Successes and Failures of Renovating Two Ponds at Imperial National Wildlife Refuge

Authors: Tammy L. Knecht, Andrea Montony, Mitch Thorson

Year: 2010 (xlii)

Abstract

In 2007 the Multi-species Conservation Program (MSCP) constructed six ponds at Imperial National Wildlife Refuge (NWR) for the purpose of grow-out facilities for bonytail, Gila elegans, and razorback sucker, Xyrauchen texanus. A secondary objective was to research different attributes of the ponds relative to native fish growth and survival. Non-native common carp, Cyprinus carpio, and mosquitofish, Gambusia affinis were present in several of the ponds after construction. Carp and mosquitofish are not piscivorous to adult native species so bonytail and razorback sucker were stocked late in 2007 despite the presence of nonnative fishes. In 2008 an increase of non-natives, plus the discovery of new and potentially piscivorous nonnative fishes began contributing to the low recruitment of native fishes. In 2009 and 2010 US Fish and Wildlife Service and US Bureau of Reclamation partnered to renovate two ponds at Imperial NWR in Yuma County, AZ. These ponds were treated with 4ppm of rotenone since Cyprinus carpio and high organic were present and at 0.5ppm of rotenone for all other treatments to eradicate non-native fish. After one rotenone treatment, Pond 3 was successfully eradicated of non-natives, however, only moderate success (nonnatives still present) was obtained on Pond 1 after two treatments. Results varied between the two ponds due to hydrologic differences in pond water level. While the immediate goal of eradicating all non-natives in Pond 1 was not accomplished, the information gained was instituted during the renovation of Pond 3 resulting in a complete kill. The next step for these ponds is to monitor and enhance water quality in an effort to improve overall survivorship of native fish within the Imperial Ponds facility.