FOOD BASE

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The Aquatic Food Base below Glen Canyon Dam 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. Desired Future Condition for the Aquatic Food Base The aquatic food base will sustainably support viable populations of desired species at all trophic levels. Assure that an adequate, diverse, productive aquatic foodbase exists for fish and other aquatic and terrestrial species that depend on those food resources.

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Updates Kennedy's 2016 Bioscience paper presents a conceptual model describing how hydropower flows could be limiting aquatic insect diversity and production by limiting the reproductive success of insects accustom to laying their eggs along the shoreline. It provides supporting data from an egg desiccation study done below Flaming Gorge Dam, light trap data collected in the Grand Canyon, and a comparison of fluctuation intensity and EPT diversity in several western US hydropower tailwaters. The paper concludes that egg desiccation from fluctuating flows is likely a leading factor in limiting aquatic insect diversity and production in tailwaters below hydropower facilities. The paper also proposes a bugflow experiment to be tested at Glen Canyon Dam as a possible mitigation for fluctuating flows made for hydropower production. Recent food web studies (2006-2009) conducted in collaboration with University of Wyoming, Montana State University, Idaho State University, and the Cary Institute for Ecosystem Studies revealed that fish populations in the Colorado River downstream from Glen Canyon Dam appear to be limited by the availability of high-quality invertebrate prey. Midge and blackfly production is low and nonnative rainbow trout in Glen Canyon and native fishes in Grand Canyon consume virtually all of the midge and blackfly biomass that is produced annually. In Glen Canyon, the invertebrate assemblage is dominated by nonnative New Zealand mudsnails, the food web has a simple structure, and transfers of energy from the base of the web (algae) to the top of the web (rainbow trout) are inefficient. The food webs in Grand Canyon are more complex relative to Glen Canyon, because, on average, each species in the web is involved in more interactions and feeding connections. Based on theory and on studies from other ecosystems, the structure and organization of Grand Canyon food webs should make them more stable and less susceptible to large changes following perturbations of the flow regime relative to food webs in Glen Canyon. In support of this hypothesis, Grand Canyon food webs were much less affected by a 2008 controlled flood relative to the food web in Glen Canyon.

Links and Information USGS- GCMRC Aquatic Food Base Link The Bugflow Experiment Papers and Presentations 2016 Aquatic Foodbase of the Little Colorado River Kennedy et al. 2016. Flow Management for Hydropower Extirpates Aquatic Insects, Undermining River Food Webs. BioScience 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 Citizen Science Insect Monitoring: A Powerful Tool for Detecting Ecosystem Change AIF: Science Updates - Recent Research on Sand, Bugs, and Fish Foodbase Enhancement Suggestions from Federation of Fly Fishers Foodbase Findings Foodbase Update Foodbase Enhancement Suggestions from Federation of Fly Fishers Foodbase Findings Foodweb Update (Kennedy) Low flows in Glen Canyon: preliminary geomorphic analysis of the potential effects on fish and food base (Melis) 2013 GCMRC Update - Status of Resources and Sediment Conditions Lessons From The Grand Canyon: Dams Destabilize River Food Webs 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 Caddis hatch below Parker Dam. There are several species of EPT below Parker and Davis Dam in spite of daily fluctuations that exceed 6 feet per day. Black Flies and Midges fuel fish production below Glen Canyon Dam. Black Flies and Midges respond positively to spring HFE's Mud Snails were introduced below Glen Canyon Dam around 1995.