7713

• UCREFRP Catalog Number: 7713
• Author: U.S. Fish and Wildlife Service, C. R. F. R. T.
• Title: Colorado Squawfish Recovery Plan.
• USFW Year: 1991.
• USFW - Doc Type: \
• Copyright Material: NO

estimated age from I to XI and the results were: I=44 mm (1.7 in.); II=95 mm '
(3.7 in.); III=162 mm (6.4 in.); IV=238 mm (9.4 in.); V=320 mm (12.6 in.);
VI=391 mm (15.4 in.); VIII=499 mm (19.6 in.); and X=600 mm (23.6 in.).
Seethaler (1978) found similar growth rates for Colorado squawfish in both the '
Green and Colorado Rivers. However, the accuracy of using scales for aging
this species has not been verified. At Willow Beach National Fish Hatchery,
Colorado squawfish hatched in the summer of 1980 doubled their length in
14 days and attained a size of 48-50 mm (1.9-1.96 in.) in 110 days (Hamman
1981). Growth of broodstock held in cold water (lOoC [50oF]) at Willow Beach
National Fish Hatchery in 1973 and 1974 was slow. Seven adult fish gained a
total of only 0.64 kg (1.41 lbs) over a 9-month period after being fed 40.8 kg '
(90 lbs.) of live fingerling trout (Toney 1974). Length-weight relationships
of these fish was similar to that for wild fish reported by Vanicek and Kramer
(1969) and Seethaler (1978). '
Fingerling Colorado squawfish (50-91 mm [2-3.6 in.] TL) stocked in grow-out
ponds near Grand Junction, Colorado, grew to a range of 185-304 mm

(7.3-12 in.) TL in 1 year (Osmundson 1987). Similar sizes were attained by '
Colorado squawfish in the adjacent Colorado River in about 4 years (Kaeding
and Osmundson 1988). The difference in growth was attributed to warmer water
temperatures (about 1.8 times more degree-days than -the river), lack of '
competitors, and an abundant food supply in the pond. Growth was slower and
more variable in other ponds in the same area, which was probably due to the
variation in food availability, because temperature regimes were similar among

ponds. Tyus and Haines (1991) found that growth of age-0 Colorado squawfish '
was related to the amount of available habitat, but reduced growth at lower
temperatures was not detected. '
Food Habits
Food of young Colorado squawfish consists mainly of zooplankton and insect '
larvae. Other fish species feed on the same food items as young-of-the-year
Colorado squawfish (McAda and Tyus 1984). Fry at Willow Beach National Fish
Hatchery fed on zooplankton in-fertilized raceways (Hamman 1981). Colorado

squawfish become predatory at a very early age. Fish as small as 30 mm '
(1 in.) have been documented to eat other fish (Tyus and Karp 1991). Nearly
86 percent of the diet of juvenile Colorado squawfish is fish, with the major
prey being red shiner (Cyprinella lutrensis) an introduced cyprinid (Jacobi
and Jacobi 1982). Adults are almost exclusively piscivorous, feeding on most
native and many introduced fishes present in the river (Vanicek and Kramer
1969). Nonnative fish presumably have entered their diet more frequently as ,
native fishes have declined (Holden and Wick 1982). However, Beckman (1952)
reported that jackrabbits and other animals were used historically by anglers
as bait for Colorado squawfish. Minckley (pers. comm.) observed a large

Colorado squawfish eat two newly hatched American coots (Fulica americana) at '
Dexter National Fish Hatchery, New Mexico. Tyus and Minckley (1988) reported
four Colorado squawfish feeding on Mormon crickets in Dinosaur National
Monument, Colorado, and speculated on the significance of large outbreaks of '
crickets as food for the native fish fauna.

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