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1997 Paria River Native Fish Monitoring • Discussion Results of continued efforts to monitor use of the Paria River by spawning adult flannelmouth suckers and rearing of larvae and YOY further reinforce this tributary's importance to native fishes. During 1997, the most abundant species was speckled dace, accounting for 62.2 % of the total number offish collected. Flannelmouth sucker comprised 34.4 % of the catch and the majority were < 70 mm TL, indicating that spawning had occurred in the Paria River. As in 1996, lazge numbers of YOY flannelmouth suckers were captured during the 1997 growing season. However, YOY were no longer collected after 4 June. The unusually high numbers of flannelmouth sucker YOY in 1996 were attributed to a lack of significant flooding in ~ the Paria River and/or high mainstem Colorado River flows which ponded the Paria River mouth (Thieme in preparation). Thieme (in preparation) suggests that the ponded Paria River mouth acted as a refuge/rearing area for YOY flannelmouth suckers. No significant flooding, when YOY prevalence was high, occurred in the Paria River from 1 January to 10 November 1997. Also, Colorado River dischazges in the spring (--20,000 cfs) and early summer (--26,000 cfs) of 1997 were relatively high and similar to those of 1996. However, the Paria River mouth was not ponded during Colorado River discharges of~ 20,000 cfs on 13 - i4 May 1997 (M. Thieme, University of Arizona, personal communication), as it was under similar flows in 1996. Thieme (in preparation) attributes the lack of a ponded tributary mouth in 1997 to prolonged periods of steady high mainstem Colorado River flows backing up the Paria River mouth, causing suspended sediments in the Paria River to be deposited in the mouth. On 4 June, a "back-eddy" was present neaz the mouth of the Paria River, caused by high Colorado River discharge, which scoured sediments and created a small pool where large numbers of YOY were caught. Young-of--year may not have been caught after this period due to a small spate of 90 cfs on 5 June in the Paria • River. In 1996, we observed post-spawning mortality of adult flannelmouth sucker (Brouder and Hoffnagle 1997).- No evidence of this was observed in 1997. We hypothesized that adult post- spawning mortality may be further evidence of an aging population as theorized by Weiss (1993). This may still be the case, however, post-spawn mortality may be a sporadic event. As in 1996, catches of speckled dace throughout 1997 appeared to, show a die-off of adults, replaced by YOY later in the summer. The life span of speckled dace is only 2 - 3 years (Hinckley 1973) and decreased catches in mid-summer 1996 may reflect adult mortality. This 12 Brouder ared Ho@6agJe, 1997 Annual Report Ariwna Game ~ Fish Department •