Off-channel habitats to conserve endangered native fish of the lower Colorado River basin

Authors: Guillermo Ley, Michael Fell, Brian R. Kesner, Paul C. Marsh, Lori McIntosh

Year: 2009 (xli)

Abstract

Persistent decline of native ‘big river’ fishes in the lower Colorado River, despite almost three decades of reintroduction efforts prompted researchers and managers to reconsider conservation measures. Among plans already being implemented is the development of numerous off-channel habitats that are intended to be devoid of non-native fish and provide adequate physicochemical conditions for native fish. A complex of six ponds at Imperial National Wildlife Refuge known as Imperial Ponds is compared to designs described in literature by leading experts of the lower Colorado River basin. Substantial design comprises were made, in part due to unanticipated difficulties encountered during construction. Among these, pumped river water and ground water were used instead of a natural flow-through system, and a wire wedge Z-alloy micromesh screen system was installed to prevent invasion of non-native fish. Due to high groundwater seepage the ponds are difficult to drain. Non-native fish contamination has occurred in all six ponds, and groundwater intrusions that provide fish refugia have made fish removal problematic during renovation. These and other post-construction issues create challenges for engineers and managers alike, but progress is being made toward a workable system where native fish conservation can move forward.