7346

• UCREFRP Catalog Number: 7346
• Author: Wick, E. J. and J. A. Hawkins.
• Title: Colorado Squawfish Winter Habitat Study, Yampa River, Colorado 1986-1988.
• USFW Year: 1989.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

Effects of ice on habitat use
Ice formation occurred on low-velocity habitats as early as November 11, '
1986, and November 17, 1987. Squawfish were observed by radiotelemetry to
move under the ice at the large backwater at RMI 95.7, at the large embayment
at RMT 81.1, and along large ice pads in pool and eddy habitat at initial ice
formation both years. On the first scheduled trip in December 1986, the main
river channel was clogged with floating ice and slush during early morning
hours. low-velocity shoreline areas were frozen over. All nine squawfish
located on that trip were in habitat areas that were iced over although the
main channel would clear of ice by late afternoon. The initial ice over
pattern outlined and identified habitat types that were used by squawfish
throughout the rest of the winter. Because lower velocity waters were the
first to freeze, ice served as a velocity indicator. Squawfish were apparently
attracted to these frozen-over law-velocity areas for the cover and security
they provided. In addition, large schools of small fish were observed through
the thin clear ice near shore, so food may have been an additional attraction.
Except for a few open riffle areas the river was completely covered by ice
throughout most of the winter (mid December through early March) both years.
Ice-out occurred March 7 in 1987 and March 21 in 1988.
The initial attraction squawfish have for ice-covered habitats at first
ice formation suggests that surface ice provides a protective cover which
permits utilization of habitat areas seldom used during other times of the

year. Ice may provide needed security from overhead predators such as hawks ,
and eagles, allowing squawfish to move into clear, shallow waters to forage
with little danger. Ice insulates the water in backwater and embayment
habitats maintaining temperatures slightly above freezing while allowing light
penetration for photosynthesis. The importance of embayment habitat as a
source of primary productivity was indicated by high dissolved oxygen levels
of 17 parts per million (ppm) compared to 12 ppm saturation (Table 6). ,
Schools of small fish were seen through the clear ice swimming along
shorelines of shallow embayments and backwaters. Maintenance of these
nutrient-rich embayment and backwater areas could be critical to the overall
productivity of the winter ecosystem.
Oxygen measurements were taken during midwinter the second year to
determine if heavy ice and snow cover affected oxygen levels. Some depression
of oxygen levels was noted in upstream study areas (Table 6). Reductions in
oxygen levels in the main channel may have been due to oxygen demand from
sewage inputs from upstream towns. The river recovered to saturation levels
at the lower Lily Park study area. Recovery to oxygen saturation was probably
assisted by open water in canyon areas (Juniper and Cross Mountain) and by
mixing with supersaturated water in embayment habitats similar to the one
measured at RU 81.1.
Ice cover insulates the river from extremely cold air eratures that
occur frequently along the Yampa River. Ice cover reduces formation of
excessive amounts of frazil ice which can o=W large volumes of run and pool
habitat and when moving in the water column may damage fish gills.

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