FOOD BASE

---

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.

EPT as Biologic Indicators of Stream Condition	Algae and Aquatic Macrophytes	Aquatic Macroinvertebrates

Updates [1] [2] [3] [4]

Links and Information GCMRC Aquatic Food Base Lab USU Buglab USU Aquatic Macroinvertebrate Key Freshwater Macroinvertebrates of NY Nutrients Page Humpback Chub Page Lees Ferry Rainbow Trout Fishery Page LTEMP Experimental Action: Aquatic Resource-Related Experimental Treatments (BA, pages 30-41) [5] Low steady weekend flows (“bug flows”) would be conducted to test whether the flows would increase insect abundance. On an experimental basis, for example, flows would be held low and steady for two days per week (weekends) from May through August to attempt to improve the productivity of the aquatic food base, and increase the diversity and abundance of mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera), which are collectively referred to as EPT. Foodbase Projects Oviposition and Egg Desiccation Studies Foodwebs and Bioenergetics Studies Measuring Primary Production in the Lees Ferry Reach Effects of BugFlows and HFEs on the Aquatic Foodbase Citizen Science Insect Monitoring Hyporheic Anoxia in the Lees Ferry Reach Downstream Recovery of the Foodbase Community in Several Colorado River Tailwaters Drift and Food Availability Studies Invertebrate Drift below Glen Canyon Dam Responses of macroinvertebrate drift, benthic assemblages and trout foraging to hydropeaking below Flaming Gorge Dam Foodbase PEP 2001 Foodbase PEP 2004 Foodbase PEP Papers and Presentations 2017 Muehlbauer et al. 2016. Deleterious effects of net clogging on the quantification of stream drift: Canadian Journal of Fisheries and Aquatic Sciences Fluvial Aquatic Ecology of the Colorado River (… especially Lees Ferry) Floods, Flows and the Aquatic Foodbase PPT The Grand Beyond: Aquatic Foodbase of the Upper Colorado River Basin 2016 Grand Canyon Monitoring and Research Center Science Updates (BO Compliance, Trout Updates, Green Sunfish, Fisheries PEP, Partners in Science) Aquatic Foodbase of the Little Colorado River 2015 Invertebrate drift in Glen Canyon 2007-2013 2014 Citizen Science Insect Monitoring: A Powerful Tool for Detecting Ecosystem Change Science Updates - Recent Research on Sand, Bugs, and Fish Foodbase Enhancement Suggestions from Federation of Fly Fishers Foodbase Findings Low flows in Glen Canyon: preliminary geomorphic analysis of the potential effects on fish and food base (Melis) 2013 Miller and Judson. 2013. Responses of macroinvertebrate drift, benthic assemblages, and trout foraging to hydropeaking. Can. J. Fish. Aquat. Sci. 71: 675–687 GCMRC Update - Status of Resources and Sediment Conditions Kennedy et al. 2013. The relation between invertebrate drift and two primary controls, discharge and benthic densities, in a large regulated river Annual Reporting Meeting: Foodbase Update Foodbase Update 2012 Temperatures, TCD, and Food Base 2011 Ecosystem ecology meets adaptive management: Food web response to a controlled flood on the Colorado River, Glen Canyon 2010 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 1999 Watershed influence on the macroinvertebrate fauna of ten major tributaries of the Colorado River through Grand Canyon, Arizona 1991 Zooplankton of the Colorado River: Glen Canyon Dam to Diamond Creek Algal and Invertebrate Biota in the Colorado River: Comparison of Pre- and Post-Dam Conditions 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 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.