Status and Distribution of Colorado River Fishes in Grand Canyon, Arizona

The Grand Canyon long-term fish monitoring program was designed to determine annual trends in catch-per-unit-effort (CPUE; fish/hr) and distribution of Colorado River fishes vulnerable to electrofishing in order for managers to evaluate experiments and policies. Electrofishing transects (N=952) were randomly selected throughout the river between Lees Ferry and Lake Mead where sampling could be conducted safely (i.e., excluding large rapids).  In 2010, a total of 6,427 fish were collected with boat electrofishing during two sampling trips comprising 14 fish species.  There were few differences in CPUE estimates between 2009 and 2010.  For example, flannelmouth sucker Catostomus latipinnis CPUE in 2010 (19.2±3.4 fish/hr) was similar to 2009 (19.9±2.9 fish/hr).  However, each fish species (native and nonnative) has shown an increasing trend in relative abundance since the mid-2000’s.  Distribution patterns varied by species, and some showed clear patterns.  For example, the distribution of brown trout Salmo trutta was centered around Bright Angel Creek, which is a known spawning location.  We hypothesize that temperature changes associated with Glen Canyon Dam water releases and nonnative removals near the confluence of the Little Colorado River (2003-2006) contributed to changes in the riverine fish community.