Post-Stocking Survival and Movement of Telemetered Bonytail Gila elegans in a Lower Colorado River Reservoir, Lake Havasu, Arizona and California

Perseverance of bonytail Gila elegans in the Colorado River basin relies entirely on stocking and Lake Havasu, a mainstream reservoir in Arizona-California, is one of few locations where they are occasionally contacted. Little information is available concerning the basic ecology of this critically endangered species and a limited number of telemetry studies have been conducted. Only one bonytail telemetry study has previously occurred in Lake Havasu and its results indicated a majority of telemetered fish dispersed near shore or in coves. Unfortunately, high mortality of tagged fish prevented conclusions from being drawn about seasonal dispersal or habitat preferences of bonytail in that system. This study examined post-stocking dispersal and mortality of bonytail stocked in Lake Havasu through two seasons. The first stocking was in April 2010, and the second was in December 2010. In both studies, 20 bonytail were implanted with acoustic transmitters. The April study utilized a 3-month battery life, but following a captive tag retention study with 100% survival of 20 fish implanted with either 3- or 6-month tags, a larger 6-month tag was utilized for the December stocking. In both field studies, fish were tracked actively by boat and passively with submersible ultrasonic receivers. Fish dispersed between 2.6 km downstream and 27.1 km upstream of the stocking location, although most remained in or near the Bill Williams River National Wildlife Refuge. Mortality for both studies was confirmed using SCUBA to recover tags. One fish died during the April study (95% survival); the December study is ongoing and results are pending.