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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Because the number of flannel mouth was low at Duffy in 2001 (n=17) (Figure A8), the 2001
mean lengths (47.5 cm) was not significantly different from prior years (Table 9). At Lily Park,
mean length was significantly less in 2001 (38.4 em) than in 2000 (41.5 cm) (Table 9). This was
due to more fish less than 29 cm in 2001 (153) than in 2000 (4) (Figure A9). Flannelmouth
sucker from the Colorado River at Com Lake (Figure All) and Clifton (Figure A12) have all
size groups represented in all study years. On the Dolores River, there was apparently very good
survival of flannel mouth YOY produced in the prior year since the vast majority of fish were
yearlings between 9 and 19 cm (Figure AI0). Yearling flannel mouth were larger (16 to 26 cm) in
2000 than in 2001. As was found for bluehead suckers on the Dolores, yearling flannel mouth
sucker were very numerous while large adult fish were very rare.

The mean length of flannel mouth sucker found at Sevens (46 cm) and Duffy (49 cm)
(Table 9) are representative of populations without juvenile fish. The decrease in mean size for
flannel mouth sucker at Sevens and Lily Park in 2001 could suggest reduced predation by
northern pike that year relative to others, or some other factor that allowed the number of smaller
fish to increase. At Lily Park in 2001, mean length decreased from 42 to 38 cm (Table 9). At
Duffy, mean length was less in 2001, but sample size was also very poor. The reason for the
lower number of flannelmouth at Duffy is difficult to pin point, but clearly very low flows and
small mouth bass are implicated. Reduced predation by northern pike at Duffy may not be
detectable since very few predators can impact a population that is already in low abundance.

Table 9. Mean lengths of flannel mouth sucker captured during the study period (1998 to 2001),
Yampa, Colorado and Dolores Rivers.

1998a 1999b 2000c 2001d
Mean length of flannel mouth sucker incm
Sevens 45.7,d 46.5,d 45.8,d 43.8,abc
Duffy 48.9 49.0 49.8 47.5
Lily Park 41.5,d 38.4,c
Corn Lake 41.2,cd 38.9,bd 40.6,bc
Clifton 38.3 38.8
Dolores 18.8d 14.2c
Total number in sam )Ie - Number less than 15 cm
Sevens 668 -0 476 - 0 404 - 1 359 - 0
Duffy 90-0 79-0 65 - 0 17 -0
Lily Park 1,935 - 0 2,022 - 0
Corn Lake 1,384 -46 928 - 65 1,495-39
Clifton 1, 1 06 - 55 1,934 - 53
Dolores 110 - 30 580 - 271

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

The Colorado River appears to represent a flannelmouth sucker population with abundant
habitat and a lack of predation and competition. Mean length of this population is 39 to 41 cm
(Table 9). The size structure of flannel mouth in the Colorado River ranges from 7 to 55 cm with
modes representative of all age groups. It is believed that in the Colorado River, both

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