Environmental Flow for Recruitment: Adaptive Management for the Endangered Rio Grande Silvery Minnow

 The Rio Grande silvery minnow (Hybognathus amarus) is a formerly widespread endemic fish species, now restricted to 170 miles of the Rio Grande in New Mexico. Silvery minnows likely use inundated riparian vegetation for spawning and nursery habitat during spring runoff. The nursery habitat concept links silvery minnow early life history to changes in river channel morphology and hydrology.

The U.S. Army Corps of Engineers (Corps) has been evaluating possible management strategies for the Rio Grande to supplement flows below Cochiti Lake for the benefit of the Rio Grande silvery minnow.  Water management is formulated to provide spawning and recruitment flows at the Albuquerque gage of 3,000 cfs for seven to ten days.  The target flow provides inundated habitat on point bars and islands for successful silvery minnow spawning and recruitment to maintain viable population densities.

Water management on the Rio Grande over the past 100 years has changed the hydrology and channel geomorphology. Manipulation of the hydrograph has reduced lateral habitat connectivity between the main channel and the floodplain. Changes in floodplain availability can have important implications for fish reproduction and recruitment. Nursery habitat for incubating native fish eggs and rearing larvae is often poorly defined for many species. The Corps continues to evaluate the relationship between flow, inundated area, and recruitment to refine criteria for adaptive management. Understanding the habitat conditions created by environmental flows provides an important tool for successful endangered species management.