7047

• UCREFRP Catalog Number: 7047
• Author: Tyus, H. M. and C. A. Karp.
• Title: Habitat Use and Streamflow Needs of Rare and Endangered Fishes in the Green River, Utah
• USFW Year: 1991.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

the former habitat (Tyus et al. 1987), behavior similar to that of spawning
northern squawfish (Beamesderfer and Congleton 1981). Turbid riverine
conditions have precluded direct observations of egg deposition; however,
cobbles removed from the substrate during this time of year are clean of
sediment and algae (Archer and Tyus 1984; FWS, unpublished data). There is
substantial field and laboratory data showing that Colorado squawfish and
other squawfish species require cleaned cobble surfaces for successful egg
adhesion (Burns 1966; Patten and Rodman 1969; Hamman 1981). Hamman (1981) also
noted hatching of Colorado squawfish larvae from cobble surfaces. The need for
cleaned cobble and boulder substrates is supported by spawning of Colorado
squawfish following peak flows and peak sediment transport (Tyus and Karp
1989). Spring scouring, a gradual decrease in summer flows, and a concomitant
decrease in sediment load aids in preventing siltation of cobble bars. Thus,
magnitude, timing and duration of spring flows are considered potential
limiting factors for successful reproduction by Colorado squawfish.
Larvae and Postlarvae
Larval Colorado squawfish emerge as sac-fry from cobble bars and drift
downstream with declining flows (Tyus et al. 1982b; Haynes et al. 1984; Tyus
and Haines 1991) to concentrate in shallow backwater habitats in the Green
River (Tyus et al. 1982b, 1987). About 6 days are required for transport of
newly emerged Colorado squawfish fry to the mouth of the Yampa River from the
midpoint of the spawning grounds, km 26.4 - 29.1 (Tyus and Haines 1991).
Nesler et al. (1988) also noted rapid downstream transport of larvae (3-15
days) following hatching. From 1979 to 1988, peaks of abundance of young
Colorado squawfish were noted about 160 km downstream of the Yampa River
spawning reach (Tyus et al. 1982b, 1987; Tyus and Haines 1991). Young fish
presumably use river transport for dispersal from upstream spawning grounds to
downstream nursery habitats (Tyus and McAda 1984; Tyus 1986; Nesler et al.
1988; Tyus and Haines 1991; Paulin et al., in prep). These productive nursery
habitats are created with gradually decreasing flows following spring runoff,
and persist with summer-winter baseflow conditions. Availability (quality and
quantity) of these habitats in the Green River are considered important to
successful recruitment of the species.
Mortality of drifting larvae is presumably related to flow, river
temperature, availability of backwater habitat, and predator load. Berry
(1988) noted that larval Colorado squawfish acclimated to about 22°C were
adversely affected by cold water of 10°C and 15°C. Young Colorado squawfish
are routinely collected in isolated pools in the Green River system (USFWS,
unpublished data). These pools farm when decreasing flows strand bodies of
water from the main channel. Natural fluctuations in-river level usually make
this a gradual process and allow entrapped fish an escape route. However,
abrupt fluctuations in river level, as is characteristic of some regulated
systems, could increase mortality of small fishes by increasing the potential
for competitive interactions with other species and exposure to aquatic and
terrestrial predation. Although difficult to detect in nature, predation on
larval Colorado squawfish by common non-native fishes has been observed in the
lab (R. Muth, personal communication). Herons (Ardeidae), raccoons (Procyon
lotor), garter snakes (Thamnophis spp.), and other terrestrial animals have
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