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<br />A total of 43 Colorado squawfish were radio-tracked
<br />to the Yampa Canyon spawning reach by the U.S. Fish
<br />and Wildlife Service (N = 38) and Colorado Division
<br />of Wildlife (N = 5) from 1981 to 1988. These included
<br />28 fish from the upper Yampa River, 13 fish from the
<br />Green River, and 2 fish from the White River. Average
<br />one-way movement of migrants radio-tracked by
<br />Service biologists was about 124.8 km. One of the White
<br />River fish migrated about 372.8 km to reach the Yampa
<br />River spawning grounds. This fish may have been en
<br />route for more than a year, because it was tagged at RK
<br />164.8 of the White River in 1983, tracked to RK 49.6 of
<br />the Yampa River in spring 1984, and recaptured at RK
<br />156.8 of the White River in 1985. These radio-tracking
<br />data show that migrating Colorado squawfish arrive in
<br />the Yampa Canyon in early summer from many areas
<br />throughout the upper Green River basin, including the
<br />White, Green, and upper Yampa rivers.
<br />The initiation of the spawning migration is an
<br />important component of the reproductive cycle of the
<br />Colorado squawfish. To better evaluate some factors
<br />influencing the onset of migration, adult Colorado
<br />squawfish were radio-tracked in early spring in the upper
<br />Yampa River by U.S. Fish and Wildlife Service biologists
<br />in 1981 and 1983 (Tyus and McAda 1984: Tyus 1985), by
<br />Colorado Division of Wildlife and National Park Service
<br />personnelin 1982 (Wick et aI. 1983), and by U.S. Fish and
<br />Wildlife Service and Colorado Division of Wildlife
<br />biologists in 1988. These fish initiated spawning
<br />migrations from 27 May to 13 June, depending on the type
<br />of water year (Table 1). Flows and water temperatures
<br />were highly variable within each migration period and
<br />among years. However, spawning migrations were
<br />initiated earlier in low-water years (e.g., 1981) and later
<br />in higher-water years (e.g., 1983; Table 1). Although
<br />radio-tracking studies were not conducted all years, data
<br />from 1981 (low-water year), 1982 and 1988
<br />
<br />(average-water years), and 1983 (high-water year) were
<br />used to investigate relations between discharge, water
<br />temperature, and date of initiation of spawning migration
<br />(Figs. 7 and 8). As shown in Fig. 8, spawning migrations
<br />of radio-tagged Colorado squawflSh (N = 24) were
<br />associated with highest spring flows and river
<br />temperatures generally exceeding 140C. However, the
<br />actual period of initiation of spawning migration of
<br />Colorado squawfish may be longer because radio-tagged
<br />fISh may not have included early and late migrants.
<br />Timing of the reproductive cycle is influenced first by
<br />intrinsic biological mechanisms and secondly by en-
<br />vironmental stimuli (Brown et a!. 1970). Identification
<br />of these stimuli is made difficult by synergistic and other
<br />confounding interrelations (Bye 1984). We believe that
<br />some complex combination of endogenous (e.g., stage
<br />of maturity, physiological condition, genetic lineage)
<br />and exogenous factors (e.g., substrate, temperature, dis-
<br />charge, photoperiod) are necessary and that neither
<br />discharge nor temperature alone is sufficient to induce
<br />spawning migrations or spawning. For example, radio-
<br />tracking data suggest that all adult Colorado squawfish
<br />do not spawn each year. Offour fish radio-tracked to
<br />spawning grounds at least once in consecutive years
<br />(1 + years) during the spawning season, two migrated
<br />only 1 year and presumably did not spawn each year.
<br />Effects of exogenous factors on reproductive cycles
<br />of cyprinid fishes are well known and many
<br />physicochemical variables have been implicated
<br />(reviewed by Brown et a!. 1970; Bye 1984; McKeown
<br />1984). We hypothesize that inputs of certain chemical
<br />substances from runoff and inundated shorelines during
<br />spring snowmelt, in concert with increasing river level
<br />and temperatures, may act to influence genetic,
<br />physiological. and behavioral mechanisms in Colorado
<br />squawfish that are associated with spawning migrations.
<br />We assume these mechanisms can only be activated at
<br />
<br />Table 1. Initiation of Colorado squawfish spawning migrations, Yampa River spawning grounds, 1981-83, 1988.
<br />Movementrecordedfor24radio-taggedftsh (1981 = 7ftsh, 1982 = 5ftsh, 1983 = 7ftsh, 1988 = 5fish).Datafol'
<br />1982 after Wick et al. (1983).
<br />
<br /> Type water Initiation of DischargecCm3/s) Water temperature (QC)c
<br />Year yeara rnigrationb Mean Range Mean Range
<br />1981 Low 27 May-20 June 121.1 33.6-171.8 14.9 12.5-18.5
<br />1982 Average 10 June-3 July 200.7 175.5-235.2 13.7 11.6-15.7
<br />1983 High 13 June-12 July 240.7 127.4-322.6 13.8 9.2-17.3
<br />1988 Average 9-23 June 129.8 93.4-193.1 15.8 13.8-19.4
<br />
<br />a Design~ion of low, avera~, and high water years based on average annual discharge for 1922-87: low. <43.15 m3/s; average, 43.15-
<br />77.83 m Is; high, > 77.83 m Is (M. Butler, personal communication).
<br />b Initiation of migration is the period between first and last departure of radio-tagged fish in upper Yampa River to Yampa Canyon spawning
<br />grounds.
<br />C Data based on daily averages during indicated period (USGS flow records, Yampa River near Maybell, Colorado).
<br />
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