3102

• UCREFRP Catalog Number: 3102
• Author: Wick, E. J., J. A. Hawkins and C. A. Carlson.
• Title: Colorado Squawfish and Humpback Chub Population and Habitat Monitoring 1983-1984.
• USFW Year: 1985.
• USFW - Doc Type: Ft. Collins, CO.
• Copyright Material: NO

12
RESULTS AND DISCUSSION
General Fish Collections
Colorado River, August 22, 25-28,1983
On the Colorado River, 3570 fish were collected by seining and
electrofishing during standardized trend zone monitoring. A total
of 15 species (5 native and 10 introduced) were collected (Table
2). Native roundtail chub (Gila robusta) and speckled dace
(Rhinichthys osculus) dominated seine collections, while native
flannelmouth (Catostomus latipinnis) and bluehead (Catostomus
discobolus) suckers were most commonly collected by electrofishing
(Figure 3). Red shiner (Notropis lutrensis), sand shiner (Notropis
stramineus), and fathead minnow (Pimephales promelas) were the most
common introduced fishes in seine collections, while carp ( rinus
carpio) and channel catfish (Ictalurus punctatus) were the most
common introduced fishes caught by electrofishing.
Results of 1983 seine and dipnet collections can be compared
to those of 1981 collections (wick et al. 1985), the only other
year the CROW sampled this river segment. Results differed
dramatically between these collections. In 1981, red shiner,
fathead minnow, and sand shiner (all introduced species) dominated
seine and dipnet collections (Figure 4). A likely explanation lies
in the effect on reproduction of extremely high flow levels of 1983
compared to the low flow conditions of 1981 (Figure 5). In 1983,
sampling was conducted during the latter portion of the decending
hydrograph, 18 days after minimum water temperature reached 200C.
In 1981, sampling occurred 53 days after the hydrograph reached
base flow levels and minimum temperature reached 200C. Based on
temperature (cumulative days exceeding 200 C) and flow, sampling