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Mechanical Removal of Non-Native Fishes in the Colorado River

The humpback chub (Gila cypha, HBC) is a large and unique cyprinid fish native to the Colorado River Basin. In 1967 this species was listed as endangered due to potential and realized adverse effects to its populations from the construction of mainstem river dams, water diversions, habitat modifications, degraded water quality, and the introduction fig 1 of non-native fishes. Recent data collected as part of the Glen Canyon Dam Adaptive Management Program suggests that the humpback chub primary population, which is centered around the confluence of the Little Colorado River and the Colorado River, Grand Canyon, has declined since the early 1990’s.  In addition, evidence has shown that non-native species within the same system, including but not limited to rainbow trout, brown trout, black bullhead, common carp, red shiner, and fathead minnow may compete with and prey on humpback chub and other native species within the system such as flannelmouth sucker, bluehead sucker, and speckled dace.  Although several factors likely contribute to the humpback chub decline, few are able to be manipulated in terms of an experimental design with measurable results on which to base management decisions. Given this, the removal of non-native fishes around the confluence of the Little Colorado River and Colorado River mainstem appeares to have potential to benefit humpback chub with little risk to other natural resources.

This experiment began in 2003 and consisted of 6 trips per year until 2006 when densities of non-native fish appeared to be reduced.  Recent data suggests, however, that densities of non-native fish have returned to similar levels observed in early phases of the experiment.  Thus, the Research Branch of the Arizona Game and Fish Department will conduct one mechanical removal trip in 2009 with the objectives of reducing non-native fish densities that may negatively interact with native species and determine if additional effort is needed in the near future. 


This monitoring effort takes place on the mainstem Colorado River near the confluence of the Little Colorado River, about 80 miles downriver of Glen Canyon Dam, in Grand Canyon National Park. 

fig 2 Project personnel will conduct several night electrofishing surveys over fixed stations upstream and downstream of the confluence of the Colorado and Little Colorado Rivers.  We conduct our sampling at night because fish tend to move towards the shoreline after sunset, and electrofishing is most effective in shallow water.  Additionally, personnel conduct hoop net surveys, designed to capture native species, to determine if native fish trends in recruitment are improving.  All fish collected during each sampling trip are measured, weighed, and checked for sexual maturity.  Captured non-native species are removed from the system and given to Colorado River tribal communities for use as fertilizer.  All native fish larger than 6 inches are implanted with tiny microchips, which allow us to identify individual fish and gather information on growth and movement if the fish is ever captured again. 




The data collected from this experiment enables us to detect changes in the fish community over time.  From this data, we can make recommendations on ways to better manage this fish community.  Data are also used to advise the Secretary of the Interior on operations of Glen Canyon Dam through the Glen Canyon Adaptive Management Program


This project is funded by USGS Grand Canyon Monitoring and Research Center as part of ongoing research activities.


For more information contact:
Andy Makinster, Arizona Game and Fish Department
506 N. Grant St. Suite L, Flagstaff, AZ 86001. 
Phone: (928) 226-7677           E-mail:


Bill Stewart, Arizona Game and Fish Department
5000 W. Carefree Highway, Phoenix, AZ 85086
Phone: (623) 236-7368           E-mail:

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