Spatial and temporal patterns of emergent aquatic insects of the San Juan River in Utah, USA from Bluff to Clay Hills

Authors: Kortenhoeven, Eric*, Muehlbauer, Jeffrey, Kennedy, Theodore, Metcalfe, Anya

Year: 2015 (xlvii)

Abstract

The San Juan River in the Southwest USA is home to a diverse assemblage of both native and non-native fishes including the Federally endangered Colorado pikeminnow, Ptychocheilus lucius, and Federal candidate for threatened status roundtail chub ,Gila robusta,. This study aims to understand the spatial and temporal patterns of emergent aquatic macroinvertebrates in the San Juan River as a proxy for the food base available to these fishes. Using a dataset of 72 light trap samples spanning approximately 90 miles of river collected from April to October 2014. We show that sensitive, large bodied, high energy content insect orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) groups decline in relative abundance with distance downstream from Sand Island to Clay Hills. EPT are high quality prey for fish and the EPT Index is an accepted method for assessing freshwater ecosystem health by the Environmental Protection Agency (EPA). These shifts in species dominance were correlated with a distinct geomorphic change in river habitat from a sinuous, multi-channel river with relatively high allochthonous input to a canyon bound, mostly bedrock habitat starting below the tributary Chinle Creek. Ideally this research will aid the San Juan River Basin Recovery and Implementation Program in understanding the quality, timing and distribution of food available to imperiled fishes in the San Juan River.