Identifying Environmental Cues for Atlantic Sturgeon and Shortnose Sturgeon Spawning Migrations in the Savannah River

We investigated environmental cues for spawning migration behavior of Atlantic Sturgeon Acipenser oxyrinchus and Shortnose Sturgeon A. brevirostrum in the lower Savannah River, South Carolina and Georgia, from January 2013 to May 2018. Sturgeon were implanted with acoustic transmitters and detected on an array of 45 stationary receivers located every 5-10 km between Savannah Harbor and the upstream-most barrier to movement (301 fluvial kilometers). Throughout the study period, we observed six Atlantic Sturgeon attempting nine fall migrations (n = 918 records), four Atlantic Sturgeon attempting eight spring migrations (n = 257 records), and 15 Shortnose Sturgeon attempting 29 spring migrations (n = 3,542 records). Cues for the initiation of migration and upriver movement were species-specific. We observed significance in the main effects of water temperature, 3-d lagged temperature, maximum discharge, and 3-d lagged discharge, as well as in the interaction effect of 3-d lagged temperature x 3-d lagged discharge. Water temperature was the primary predictor of sturgeon migrations, which can be used to determine spawning season, but discharge also played a significant role in predicting upriver movement, particularly when high flows began to diminish. Directed flow regulation (e.g., intermittent flood pulsing) during key temperature thresholds may better facilitate the upriver movement of sturgeons and aid in the conservation of these imperiled species.