Technical Report

Rio Grande Silvery Minnow Reproductive Monitoring During 2017

URL: https://webapps.usgs.gov/mrgescp/documents/Dudley%20et%20al._2017_RGSM%20Reproductive%20monitoring%20during%202017.pdf

Date: 2017/10/19

Author(s): Dudley R.K., Platania S.P., White G.C.

Publication: Prepared for U.S. Bureau of Reclamation, 30 p.

Abstract:

Systematic monitoring of the reproduction of Rio Grande Silvery Minnow has been conducted annually since 2001. Previous studies demonstrated mid-April to mid-June as the primary period of spawning activity. The 2017 study was a continuation of the long-term monitoring effort in the lower portion of the San Acacia Reach, just upstream of Elephant Butte Reservoir. Two additional sites (one in the Angostura Reach and one in the Isleta Reach), which had been sampled periodically from 2006 to 2011, were also sampled intensively in 2017.

Rio Grande Silvery Minnow mixture-model estimates (E(x)), using standardized egg passage rate data (Ep = eggs / s) from 2003 to 2017, were highest in 2011 (6.05 x 10¹ ) and lowest in 2004 (1.36 x 10^-3 ). Values of Ep are indicative of the relative downstream transport of eggs across years, corrected for annual differences in flow magnitude. There was a steady decline in estimated egg passage rates from 2011 to 2013, followed by an increase in 2014. Egg passage rates declined (P < 0.05) from 2015 (7.75 x 10^-1 ) to 2016 (6.12 x 10^-2 ), but increased slightly in 2017.