Ecological risk assessment of environmental stress and bioactive chemicals to riverine fish populations: an individual-based model of smallmouth bass

Ecological risk assessments of environmental stress and bioactive chemicals for fish and wildlife populations play an important role in environmental management and decision-making, especially when evaluating population-level risks. In this study, we developed a modeling framework to evaluate population-level risks of environmental stress and bioactive chemicals and applied it to a riverine population of an ecologically and socioeconomically important fish species, the smallmouth bass. The modeling framework includes (1) an individual-based model that incorporates complex and interacting biological and ecological processes, and environmental stochasticity, (2) an effect module that links impacts of environmental factors and chemicals to individual characteristics, and (3) a population module that aggregates individual information to allow for population-level inferences. We evaluated the impacts of water temperature, flow and exposure to estrogenic compounds on smallmouth bass population dynamics. We simulated population dynamics under scenarios that represented year-round warm temperature, extremely warm summers, elevated flow year-round, extremely high flow in summers due to intense storms, and various exposures to estrogenic compounds. Extremely warm summers and elevated flow year-round had the most negative impacts on the smallmouth bass population (e.g., declines in abundance). Increased exposure to estrogenic compounds, both year-round an during summer months, substantially accelerated the reduction in population size. Acute exposure to estrogenic compounds imposed more negative impacts than chronic exposure. Acute exposure during spawning season had the worst impacts. This modeling framework can be extended to other species, other environmental stressors and chemicals of concern and interest with a broad application.