Determining preferred spawning habitat of the endangered Rio Grande silvery minnow by hydrological manipulation of a conservation aquaculture facility and the implications for management

Abstract

The endangered Rio Grande silvery minnow (Hybognathus amarus) was induced to spawn in both 2012 and 2013, using hydrological manipulation of a conservation aquaculture facility to create floodplain habitat. Fish responded to the flood by leaving the stream and entered both deep (20–97 cm) and shallow (14–18 cm) low‐velocity off‐channel habitats, spawning in the deep ones; fish did not spawn in the stream. When water level was brought down from flood stage, fry actively moved into the stream 2.5 weeks postspawn. This study supports the hypothesis that this species is a floodplain spawner. The results show that habitat restoration of the Rio Grande to create floodplains is needed for recovery of this species as floodplains are both spawning and nursery habitats. The study provides guidelines about how deep floodplain inundation must inundate for spawning to occur and for the duration of inundation so fry can actively swim with the water when flood waters recede. This project also shows that a conservation facility can be used for all stages of fish's life history. Equally important, it shows that a conservation aquaculture facility can be used to conduct hydrological experiments to determine how an endangered fish will respond to changes in river management.

Managed spring runoff to improve nursery floodplain habitat for endangered Rio Grande silvery minnow

“…Large numbers of adults were not available from our study, but of the 127 captured, 13%, 9%, and 14% were gravid females, spent females, and males expressing milt, respectively, which also indicate active floodplain spawning in 2016. The evidence that the species is a floodplain spawner is further supported by studies in an outdoor aquaculture facility (Tave & Hutson, ), in which RGSM adults left the stream during hydrological manipulation and entered off‐channel, low‐velocity habitats where they spawned exclusively (Hutson et al, ). Medley and Shirey () examined the characteristics of RGSM eggs and proposed that the species is primarily a demersal floodplain spawner with evolved eggs that are secondarily buoyant in high sediment environments rather than a main channel pelagic, broadcast spawning species with an evolved long‐distance downstream drift phase.…”

“…Large numbers of adult RGSM in floodplains of the MRG (Gonzales et al, ; Hatch & Gonzales, ) and the results of controlled studies in an aquaculture facility (Hutson et al, ) also indicate a concerted lateral movement by adults from the mainstem to newly inundated habitats, where most appear to remain, or move in and out, throughout inundation. Movement of adults to floodplains has also been observed for the related eastern silvery minnow ( Hybognathus regius ; Raney, ).…”

“…Alternatively, the RGSM is thought to be primarily a demersal floodplain spawning species with evolved eggs that are secondarily buoyant in high sediment environments created by expansive flooding, with little downstream transport of propagules (Medley & Shirey, ). A series of laboratory and floodplain studies have been conducted to inform these hypotheses (e.g., Gonzales et al, ; Hutson, Toya, & Tave, ; Tave, Toya, & Hutson, ; Widmer, Fluder, Kehmeier, Medley, & Valdez, ), including the current study.…”

Raising Fish in a Purpose‐Built Conservation Aquaculture Facility Using Conservation Aquaculture Management

“…That is, such levees were used to turn two ponds into off‐channel floodplains and to prevent their access to other ponds, which gave broodfish a choice of in‐channel or floodplain habitats during simulated spring runoff floods (Hutson et al. ).…”

“…It also enables one to test hypotheses about key aspects of species’ life history and determine how the species responds to environmental variables (Hutson et al. ). This information could be invaluable in guiding recovery efforts.…”