6042

• UCREFRP Catalog Number: 6042
• Author: Haynes, C. M., R. T. Muth and T. P. Nesler.
• Title: Identification of Habitat Requirements and Limiting Factors For Colorado Squawfish and Humpback Chub.
• USFW Year: 1985.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

25

Colorado Squawfish

Colorado squawfish YOY were present in 71 of 1,438 seine and dip net
samples taken in the Yampa River during 1980-1984 (Table 9). A total of 556
specimens were collected during the study, of which 477 were sampled in 1983
and 1984 combined. Specimens were collected in low velocity shoreline areas
and ephemeral backwaters, embayments, concavities, and isolated pools between
river km 28.8 and 0.2. Colorado squawfish YOY were seined as early as 24
July in 1981 and as late as 25 August in 1982. Size (mm TL) at time of
capture ranged from 8.1 (27 July 1984) to 29.0 (8 August 1980). C/f ranged
from 0.19 in 1982 (20 individuals) to 6.0 in 1983 (228 individuals).
Colorado squawfish spawning was estimated to have occurred as early as 2 July
(1980) and as late as 11 August (1983).

In 1983, Colorado squawfish larvae first appeared in drift-net samples on
20 July (Harding Hole) and were collected through 21 August at Box Elder
(Table 10). In 1984, Colorado squawfish larvae were sampled from 16 July
(both sampling sites) through 8 August at Box Elder (Tables 11 and 12). A
total of 192 specimens were collected in the Yampa River during 1983 and 1984
combined and 27 were sampled at State Line in 1984. Size (mm TL) at time of
capture ranged from 7.2 to 9.5 (Box Elder, 8 August and 19 July 1984,
respectively). Based on age predictions of larvae sampled at Box Elder,
estimated Colorado squawfish spawning dates were 11 July-19 August (1983) and
5 July-6 August (1984); using predicted ages of larvae collected at State
Line in 1984, estimated spawning dates were 8-27 July. The collection of one
larval Colorado squawfish at Harding Hole in 1983 (20-21 July; 7.3 mm TL)
established that at least limited spawning occurred above this site.

Colorado squawfish larvae drift densities at Box Elder peaked on 8-9
August in 1983 and 28-29 July in 1984 (Tables 13 and 14). At State Line in
1984, drift densities peaked on 29-30 July (Table 15). Die1 variations in
drift densities at Box Elder in 1983 and 1984 were not statistically
significant (P ~O.05). Overall mean total abundance ratios (proto1arvae +
mesolarvae) at Box Elder were 1:2:1:2 and 4:2:1:1 (i.e., sunrise:noon:
sunset:midnight) and 1:1 and 3:1 (i.e., day:night) for 1983 and 1984,
respectively (Table 16). At State Line in 1984, protolarvae were more
abundant in dawn and noon samples with total mean densities of 2.01 and
0.4/l000m3 for day and night, respectively. This difference was considered
significant (P~0.05). Mean total abundance ratio at State Line was 5:5:1:1
(Table 16).

Estimated ages of combined seine- and drift-net-co11ected Colorado
squawfish YOY yielded an overall projected spawning period of 11 Ju1y-19
August in 1983 and 4 July-6 August in 1984 (Figs. 4 and 5; Table 17). In
1983, Colorado squawfish spawning apparently peaked between 25 July-10 August
with both seine- and drift-net-co11ected YOY defining the spawning peak.
Peak spawning activity in 1984 was estimated to have occurred in mid-July
with a second, less intense period during late July through early August.
Larvae spawned during 12-20 July were mostly collected in seines, while those
spawned after approximately 20 July were almost entirely collected in drift-
nets.