Contemporary assessment of benthic macroinvertebrates and fish interactions in the Truckee River, NV

The Lower Truckee River is one of the largest rivers in the western Great Basin, in California and Nevada, USA, connecting Lake Tahoe in the Sierra Nevada mountain range to Pyramid Lake, a semi-arid desert terminus lake in Nevada. In the middle of these two ecotones is a large metropolitan area, Reno-Sparks. The Truckee River is a valuable resource providing water for municipalities, agriculture, and recreation. In addition, both federal and state agencies are currently involved in efforts to re-introduce a native trout in the Truckee River, Lahontan cutthroat trout (Oncorhynchus clarkii henshawi), which was extirpated from the system by the middle of the 20th century. As such, there is much to be gained from understanding the response of aquatic biota to natural and human induced disturbances, in addition to understanding the interactions among fishes to further assist cutthroat trout re-introduction efforts. This study examined the longitudinal changes in water quality and investigated the response of benthic macroinvertebrates to these changes. In addition, the interactions among native and non-native fishes were investigated. In chapter 1, the longitudinal trends of water quality and benthic macroinvertebrates were examined. A linear mixed model was utilized to determine relationships between water quality parameters and macroinvertebrate communities. Results suggest the biomass and abundance of macroinvertebrates is related to seasonal influences, where these measurements were much higher during the summer than spring. Measurments of macroinvertebrate diversity and tolerance to water quality did not relate to any of the water quality parameters, suggesting biotic communities respond to other unmeasured variables. In chapter 2, the competitive and predatory interactions between native and non-native fishes were examined. Diet analysis revealed younger age-class salmonid diets significantly overlap as species selected similar prey items. A bioenergetics model predicted brown trout, the top predator in the system, could potentially consume up to 60 % of the resident prey fish biomass during a single month. Estimates from the bioenergetics model also predicted the effect of brown trout predation on stocked cutthroat and rainbow trout is not large, suggesting re-introduced cutthroat trout survival may be largely influenced by competitive interactions instead of by predation. This is the first contemporary study that examined water quality, macroinvertebrate communities, and fish interactions during the same time period. The purpose of this study is to enhance our understanding of the response of aquatic communities to both natural and human-induced influences, and assist managers in their efforts re-introduce native cutthroat trout.