Larval trigger flows for Green River razorback sucker

Authors: David W. Speas, Kevin R. Bestgen, Joseph A. Skorupski, Aaron Webber

Year: 2012 (xliv)

Abstract

Recommendations for operation of Flaming Gorge Dam in northeastern Utah provide spring peak flows so razorback sucker Xyrauchen texanus larvae can access Green River floodplain wetlands, areas which provide favorable conditions for growth and survival. It was previously believed that timing spring peak releases from the dam to coincide with and augment the relatively unregulated Yampa River peak flow would provide wetland access for drifting larvae. Recent studies have shown, however, that this strategy provides the river-floodplain connection before most larvae are present. To maximize overlap between periods of larvae presence and wetland connection, captures of razorback sucker larvae in the Green River—rather than the Yampa River peak flow—was proposed as a trigger for increased spring flow releases from Flaming Gorge Dam. This larval trigger approach was implemented experimentally during the spring of 2011 and 2012. Extremely wet conditions in 2011 prompted dam managers to operate with dam safety as a top priority over endangered fish, but the period of floodplain connection nevertheless overlapped with razorback sucker larvae presence for a longer period of time than had been observed in the previous 19 years. Wetland sampling during autumn 2011 indicated that some of these larvae had been entrained into wetlands and survived their first summer, a rare and important observation. In contrast, 2012 proved to be exceedingly dry, and although larvae were successfully entrained into the few low elevation habitats that connected with the river, the spring peak volume and subsequent summer flow levels were insufficient to sustain these wetlands into autumn. Implementation of larval trigger flows in 2012 was successful because close real-time coordination between field biologists and dam managers resulted in flows which entrained razorback sucker larvae in designated wetlands. Moreover, valuable information on effects of larval trigger flows on razorback sucker was gained during extremely wet (2011) and dry (2012) conditions, and managers learned valuable lessons on the challenges of implementing larval trigger flows, particularly in dry years. Consistent with adaptive management principles, future experimentation may help define the role of larval trigger flows for recruitment of razorback sucker and refine management strategies as needed to promote recovery of this endangered species.