Technical Report

Rio Grande Silvery Minnow Population Monitoring Program Results From December 2011 to October 2012

URL: https://webapps.usgs.gov/mrgescp/documents/Dudley%20et%20al_2013_RGSM%20Population%20Monitoring%20Program%20Results%20from%20December%202011%20to%20October%202012.pdf

Date: 2013/04/26

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

Publication: Prepared for the U.S. Bureau of Reclamation, 158 p.

Abstract:

Rio Grande silvery minnow estimated densities (E(x)), using October sampling-site density data (1993–2012), were highest in 1995 (36.03) and 2005 (44.84) and lowest in 2003 (0.02) and 2012 (0.00). The estimated densities of Rio Grande silvery minnow were significantly lower (p < 0.05) in 2010, 2011, or 2012 as compared with 2007, 2008, or 2009. October population monitoring efforts in 2012 yielded no Rio Grande silvery minnow, which was the first and only sampling effort (in any month) that yielded no individuals of this species since the population monitoring study was initiated in February of 1993. Bivariate relationships among Rio Grande silvery minnow estimates of Delta (δ = probability of absence) and Mu (μ = mean of the lognormal distribution), using October sampling-site density data (1993–2012), revealed general positive or negative associations with several hydraulic variables. Estimates of δ decreased with hydraulic variables indicative of higher flows but increased with variables indicative of lower flows. Estimates of μ exhibited the opposite relationships with hydraulic variables (i.e., positive relationships with higher-flow hydraulic variables but negative relationships with lower-flow hydraulic variables).