WSP07697

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 7/1/2001
• Author: CDOW
• Title: Riverine Fish Flow Investigations 2001
• Water Supply Pro - Doc Type: Publication

Size distribution for channel catfish for the Yampa River in 2000 at Sevens and Duffy

(Figures A37 and A38) was fairly similar to 1998 and 1999 in that catfish smaller than 30 em

have not been found at Sevens or Duffy over the three years. The main difference observed

for catfish was sample size was much less at Sevens in 2000 (14) and Duffy in 2000 (41) than

in earlier years. In contrast to these two upstream sites, catfish were super-abundant in Lily

Park with a sample size of 1,631. Also catfish in the size range of 24 to 30 cm was very

common and the minimum size at Lily Park was 17 em. The Dolores River catfish sample

had fish between 14 and 61 cm, with most below 30 cm in length (Figure A 40). The

Colorado River catfish sample ranged in size from 25 to 60 em (Figures A41 and A42) and

size structure was fairly similar to the 1999 sample.

Apparently catfish do not reproduce in the Yampa River near the Sevens and Duffy

sites or this part of the river lacks some important aspect of habitat for small catfish. Tim

Modde of the USFWS routinely finds high numbers of small catfish (<30 cm) in Dinosaur

Canyon (per. comm.). It has been suggested by Recovery Program biologists that large

catfish migrate to Dinosaur Canyon for spawning and move upstream after they reach a

minimum size of near 30 em. The catfish size data from this study support this concept.

Small catfish on the Dolores indicate that nursery and juvenile habitat is available in the Big

Gypsum site.

The majority of both largemouth bass in the Colorado River (Figures A 43 and A44),

and small mouth bass in the Yampa River at Sevens (Figure A45) and Duffy (Figure A 46) are

smaller than 15 cm in length. In the Colorado River bass are generally found in backwaters

and are not a predator on main channel species like speckled dace and mottled sculpin, but are

considered a potential predator on young life stages of native fish that occupy backwaters

during nursery and YOY periods. Both adult and young small mouth bass in the Yampa River

are in the main channel and are probably important predators on all small fish in all habitats.

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