The importance of small tributary streams to endangered fishes of the Colorado River Basin: an example from the San Rafael River, Utah

Authors: Phaedra Budy, Gary P. Thiede, Jared L. Bottcher, Timothy Walsworth

Year: 2010 (xlii)

Abstract

The importance of mainstem rivers and major tributaries to the endangered Colorado River fishes (Colorado pikeminnow, Ptychocheilus lucius, bonytail, Gila elegans, razorback sucker, Xyrauchen texanus, and humpback chub, Gila cypha) is well documented; conversely, the use and significance of small tributary streams is poorly understood. Historically, these fishes likely used smaller tributaries, such as the San Rafael River, to a high degree for spawning, rearing, feeding, and refuge. Currently, the proliferation of non-native species and severely altered flows, including dewatering events, may have altered tributary use by endangered fishes. In February 2008, we installed a full-duplex (134 kHz), PIT-tag detector station in the San Rafael River approximately 2 km upstream from the confluence with the Green River, an area representing a distinct habitat shift between tributary and mainstem systems. In April 2009, we installed a second PIT-tag detector station approximately 60 km upstream from the Green River confluence, and 3.5 km downstream from an impassible diversion dam. These tag-detector systems are also able to detect direction of movement. Using passive tag recaptures in the San Rafael River from 2008 to 2010, we have ‘recaptured’ 12 Colorado pikeminnow, 13 bonytail, 6 razorback sucker, and 5 ‘unidentified’ fish (whose PIT-tag numbers indicate they are indeed endangered species), including 1 Colorado pikeminnow detected at the uppermost detector station. Several endangered fish detections occurred on multiple occasions, often moving into and out of the San Rafael River, for a total of 47 detections since 2008. In addition to frequent use, our detection data indicate that these fishes have migrated great distances from initial tagging locations to the San Rafael River: one Colorado pikeminnow moved 282 km and one bonytail moved 333 km. Our findings, along with recent captures by researchers in similar tributary streams, demonstrate their frequent use and the importance of small tributaries and their fragile habitats to endangered fishes. Further, we draw attention to our continued inability to account for unknown tags, a full 11% of detections, an inter-agency management hurdle that must be overcome.