8068

• UCREFRP Catalog Number: 8068
• Author: Bestgen, K. R., R. T. Muth and M. A. Trammell.
• Title: Downstream transport of Colorado squawfish larvae in the Green River drainage
• USFW Year: 1998.
• USFW - Doc Type: temporal and spatial variation in abundance and relationships with juvenile recruitment.
• Copyright Material: NO

' EXECUTIVE SUMMARY
This study was initiated in 1990 and was part of the Five-Year Flaming Gorge Flow
Recommendations Investigations, 1992-1996. It was designed to assess aspects of reproduction,
' recruitment, and status of Colorado s uawfish in the Green and Yam a rivers. Colorado
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' squawfish reproduced in early to mid-summer in the Green River basin. Initiation of
reproduction by Colorado squawfish each year was generally associated with increasing water
' temperature and diminishing spring runoff. Earlier spawning was associated with earlier
occurrence of peak runoff and warmer water temperatures.
' No single variable accurately predicted when Colorado squawfish first reproduce among
sites or years. Water temperature at initiati n of reproduction ranged from 16.0 to 22.3°C in the
lower Yampa River and was 19.8 to 23.0°C in the lower Green River. In the lower Yampa River,
Colorado squawfish generally initiated repr duction a few days prior to or within a few days after
' mean daily water temperature exceeded 18° . In contrast, Colorado squawfish in the lower
Green River initiated reproduction after me n daily temperature exceeded 18°C for 13 to 39 days.
' Time of year and accumulated degree days ere also reasonable predictors of initiation of
reproduction by Colorado squawfish. Initi tion of reproduction was not closely associated with
' days post-peak discharge.
Abundance of larvae was generally igher in the Yampa River than in the lower Green
River, and varied widely on diel, spatial, in ra-annual and inter-annual scales. High transport
abundance of larvae associated with increa ed turbidity, discharge, and darkness may be due to
' several factors including loss of orientation High transport abundance under those conditions
' may also be a behavioral response to avoid sight-feeding predators. Increased transport
abundance during turbidity events may hav been caused by increased sediment deposition in
' interstitial spaces in the substrate, a stress hich may have motivated larvae to emerge and drift.
Differences in transport abundance of larv across years and the patterns of abundance within a
' year may be due to several factors includin timing of arrival, condition, and number of
reproducing adults at the spawning areas.
' Transport abundance appeared to b associated with discharge only during extreme years.
High discharge was negatively associated ith transport abundance in both the lower Yampa
' River and the lower Green River while to discharge was negatively associated with transport
' iii