9433

• UCREFRP Catalog Number: 9433
• Author: Anderson, R.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2002.
• USFW - Doc Type: Federal Aid Project F-288-R5,
• Copyright Material: NO

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flannelmouth and bluehead sucker are at 'carrying capacity' of the physical habitat. On the
Dolores River only three adult flannelmouth were collected, less than in 2000. The low mean
length is representative of a population that has either poor habitat or limited forage availability
for adult size fish.

Size structures of round tail chub at Sevens (Figure Al3) and Duffy (Figure A14) in 2001
were very similar (not significantly different) to prior years, but sample size was less at both sites
(Table 10). The small decrease in mean lengths in 2001 (Table 10) was due to only one or two
additional small fish in the sample, not a shift in size distribution. The high mean length at
Sevens (38 to 40 cm) and at Duffy (43 to 44 cm) for the study period are due to few yearling and
juvenile fish in the population. Only one chub was collected at Lily Park in 2000 and the single
chub in 2001was 18 cm in length (Figure AI5). On the Colorado River, both large and small
chubs were present in 2000 and again in 2001 at Com Lake (Figure A17) and at Clifton (Figure
AI8).Mean lengths were not significantly different between Com Lake (23.5,20.9 cm) and
Clifton (25.0,22.1 cm) in the same year, but the differences were significant between 2000 and
2001 at both sites. On the Dolores River, chub ranged in size from 2 cm to 27 except for one
large chub at 40 cm (Figure AI6).

Table 10. Mean lengths of round tail chub captured during the study period (1998 to 2001),
Yampa, Colorado and Dolores Rivers.

1998a 1999b 2000c 2001d
Mean lenoth of roundtail chub in cm
Sevens 39.0 40.0,d 39.2 37.9,b
Duffy 43.5 44.5 44.2 43.4
Lily Park 40.3 18.0
Corn Lake 23.3,d 23.5,d 20.9,bc
Clifton* 28.9 25.0,d 22.1,c
Dolores 14.1,d 10.9,c
Total number in sample - Number less than 15 cm
Sevens 73-0 39 - 0 31 - 0 23 - 0
Duffy 55 -1 44 -0 46 -0 27 -1
Lily Park 1-0 1-0
Corn Lake 188 - 78 145 - 26 193 - 89
Clifton* 47 - 4 196 - 29 446 - 186
Dolores 275 - 277 145 - 367

* a, b, c, d following a mean length indicates significant difference (2 tail test) at @=0.5 for
those years.

The high mean size (38 to 44 cm) of round tail chub in the Yampa River is a result of
predation on small fish. The smallest mean length (10.9 cm) on the Dolores in 2001 was less
than in 2000 (14. 1) (Table 10). As was the case for native suckers, there were few larger fish
(>20 cm) in the Dolores River in 2001. The lack of adult size fish is consistent for all native
species and between years and indicates a lack of habitat or forage availability. The size
structure for roundtail chub on the Colorado River may be near ideal for this species and mean
length was from 21 to 25 cm (Table 10).