Technical Report

Spatial Spawning Periodicity of Rio Grande Silvery Minnow During 2010

URL: https://webapps.usgs.gov/mrgescp/documents/Dudley%20and%20Platania_2010_Spatial%20Spawning%20Periodicity%20of%20RGSM%20During%202010.pdf

Date: 2010/09/30

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

Publication: Report prepared for U.S. Bureau of Reclamation, 43 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 2009-2010 studies were structured to monitor the spatial and temporal (May-June) reproductive output of Rio Grande silvery minnow in the two downstream-most river reaches (Isleta and San Acacia), where the majority of the population currently persists.

Sampling at both 2010 Rio Grande silvery minnow spawning periodicity study sites was conducted from 5 May through 19 June 2010 (47 days). The cumulative volume of water sampled at the two Rio Grande sites in 2010 was 171,335.8 m3 (138.9 acre-feet). The total volume of water filtered was higher at the San Marical Site (105,421 m3 ) as compared with the Sevilleta Site (65,915 m3 ). A cumulative total of 586 Rio Grande silvery minnow eggs were collected at the two sites during 2010. The majority (n = 364; 62.1%) of the catch was taken at the San Marcial Site while the number and cumulative percent of Rio Grande silvery minnow eggs collected at the Sevilleta site (n = 222; 37.9%) was slightly lower. Daily egg catch rates at the Sevilleta Site ranged between 0.04 and 5.57 eggs per 100 m3 of water sampled (n = 1 and n = 125, respectively) while daily egg catch rates at the San Marcial Site ranged between 0.03 and 9.47 eggs per 100 m3 of water sampled (n = 1 and n = 223, respectively). During the study, mean daily egg catch rates at the Sevilleta and San Marcial sites were 0.34 and 0.35 eggs per 100 m3 of water sampled, respectively. The number of eggs estimated to be transported downstream of the Sevilleta Site over the duration of the study was 727,010 with a daily maximum of 365,187. The number of eggs estimated to be transported downstream of the San Marcial Site over the duration of the study was 500,755 with a daily maximum of 217,576.

Analysis of reproductive output revealed a significant difference (F = 6.36; p < 0.0001) among mean values of catch rate (#/100m3 ) at the San Marcial Site for the eight years of the study (2002-2004, 2006-2010). The natural log-transformed mean egg catch rate (standardized for discharge) was highest in 2002 (5.86 ± 0.87), followed by 2007 (4.77 ± 0.34), 2008 (3.22 ± 1.22), 2003 (2.89 ± 0.50), 2009 (2.57 ± 0.59), 2010 (2.24 ± 0.55), 2006 (1.44 ± 0.67), and 2004 (0.96 ± 1.22). Additional statistical analyses for the Isleta Reach (2006-2010) revealed a significant difference (F = 9.45; p < 0.0001) among mean values of catch rate (#/100m3 ) among years. The natural log-transformed mean egg catch rate (standardized for discharge) was highest in 2009 (4.68 ± 0.45), followed by 2008 (4.28 ± 0.40), 2007 (4.19 ± 0.36), 2010 (2.60 ± 0.36), and 2006 (1.97 ± 0.40) in the Isleta Reach.