Predatory interrelations in Weber & Davis County streams

Authors: Jackeline Bedoya-Wilkinson, Blake Hansen, Brennen Slagowski, Desiree Peck, Crystal Price, Mckenna Merrill

Year: 2019

Abstract

Studies of aquatic-riparian ecosystems suggest that trout (Salmonidae) can impact associated invertebrate predators, like aquatic larvae of perlid stoneflies, water-surface dwelling water striders (Gerridae), and riparian tetragnathid spiders. We studied 100 m reaches in seven small streams along the northern Wasatch Front (Weber and Davis counties, Utah). In each stream, we counted water striders, horizontal spider webs (characteristic of tetragnathids), and used kick nets to sample perlid larvae along 10 evenly spaced transects. We also measured wetted width and water depth. We made pebble counts every 0.2 m across transects and measured all submerged and aerial branches (stem width). We sampled trout through each reach with a backpack electrofisher and calculated habitat volume as median width x median depth x reach length to calculate biomass based on trout total length. We used Pearson correlations to explore potential relationships of depth, width, substrate, submerged branch, aerial branch, and trout biomass with the densities of water striders, spider webs, and perlid larvae. We found most significantly that water-strider and spider-web density were inversely correlated with depth and spider-web density was positively correlated with median width and with submerged-branch density. Interestingly, perlid density correlated positively with trout biomass. Overall, this suggests trout abundance is not necessarily the primary driver of abundance in other aquatic or riparian predatory invertebrates and that habitat features can be important. For instance, in streams with higher productivity, multiple predator populations might increase. Also, streams with greater width may have a higher diversity of habitats, with more opportunities for different predators.