Use of remote PIT scanners to determine post-stocking fate of razorback sucker in Lake Mohave

Authors: Brian R. Kesner, Abraham P. Karam, Jerry Warmbold, Carol A. Pacey, Paul C. Marsh

Year: 2012 (xliv)

Abstract

Passive Integrated Transponder (PIT) remote scanner systems were developed and deployed in Lake Mohave, Arizona and Nevada, to determine post-stocking fate of stocked razorback sucker Xyrauchen texanus in 2011 and 2012. Scanners were deployed among three zones within the lake; the riverine zone from Hoover Dam downstream to Willow Beach, an upper reservoir zone centered at Liberty Cove, and a basin zone centered around Yuma Cove. Known spawning sites were targeted in winter and spring, and additional aggregation sites were located in the river and investigated throughout summer. Totals of 3,262 and 8,330 scanning hours resulted in contact with 1,042 and 2,748 razorback sucker in 2011 and 2012, respectively. Scanning effort in the river zone was 61 and 53% of total effort in 2011 and 2012 respectively, and resulted in 70% of contacts both years. Total number of fish scanned in 2012 exceeded the most recent mark-recapture population estimate of 2,577 (1,139 - 6,284 95% confidence interval). The annual population estimate is based on annual roundup data, which does not include captures from the river zone. The razorback sucker population in the river zone was estimated at 1,785 based on remote PIT scanning data from 2011 and 2012. Results suggest the three zones are demographically isolated with only seven fish (0.6% of contacts) scanned in more than one zone in 2011 and 40 (1.1% of contacts) in 2012. Use of remote PIT scanning has provided nearly a ten-fold increase in number of contacts with repatriated razorback sucker in Lake Mohave, which will increase accuracy of demographic parameter estimates to support management recommendations that will help ensure long-term persistence of a genetically viable stock of adult razorback sucker in the reservoir. Future analyses of post-release dispersal and survival for razorback sucker in Lake Mohave should include metapopulation dynamics given the apparent isolation of razorback sucker among zones.