Technical Report

Spatial Spawning Periodicity of Rio Grande Silvery Minnow During 1999

URL: https://webapps.usgs.gov/mrgescp/documents/PlataniaandDudley_2000_SpatialspawningperiodicityofRGSMduring1999.pdf

Date: 1999/01/01

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

Publication: Final report to the Bureau of Reclamation

Abstract:

The historical Middle Rio Grande fish fauna was reflective of a Great Plains river. At least five cyprinid species that can be characterized as Great Plains river fishes formerly occurred throughout the Middle Rio Grande. Spawning by members of this reproductive guild is associated with high-flow events such as spring runoff or summer rainstorms. Upon release, eggs are about 1.6 mm in diameter but quickly swell (ca. 3.0 mm) and remain suspended in the water column during development. The last remaining member of this reproductive guild in the Rio Grande, NM is the federally endangered Rio Grande silvery minnow (Hybognathus amarus). Population monitoring studies have shown an annual decline in the number and catch rate of Rio Grande silvery minnow since 1996. Currently over 90% of the catch of Rio Grande silvery minnow is in the San Acacia Reach of the Middle Rio Grande.

Sampling for this study began on 29 March 1999 and concluded with collections made on 2 July 1999. Each of the nine collection localities were sampled every weekday during this period (n=96 dates). The 96 days between 29 March 1999 and 2 July 1999 on which collection efforts for Rio Grande silvery minnow eggs occurred resulted in sampling of over 300 acre-feet of water (369,933 m³; 13,062,333 ft³) and a cumulative total of 24,786 silvery minnow eggs from the nine stations. There was a general downstream longitudinal increase in the number and catch rate of Rio Grande silvery minnow eggs. The two sites in the Angostura Reach yielded the fewest eggs (n=4) while the five sites in the San Acacia Reach produced 97% of the total egg catch (n=24,152). Maximum catch rates were recorded between 19-21 May 1999 at four sites and between 11-14 May at three sites. The principal spawn of Rio Grande silvery minnow at the Los Lunas, Bernardo, and San Acacia sites, as determined by egg catch rate, occurred in mid-May in response to the ca. 600 cfs increase in flow (Albuquerque Gauge) between 16 - 17 May 1999. Mean daily water temperature at Albuquerque during this period was 17° C. As spring discharge continued to rise towards its maximum level for the year, Rio Grande silvery minnow continued to spawn at all sites, although at reduced levels, through late May.

Spawning periodicity investigations on species of the semibuoyant egg reproductive guild have consistently demonstrated that the majority of the reproductive effort occurs during a single short duration event. It is not unusual for >99% of all eggs collected in such studies to be taken during a one or two day period. Low levels or “background” spawning may continue for several weeks but the number of eggs produced is insignificant compared to the primary event. This investigation provides support for the hypothesis that the current distribution of Rio Grande silvery minnow is largely the result of downstream displacement of propagules.