The Gulf sturgeon (Acipenser oxyrinchus desotoi) is a federally threatened, anadromous species, inhabiting Gulf Coast rivers, estuaries, and coastal waters from Louisiana to Florida. Recovery objectives for Gulf sturgeon focus on the establishment of self-sustaining populations, where the number of juveniles surviving to maturity is at least equal to mortality. The success of recovery efforts hinge on knowing where conservation or restoration efforts most efficiently achieve these objectives. Knowledge gaps in sturgeon ecology, however, have impeded the development of objectives for juvenile Gulf sturgeon. Therefore, this study’s goal was to identify knowledge gaps that limit the development of quantitative models from which habitat objectives can be derived. Working with species experts, we developed an influence diagram (ID) that hypothesized relationships between estuarine habitat characteristics (e.g., river discharge, water chemistry), juvenile behavior and physiology (e.g., timing of migration, acclimation to salinity), and the total days per winter month that age-0 juveniles use critical estuarine habitat. We translated the ID into a spatially explicit Bayesian network (BN) by quantifying the hypothesized relationships using expert elicitation and literature surveys. We then collated geospatial datasets and, where data were sufficient, generated model predictions for Gulf sturgeon critical estuarine habitat.
Results/Conclusions
The ID hypothesized that juvenile sturgeon occupancy is influenced directly or indirectly by food availability, habitat characteristics, water chemistry conditions given month and river discharge, and the physiological tolerances of fish given timing of migration. Sensitivity analysis suggested that the uncertainty in juvenile occupancy at the local (30 m2) scale is most greatly reduced by knowing the number of acceptable water chemistry days. Water chemistry monitoring data used to calculate acceptable water chemistry days was the most limited, and resulted in spatial outputs for only one (Apalachicola Bay) out of six critical habitat estuaries. Spatial outputs for Apalachicola Bay suggest that both river discharge and time since arrival increased the total number of days that age-0 juvenile Gulf sturgeon occupy critical estuarine habitat by 101% and 68%, respectively. Our results support Gulf sturgeon adaptive management through the creation of an ID that incorporates experts’ hypotheses of juvenile-habitat relationships based on their knowledge of adult and sub-adult sturgeon, thus offering insight that may help guide and prioritize future data acquisition and research.