A comparative investigation of population size, structure, movement patterns and vital rates between two populations of bluehead sucker (Catostomus discobolus) in the Weber River, Utah: Identifying limiting factors to guide conservation

Authors: Paul D. Thompson, Aaron Webber, Phaedra Budy, Samuel McKay

Year: 2010 (xlii)

Abstract

Bluehead suckers (Catostomus discobolus) historically occurred in the Colorado River Basin and the Upper Snake, Bear, and Weber rivers; however, sampling in the Bonneville Basin in Utah has identified viable populations remaining only in the Weber River. Towards a goal of identifying limiting factors and prioritizing conservation efforts, we compared population size, structure, movement patterns, and vital rates of two populations of bluehead sucker that occupy very different 10+ km river reaches of the Weber River. Multiple pass, mark-recapture electrofishing indicated that relatively small populations of 225 (141-416) and 546 (423-772) fish/reach remain with little variation in population size across the three years of study. Bluehead sucker in the Weber River appear to obtain larger sizes than other systems (up to 575 mm TL). Based on recapture data, growth of larger bluehead sucker (>400 mm TL) was 12.5 g/year; however, growth of smaller fish (250-300 mm TL) was 167 g/year. In addition, recruitment appears to be limited in one reach; in contrast, annual adult survival rates are high (~80%) and decrease only slightly with size, likely due to natural senescence. The largest bluehead sucker movements observed during the study were 15 km downstream (over 6 months) and 5 km upstream (over 12 months), indicating that these fish historically used large sections of the Weber mainstem. PIT tag detections at a small flat-plate antenna indicated that 88% of movements occurred during night periods. Based on these results and the history of the Weber River, probable limiting factors for bluehead suckers include: 1) an extremely modified hydrograph during spring peak flows (magnitude, duration, and timing), 2) cooler on-average summer water temperatures due to upstream dam releases, and 3) high densities of exotic brown trout.