Technical Report
Spatial Spawning Periodicity of Rio Grande Silvery Minnow During 2013
Date: 2013/10/15
Author(s): Dudley R.K., Platania S.P.
Publication: Prepared for U.S. Bureau of Reclamation, 40 p.
Abstract:
Systematic monitoring of the reproductive output of Rio Grande Silvery Minnow at multiple sites in the Middle Rio Grande was first conducted in 1999 and has continued annually (except 2005) since 2001. Previous studies demonstrated May and June as the primary period of spawning activity. The 2013 study was a continuation of the long-term monitoring of Rio Grande Silvery Minnow spawning in the downstream-most river reach just upstream of Elephant Butte Reservoir. Additionally, five new sites were added to the study during 2013 (three in the Isleta Reach and two in the San Acacia Reach) in the proximity of the Isleta and San Acacia diversion dams. These sites were established to assess the entrainment of Rio Grande Silvery Minnow eggs into the Middle Rio Grande irrigation canal network and compare the density of eggs in the river with the density of eggs in the canals.
At the long-term monitoring site (San Marcial), daily water temperatures during the initial and peak spawning events were relatively similar among years. In general, mean daily water temperatures ranged from about 18 to 22°C during peak spawning events over the period of study. Mean daily water temperatures ranged between 14.8°C and 21.3°C during spawning in 2013 at the San Marcial Site. Rio Grande Silvery Minnow mixture-model estimates (E(x)), using standardized egg passage rate data (Eggs_P = N [eggs] · 100 · second -1 ) from 2002–2013 at the San Marcial Site, revealed that values of E(x) were highest in 2002 (9.48 x 104 ) and lowest in 2004 (1.00 x 10-1 ). There was a steady decline in E(x) values from 2011–2013. The estimated value of E(x) was significantly lower (p < 0.05) in 2013 as compared with 2011.