Comparison of Streamside Visual Counts to Electrofishing Estimates of Colorado River Cutthroat Trout Fry and Adults

Streamside visual counts and depletion-removal electrofishing were compared for estimating fry and adult abundances of Colorado River cutthroat trout Oncorhynchus clarki pleuriticus. Visual counts of fry were significantly correlated (R = 0.92) with three-pass depletion-removal electrofishing estimates of abundance. Streamside visual counts were generally lower than electrofishing estimates, except in streams having turbulent water, where electrofishing was difficult. Disturbance of fry by observers reduced estimates obtained with the visual counts; however, visual counts can be a useful method for estimating the abundance of cutthroat trout fry in small streams with shallow water. For adults, correlations between streamside visual counts and electrofishing population estimates were low, and therefore visual counts were not considered a viable method for older fish.