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<br />Federal Regi.slfi..' Vol. sa, No. 18 I Friday, January 29. ',~93 I Proposed Rules
<br />
<br />6579
<br />
<br />basic life history information and
<br />hebitat use has been difficult to obtain.
<br />Soma areas used by Colorado squawfish
<br />and razorback sucker for spawning have
<br />been detectad hy radiotracking, tagging.
<br />and collection of eggs or larvae (Tyus
<br />and Karp'1990; Tyus 1990), hut thBse
<br />areas support the largest riverine
<br />conceotrBtions of the.. species. Such
<br />mformallon IS le.. available 111 plac8s
<br />where these species are more rare, and
<br />the low numbers or lack of young for
<br />some speci.. have lead to hypoth......
<br />ahout a lack of repniduction and/or
<br />recruitment as a pouible cause of their
<br />endan~ermant (USFWS 1990&, 19901>.
<br />1991), In this case, not only wou.ld a
<br />lack of successful recruitment lead to
<br />small numbers of fish, hut over time,
<br />remnant stocks may los8 genetic
<br />diversity, Ultimetely, extinction could
<br />result because the lose of genetic
<br />diversity may mab'populetion. more
<br />susceplible to 8Dvironm9Dtal change.
<br />The historicalrang<lS of the four
<br />endengered speci.. have been
<br />fregmented hy construction of dama and
<br />weter diversions throughout the Basin
<br />(Carlson and Muth 1989); The Sam""
<br />believes that it is important to the
<br />survival and recovery of thase sped.. to
<br />reestablish populations in areas within '
<br />their former range, Providing'
<br />geographically distinct areas that
<br />contain varying thermal. chemical.
<br />geological. and physical parameters will
<br />encourage maintanance of the current
<br />genetic pooL These parameters
<br />influence important life history
<br />characteristics such as time of
<br />spewning. IeCrUitment, growth.
<br />mortality rat... and longevity,
<br />
<br />Habitats and Status of Endangered
<br />Fish..
<br />
<br />General
<br />
<br />The four endangered Colorado River
<br />fishes evolved in the Colorado River and
<br />were adapted to the natural
<br />environment that existed prior to the
<br />beginning of large-scale waler
<br />development. Thus, they were adapted
<br />to a system of fluctuating seesonal and
<br />annual flows influenced by wet,
<br />average, and dry climatic periods,
<br />Recent population declines and
<br />disappearances of endemic fish species
<br />in much of their former range ha\"8 been
<br />associated with relatively rapid and
<br />widespread anthropogenic changes,
<br />These changes bave alt....d the physical
<br />and biolQ<Oical cliaracteristics of many
<br />mainstream rivers in the Basin and
<br />occurred so rapidly that the fishes have
<br />not had time to adapt to them (Carlson
<br />and Muth 1989), Dams end diversions
<br />have fragmented former fisb habitat by
<br />restricting fish movement. As a result,
<br />
<br />genetic intelCbange (emigration,and
<br />immigration of individuals) between
<br />some fish populations is nonexistent.
<br />Large floods were onca normal in the
<br />Basin end provided food and nutrient,
<br />exchange between river channels and
<br />shallow-weIer floodplain hahitats,
<br />These floods are now controlled by
<br />numerous da.ms. As 8 result of these
<br />dams, major changes also have occurred
<br />in water quality, quantity, temperature.
<br />sediment and nutrient transport. and
<br />other characteristics of the aquatic
<br />environment (Carlson and Muth 1989),
<br />Th.e eltered habitats that have resulted
<br />are now mora suitable for introduced..
<br />normative fishes, same of which have
<br />flourished (Minckley at aL 1982: Tyus et
<br />al, 1982; Carlson and Muth 1989), These
<br />changes have greatly altOT'lld the river
<br />environment and little or no unaltered
<br />habitat rameins in the Basin for the four
<br />Colorado River endangered fish species
<br />addressed in this proposed role, '
<br />Additional detail on the status and life
<br />bistories of these species will be
<br />provided in the biological support
<br />d acument.
<br />
<br />Razorback Sucker
<br />
<br />ThIs species WlIS on"" one of tha inost
<br />abundant and widely distributed fish in
<br />mainstream rivers of the Colorado River
<br />(Jordan and Evermann 1896: Minckley
<br />1973). A n>latively Iaxge Slock of
<br />razorback suckers remain in Laks
<br />Moheve (Minckley et aL 1991).,
<br />However. the formerly large Lower
<br />Basin populations hava been extirpated '
<br />from all natural riverine environments,
<br />and recruitmant is virtually nonexistent
<br />in the ramnant stocks (Minckleyat ai,
<br />1991), In the Upper Basin, tha fish
<br />persists in thalower Yampa'and Green
<br />Rivers, main.tream Colorado River. and
<br />lower San Juan River (Tyus et ai, 1982:
<br />Minckley el al, 1991; PlalaIlia al aL
<br />1991), but there ialittle indication of
<br />=itment in these remnanl &tocks.
<br />The largest extant riverine population
<br />OCCUIS in the upper Green River Basin.
<br />but it consists of only ebout 1.000 fish
<br />(Lanigan and Tyus 1989), In the ahsan""
<br />of conservation elforts. it is presumed
<br />that wild populations will be lost as old
<br />fish die and are not replaced. ,
<br />Reproduction and hahitat use of
<br />razorback suckBrs has been studiad in
<br />lower basin reservoirs. especially in
<br />Lake Mobave, Fish reproduction has
<br />been visually observed in reservoir
<br />shoreUnes for many years. and
<br />spawning in the reservoir usually lasts
<br />from January or February to April or
<br />May, The fish spawn over mixed
<br />substrates that ranga from silt to cobble.
<br />and at water temperatures ranging from
<br />10,5 to 21 degrees Cd!sius (reviewed by
<br />Minckley ot aJ, 1991),
<br />
<br />Habitat usa and .pawning behavior of
<br />adult razorback suckers in riverine
<br />habitats have been studied hy
<br />radiotelemetry in the Green River Basin
<br />(Tyus and Karp 1990), The fish there
<br />spawned In the spring with rising water
<br />levels and increasing t8Jllperaturas. ThB
<br />fish moved into flooded areas in early
<br />spring. and they made spawning
<br />migrations to specific locations as they
<br />became reproductively active, Spawning
<br />occurred over rocky runs and gravel
<br />bars,
<br />In nonreproductive periods, edult
<br />razorback suckers occupy a variety of
<br />habitet types. These includa impounded
<br />and riverine areas and hahiJats
<br />reprasented hy: Eddill8, backwaters.
<br />gravel pits, flooded bottwna and the
<br />flooded mouths of tributary stre8JllS.
<br />slow runs. sandy riffles. and others
<br />(reviewed hy Minckley et el, 1991),
<br />Summer habitat use included deeper
<br />eddies, backwatars. holes, and
<br />midchannel sandbars (Tyus and Karp
<br />1990; Minckley et aL 1991~
<br />Habitats usaa by young 1lIZorback
<br />suckers have not been fully evaluated
<br />because of the low number of young fish
<br />present in the river system. However,
<br />most studies agree that the larvaa prefer
<br />shellow, littoral zonos'for'a few weeks
<br />after hatching. then they disperse to
<br />deeper water areas (raviewed by ,
<br />Mlnckley et ai, 1991). Lahoratory
<br />studies 'indicated that. in e riverine
<br />environment. the larvae enter stream
<br />drift and ere transported doWnstream
<br />(Paulin et al1989).
<br />During winter. adult razoroack
<br />suckers utiliza maln channel habitats
<br />that ara similar to those used during
<br />other times of tha year, including
<br />eddies. slow runs. riffill8, and
<br />slackwaters (Valdez and Masslich 1989;
<br />Tyus and Karp 1990~
<br />Although habitat use of razorilacl<
<br />suckers has heen studied for years. the
<br />habitat preferences and faanrs limiting
<br />their abundance in nati oe riverine
<br />habilats ara not well known because of
<br />the scarcity of extant populatinns
<br />(Minckley 1983: Lanigan and Tyus
<br />1989) and the absence of younger life
<br />history stages (Mincklay at a1. 1991),
<br />However. based on available data teken
<br />from the Green River. Tyus and Karp -
<br />(1989) considered low winter flows,
<br />high spring flows, seasonal chang.. in
<br />river temperatures., and inundated
<br />shorelines and bouomlands as factors
<br />that potentially limit the survival,
<br />successful reproduction. and
<br />recruitment of this species,
<br />
<br />Colorado Squawfish
<br />
<br />This species is tha only living
<br />representative oftha genus
<br />Ptychocheilus in the Basin, where it is
<br />
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