Post-Stocking Fate of Razorback Sucker in Topock Marsh, AZ

Authors: Chase Ehlo

Year: 2018

Abstract

Razorback Sucker Xyrauchen texanus is an endangered species endemic to the Colorado River Basin. In the lower Colorado River, recruitment in the wild is nonexistent and adult survival is low due to habitat alterations and negative interactions with nonnative species. Topock Marsh is a large (1618 hectares) backwater adjacent to the Colorado River. Preliminary Remote PIT scanning in 2016 determined that 551 Razorback Sucker of the original 3244 stocked in 2010 still persist in the Marsh. Due to this persistence, a telemetry study was implemented in the Winter of 2016. A total of 20 wild fish captured in Topock Marsh and 20 hatchery fish were implanted with acoustic telemetry tags and tracked for one year post release to determine survival and utilization of the Marsh. A combination of active tracking with directional and omnidirectional hydrophones and passive tracking with Submersible Ultrasonic Receivers (SUR) determined that a total of 2 hatchery fish and 8 wild fish survived to the end of the study. Kaplan-Meier survival estimates (95% CI) were 0.62 (0.38-0.82) and 0.51 (0.29-0.73) for hatchery fish and wild fish respectively. Although survival was not significantly different between hatchery and wild fish, several of the hatchery fish were lost to the study therefore inflating their survival estimates. The SUR network determined that fish utilized the whole Marsh during the winter months, and in the summer months concentrated where cool fresh water is delivered into the Marsh from the Colorado River. Given the relatively high survival of fish in Topock Marsh, particularly the 2010 stocking cohort, it has the potential to be an important recovery habitat. Using the information that was learned from the telemetry study, the population in Topock Marsh will continue to be monitored and information will be used to aid in the recovery of Razorback Sucker.