A Post-Stocking Survival and Movement Analysis of Razorback Sucker and Bonytail in the Lower Colorado River.

Authors: Taylor Haas, Brian Kesner, Paul Marsh

Year: 2018

Abstract

Bonytail Gila elegans and Razorback Sucker Xyrauchen texanus are both listed as endangered by the United State Fish and Wildlife Service. A stocking initiative by the Bureau of Reclamation, Lower Colorado River Multi-Species Conservation Program has maintained these native species in parts of their historic range, including below Palo Verde Dam in the area around Blythe, CA. Since 2007, 21,749 Razorback Sucker and 18,475 Bonytail have been stocked in the area with passive integrated transponder (PIT) tags implanted in them. The focus of stockings has been 5 primary “backwaters”. These backwater habitats are connected to the main river channel, allowing stocked fish to disperse into the main channel of the Colorado River. Since 2016, 38 subadults of each species and 20 adult Razorback Sucker were surgically implanted with acoustic telemetry tags so manual and passive tracking of movement could take place. Biologists from Marsh & Associates have monitored the movements of the stocked fish via PIT tag scanners, Submersible Ultrasonic Receiver, and an acoustic hydrophone and receiver. Collection efforts from this year resulted in contacting 1,234 unique Razorback Sucker (5.6%) and 535 Bonytail (2.8%). 103 Razorback Sucker contacted this year were stocked prior to this year, whereas there were no Bonytail contacted that were released prior to this year. PIT scanning effort in the main stem was increased this past year which resulted in 9 Razorback Sucker and 6 Bonytail contacts. Mean days at large was 156.5 for Razorback Sucker and 27.8 for Bonytail.