Stonefly assemblages vs trout in low-order creeks along the Northern Wasatch Front.

Authors: Blake Hansen, Amber Bell, Jackeline Wilkinson

Year: 2019

Abstract

A previous study in Northern Utah suggested there is competition between large predatory Perlid stoneflies and trout (salmonidae). We examined stonefly abundance in two small Wasatch Front creeks, expecting fewer perlids to co-occur with trout. Each creek system had a trout (lower Strongs Creek and Steed Creek) and troutless (upper Strongs Creek and Davis Creek) reach. We sampled 24 pools with trout and 27 troutless pools. We electrofished each pool to confirm the presence or absence of trout and mini-Surber sampled for two common families of stoneflies: Chloroperlidae (Sweltsa) and Perlidae (Hesperolperla, Eccoptura, Neoperla). Mean number of Perlidae per pool was lower in reaches with trout than without (Strongs Creek: 0.46 ± 0.22 SE with trout, 1.80 ± 0.51 SE troutless; Davis-Steed Creek: 0.00 ± 0.00 SE with trout versus 2.75 ± 1.12 SE troutless). This fit our prediction. The opposite trend was seen with the Chloroperlidae mean numbers (Strongs Creek: 0.85 ± 0.42 with trout versus 0.30 ± 0.15 SE troutless; Davis-Steed Creek: 6.08 ± 2.04 SE with trout versus 2.94 ± 0.77 SE troutless), but their abundance difference was not statistically significant. Competition or predation by trout may limit perlid abundance, whereas chloroperlids might not compete with or be preferred food for trout because they are much smaller than perlids.