Assessment of Pelagic Fish Entrainment at Glen Canyon Dam Using Experimental Fyke-type Netting Systems
This is a scoping proposal that will gather information pertinent to the following questions regarding fish entrainment from Lake Powell into the Colorado River downstream. The full research proposal will likely address the following questions:1)What methodologies can be used to install and operate an entrainment netting system in the tail-race below Glen Canyon Dam, 2)To what extent, if any, is entrainment of piscivorous fishes occuring, and 3) What is the physiological condition (e.g. survival) of these fishes.
Need and Benefit
The Glen Canyon Dam Adaptive Management Program (GCDAMP)was established in 1996 by the Secretary of the Interior to implement the Grand Canyon Protection Act of 1992, the 1995 Operation of Glen Canyon Dam Final Environmental Impact Statement, and the 1996 Record of Decision (ROD).The ROD implemented a modified low fluctuating flow (MLFF) regime as the basis for the operation of Glen Canyon Dam. In selecting the MLFF alternative, the ROD noted that the goal was to permit recovery and long-term sustainability of downstream resources while limiting hydropower capacity and flexibility only to the extent necessary to achieve recovery and long-term sustainability. In addition to variations in flow regime, the experimental options also have nonflow components that vary(USGS 2006).
Implementation of a temperature control device (TCD) to elevate mainstem water temperatures
and promote humpback chub spawning and recruitment is a proposed non-flow component that directly affects Reclamation. Reclamation currently spends 8 million dollars annually on recovery efforts associated with the federally endangered humpback chub. Reclamation is considering the installation of TCDs'on 2 (units #4 and #6) of 8 turbines at Glenn Canyon Dam. A TCD is a device that can selectively withdraw water from different depths, so that desired downstream temperatures can be attained while still generating power. Proposed cost of this installation is estimated at 71 million dollars. The TCDs will be used to withdraw water from warmer reservoir strata above the thermocline. This warmer water will more closely mimic pre-impoundment water temperatures in the Grand Canyon with the intent to 1)improve optimum spawning conditions for humpback chub, and 2)adversely impact cold-water, piscivorous salmonids that are implicated in the decline of chub populations. Proposed water withdrawals from the warmer epilimnion layers of Lake Powell has potential to complicate recovery of the humpback chub in the following manner: The majority of this reservoir's pelagic species are piscivorous (e.g. striped bass, walleye) and are generally associated with this water strata for a majority of the year. It has been speculated (based on limited data from a 1996 acoustic survey near the Glenn Canyon Dam) that water withdrawals from the epilimnion could entrain 250,000 fish (many of these fish being striped bass) per week (Mueller and Horn 1999). Further, Arizona Game and Fish have proven that these piscivorous species can be passed alive through the dam's turbines. Currently, water withdrawal at Lake Powell occurs in the reservoirs hypolimnion (deep, cold, oxygen poor water with very low fish densities) to maintain downstream trout fisheries at Lee's Ferry and below. This, coupled with poor survival through facility turbines has likely been responsible for the absence of piscivors (other that trout) in the reservoirs tail-race. Water withdrawal from Lake Powell's epilimnion has potential to add many more predators into a river that will be warmer and much more suitable to their survival and reproduction. Humpback chub densities (believed to be less than 4000 fish over 150 mm) would undoubtedly be impacted, and would in effect prolong non-native eradication efforts indefinitely, with little hope of de-listing this species. The long-term Cost to Recalamtion and its shareholders could be enormous (over and above the 8 million dollar annual outlay of resources currently allocated.) This scoping proposal seeks to pursue information that would be used develop methodologies (based on submission of a full research proposal in FY 2009) to quantify this entrainment in the tail-race below Glen Canyon Dam.
Literature Cited: Mueller, G., and M. J. Horn. 1999. Description of the pelagic zooplankton and fish communities of Lakes Powell and Mead. Open File Report 99-109. U.S. Department of the Interior, U.S. Geological Survey, and U.S.Bureau of Reclamation.
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