Distribution and abundance of fishes in Shinumo Creek in the Grand Canyon

Bluehead sucker (Catostomus discobolus) and speckled dace (Rhinichthys osculus) were the only native species in Shinumo Creek above a waterfall located about 120 m upstream from the confluence of Shinumo Creek and the Colorado River. Rainbow trout (Oncorhynchus mykiss) was the only introduced species found upstream of the waterfall. I attribute the coexistence of the native and introduced species is attributed to differential use in resources and the similarly small size of bluehead sucker and rainbow trout. Mean total length of bluehead suckers was 160 mm and the largest fish captured was 230 mm (n = 77). Mean length of rainbow trout was 149 mm (maximum = 300 mm; n = 46). Bluehead suckers in Shinumo Creek were smaller than individuals observed in the mainstem Colorado River. Small size may be a response to the decreased size of the habitat available. The permanence of the waterfall barrier near the mouth of Shinumo Creek is a result of regulation of the Colorado River that prevents inundation of the waterfall