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Quantifying Sturgeon Recruitment and Abundance using Mark/Recapture
Young juvenile Atlantic and Shortnose Sturgeons use their natal estuary as nursery habitat. Using standard mark-recapture methods and population modeling, the abundance of age-1 juveniles can be estimated each year; this provides a quantified measure of annual recruitment for the species. By collecting this information for each Georgia River over many years, it becomes possible to observe trends in recruitment, to model the effects of natural covariates on recruitment, and to observe how populations respond to anthropogenic or other disturbances.
Juvenile Atlantic Sturgeon Telemetry
River-resident juvenile (RRJ) Atlantic Sturgeon use the estuary of their natal river as a nursery area. In order to better understand the seasonal movement patterns of RRJs and to learn about the transition from the RRJ life stage to the marine-migratory juvenile (MMJ) life stage, we deployed acoustic transmitters in 79 age-1 juveniles in the Ogeechee, Altamaha, and Satilla rivers during the summers of 2014–2016. Movements of tagged fish were monitored using an array of stationary receivers deployed downstream from the heads of tide in each river system. During the summer months in each river, the fish congregated in upriver, freshwater reaches, but during the winter months they moved downriver and became more broadly distributed. Some fish migrated back up their natal river in the spring and remained there as age-2 RRJs, but we observed that about 30% of juveniles left their natal river system as age-2 MMJs during the winter months. These MMJs were detected in other Georgia estuaries and in systems as far away as Charleston Harbor, SC, and in Little River, at the border between North and South Carolina.
Assessing the Southernmost Sturgeon Populations
The St. Marys River, GA and the St. Johns River, FL historically hosted the southernmost populations of both Shortnose and Atlantic Sturgeon. These populations were understudied but thought to have been extirpated due to exploitation by commercial fisheries, bycatch, and anthropogenic development, including dam construction in the St. Johns.
Our studies have indicated that although sturgeon may no longer reproduce in the St. Johns River, the system remains important for the species - sturgeon from many other river systems were detected visiting the estuary and lower reaches of the river.
We confirmed that there are still Atlantic Sturgeon spawning in the St. Marys River, although this population is likely quite fragile. Additionally, Cumberland Sound regularly sees visits by sturgeon from other Georgia and East Coast rivers.
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