Spawning periodicity of Rio Grande Silvery Minnow from 2002-2013
Authors: Robert K. Dudley, Steven P. Platania
Year: 2013 (xlv)
Abstract
The reproductive output of the federally endangered Rio Grande Silvery Minnow, Hybognathus amarus, has been monitored annually (2002-2013) at a site just upstream of Elephant Butte Reservoir in the Rio Grande, NM. While spawning appears to occur over a wide range of mean daily water temperatures (ca. 13 to 26°C), the majority of spawning occurs over a much narrower range (ca. 18 to 22°C). Rio Grande Silvery Minnow mixture-model estimates (E(x)), using standardized egg passage rate data, revealed that values of E(x) were highest in 2002, lowest in 2004, and declined significantly (p < 0.05) from 2011 to 2013. General linear models of mixture-model egg passage rate estimates (Delta (Á¤) and Mu (Á¬)) yielded a top model (Á¤(Year) Á¬(ABQ>2,000+random)) that received about 18% of the AICC weight (wi) and had a scaled r 2 value of 0.39 (p < 0.001). The top three models, which accounted for about 44% of the cumulative wi, were related to the interaction among Á¬ and hydraulic variables representing elevated spring flows. Logistic regression modeling of egg presence-absence data revealed that the probability of collecting eggs ranged from only 0.13 (Á„ discharge = -50%) to 0.33 (Á„ discharge = 0%) during periods of declining or stable flows, but increased to 0.84 during a 100% increase in flow. Further, a substantial increase in flow (e.g., Á„ discharge = 200%) was predicted to result in a very high probability of collecting eggs (0.98; LCI > 90%). Increased flow led to a series of changes in the physical dynamics of the river and water chemistry conditions that likely serve as important spawning cues for Rio Grande Silvery Minnow. Despite the seemingly large number of propagules transported downstream every year following peak spawning events, elevated and extended spring runoff conditions appear to create the favorable habitat conditions required for the successful retention and recruitment of early life stages of Rio Grande Silvery Minnow. The successful conservation of Rio Grande Silvery Minnow appears to be strongly dependent on ensuring appropriate flow and habitat conditions that are timed with the typical spawning and early recruitment phases of this imperiled species.