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<br />-18- <br /> <br />Based on the above information, few conclusions can be made. Unfortunately, <br />it was as unusually cool through July and August 1991, as it was unusually hot <br />the previous summer, as evidenced by the water temperature data for the <br />summers of 1990 and 1991 (Table 16). The warmest daytime air temperature <br />recorded during our trapping operations was 840 F. Maximum water temperature <br />never exceeded 670 F during trapping operations, and in most instances, the <br />water temperature was rarely over 650 F. Overnight low water temperatures <br />were often in the high 40s to mid-500s F. It is the author's conclusion that <br />water temperatures in 1991 were not warm enough to stimulate trout to move <br />upstream. <br /> <br />Another question that arose out of the fish'trapping experience this summer <br />concerned whether there is some minimum flow below which larger trout would be <br />blocked from upstream movement. It is the author's conclusion that upstream <br />movement (for trout ~ 40 cm) of more than a half mile at most locations in the <br />river would be impossible at flows less than 60-70 cfs. <br /> <br />This conclusion is based on two pieces of information. First, several riffle <br />areas were examined at the end of the August trapping operation when there had <br />been no demonstrable movement of large trout into the fish traps after 22 days <br />of trapping. The flow in the Dolores River below the dam at this point had <br />been reduced to 61 cfs. It was discovered that many riffle areas were <br />extremely wide and very shallow at this flow. Such areas would effectively <br />block upstream movement of trout ~ 40 cm (16 in.). Several such shallow <br />riffles were located immediately below and above the trap site at river mile <br />8.8. No trout or sucker species larger than 28 cm were trapped at this site <br />in July or August 1991. <br /> <br />Similarly, a wide shallow riffle existed immediately above the trap site at <br />river mile 5.5. Another shallow riffle (at 60 cfs discharge) approximately <br />1000 feet downstream blocked upstream movement in this section of the river. <br />This trap was located at the upper end of a series of long pools and deep runs <br />that comprise the electrofishing station at river mile 6 (near Ferris Canyon <br />Campground). This trap was the only trap that had trout over 30 cm attempting <br />to move through it during either the July or August trapping operations. <br /> <br />Several more very shallow riffles blocked effective movement of large trout at <br />river miles 1, 2, 4, 7, and 10. Most of these riffle areas were no more than <br />5 cm (2 in.) deep on average with maximum depths of s 10 cm (S 4 in.). It is <br />highly unlikely that trout 16 inches and larger could effectively negotiate <br />their way upstream through a cobble maze in many instances only 2-4 inches <br />deep and more than 100 yards long. <br /> <br />Visual Implant (VI) Tagging and Movement Studies <br /> <br />Results of the VI tagging and movement information provides the second piece <br />of information that would lead to the conclusion that large trout movement is <br />effectively blocked in this segment of river at flows less than 60-70 cfs. <br />Three of the four VI tagged and recaptured trout that demonstrated some <br />upstream movement during the spring and summer of 1991 were 40 cm and larger. <br />The other one was a 34 cm (13.4 in.) rainbow. All of these trout were <br />