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14 I I I I I I I I I I I I I I I I I I I The mechanism and timing for Colorado squawfish entering the inflow region of Lake Powell is not well understood. The discovery of larval squawfish in the inflow in early August, 1993, suggests that the post- hatching transport phenomenon extends into Lake Powell from perhaps as far away as the lower Yampa River, about 360 miles upstream or' from Three Fords Rapid, about 180 miles upstream. Post-larvae may be transported into the inflow by late summer freshets caused by monsoonal convective thunderstorms, as reported by Valdez and Masslich (1990), as well as by periodic mid-winter thawing events that inundate nursery backwaters. Although sampling the inflow before and after runoff precludes segregating these effects, other investigations of larval transport by the Larval Fish Laboratory and winter ice conditions in the Green River (Valdez and Cowde1l1994) should provide further insighL The low numbers of Colorado squawfish captured in 1993 after runoff does not necessarily indicate little or no transport occurs with runoff. Variable numbers captured in other years by season indicates that larval drift, rain-freshet transport, winter-thaw transport, and spring runoff all effectively move young Colorado squawfish in the Lake Powell inflow. The presence of adults in the inflow is probably the result of young fish maturing in the region or older fish descending from the river upstream. Management implications for enhancing survival of Colorado squawfish in the inflow are not immediately apparent, since the inflow habitat is so dynamic. However, the presence of larval Colorado squawfish and razorback suckers in the inflow suggests that protection and enhancement of nursery habitat in the Green and Colorado rivers above the confluence can reduce occurrence of these fish in the inflow. Furthermore, more thorough and intensive surveys of Lake Powell may reveal greater numbers of Colorado squawfish and razorback suckers in that impoundment than currently reported. Long-time survival of razorback suckers in Lake Mohave of the lower basin is evidence of the ability of these fishes to survive in lentic environments. One new sampling technique, that will increase sampling efficiency in the lentic habitat of the inflow region, is the use of larval light traps. This sampling device proved very successful in capturing fish in areas previously unsampled with conventional gear (i.e. seines and nets). Light traps were used in the Lake Powell inflow to collect fifteen suckers preliminarily identified as razorback suckers and nine larval Colorado squawfish. Use of larval light traps in future sampling will greatly aide in the estimation of the numbers of larval Colorado squawfish and larval razorback suckers transported into Lake Powell. Other native fish species found in the Lake Powell inflow were bluehead sucker, tlannelmouth sucker, speckled dace and Gila. The 33 Gila captured during post-runoff sampling were all classified as age-O and likely originated from Cataract Canyon. The capture of this fish is significant because it indicates that the inflow region may also influence age-O humpback, roundtail and possibly bonytail chub moving downstream from Cataract Canyon. 6.0 RECOMMENDATIONS The following recommendations are made relative to the objectives of this study as a result of the 1993 investigations: 1. Use of electro fishing should be continued in order to assess the level of predation on age-O Colorado squawfish and to monitor densities and location of adult squawfish. 2. Due to the inefficiency of gill and trammel nets in sampling predatory fish, their use is not recommended for 1994. 3. Larval light traps should be use during both pre and post-runoff sampling in 1994.