Technical Report
Rio Grande Silvery Minnow Population Monitoring During 2019
Date: 2020/05/07
Author(s): Dudley R.K., Platania S.P., White G.C.
Publication: Prepared for U.S. Bureau of Reclamation, 198 p.
Abstract:
As part of the Rio Grande Silvery Minnow Population Monitoring Program, the status of this imperiled species and the associated Middle Rio Grande ichthyofaunal community has been systematically monitored since 1993. This effort is unique among ichthyofaunal research studies in the Middle Rio Grande in that it has been providing consistent sampling of fishes over a very long duration. Long-term sampling studies, like this one, also provide the data necessary to test and compare different ecological hypotheses. Our primary research objective was to evaluate how seasonal and annual changes in river flows affect the distribution and abundance of Rio Grande Silvery Minnow throughout its current range over time (1993–2019).
The annual occurrence and density of Rio Grande Silvery Minnow, using October data (i.e., as required by USFWS’s Biological Opinion), has fluctuated widely over the past two decades (1993–2019). While its estimated density (E(x); fish per 100 m2 ) was notably elevated from 2016 to 2017, there was a dramatic decline in 2018, followed by a marked rebound in 2019. Population monitoring efforts in 2019 revealed an elevated density (2.10), which represented a 2,285% increase from 2018 (0.09). While Rio Grande Silvery Minnow represented < 0.2% of the fish community in 2018, it had increased to 8.61% by 2019.