8027

• UCREFRP Catalog Number: 8027
• Author: U.S. Fish and Wildlife Service.
• Title: A comparison of captures of Colorado squawfish and razorback suckers from adjacent Colorado River reaches upstream and downstream from the confluence with the Gunnison River - Draft.
• USFW Year: 1985.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

*****DRAFT*****
they hatched from the egg.
Post-larval aqe-U Colorado squawfish
The relative abundance of post-larval age-0 Colorado squawfish in
adjacent river reaches upstream and downstream from the confluence with
the Gunnison River was similar to that for larvae (Table 2}. All post-
larval squawfish were collected from the downstream reach.
Adult-size Colorado squawfish and razorback suckers
Almost all of the adult-size Colorado squawfish and razorback suckers
collected from riverine habitat within the study area were collected
from the upstream river reach (Tables 3 and 4). Although not included
in these analyses, many additional squawfish and razorbacks were
collected from flooded gravel pit ponds adjacent to the Colorado River
within this reach.
"_ - Conclusions
Results of our three-year investigation of larval and post-larval
age-0 Colorado squawfish from the Colorado River indicate that use of
the adjacent river reaches upstream and downstream from the confluence
with the Gunnison River differs markedly between reaches. The
occurrence of larvae suggests that spawning of Colorado squawfish occurs
only rarely in the upstream reach; most spawning of Colorado squawfish
and all of the rearing of subsequent. age-0 young apparently occurs in
the downstream reach. This observation is not unexpected. Colorado
squawfish spawn when water temperatures reach 20-22 C. In the upper
Colorado River, such temperatures are not reached until annual seasonal
runoff recedes. Recession of seasonal runoff in the upstream reach
typically results in severe dewatering of the channel because much of
'-----~
~~
• 4