FOOD BASE

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USGS- GCMRC Definition The Colorado River below Glen Canyon Dam has been altered by dam-induced modifications to the river’s flow, temperature, and sediment supply. Nonnative species have also changed the natural system. Nonnative fish are thought to prey on and compete with native fish, including the endangered humpback chub (Gila cypha). These impacts have likely changed both the amount and sources of energy that fuel the aquatic food web and the flows of energy within the food web. Installation of the dam created a relatively clear, cool aquatic environment below the dam that now allows aquatic plants to capture the sun’s energy, and they in turn are now consumed by a few species, including scuds (Gammarus lacustris), midges (Family: Chironomidae), blackflies (Simulium arcticum), and New Zealand mudsnails (Potamopyrgus antipodarum). The first three species can provide food for both native and nonnative fishes, but fish cannot digest the New Zealand mudsnail.

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General History Updates 2016 River Food Webs Threatened by Widespread Hydropower Practice Hydropeaking of river water levels is disrupting insect survival, river ecosystems 2013 Lessons From The Grand Canyon: Dams Destabilize River Food Webs Recent slides

Information USGS- GCMRC Aquatic Food Base Link Reports and Links 2016 File:Kennedy 2016 HydropowerEPT.pdf- Kennedy et al. 2016: Flow Management for Hydropower Extirpates Aquatic Insects, Undermining River Food Webs Food availability in the Little Colorado River over space and time A Life History Bottleneck for Aquatic Insects Arising from Load Following 2015 Invertebrate drift in Glen Canyon 2007-2013 2014 Foodbase Enhancement Suggestions from Federation of Fly Fishers Foodbase Findings Foodbase Update 2013 Cross et al. 2013: Food-web dynamics in a large river discontinuum USGS fact sheet: Native and nonnative fish populations of the Colorado River are food limited - Evidence from new food web analyses Macroinvertebrate diets reflect tributary inputs and turbidity-driven changes in food availability in the Colorado River downstream of Glen Canyon Dam Kennedy et al. 2013: The relation between invertebrate drift and two primary controls, discharge and benthic densities, in a large regulated river 2012 Air –water oxygen exchange in a large whitewater river Temperatures, TCD, and Food Base 2011 Ecosystem ecology meets adaptive management: Food web response to a controlled flood on the Colorado River, Glen Canyon Secondary production rates, consumption rates, and trophic basis of production of fishes in the Colorado River, Grand Canyon, AZ: An assessment of potential competition for food Diet overlap and competition among native and non-native small-bodied fishes in the Colorado River, Arizona 2010 Resource composition and macroinvertebrate resource consumption in the Colorado River below Glen Canyon Dam Short-Term Effects of the 2008 High-Flow Experiment on Macroinvertebrates in Colorado River Below Glen Canyon Dam, Arizona Basal Resources in Backwaters of the Colorado River Below Glen Canyon Dam—Effects of Discharge Regimes and Comparison with Mainstem Depositional Environments Aquatic production and carbon flow in the Colorado River Pages 105-112 in Proceedings of the Colorado River Basin Science and Resource Management Symposium, November 18–20, 2008, Scottsdale, Arizona Invasion and production of New Zealand mud snails in the Colorado River, Glen Canyon 1999 Watershed influence on the macroinvertebrate fauna of ten major tributaries of the Colorado River through Grand Canyon, Arizona 1981 A survey of the aquatic flora and fauna of the Grand Canyon 1959 Ecological Studies of the Flora and Fauna in Glen Canyon (Woodbury 1959) Other Stuff Black Flies and Midges fuel RBT growth. Black Flies and Midges respond positively to spring HFE's Mud Snails were introduced to the system around 1995.