Dissolved oxygen is a critical component of river water quality. This study investigated average weekly dissolved oxygen (AWDO) and average weekly water temperature (AWT) in the Savannah River during 2015 and 2016 using data from the Intelligent River sensor network. Weekly data and seasonal summary statistics revealed distinct seasonal patterns that impact both AWDO and AWT regardless of location along the river. Within seasons, spatial patterns of AWDO and AWT along the river are also evident. Linear mixed effects models indicate that AWT and low and high river flow conditions had a significant impact on AWDO, but added little predictive information to the models. Low and high river flow conditions had a significant impact on AWT, but also added little predictive information to the models. Spatial linear mixed effects models yielded parameter estimates that were effectively the same as non-spatial linear mixed effects models. However, components of variance from spatial linear mixed effects models indicate that 23-32% of the total variance in AWDO and that 12-18% of total variance in AWT can be apportioned to the effect of spatial covariance. These results indicate that location, week, and flow-directional spatial relationships are critically important considerations for investigating relationships between space- and time-varying water quality metrics.

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 × 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.

Understanding the relationship between number of spawners and recruitment is essential for managing fish populations. Atlantic Sturgeon Acipenser oxyrinchus (ATS) are endangered anadromous fish inhabiting the rivers, estuaries, and marine environments along the Atlantic coast of North America. Atlantic Sturgeon are periodic life history strategists that exhibit both spring and fall spawning migrations. Traditional capture–mark–recapture techniques can be used to estimate spawning run abundance but are resource intensive and potentially stressful on migrating individuals. Noninvasive methods, such as side‐scan sonar, can be a less stressful alternative to estimating abundance. We sampled the uppermost portion of the Savannah River, USA, over 50 occasions from August to November 2017 using side‐scan sonar. Bayesian N‐mixture modeling was used to estimate spawner abundance and covariate effects based on spatially and temporally replicated count data obtained from sonar recordings. We detected at least one ATS on each sampling occasion and estimated a maximum daily spawner abundance between 35 and 55 individuals (95% credible interval) within the sampled area during the 2017 fall spawning season. Maximum discharge significantly affected ATS detection, and site average maximum depth significantly affected ATS abundance. Our results suggest that side‐scan sonar can be used as an alternative to traditional mark–recapture techniques for spawner abundance estimation. Routine sampling by using our methods will efficiently produce spawning run estimates and provide insight regarding the effects of environmental covariates on spawner abundance seasonally.