7157

• UCREFRP Catalog Number: 7157
• Author: Haynes, C. M., et al.
• Title: Larval Colorado Squawfish ‎(
• USFW Year: 1984
• Copyright Material: YES

March 1984 Haynes t:t at-Larval Colorado Squawfish 27
u 30 30
0 26 ~ 26
-
W 22 22
0: 18 18
:J
~ 14 14
0: 10 10
~ 6 6
:a 2
~I~ A M .J .J A S A M .J .J A S 1000
900 900
800 800
~700 700
Q)
,~ 600
If) 600
E
W500 500
~
<3:400 400
:r:
~ 300
5300
200 200
100 100
~ AM" .J A S A M .J .J A S A M .J .J A S
~ 1979 1980 1981
(8) (77) III
6/29=at2 - 6118-24
85 6/28-8/26

FIG. 2.-Relationship of temperature (upper) and discharge (middle) to estimated spawning
periods of Colorado squawfish (lower), Colorado River (April-Sept.. 1979-1981). Max.imum and
minimum temperatures per month are represented by heavy lines; mean maximum and minimum
temperatures are represented by thin lines. Maximum and minimum discharge per month are
represented by heavy lines; mean monthly discharge is represented by a thin line. Estimated
spawning periods are represented by horizonlallines (-), dates included. Numbers in parentheses
represent number of larvae collected per year.

1981; Wick et al., 1981) the capture of young-of-the-year is an indication of
successful reproduction for the species in these areas. However, it can be
stated with certainty only that reproduction occurred at and/or upstream of
the lowermost larval collection locations.
Sampling effort apparently had no relationship to collection success
(Table 1). In the Colorado River, the highest number of larvae (i.e. 77
individuals in 114 samples) was collected in 1980, while only one individual
was found in 1981 in 319 samples. Similarly, in the Yampa 215 samples
yielded 46 squawfish in 1980 while 519 samples yielded only 23 in 1981.
Furthermore, samples were collected in approximately the same time period
(July-October) each year. Therefore, variation in squawfish numbers
appears to reflect a real difference in spawning success and/or larval
survivorship in 1979-1981.
Our estimated spawning periods indicate that spawning occurred as water
levels were dropping and ceased with the onset of lower late-summer and
fall flows (Figs. 2 and 3) and it is reasonable to suggest that the seasonal