on southern populations. The objective of this study was to estimate the abundance, annual survival, and temporary emigration rates of shortnose sturgeon in the Ogeechee River, Georgia. Shortnose sturgeon were captured with gill and trammel nets for a mark–recapture analysis from 1 June to 31 August in each of the 3 years from 2007 to 2009. Over the three summers of sampling, we conducted a total of 864 net sets and captured 168 individual shortnose sturgeon with an additional 51 recaptures. Our analysis revealed that the best‐fitting robust design population models incorporated interactions among water temperature, dissolved oxygen, and total effort in which capture and recapture probabilities were set equal and temporary emigration parameters were set to zero or held constant. Abundance estimates (95% confidence interval [CI]) were 404 (175–633), 264 (126–402), and 203 (32–446) individual sturgeon for 2007, 2008, and 2009, respectively. Population parameter estimates of annual survival and temporary emigration, combined with documented emigration and immigration of tagged individuals to and from the adjacent Altamaha River, provided evidence that the Ogeechee River stock is not discrete but possibly a metapopulation with the Altamaha River.