7911 - Laserfiche WebLink

Home Browse Search

278 Dolly Varden numbers peaked at gradients between 6 and 9 percent--a range in which rainbow trout populations were declining. Brook trout and sculpin numbers peaked at 3 percent gradients, and their populations declined as gradients increased above 4 percent. Dace were the first fish and mountain whitefish were the second to disappear from the environment as channel gradi- ents increased. Chinook salmon were not found where channel gradients were over 10 percent because they only utilize streams at the lower elevations. Brook trout and cutthroat trout were not found in stream areas with chan- nel gradients above 17 and 14 percent, respectively. Although cutthroat trout populations were higher at higher elevations than rainbow trout, rainbows were found in stream areas with gradients almost twice as high. Rainbow trout were the only species analyzed for which gradients accounted for some explained variation. For unknown reasons, rainbow trout appeared to be better adapted to a higher and much more extensive range of channel gradients than were any of the other fish species. Relation of Channel Elevation to Fish Populations The lower the channel elevation, the higher the fish population per unit of stream length. The average total length of all fish collected per sample, however, did not follow this relationship. About 80 percent of the fish col- lected (84 samples) were in streams between 3,600 and 5,200 feet in elevation and 20 percent of the fish collected (207 samples) were taken from streams be- tween 5,200 and 8,400 feet in elevation. Physical stream conditions (depth and width) and water temperatures in the lower elevation areas are more favor- able for fish. Elevation was the most influential among the variables in accounting for explained observed variation in total fish numbers. Dace were the first to disappear from sample collections as elevation increased, and chinook salmon and sculpin followed. Mountain whitefish were not found above-6,000 feet, brook trout were not taken above 6,400 feet. Areas of streams with elevations about 6,800 feet produced only cutthroat trout and Dolly Varden. Surprisingly, rainbow trout inhabited a wide range of channel gradients but disappeared from the samples once channel elevations exceeded 6,800 feet. Streamside Environment and Fish Fish populations based on population means, were higher in streams having grass and brush habitats. Chinook salmon, Dolly Varden, brook trout, sculpin, mountain whitefish,and dace had higher population means along grass-dominated streambanks. Rainbow trout populations were higher in stream areas having ,