Technical Report
Rio Grande Silvery Minnow Population Estimation Program Results From October 2011
Date: 2012/05/31
Author(s): Dudley R.K., White G.C., Platania S.P., Helfrich D.A.
Publication: Prepared for U.S. Bureau of Reclamation, 87 p.
Abstract:
Systematic monitoring of Rio Grande silvery minnow, Hybognathus amarus, and the associated Middle Rio Grande fish community has been conducted since 1993 and has provided relevant, quantifiable, and timely information regarding the status of this species both spatially and temporally. In contrast to the Population Monitoring Program, which continues to provide necessary year-round documentation of trends for the entire ichthyofaunal community, the Population Estimation Program has provided a statistically defensible annual estimate of the Rio Grande silvery minnow population during a single time-period (October) since 2006. The objectives of this study were to 1) Develop and implement methods that provide statistically robust population estimates of Rio Grande silvery minnow, 2) Provide a population estimate of Rio Grande silvery minnow based on fish densities stratified by mesohabitat for 20 sampling units, 3) Develop site occupancy rates for Rio Grande silvery minnow populations, and 4) Calculate a population estimate of Rio Grande silvery minnow using Population Monitoring Program data, controlling for mesohabitat, and compare this value to that generated in Objective #2.
The best model for the mesohabitat-specific depletion data (based on the lowest AICC value) of Rio Grande silvery minnow was by mesohabitat and location (for BW, PO, SHPO, and SHRU) and was supported by a high model weight. The capture probability estimates (i.e., proportion of fish removed per depletion pass) for the different mesohabitats ranged from 0.6858 (shoreline pools) to 0.8444 (runs). The associated standard errors for estimates were consistent among mesohabitats and ranged from 0.0157 to 0.0382.