Spatial Distribution and Habitat Use of Least Chub in Three Geographically Distinct Spring Systems

Authors: Mark Grover

Year: 2010 (xlii)

Abstract

The least chub, Iotichthys phlegethontis, is a cyprinid species endemic to the Great Basin of Utah, but currently restricted to six isolated natural populations. Population surveys, using minnow traps, and standardized habitat inventories were conducted in 2010 for three genetically distinct populations occupying spring systems in three separate drainage basins: Mona Springs in the Utah Lake Drainage, Mills Valley in the Sevier River Drainage, and the Leland Harris spring complex in the Snake Valley of Utah’s West Desert. Least chub were abundant in many of the springs and associated pools at Mills Valley and Leland Harris, but were absent from terminal pools characterized by high salinity, high conductivity, and sparse vegetative cover. Numbers of least chub captured per trap at sampling sites were positively correlated with the maximum water depth and steepness of the shoreline within the sampling area, but not with average depth or surface area. Least chub were rarely detected at Mona Springs, where the fish community was dominated by introduced cyprinidontiform species, including western mosquitofish, Gambusia affinis, which adversely impact least chub through interference competition. Extensive habitat connectivity, relatively stable water levels, and benign water chemistry (e.g., pH values of 7-8) probably permit the movement of non-native species throughout the Mona Springs system. By contrast, non-native fish species were absent from Leland Harris and made up a small proportion of the fish community at Mills Valley. Non-native fishes were apparently transient at Mills Valley sites where least chub were most abundant, which tended to be complex, semi-isolated, and prone to spatial or seasonal variation in water chemistry (e.g., pH values >10 during late summer). Favorable habitat for least chub in the three spring systems consists of springheads, channels, and pools characterized by adequate vegetative cover, areas of deep water, and the absence of invasive cyprinidontiform fishes.