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

these native fish may be less tolerant oflow base flows (those observed in 2000) than

nonnative cyprinids.
Species Composition - 2000

Species composition was highly variable between the three stations (Lily Park, Sevens

and Duffy) sampled in 2000. Lily Park had by far the largest sample size, with 4058 fish

handled in four passes (Table 2). The most common species in Lily Park was flannelmouth

sucker, which comprised 48% of the total catch offish >15 em. The next most common fish

was channel catfish, which was 40% and the third most common species was bluehead sucker

at 9"10. Because of the very high number offlannelmouth sucker and channel catfish at Lily

Park, the percentage of other species such as small mouth bass, carp, northern pike and

Colorado pikeminnow were smaller than at other stations, relative to numbers caught. White

sucker were rare and only one roundtail chub was caught in Lily Park (Table 2).

Species composition was found to vary between electrofishing passes at Lily Park

(Table 3). On the first pass only the lower half of the site was sampled, on September 13 at a

flow of70 cfs, flannel mouth were 74% of the total fish captured. At 70 cfs most

Ilannelmouth were confined in deeper non-flowing habitats and sampling efficiency was felt

to be very high. Subsequent passes were made for the entire station at flows of 420, 260 and

216 cfs, respectively. The second pass was made at a high flow and was also the first time

the entire reach was sampled. Under these conditions channel catfish were the most common

fish and percent composition of blue head sucker increased. Species composition was fairly

similar for the third and fourth passes (Table 3).

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