Conservation Implications of a Newly Formed Waterfall at the River-Reservoir Interface of Lake Powell

Authors: Nathan Cathcart, Christopher A Cheek, Mark C. McKinstry, MacKinnon D. Peter, Keith B. Gido

Year: 2016 (xlviii)

Abstract

The connectivity of the Colorado River Basin, like most western riverscapes, has been drastically altered by water development. The introduction of nonnative fishes and removal of native species coincided with impoundment. Downstream effects of dam construction are well known to negatively affect river channel morphology, habitat connectivity and the hydrological regime. However, upstream effects of large reservoirs on fish populations are poorly documented. We designed a study to illustrate ho w reservoir construction, drought, and endangered fish management have combined to create a contemporary dilemma for water resource managers stemming from the recent formation of a waterfall in the transitional area between the San Juan River and Lake Powell. We used passive integrated transponder (PIT) antennas stationed downstream of the waterfall in 2015 combined with fish sampling gears to assess fish abundance from March through July. We detected 524 unique PIT tags including 499 Razorback Sucker (Xyrauchen texanus), 15 Colorado Pikeminnow (Ptychocheilus lucius), six Channel Catfish (Ictalurus punctatus), three Flannelmouth Sucker (Catostomus latipinnis), and one Bonytail (Gila elegans). Razorback Sucker primarily originated from stocking or tagging events in the San Juan River basin but some detection originated in the upper Colorado River basin and Lake Powell. Results show the waterfall is a barrier to endangered fishes but also prevents nonnative fishes from entering the system. Trans-basin connectivity is unlikely without mechanical alteration, fish passage construction, or manual movement of fish. The presence of so many adult Razorback Sucker and past findings of larval fish in the area suggest proper management could turn Lake Powell from an ecological sink into a source habitat. The challenge of recovering migratory endangered species in the west will likely have to reconcile habitat connectivity with prolonged drought and less water storage.