Technical Report

Spatial Spawning Periodicity of Rio Grande Silvery Minnow During 2009

URL: https://webapps.usgs.gov/mrgescp/documents/Platania%20and%20Dudley_2009_Spatial%20Spawning%20Periodicity%20of%20RGSM%20During%202009.pdf

Date: 2009/09/30

Author(s): Platania, S. and Dudley, R.

Publication: Report prepared for U.S. Bureau of Reclamation, 33 p.

Abstract:

Systematic monitoring of the reproductive output of Rio Grande silvery minnow at several 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 silvery minnow reproductive activity. The 2006-2008 studies were structured to monitor the spatial and temporal (May-June) reproductive output of Rio Grande silvery minnow in the Middle Rio Grande and therefore, given the downstream drift of the eggs, were conducted near the downstream-most portion of each of the three accessible river reaches (Angostura, Isleta, and San Acacia). The 2009 study was 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).

Sampling at both 2009 Rio Grande silvery minnow spawning periodicity study sites was conducted from 27 April through 12 June 2009 (n= 47 days). The cumulative volume of water sampled at the two Rio Grande sites was 263,347 m3 (213.5 acre-feet). There was a slight increase, from upstream to downstream, in the total volume of water filtered per sampling site. The cumulative volume of water sampled at the Sevilleta Site was 118,555 m3 and the total amount of water sampled at the San Marcial Site was 144,792 m3 . A cumulative total of 1,489 Rio Grande silvery minnow eggs were collected at the two sites during 2009. The majority (n= 844; 56.7%) of the catch was taken at the Sevilleta Site while the number and cumulative percent of Rio Grande silvery minnow eggs collected at the San Marcial site (n= 645; 43.3%) was slightly lower. Rio Grande silvery minnow eggs were collected on 14 days at the Sevilleta Site and 13 days at the San Marcial Site. On 12 days, Rio Grande silvery minnow eggs were taken concurrently at both the Sevilleta and San Marcial sites. Daily egg catch rates at the Sevilleta Site ranged between 0.18 and 24.42 eggs per 100 m3 of water sampled (n= 6 and n= 331, respectively) while daily egg catch rates at the San Marcial Site ranged between 0.03 and 8.05 eggs per 100 m3 of water sampled (n= 1 and n= 281, respectively). During the study, mean daily egg catch rates at the Sevilleta and San Marcial sites were 0.71 and 0.45 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 3,554,295 with a daily maximum of 1,523,783. The number of eggs estimated to be transported downstream of the San Marcial Site over the duration of the study was 436,924 with a daily maximum of 206,707.