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

RESULTS
Based on the timing and location of each sampling effort data collection was designed to
address one project objective at a time. In the context of the present study, the purpose behind
spring electrofishing in the vicinity of the San Rafael confluence and azeas upstream was to
collect adult razorback suckers. However, since there is a known population of Colorado
pikeminnow in this area (McAda et al. 1994), many pikeminnow were collected as result of this
project's efforts. The collections of pikeminnow from this portion of the river are reported
herein, but they have no bearing on the Millazd Canyon spawning investigations (Objective 5).
Similazly, larval pikeminnow were collected in and near the mouth of the San Rafael, in 1995.
These fish were likely produced upstream at the know spawning azea in Gray Canyon and
although important collections in their own regazd, are not relevant to this project's objective 6.
Congregations of adults at suspected spawning areas -razorback suckers
Electrofishing in 1994 and 1995 did not locate a concentration of adult razorback suckers
in the lower Green River. One adult was collected in related endeavors 69 km below the mouth
of the San Rafael River on 16 May 1995 (Table 1). In efforts prior to and since this study,
incidental collections of razorback sucker have been reported from the lower Green River since
1980 (Table 1). Most notable were two recent collections of adult razorback from the mouth of
the San Rafael River; one on 14 May 1996 collected during ISMP monitoring (McAda et al.
1997) and the other on 7 May 1997 collected as part of basin-wide razorback sucker monitoring
(Muth and Wick 1997).
In 1994, a total of 20.4 h of electrofishing effort was accumulated between the town of
Green River and the San Rafael River confluence azea (37 RK). Thirty-five juvenile to adult
Colorado pikeminnow were captured ranging from 164 mm to 567 mm TL. In 1995, 26.9 h of
effort again yielded no razorback sucker but 36 sub-adult/adult Colorado pikeminnow (206-759
mm TL) were captured between RK 193.2 (RM 120.0) and RK 138.5 (RM 86.0). An additional
3.28 hours of electrofishing conducted throughout a 16 km stretch immediately upstream of
Green River, Utah, on 9 June 1995 amassed 16 subadult/adult Colorado pikeminnow ranging
from 371 mm to 595 mm TL.
Flannehnouth suckers (Catostomus latipinnis) were the most abundant species collected
via electrofishing both yeazs. Both flannelmouth sucker and bluehead sucker (Catostomus
discobolus) showed signs of sexual readiness. Other species collected via electrofishing
included: channel catfish (Ictalurus punctatus), common carp (Cyprinus carpio), and walleye
(Stizostedion vitreum) (Figure 3 and 4).
Congregations of adults at suspected spawning areas - Colorado pikeminnow
Sampling for Colorado pikeminnow adults in 1994 was limited to trammel netting due to
low flows and an inability to effectively sample the suspected spawning site with electrofishing
equipment. A total of 46.3 net hours were accumulated at the mouth of Millazd Canyon in 1994
and no adult Colorado pikeminnow were captured. Channel catfish dominated the net catch in
1994 followed by flannelmouth sucker and common carp.
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