Aggregations Projects

Aggregation: “A consistent and disjunct group of fish with no significant exchange of individuals with other aggregations, as indicated by recapture of PIT‐tagged juveniles and adults and movement of radio‐tagged adults.” (Valdez and Ryel 1995) There are eight recognized aggregations below Glen Canyon Dam: 30 Mile Little Colorado River inflow Bright Angel Creek inflow Shinumo Creek inflow Stephen Aisle Middle Granite Gorge Havasu Creek inflow (RM 157-160) Pumpkin Spring (RM 212.5-216) Humpback chub are also caught outside of the aggregations. Samples are also being collected at: Fern Glen - Stairway (RM 168.5-172.9) Froggy Fault (RM 196-198.5) Fall Canyon (RM 210-212) Bridge City (RM 237-244) Spencer & Surprise (RM 245-249.5)

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Updates There have been substantial increases in the captures of humpback chub in aggregation sampling since 2014, particularly at the LCR, Havasu, Pumpkin Spring, and in Western Grand Canyon. [1] [2] [3] Immigration 2016 Aggregation sampling Of 79 recaptures, Havasu & below (2014-2016): 8 moved down from Havasu (3 Pumpkin; 5 Fern Glen) 5 moved up from Pumpkin (3 Froggy; 2 Fall Canyon) [4] Temperature: consistently >19C in Western Grand Canyon [5] Humpback chub increases coincide with increases of other native fish like flannelmouth sucker [6] Local Recruitment 2016 System Wide Electrofishing (and hoopnetting) Above RM 220: 21/37 recaptures (57%) At Little Colorado River confluence ~80% recaptures Below RM 220: 3/146 recaptures (2%) 3 were tagged recently and at RM 238-239 [7] Translocations: Population may be reaching a critical mass Havasu translocations

Links and Information The Humpback Chub Page Projects System Wide Electrofishing: 3 trips: 2 spring/summer, 1 in fall. Boat Electrofishing – near shore. Baited hoop nets and extended below Diamond to Pierce (new in 2016) Presentations and Papers 2017 System Wide Monitoring PPT Humpback Chub Aggregations Persons et al. 2017. Colorado River fish monitoring in Grand Canyon, Arizona; 2002–14 humpback chub aggregations: U.S. Geological Survey Open-File Report 2016–1177, 43 p. 2016 Monitoring Humpback Chub Aggregations in the Mainstem, 1991-2015 2015 Humpback Chub in the Colorado river: Status and Trends of Aggregations, Changes in Range 2014 Colorado River fish monitoring in Grand Canyon, Arizona: 1990-2013 humpback chub, Gila cypha, aggregations 2013 Colorado River Fish Monitoring in Grand Canyon, Arizona: 2002-2012 HBC Other Stuff