7612 ‎(2)‎

• UCREFRP Catalog Number: 7612
• Author: Roberts, B. and M. Moretti.
• Title: Final Fisheries Survey of the San Juan River, Utah 1988.
• USFW Year: 1988.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: NO

of new fish to recaptured fish in 1988, the population of razorback suckers is
extremely low unless other small populations exist in the San Juan Arm. Most
of these fish were old, battered and commonly blind in one eye. No Colorado
squawfish were collected during the 1988 trammel netting efforts.

Canyon NettinQ

No Colorado River rare fishes were collected in the canyon reaches of the
San Juan River during the trammel netting efforts. Only 4 species were
co 11 ected: channe 1 cat fi sh, carp, b 1 uehead sucker and fl anne 1 mouth sucker
(Tables 2 and 5). Nets were set at 19 different locations in the two canyon
reaches (RMI 80.3-66.2 and RMI 55.9-23.1) for a total of 1,048.1 net-hours
(Appendix C and D). Seventy-five foot nets were set for a total of 778.3 net-
hours and 50 ft nets for a total of 269.8 net-hours. The upper canyon reach was
sampled between 8-10 and 16-21 July, while the lower canyon reach was sampled
between 3-7 and 17-20 August.

A total of 339 fish were collected between RMI 80.3-66.2, versus 105 fish
between RMI 55.9-23.1 (Table 5 and Figure 8). Catch rates (fish/net-hr) for all
species were considerably higher in the upper canyon reach for both the 75 ft
and 50 ft nets. Bluehead suckers were not collected in the lower canyon reach.
Catch rates (fish per mile) from 1987's electrofi~hing efforts show no evidence
that channel catfish, carp, bluehead sucker and flannel-mouth sucker populations
are lower in the lower canyon reach than in the upper canyon reach as indicated
by this summer's trammel netting efforts. Differences in netting catch rates
between the upper and lower canyon reaches are probably related to the
differences in river flow between July and August (Figure 9). Sampling in the
upper canyon reach appeared to be very efficient as a result of lower flows.
Mean river flows for the days in which the upper canyon reach was sampled was
724 cfs, versus 1,585 cfs on the days in which the lower canyon reach was
sampled. The true mean flows for the latter were considerably higher than 1,585
cfs since washes (i.e., Chinle Creek, Butler Wash and Comb Wash) below the gaging
station at Bluff, Utah were flooding from storm events. Percent species
composition remained nearly the same between reaches for both 75 ft and 50 ft
nets (Table 5). Within each of the canyons reaches, habitats sampled with the
50 ft nets contai ned a higher percentage of channel catfi sh and a 1 esser
percentage of flannelmouth suckers (Table 5).

YounQ-of-the-Year SeininQ

Only one rare YOY fish was collected during the selnlng efforts
(standardized or incidental); a 19 mm Colorado squawfish (Tables 6 and 7). This
fish was collected at RMI 11.5 on 21 August. Using the formula developed by
Haynes and Muth (1984) to back date the hatching date, this YOY Colorado
squawfish was hatched on or near 26 July. Hamman (1981) reported an incubation
time for Colorado squawfish embryos of 90-121 hrs at 20-240C. If an incubation
period of 3-5 days is assumed, this fish was probably spawned between 21-23 July;
during a period of extremely low flows (Figure 9). In August and early
September, most of the backwater habitats in the lower canyon became inhabitable
to YOY Colorado squawfish at one time or another as a result of extreme flow

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