Found in the headwaters of the Comal and San Marcos River, the fountain darter (Etheostoma fonticola) is an on average three-centimeter length fish that feeds upon small invertebrates. Considered endangered by the United States and the International Union for Conservation of Nature (IUCN). The darter has been controversial due to its location in the Edwards Aquifer in south-central Texas, which is recognized worldwide for its aquatic species of flora and fauna, many of which are endangered or threatened like the fountain darter. The Edwards Aquifer is also the sole water source supporting the industrial, agricultural, municipal, and recreational needs of nearly 2 million people. Because the darter is a generally poor competitor and is the first species affected by habitat disruption, the endangered fountain darter has been a focal point for controversies involving the endangered species act, state of Texas groundwater law, and private property rights. We developed a stage-structured population matrix model for the fountain darter, calibrated the model within the constraints of published parameter estimates. We then integrated the available synthetic estrogen contamination data of fathead minnow (Pimephales promelas) into the model. We finally used the model to project population dynamics under scenarios of increased synthetic estrogen contaminations.
Results/Conclusions
The population growth rate was 1.0185 without the synthetic estrogen contamination. However, population projections indicated that increased synthetic estrogen concentrations led to a decrease in population growth. With contamination concentration of 0.2 and 1.0, the population growth rate decreased to 1.0160 and 1.0137, respectively. A decreasing population was found at a contamination concentration of 4.0 ng/l with population growth rate of 0.9992. At even higher concentrations, the darter did not survive through its full life cycle.