Glen Canyon Dam Adaptive Management Program Administrative History
This administrative history of the Grand Canyon Dam Adaptive Management Program (GCDAMP) includes government reports, oral history interviews and other relevant information about Colorado River law, environmental protection law, hydropower regulation, the Glen Canyon Environmental Studies that served as a precursor to GCDAMP, and the activities of the Adaptive Management Work Group, the Technical Work Group, and the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center.
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- Creators: James, Leslie
- Creators: Yard, Michael
ABSTRACT: The Colorado River below Glen Canyon Dam, Arizona, is part of an adaptive management programme which optimizes dam operations to improve various resources in the downstream ecosystem within Grand Canyon. Understanding how populations of federally endangered humpback chub Gila cypha respond to these dam operations is a high priority. Here, we test hypotheses concerning temporal variation in juvenile humpback chub apparent survival rates and abundance by comparing estimates between hydropeaking and steady discharge regimes over a 3-year period (July 2009–July 2012). The most supported model ignored flow type (steady vs hydropeaking) and estimated a declining trend in daily apparent survival rate across years (99.90%, 99.79% and 99.67% for 2009, 2010 and 2011, respectively). Corresponding abundance of juvenile humpback chub increased temporally; open population model estimates ranged from 615 to 2802 individuals/km, and closed model estimates ranged from 94 to 1515 individuals/km. These changes in apparent survival and abundance may reflect broader trends, or simply represent inter-annual variation. Important findings include (i) juvenile humpback chub are currently surviving and recruiting in the mainstem Colorado River with increasing abundance; (ii) apparent survival does not benefit from steady fall discharges from Glen Canyon Dam; and (iii) direct assessment of demographic parameters for juvenile endangered fish are possible and can rapidly inform management actions in regulated rivers.