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.._~a-- ._ RF,~SG~Ifi t`OR D~,CLINE Decline i_n abundance of razorback sucker has been attributed `to physical, c}iemica]_ and biolcigical ~:lterations o£ the Colorado River ecosystem through construction of dams (19~38s-1950s)~ mainstream channeli•~ation and dredging, and introduc:;tions of exotic species (Miller 1961; Jonez and Sumner 1954; i~inckley -and Daacon 1963; Behnke and Benson 1980; Wydoski ~t al. 1980, McAda and Fdydoslsi 193t~; i~4ickley 1.933) . Vanicek et al . (1970) reported a]_teration of seasonal flow and temperature regimes for 104 kilometers (65 miles) of_ the Green River downstr.eaY~tt from Flaming Gorge Dam, Utah, that were considered severe enouh to exclude native fishes, including razorback. Similar alterations have -, occurr.~rd below HoovF~r, Davis, Barker and Imp~arial dams along the lower river. C}iannvlizaticr~ and dredging along the lower mainstr.earn also have altered flow character°istics by cre~~ting a dt~eper, ;lore uniform channel. Confining the channel between stabilized banks eliminates cruiet baci;craters and oxbows, ~rahich rna~= b:: nec~~ssa.ry as razorback spaoaning, nuY.~sery, ar~~zc~ refug~:~ }gab%tats. Dredging creates and L,erpet~.ratc~s unstable, shifting channE~l bott.ons. ~ntY`ot111Ct1.0i1~ of e3~:Ot1.^ f 1~)7r?S b~/ ~'+t~tc ~:I1t1 ~~?der~Yl ~1Sh and ~nrildlif~~ ncJ~.ncic~J ~~nd t~.?Zrc~~.tc]h inc,iden~:: ~1_ a~.ca. acr.i.~ental r.t~lr~•~ses _ ~~ls~~ 'rr=~~rc corlt,Y°:i.'~ut:~d t<~ c]t~cli.r~~:~ o~ rr~.~.ia~~: f 3.;~~~it:~~, in t}~e 1c3~~Te~° _' C(?~.C}C~~G~ ~;1llE:r, c~tE;:i"}:?"C_~i.U[1 (7y f?::i;].C. i`a' ~;I:~~ C?1°1 Y"-~"!,C?Ya~~w3Ck> laCkt3Y' ,~ , „~„F, e,• c-, ~~ t . 1 980 • f';~',~]a T.:xn~l r11rt?r>k~. !. ` i~:~ r s.Jlr~~;>r 1`~~31; c_Es~:~ (1~~~,,,_A.,.~,a3. ~t ~._ _