In many coastal systems, pertinent management questions are: What are the predominant stressor trends? and How do they impact fisheries? Here, we focused on addressing these questions in Mobile Bay, AL, where river discharge, salinity, and temperature extremes act as stressors on important fisheries species: eastern oyster, blue crab, spotted sea trout, and southern flounder.

Based on long-term observations, there is a declining trend in river discharge to Mobile Bay from the Alabama and Tombigbee rivers (mean discharge 1,800 m³ s^-1), with increased frequency of low flows since the 2000s. As a result, salinity in the bay is trending up and there can be large increases in salinity, especially in the upper bay and delta, during low flows. Concurrently, there is a significant warming trend of 0.08 °C y^-1, with a notable increase of  2 °C  since 2020. In order to develop comparable time-series data spanning the same time period and locations as fisheries data (described below) we used numerical models for watershed hydrology (SWAT) and bay hydrodynamics (SCHISM). The models were calibrated and validated with the observations to create time series of freshwater discharge, salinity, and temperature from 1970 to 2025.

The modeled time-series were analyzed relative to fisheries independent monitoring data for oyster, crab, trout, and flounder from 1970s to 2020s. Several simple, robust relationships between temperature, salinity, and fishery population deviations were identified: Poor oyster recruitment occurred after warm summers with extended marine heat waves. Increased salinity and warmer temperatures were positively associated with population deviations for spotted seatrout and blue crab but negatively associated with southern flounder. These are novel findings that enable a better understanding of inter-annual variations in important fishery populations. They are also useful for managers to provide better explanations of harvest variability and harvest limit decisions.