Population Viability Analysis for Endangered Roanoke Logperch

A common strategy for recovering endangered species is ensuring that populations exceed the minimum viable population size (MVP), a demographic benchmark that theoretically ensures low long-term extinction risk. One method of establishing MVP is population viability analysis, a modeling technique that simulates population trajectories and forecasts extinction risk based on a series of biological, environmental, and management assumptions. Such models also help identify key uncertainties that have a large influence on extinction risk. We used stochastic count-based simulation models to explore extinction risk, MVP, and the possible benefits of alternative management strategies in populations of Roanoke logperch Percina rex, an endangered stream fish. Estimates of extinction risk were sensitive to the assumed population growth rate and model type, carrying capacity, and catastrophe regime (frequency and severity of anthropogenic fish kills), whereas demographic augmentation did little to reduce extinction risk. Under density-dependent growth, the estimated MVP for Roanoke logperch ranged from 200 to 4200 individuals, depending on the assumed severity of catastrophes. Thus, depending on the MVP threshold, anywhere from two to all five of the logperch populations we assessed were projected to be viable. Despite this uncertainty, these results help identify populations with the greatest relative extinction risk, as well as management strategies that might reduce this risk the most, such as increasing carrying capacity and reducing fish kills. Better estimates of population growth parameters and catastrophe regimes would facilitate the refinement of MVP and extinction-risk estimates, and they should be a high priority for future research on Roanoke logperch and other imperiled stream-fish species.

CFD Simulation of Flow in a Circular Pipe With Percina Rex Fish

We tried to correlate the fish behavior observed in the laboratory during the development of the exhaustion threshold curves with flow field in the fish passage with culverts and other impediments. In particular, we focused on aspects of fish behavior which may have exploited the velocity and turbulence fields in a circular passage. Roanoke logperch ( Percina rex ), the largest of the Virginia’s darters are federally endangered species. Logperch of different sizes were tested during the development of the exhaustion threshold curves at different velocities ranging from 40 to 70 cm/s in the laboratory in a circular pipe. The pipe was divided into four quadrants in the streamwise direction. Simulations were run at velocities 40 and 70 cm/s using Computational Fluid Dynamics (CFD) software Fluent with fish at center and bottom of the pipe. The velocity and turbulence kinetic energy contours of all the positions of the fish were compared to correlate the fish behavior observed in the laboratory.