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<br />2000] COLORADO PIKEMINNOW IN WHITE RIVER
<br />initiated by changes in discharge, temperature,
<br />and photoperiod (Tyus 1986, 1990). Using an
<br />extensive telemetry and mark-recapture data
<br />set, Tyus (1990) described factors initiating
<br />migration and spawning of Colorado pike-
<br />minnow in the Green River subbasin, includ-
<br />ing the White River. Some fish migrated 1-way
<br />distances >300 km to 1 of 2 known spawning
<br />areas (Yampa Canyon in Yampa River or Gray/
<br />Desolation Canyon in Green River), and indi-
<br />viduals were captured on the same spawning
<br />sites in multiple years. Of 153 fish implanted
<br />with radio transmitters, 41% migrated >_1 times
<br />to 1 of the 2 known spawning areas, with an
<br />additional 11% suspected of doing so (Tyus
<br />1990). Spawning migration was not detected in
<br />approximately half the fishes implanted with
<br />radio transmitters. Lack of movement was pre-
<br />sumably because fish were either immature or
<br />nonannual spawners (Tyus 1990). Ryden and
<br />Ahhn (1996) found similar behavior in Col-
<br />orado pikeminnow radio-tracked over a 3.5-yr
<br />period on the San Juan River in New Mexico,
<br />Colorado, and Utah. Movement of 12 of 13
<br />fish they studied averaged 17.7 km (range:
<br />1.82.8 km). The other fish moved a total of
<br />93.0 km and was the only one thought to dis-
<br />play migratory behavior. Although factors initi-
<br />ating spawning migrations and spawning-site
<br />fidelity have been well described (Tyus 1986,
<br />1990), movement patterns of individual fish in
<br />consecutive years are not well understood.
<br />Previous studies have found no early life
<br />stages and few juvenile Colorado pikeminnow
<br />in the White River; most fish in the river are
<br />adults (Tyus 1986). Taylor Draw Dam, con-
<br />stntcted in 1985 on the White River, created a
<br />barrier to upstream movement, preventing
<br />access to about 32% (77.8 km) of the habitat in
<br />the White River historically used by adult Colo-
<br />rado pikeminnow (Carlson et al. 1979, Wick et
<br />al. 1985, Trammell et al. 1993). It is assumed
<br />that after closure of the dam those Colorado
<br />pikeminnow upstream of the dam migrated
<br />over the dam to downstream spawning areas.
<br />Post-spawning fish moving back upstream were
<br />blocked from returning to their previously
<br />occupied home range above Taylor Draw Dam.
<br />.~1s a result, fish congregated below the dam in
<br />densities up to 37 adults per 0.4 km as recent-
<br />l~- iu 1993 (Inzng and Modde 1994). These den-
<br />sities may also be the result of recent high re-
<br />cniitment of Colorado pikeminnow throughout
<br />die Green River basin (McAda et al. 1998).
<br />17
<br />This study examined migratory movements
<br />of 12 adult Colorado pikeminnow in the White
<br />River through 2 successive spawning periods
<br />and determined where these fish spawned. It
<br />also tested whether some of these fish that
<br />were translocated into formerly occupied habi-
<br />tats above Taylor Draw Dam would remain in
<br />that habitat, move into the reservoir, or return
<br />to home ranges below the dam.
<br />STUDY AREA
<br />The White River drainage encompasses 1.3
<br />million ha of grid pinion-juniper and sage-
<br />brush desert in northwestern Colorado and
<br />northeastern Utah (Fig. 1). The river drains
<br />into the Green River, a major tributary to the
<br />Colorado River in southeastern Utah. The
<br />high-gradient, cool-headwater, canyon-bound
<br />reaches consist of riffles, runs, and rapids with
<br />boulder, cobble, and gravel substrates. The
<br />low-gradient warmwater reaches are charac-
<br />terized by deep eddies, pools, and runs that
<br />meander through slower, turbid waters, with
<br />vegetated shorelines and gravel, sand, and silt
<br />substrates. Summer water temperatures often
<br />reach 20°C. Peak spring discharge ranges
<br />between 100 and 170 m3 s-I. Taylor Draw
<br />Dam is operated as arun-of--the river facility
<br />and provides water storage, flood control, and
<br />hydroelectric power. Kenney Reservoir, above
<br />the dam, is 275 ha and provides recreational
<br />boating and fishing.
<br />MATERIALS AND METHODS
<br />We captured 12 wild adult Colorado pike-
<br />minnow by electrofishing and trammel-netting
<br />in a 0.5-km reach (km 163-168) of the White
<br />River below Taylor Draw Dam. Six fish (#1~)
<br />were caught in September 1992 and 6 more
<br />(#7-12) in April 1993. Each fish was mea-
<br />sured for total length (TL), tagged with a PIT
<br />(passive integrated transponder), and surgi-
<br />cally implanted with a 24-month (16-g) radio
<br />transmitter. Fish were anesthetized with tri-
<br />caine methanesulfonate and radio transmitters
<br />(internal loop antennas) placed into the body
<br />cavity via a surgical incision as quickly as pos-
<br />sible following capture. Fish were released
<br />within 10 min after surgery.
<br />Eight fish, 2 recaptured from the 1992 group
<br />and 6 from the 1993 group, were translocated
<br />30 km upstream of the dam to determine if fish
<br />would remain in habitats previously occupied
<br />
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