Distribution and Post-Stocking Survival of Bonytail in Lake Havasu 2013 Annual Report

Lake Havasu, Arizona, California, and Nevada, is one of the few locations where critically endangered bonytail (Gila elegans) have been captured. Since wild populations have been extirpated, the presence of this species relies entirely on stocking programs. Very little is known about the basic ecology of these stocked fish because most data are limited to past field observations of the now-extirpated wild population. Further, no conclusions could be made on the basis of previous telemetry studies conducted within the reservoir due to possible transmitter loss, premature mortality, and loss of contact with tagged fish. Therefore, minimal information exists on post-stocking fate and habitat use of hatchery-reared bonytail.

We are in the process of completing the second part of an acoustic telemetry study within Lake Havasu that will attempt to describe and characterize the inhabitance and dispersal of hatchery-reared bonytail. Fish were surgically implanted with sonic tags and released into two distinct locations in April and October 2013. Six implanted fish were released within the Bill Williams River National Wildlife Refuge in April, and 10 were released near Blankenship Bend in October. A directional hydrophone and receiver were used to actively track fish, and multiple submersible ultrasonic receivers that continuously scanned for tags were placed throughout the study area for passive tracking.

In the spring study, all bonytail were determined dead within 2 weeks postrelease, and all six tags were recovered via diver. As a result, we were unable to draw any conclusions about post-stocking habitat preference within the reservoir.

We are in the process of completing the autumn study. To date, with the use of active tracking, at least half of the original 10 bonytail have been contacted; with the use of passive tracking, that number has further increased. The study now is transitioning to a biweekly sampling schedule. Both sampling methods will be utilized for a complete 3 months of tracking or until all tags are recovered.

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