9443

• UCREFRP Catalog Number: 9443
• Author: Bestgen, K. R., G. B. Haines, R. Brunson, T. Chart, M. Trammell, R. T. Muth, G. Birchell, K. Chrisopherson and J. M. Bundy.
• Title: Status of Wild Razorback Sucker in the Green River Basin, Utah and Colorado, Determined From Basinwide Monitoring and Other Sampling Programs.
• USFW Year: 2002.
• USFW - Doc Type: Project Number 22D,
• Copyright Material: NO

1

flannelmouth suckers. The CPUE for razorback sucker was highest in 1993 when the only
samples were collected from 17 and 19 June, second highest in 1994, and declined to relatively
low levels after that. Similar to the middle Green River, the proportion of razorback sucker
larvae to all catostomid larvae in lower Green River samples was relatively high in the sparse
sampling year 1993 and in 1994 but declined after that (Fig. 7).
Razorback sucker larvae were relatively rare in samples collected from 1996 to 1999.
Number of razorback sucker larvae captured varied from 3 to 214, in spite of the relatively even
numbers of samples collected (263 to 295) and a relatively constant (2,480 to 3,644) number of
sampling hours among those four years. Sampling effort and number of razorback suckers
captured were positively, but only weakly (r = 0.44) related to sampling effort.
Most razorback sucker larvae captured in the lower Green River area from 1997 to 1999
(67 of 90, 74%) were from the vicinity of the mouth of the San Rafael River (in lower San Rafael
River and Green River, RK 156.1 - 152.0). Ten of the remaining larvae were from upstream of
the San Rafael near Anvil Bottom (RK 161.6} and the other thirteen were captured downstream
from the Anderson Bottom and Millard Canyon areas. Larvae collected in the lower Green River
from 1997 to 1999 were slightly larger than those collected in the middle Green River, and in
1998, several relatively large larvae were found in samples collected in the mouth of the San
Rafael River (Table 7). For example, on May 4 and 5, a I6 mm TL larva was captured on each
day, which produced estimated spawning dates of 21 and 22 March, respectively. Water
temperature in the San Rafael was 19 to 20°C, compared to 15°C in the Green River. Larvae up
to 19 mm TL were captured that year.
Timing of captures of razorback sucker larvae in the lower Green River from 1997 to

1999 were relatively early, generally ranging from early May to early June, although a single
19