Bonytail post-stocking monitoring in Lake Havasu

Authors: Kristen* Humphrey, Brian Kesner, Paul Marsh

Year: 2015 (xlvii)

Abstract

The persistence of bonytail, Gila elegans, a federally endangered and functionally extirpated fish species, relies entirely on stocking programs. Since 2006, and for the next 41 years, the Lower Colorado River Multi-Species Conservation Program (LCR MSCP) will stock 4,000 bonytail per year greater than 300mm TL into Reach 3 of the lower Colorado River. In an effort to guide future stocking endeavors, we investigated short-term survival, habitat use, and movement of stocked bonytail through the use of acoustic telemetry and remote passive integrated transponder (PIT) scanning from spring 2013 to spring 2015 in the lower Colorado River basin between Davis and Parker dams. Sixty one study fish (306 Á¢â‚¬ ’ 349mm TL) were surgically implanted with acoustic tags and stocked into three general stocking locations Bill Williams River National Wildlife Refuge, Arizona, Blankenship Bend, Arizona, and Regional Park Moabi, California. Thirty one study fish were determined mortalities and 23 were permanently lost to the study within the ten weeks after release. Data from tracking and tag recoveries indicate that most mortalities were the result of predation by fish species. In addition, a large proportion of study fish were lost to the study, and data from SURs (submersible ultrasonic receivers) indicate that lost fish were removed from the water (e.g. avian predation). Contact rates of stocked bonytail through remote PIT scanning ranged from 5 Á¢â‚¬ ’ 68% of bonytail from each stocking event. Most contacts (73% or more) occurred within the first two weeks post stocking and contact rates steeply declined thereafter. Daily post-release survival was estimated from PIT scanning data using the Cormack-Jolly-Seber (CJS) model within the Program MARK for two of the three release sites. Model averaged estimates of apparent survival ranged from 70.3 Á¢â‚¬ ’ 71.6% per day at Blankenship Bend and 93.2 Á¢â‚¬ ’ 93.9% per day at Regional Park Moabi. The probability of long term survival (over three months) for stocked bonytail under any stocking regime was estimated at less than one percent, although statistically significant differences in apparent survival among stocking locations warrant further investigation.