8233

• UCREFRP Catalog Number: 8233
• Author: Chart, T. E., D. P. Svendson and L. Lentsch.
• Title: Investigation of Potential Razorback Sucker ‎(Xyrauchen texanus)‎ and Colorado Pikeminnow ‎(Ptychocheilus lucius
• USFW Year: 1999.
• USFW - Doc Type: Spawning in the Lower Green River, 1994 and 1995.
• Copyright Material: NO

EXECUTIVE SUMMARY
In 1994 and 1995, sampling was conducted to determine if razorback sucker and
Colorado pikeminnow spawn in the lower 210 km of the Green River. Based on the infrequent
collections of adults in the past ten years, sampling efforts for razorback sucker were focused
around the mouth of the San Rafael River at Green River kilometer (RK) 156. Investigations of
Colorado pikeminnow spawning were centered on a cobble baz at the mouth of Millard Canyon
(RK 53.9). Electrofishing and trammel nets were used to sample adults; lazval light traps and
seines were used to sample the eazly life stages. One adult razorback sucker was collected while
conducting Interagency Standardized Monitoring Program (ISMP) electrofishing in 1995 neaz
Mineral Bottom (RK 83.7). This fish (TL= 559 mm, Wt = 2150 g, PIT # =1F74374E68) was
caught 69 km below the San Rafael River at RK 86; on 16 May, 1995. No adult razorback
suckers were collected as result of specific project efforts near the mouth of the San Rafael River.
A total of 481arva1 razorback suckers were collected during this study, with the majority (91.7%;
n=44) of those collected in 1994 near the mouth of the San Rafael River. Twenty-eight Iazvae
were collected in the mouth of the San Rafael River and the remaining larvae were collected in
habitats immediately downstream. No lazvae were collected in habitats upstream of the San
Rafael River/Green River confluence. Incorporating the results of this study with those of
concurrent efforts in the middle Green River, Muth et al, (1998) determined that larval razorback
suckers collected in the lower Green River were likely spawned there. Water temperatures warm
earlier each spring in the lower Green River than the middle Green River. The thermal regimes
of the Green River at Jensen, Utah, and at Green River, Utah, aze discussed in light of razorback
sucker spawning time. Further investigation into the timing, magnitude, and specific location of
razorback sucker spawning in the lower Green River is recommended. No evidence was found
of Colorado pikeminnow spawning in the lower 60 km of the Green River. Based on the results
of other project efforts it was determined that the timing of sampling for adults at the Millazd
Canyon baz was likely better in June, 1994, than in June, 1995. Pikeminnow spawning was
delayed throughout the Upper Colorado River basin until the latter part of July in 1995. Further
investigations into pikeminnow spawning in the lower Green should be more intensive than this
effort and should occur within the next five years.
LIST OF KEY WORDS
Razorback sucker, Colorado pikeminnow, larvae, reproduction, spawning, Green River.
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