Short and Long Term Risk Reduction for Green Sunfish Lepomis cyanellus in Lees Ferry Reach of the Colorado River in Glen Canyon National Recreation Area

Authors: Melissa Trammell, David L. Ward, Ken Hyde

Year: 2016 (xlviii)

Abstract

In November 2015, Green Sunfish (Lepomis cyanellus) were eradicated from the Upper and Lower Sloughs adjacent to the Colorado River mainstem in Glen Canyon National Recreation Area (GCNRA) with rotenone in partnership with Arizona Game and Fish Department (AGFD) and U.S. Fish and Wildlife Service (FWS). The population found in 2015 and the subsequent work on its eradication resulted foregoing a High Flow Event (HFE) from Glen Canyon Dam that would have normally occurred in November 2015. After two monitoring trips in June and July 2016 which captured no Green Sunfish (GSF), in August 2016 they were found to have re-invaded the sloughs. We developed a phased response involving mechanical removal, and a proposed experimental ammonia treatment in the isolated 1/3 acre Upper Slough; few GSF were captured in the Lower Slough in 2016. Previous work by Ward et al. (2013) demonstrated that ammonia can be an effective non-native fish control tool, but it is not yet registered as a piscicide. The treatment is planned for the first week in November, if Arizona Department of Environmental Quality approves the experimental use of ammonia. If no permit is received, intense mechanical removal with multiple passes over several days will be conducted. Mechanical removal is not expected to eliminate the Green Sunfish but is expected to reduce abundance down to minimum acceptable risk levels, estimated to be 300 GSF less than 50 mm TL, before an HFE in mid -November. To avoid both the risks of establishing GSF downstream and foregoing another HFE in the future, we have committed to conducting NEPA compliance to evaluate a full range of alternatives for a long term risk reduction action to minimize the potential of GSF or other warm-water nonnative fish to establish populations in the Lees Ferry reach of GLCA. The compliance and implementation is planned for completion by October 2017.