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196 The Southwestern Naturalist vol. 29. no. 3 SAND SILT BOULDER RUBBLE GRAVEL FIG. 4.-HabitaI (A) and substrate (B) types recorded for radiotelemetered Colorado squawfish, Green, White and Yampa rivers, 1980 and 1981. n = number of 15 minute observauons. SUMMARY AND DISCUSSION.- This study documents three types of behavior exhibited by the radio tagged fish. The first type, a steady. dow.nstream movement that perhaps is passive, is probably a result of phYSIOlogIC s.tress, either imposed by surgery, or indicative of a fish in poor ~OndI~I~n. Physiologic stress has been implicated by Wedemyer 0.980) as Impaumg migratory behavior. The remaining two types produce dIvergent mo.vement patterns which were associated with the degree of sexual ~atuflty a~d spawning migration. Eight radio-implanted fish that were hI.ghly mobIle migrated from the upper Yampa and Green rivers to spaw~ m the Im~er 32 km oE Yampa Canyon. Three sedentary [ish were smaller m average SIZe and were linked with sexual immaturity; immature fish were sedentary and mature fish highly mobile. Spawning habitat Eor Colorado squaw fish was located in Yampa Canyon in 1981, when seven radiotagged fish moved downstream III the :ampa River and one radio tagged fish moved upstream from the Green Rlve~ to reach the spawning grounds located between km 8 and km 30. ~ollecuo~s of ripe adults and larvae, and observations of fish behavior con~Irmed t.hIS site as a spawning area. A physical characterization of the spawmng habllat indicated the C'olorado squawfish spawned at 22 C temperature over rubble substrate. Water depths and water velocities at the primary site studied (km 26.4) ranged from 0.9 to 2.1 m depth and 0 to 0.1 mls velocity.. . When all die! observations were lumped for the three flvers studIed, a strong die! rhythm was observed during the post-spawning period, with. the most active time of day between 0800-1200 h. Radiotelemetry observauons from the Yampa River indicated more movement may occur at night dur~ng spawning. This nocturnal movement could be characteristic of spawnmg August 1984 Tyus and McAda-Squawfish Movements 297 TABLE 3.-Depths and velocities recorded /or habitat occuPied by Colorado squaw/ish, radiotelemetry studies, /980-/98/. n = multiple /5 minute observations. River Year Parameter Range Average 1980 Depth' 523 0.24-3.2 1.20 1981 Depth 475 0.18-6.0 1.68 X=1.4 1980 Velocity' 503 0-.87 0.17 1981 Velocity 440 0-.90 0.20 X=0.2 1981 Depth 454 0.33-2.6 0.93 Velocity 464 0.-0.112 0.11 1981 Depth 260 0.27-1.6 0.72 Velocity 260 0-0.84 0.45 Green Green Yampa White 'm 2m/s activity since Manteifel et aI. (1978) reported twilight migration occurred in Russian cyprinids. Results from the Yampa River in 1981 indicate that the Colorado squawfish may have a homing ability, since it is able to undertake potamodromous migrations of a hundred kilometers or more. Long distance (over 100 km) spawning migrations in freshwater fish species are generally uncommon in North America although Nikolsky (1961) cites examples in Asia of other predaceous cyprinid fishes that migrate over 1,000 km. The northern squawfish, (P. oregonensis) and the Sacramento squawfish (P. grandis) are also reported to make freshwater spawning migrations (Reid, 1971; Moyle, 1976). Other workers have postulated spawning migration in Colorado squawfish and there are many reports of spring spawning migrations by early settlers who called the Colorado squawEish "salmon" (Sigler and Miller, 1963). Joseph et aI. (1977) reviewed information concerning movement and spawning and concluded that large individuals possibly migrate long distances. Even so, the possible impact of movement and long distance migration has not been considered in previous studies and may lead to erroneous conclusions about distribution, abundance, survivorship, habitat preferences and other life history (actors. As suggested by Northcote (1967) such movement increases the chance of capture and confounds determinations of recruitment and production. Extensive movement could bias apparent habitat preference data obtained by the use of passive gear (set nets), since a fish would have a greater susceptibility for capture while moving between preferred habitats. For these reasons it is recommended that earlier habitat preference data for Colorado squawfish be carefully examined for representativeness before use. Even radiotelemetry data should be examined carefully when studying such a highly migratory species as the Colorado squaw fish since we have shown that this fish can move hundreds of kilometers in a short period of time. According to Northcote (1967) spawning migrations bene[it fish species by increasing reproductive success, since the location of mates and