7144 - Laserfiche WebLink

Home Browse Search

I I I I I I I r I I I , I I I I I I I 35 habitat does not change from a backwater to a run on a daily basis, thus reducing the need for daily movement to new areas or the increased exertion of remaining in one area. This data should be compared to in- formation from areas without daily fluctuations, as this habitat prefer- ence may have considerable survival value in the natural situation. The permanency or longevity of these small backwaters is generally no more than a month during mid-late summer as the river is receding fairly rapidly. We suspect they are more permanent in fall and winter, although we have never conducted studies during those months. The failure to capture any bony tail chubs was normal as this spe- cies is very rare and may be well on the road to extinction. The last known adult bony tail in the upper Colorado Basin was taken from the study area in 1977 (Holden 1977). Failure to capture humpback chubs was also expected as they prefer canyon areas with swifter current and have rarely been taken in this section of the river. Benthic Macroinvertebrates The general trend noted in the invertebrate data is typical for rivers with large spring floods. During the high water period, samples are taken in areas that are generally dry and therefore numbers of or- ganisms are usually low compared to lower flow periods. This was obvious in the Moon Lake data as well as that collected by Holden and Crist (1978) in the Green River about 40 km upstream. The large num- ber of organisms found in the May lower station sample exemplifies this phenomenon very well. The river rose over 60 cm between May 15 when