Habitat preferences and movement of three desert fishes in a highly altered stream: implications for maintaining viable populations

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

Year: 2008 (xl)

Abstract

An organisms’ ability to disperse to suitable habitats across multiple life-history stages, especially in modified and fragmented systems typical of desert streams, influences individual fitness and overall population viability. The bluehead sucker, Catostomus discobolus, flannelmouth sucker, Catostomus latipinnis, and roundtail chub, Gila robusta, are three species native to the upper Colorado River Basin that now occupy 50% of their historic range, likely as a result of widespread habitat degradation, interactions with non-native species, and a mismatch between past adaptations and the current environmental template. Despite these declines, populations of all three species are present in the San Rafael River, a highly-regulated tributary of the Green River, Utah, providing an area of high conservation priority and an opportunity for research. Our goal is to determine the extent, timing, and environmental cues associated with movement, habitat preferences for each species and life stage, and limiting factors, ultimately to guide effective management and recovery of these species. In 2007-2008, we sampled fish using a variety of methods from 25 systematically-selected, 300-m reaches in the lower 64 km of the San Rafael River, spaced to capture the range of species, life-stages, and habitat conditions present. We implanted all target species with a passive integrated transponder (PIT) tag, installed a passive PIT tag antennae, and measured key habitat parameters throughout each reach and at the site of native fish capture. Multiple age-classes of each species were collected in the San Rafael River, with the highest total densities occurring in complex habitats near the confluence with the Green River and in the most upstream reaches of our research area. Flannelmouth sucker were habitat generalists, whereas bluehead sucker and roundtail chub actively selected for riffles and pools, respectively. These discrete channel units, along with important rearing habitat (e.g. backwaters, eddies) are relatively rare in the lower San Rafael River, possibly limiting recruitment and overall population viability. Both local (<1 km) and long-distance (>50 km) movement is pervasive for the entire Colorado River fish assemblage, as all but one recaptured individual (passive and active) was captured at a location different from the initial tagging location. The abundance of age-0 and juvenile fish throughout the sampling period, along with a significant peak in adult downstream movement after the spawning period, suggests that the San Rafael River may provide important spawning and rearing habitat for several sensitive species. These results will allow us to better understand the importance of tributaries and complex habitats for native fish persistence and provide the first step towards completing population viability analyses within a spatially-explicit framework.