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<br />~O!-2~/2(]~~ t.,o..i 3q It-tap <br /> <br />le <br /> <br />reach measured with a. m.ap wheel- We used lhe regres. <br />Si.oJl ~quati.on. of Laak 3r'trl nr.ne~ (1999) to correct <br />~rimateS li-um maps: actual sradien ~ 't:::: 0..72 measured <br />gradicnt~ La[e summer" stream width (at natural base <br />.flow) was measured in the fieJd a !'ihnn distance u~ <br />sU'eam from ,the dJ"ersio~ StruCtures in areas not im.. <br />pounded by the dams. Because no additional s:treams <br />flowed in~o any of [he segments4 this width es"tmate was <br />applied to (h e entire dOMlstream segmen t. <br />Trout cover was esrimated rtom riparian features <br />identified On :aerial photographs foUoMng Co~ngtnn <br />and Httbert (2000) a A riparian vegetation. ir1 dcx (RVI) <br />\.-f"'dS assiglled EO each reach: 0 =- bank! having vegeta- <br />tion' growing on [hem. but plants are' closely cropped <br />giving the banks an essentially baJTe a.ppe.8.1aa:r.ce; 1 ~ <br />vcger.adon is not so i;losely cropped or sparse as to make <br />the banks look bare. but lilde :shading of sr..re.am and <br />little placu growth l1anging over and into ,.yarer is <br />found; 2 ~ vegetative growlh is intermediate with some <br />shadlQg or stream and. plant growth banging over and <br />into water: !I == considerabJe vegetative grow[hJ with <br />shading of SCream and some plant growth hanging into <br />3.nd ever strcam~ and 4 =- vegetative growth ~ong banks <br />ia lush \vir:h cOnsiderabJe shading of stream and plant <br />growth hanging over and ill to water, A regression equa.. <br />tion was used to predict the amount ot t~out CO~l" <br />(percent of watc::r surface area) from me RVl fot" each <br />reach (;f ::c: 0.,67, P < O~OOll SE = 0_49): <br /> <br />Cover (%) ;:: 0.0522 + 0.0772 RVl <br /> <br />The equation \\'as developed using 36 .stream re;q,t'hes <br />;;l(r05S Wyoft'ing and pr<:dicnons wer.: rested against 16 <br />oche!" streams in the Stat;e (Covington and liuben <br />2000). <br /> <br />B]omass at Natural Flows <br /> <br />We used a regression equation. de"eloped by Hubert <br />~and. OthBI'S (1996) to prediC:t mean biomtiS" of troUt ItJ <br />each reach at namra.l flows. The equation wa.s com- <br />puted using habitat and trOUl population data frOm 166 <br />.stream re-d.ches dIstributed across Wyoming. The rnuf- <br />r.iple-rc~ession c:quation (~ !II: 0.40, P < 0-<)01) l't'3S.: <br /> <br />mea.n biomassll! = ..... 14.83 <br />+ 0_0086 ELEV <br />,.. 8..2g GRADE <br />+ !L38 LNW1DE <br />+ 0..13.COVER <br />- 0,0014 .ELGR <br />- O~0026 ELLW <br /> <br />Independent vanables incJudc:d eJewdan (ELEV)~ ~ <br />charin~1 gradient (GRADE) I natu.cal log or summer <br />weued width (It\T\VIDE) a (;"ovet' (COVER). and two in... <br /> <br /> <br />1 <br /> <br />~009 <br /> <br /> <br />2 <br /> <br />p.s <br /> <br />Trout Responses to Row Restoration 139 <br /> <br /> 1000 <br />.= 800 <br />I;I.t <br />ll:: <br />~ 600 <br />0 <br />i3 400 <br />~ <br />:= 200 <br />Z <br /> 0 <br /> <br /> <br /> <br />I, , <br /> <br /> <br />, 2 345 <br />Age class (years) <br /> <br />Plgu(e 3.. Age cl:as5 t1istrlbutlon of bl"OWn tJT.Iut popu.lation <br />bepnnin g: with 1 nOD 3ge class 1 fisl1 and an ann ua.1 survlval <br />tate QC O.SO. ,I, <br />~ <br /> <br />lcraction tt:l'1llS, elevation x gradlen t (ELGR) and c:lc. <br />varian X the natural log of summer wetted width <br />(ELLW) l Biomass estimate:5 for each reac;h were <br />summc:d for each Slrcam segmen~ to estimate tor.al <br />biomass in the segment. ' <br />We assumed that bro\'JT1 lrOul would be [he predom. <br />inant species to colon izc: the low..gr.adicnt stream seg~ <br />ment'i it flcrws were restored~ The lower portions of <br />trtbuUlries nor [otally d~tered and flowing 3C.rO~~ the <br />\ a.lh.lvial floor of me Salt RiYJe%. Valley have predoJni- <br />aantly brown trout in them. <br /> <br />Abundance at N~tural FJows <br /> <br />The abundance of bt'OYm '[J'Ollt in each segment at <br />nalllral flows \vas conlputed from estimaocd biomass in <br />dle segment and an estimared (pOpUlation structure of <br />fish age 1 and greatera Wr: a.~s~med. an 3.n~ual survival <br />rate of 0.30 (Scnuk 1945.. McFa.dden and Coope~ 1962)_ <br />An age class distribution was breatcd from m1 initial <br />population of 1000 trout of a~c 1 (Figure 3) .and me:: <br />mean length 'WaS estimated (166 mm) fOT fish of .ages <br />1-5. Using tIle stand~rd le~gth.!wl eight reJations~ips for <br />lone brown trou~ (MiJe\'Jskl and Brown 1994) _ tJi e .rn ean <br />weight (51 g) of brown trout: was estima.ted. <br />- . 1 <br />Biomass and Abundance at l!.ess than Natural Flows <br /> <br />W~ predicted. changes in bjO~ass and abundance of <br />brown trout wjth changes in s\!1mmer flows using the <br />h !slotic flow approach_ JiydroJ6gic data. were 3'YaJ table <br />for four streams '\o'/tchin me vdlley (Table 1). We: esti- <br />mated dischar&"c (cubic me [ers ~er seto nd) by r~gressjlo <br />ing wetted width (VlW) against fnown discha.rge values. <br />(average: daily flow, ADF} using ~rce"S'rC'ams for Which <br />we had dal3. (12 ~ 0..99. P < 0,,017): <br /> <br />< ADF:; -II}'S + k2,5 WW <br />I <br />~ <br />j <br />I <br />I <br />l <br />