Physical Habitat Model for the Rio Grande Silvery Minnow

The Rio Grande Silvery Minnow (RGSM) is an endangered species found in the Middle Rio Grande River in New Mexico. RGSM were historically abundant throughout the Rio Grande Basin, but now only occur downstream of Cochiti Dam to the tailwater of Elephant Butte Reservoir (designated as critical habitat). The decline of this species is primarily attributed to hydrologic manipulations caused by extensive diversions and impoundments. Further habitat degradation has resulted from stream channelization, loss of floodplain connectivity, invasive species, and watershed and riparian degradation. The primary objective of this study was to develop a habitat evaluation model driven by a two-dimensional hydrodynamic model and to apply the model to the Rio Grande Silvery Minnow in order to evaluate habitat suitability under unsteady flow conditions. An emphasis was placed on the availability and fragmentation of overbank habitats. The model results revealed high variability in habitat abundance and patchiness as a function of streamflow. Also, the quantity and connectivity of habitat was substantially different during the rising limb of an unsteady hydrograph when compared with the receding limb. The results demonstrate that this modeling technique provides valuable information for evaluating RGSM habitat and for targeting restoration sites on the Middle Rio Grande.