Technical Report

Spawning Periodicity of Rio Grande Silvery Minnow During 2004

URL: https://webapps.usgs.gov/mrgescp/documents/Platania%20and%20Dudley_2005_Spawning%20periodicity%20of%20RGSM%20during%202004.pdf

Date: 2005/04/01

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

Publication: Report prepared for U.S. Bureau of Reclamation, 27 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 (Platania and Dudley, 2002a) and has continued annually since 2001. The 2004 catch rate of Rio Grande silvery minnow eggs was orders of magnitude lower than that taken in 2003 and 2002. During the 61-day duration of this 2004 project but only five Rio Grande silvery minnow eggs were taken in this study. Mean daily catch rates on dates that eggs were collected ranged from 0.08 to 0.22 eggs/100 m3 of water sampled with the mean daily cumulative catch rate on these dates being 0.06 eggs/100 m3 of water sampled.

Rio Grande silvery minnow eggs were collected in three separate samples during 2004. The first eggs were collected on 7 May 2004 at 1500 h while mean daily discharge in the river was about 498 cfs (Table 1). That sample produced two Rio Grande silvery minnow eggs in the 917 m3 of water filtered during the specific effort. On 9 May 2004, a single Rio Grande silvery minnow egg was taken during the morning sampling effort (0745-0945 h) in the 1,196 m3 of water filtered. Mean daily discharge in the river on 9 May 2004 was 1,030 cfs or over twice that recorded on 7 May 2004 (date of first egg collection). The final Rio Grande silvery minnow eggs taken during this 2004 project were collected between 1530-1730 h on 11 May. Two eggs were present in the 912 m3 of water filtered. Mean daily discharge on 11 May 2004 had risen to 1,560 cfs. No additional Rio Grande silvery minnow eggs were collected in the 79,143 m3 of water filtered during the subsequent 54 days of the 2004 study. The volume of water sampled from 12 May 2004 through 4 July 2004 was almost twice (1.8 times) that sampled during the entire 2003 Rio Grande silvery minnow egg sampling effort.