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<br />6580
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<br />Federal Register I Vol. 58, No, 1B I Friday. January 29. 1993 I Proposed Rules
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<br />endemic, Its origins there predate
<br />recorded bistory, but by the mid-
<br />Pliocene epoch (about 6 million years
<br />ago} fossils indicate that .ariy
<br />PtychocheiJus bad riverine adaptations
<br />that were similar to modem forms.
<br />, During the Pleistocene epoch (about 1
<br />million years ago). an earil.r wet
<br />climat. was int.rrupted by periods of
<br />d.sart conditions (M, Smith 19B1),1t
<br />has been bypothesized that the
<br />migrations report.d for Colorado
<br />squawfisb are a perfect ilf. history
<br />strategy for tha survival of a large
<br />predaceous fish in the historic Colorado
<br />River environm.nt (G, Smith 1981; Tyus
<br />19B6, 1990), During tha spawning
<br />season, adult Colorado squawfish have
<br />been known to migrate up to 320
<br />kilomaters (200 miles) upstream or
<br />downstream to reach spawning areas
<br />(Tyus 1990),
<br />During winter, adult Colorado
<br />squawfish in the Yampa 'River use
<br />baelewaters. runs, and addies, hut are
<br />mast common in shallow I ice-covered
<br />sboreline areas (Wiele and Hawkins
<br />1989), In spring and .arly summar,
<br />adult squawfisb utiliz.d shorelin.s and
<br />lowlands that ware inundat.d during
<br />typical spring flooding, and this natural
<br />lowland inundation was viewed as
<br />impnrtant for their gan.ral haalth and
<br />reproductive conditioning (Tyus 1990),
<br />Use of these habitats may mitigate some
<br />of the .ffects of wint.r stress and aid in
<br />offsetting a large energy expenditure
<br />requir.d for migration and spawning,
<br />Migration is an important component in
<br />the reproductive cycle of Colorado
<br />squawfish, and Tyus (1990) reported
<br />that migration cues. such as high spring
<br />flows, increasing river temperatures.
<br />and possible chemical inputs from,
<br />flooded lands and springs. w.re
<br />important to successful reproduction.
<br />Colorado squawiish spawn in whit.
<br />water canyons in the Yampa and Green
<br />Rivers. This reproduction was .
<br />associated with declining flows in June,
<br />July, or August, and average water
<br />tamperatur.s ranging from 22-25
<br />degrees Calsius dep.nding on annual
<br />hydrology, Aft.r spawning, adult
<br />Colorado squawfisb utiliz.d a vari.ty of
<br />riverine habitats, including .ddies;
<br />backwaters, shorelines, and' oth.rs (Tyus
<br />19901, Specific spawning sit.s of
<br />Colorado squaw fish bav. not been
<br />ia.ntified outside of tha Green River
<br />Basin, In the mainstream Colorado
<br />River, McAda and Keading (1991)
<br />sugg.sted that Colorado squawfish
<br />s08\N11ing may have been adversely
<br />impacted by construction of mainstream
<br />dams and a 48 percent reduction in
<br />peak discharge,
<br />In the Green River Basin, larval
<br />Colorado squawfish amerge from
<br />
<br />spawning substrates and ent.r the
<br />stream drift as young fry (Hayn.s .t al.
<br />19B9), Th. fish are th.n actively or
<br />passively transportad downstream for
<br />about 6 days, and th.y may travel
<br />av.rag. distances of up to 160
<br />kilometers (100 miles) to reach nurs.ry
<br />areas (Tyus and Haines 1991), Th.se
<br />araas al'9 productiva babitats that
<br />consist of epbemaral alongshore
<br />embayments that d.v.lop as spring
<br />flows declin., Such habitat is associated
<br />with lowar gradient reaches,
<br />
<br />Humpback Chub
<br />
<br />Humpback chub remains have been
<br />dat.d to about 4000 B,C,. but the fish
<br />was not d.scribad as a sp.cies until
<br />recent tim.s (Miller 1946). This recent
<br />discov.ry has been attribut.d to its
<br />restrictad distribution in remOle. whit.
<br />water canyons (USFWS 1990b), and its
<br />ear liar abundance and distribution is
<br />not well known, The largest populations
<br />of this species occur in the Little
<br />Colorado and Colorado Riv.rs in the
<br />Grand Canvon, and in the Blad Rods
<br />area ofth'-Colorado Riv.r, Oth.r
<br />populations have been reported in
<br />W.stwater and Debeque Canyons of the
<br />Colorado Riv.r, Desolation IlDd Gray
<br />Canyons of the Gre.n Riv.r, and Yampa
<br />and Whirlpool Canyons in Dinosaur
<br />National Monum.nt (USFWS 1990b),
<br />Populations of bumpback chub are
<br />found in river canyons.'where they
<br />utilize a vari.ty of habitats, including
<br />pools. rimes, and eddies, Most of the
<br />existing information on habitat
<br />pl'9f.rences has been obtain.d from
<br />adult fish in the Littl. Colorado River.
<br />the Grand Canyon, and the Black Rocks
<br />of the Colorado River (Hold.n and
<br />Stalnaleer 1975: Ka.ding and
<br />Zimmerman 19B3; Kaeding.t el. 1990),'
<br />In these locations, tha fish are found
<br />associated with bould.r-strawn
<br />canyons, travertine dams. pools. and
<br />.ddi.s, Some habitat-us. data are also
<br />available from tha Yampa River Canyon
<br />where the fish occupy similar habitats,
<br />but also use rody runs, rim.s, rapids,
<br />and sborelin. eddi.s (Karp and Tyus
<br />1990), This diversity in habitat usa'
<br />suggests that the adult fish is adapted to
<br />a variety of habitats, and studies of
<br />tagg.d fish indicated that th.y move
<br />b.twe.n habitats. presumably in
<br />response to saasonal habitat changes
<br />and life history needs (Ka.ding and
<br />Zimmerman 19B3: Karp and Tyus 1990),
<br />Spring peale flows, availahility of
<br />shoreline eddy and deep canyon
<br />babitats, and comp.tition and predation
<br />by nonnative fishes were reported as
<br />pot.ntiallimiting factors for humpback
<br />chub in the Yampa Riv.r (Tyus and
<br />Karp 1989),
<br />
<br />Humpback chub in reproductive
<br />condition are usually captured in May,
<br />Jun., and July. d.pending on location,
<br />Littl. is known about th.ir specific
<br />spawning requiraments. other than the
<br />fish spawn soon after the highest spring
<br />flows when water temperatures
<br />approach 20 d.grees Celsius (Karp and
<br />Tyus 1990: USFWS 1990b), The
<br />importance of spring flows and prop.r
<br />t.mp.ratures for humpback chub is
<br />strassed by Ka.ding and Zimmerman
<br />(19B3), who implicat.d flow reductions
<br />and low wat.r t.mperatures in the
<br />Grand Canyon as factors curtailing
<br />successful spawn of the fish and
<br />increasing its competition with other
<br />species.
<br />
<br />Bonytail Chub
<br />
<br />Th. bonytail chub is the rarest native
<br />fisb in the Colorado River, Formerly
<br />report.d as wid.spread and abundant in
<br />mainstream rivers (Jordan and
<br />Ev.rmann IB96), its populations have
<br />been greatly reri~ced, The fish is
<br />presently repres.nted in the wild by a
<br />low number of old adult fish (i.... ages
<br />of 40 ye"", or more) in Lake Mohav.
<br />and p.rhaps other lower basin
<br />res.rvoirs (USFWS 1990a), The fish
<br />were once common in Lake Mobave and
<br />W.gner (1955) observed the fish in eddy
<br />habitats, A few individuals were
<br />reported in other locations, but
<br />concentrations of the fish have not heen
<br />I'9c.ntly reported (Ka.ding et al. 1986).
<br />Tha bonytail chub always has been
<br />considered a species that is adapt.d to
<br />mainstream rivers. whore it has been
<br />observed in poola and eddias (Minckley
<br />1973; Vanic.k 1967), In reservoirs, the
<br />fish occupi.s an activ. limnetic niche
<br />(Mincklay 1973), Spawning ofth. fish
<br />nav.r has been observed in nature, but
<br />, Vanicek and Kram.r (1969) reported
<br />that spawning occurred in June and July
<br />at wat.r temperatures of about 1B
<br />d.grees Celsius, Although wild
<br />bonytails are old fish. th.y are still
<br />capable of succ.ssful reproduction. and
<br />bonytail chubs placed in ponds have
<br />produced large numbers of young (B.
<br />J.ns.n, Fish and Wildlife Servic., pers,
<br />comm,; USFWS 1990a~ Although
<br />babitats that are required for
<br />conservation of the bonytail chub are
<br />not welll:nown. th.limited data
<br />sugg.sts that flooded, ponded. or .ven
<br />inundated riv.rin. habitats may be
<br />suitable for adults. especially in the
<br />absence of comp.ting nonnative fishes
<br />(USFWS 1990a),
<br />
<br />Previous Federal Actio...
<br />
<br />Th. Colorado squawfish and
<br />humpback chub w.re listed as
<br />andangared speci.s on March 11. 1967
<br />{32 FR 4001}, Tha bonytail chub was
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