E:e! River Sur vey: Final Repor t

Lar~y R. Brown

=d

Peter B. Moyle

Report to;

California De p ll r tment 01 Fish and Game

Contract: F-46-R- 2

DIII)!Irtment of Wildlife and Fisheries Biolo&:y

University of C!Ili!orn ia

Davia, Cali!ornia 95616 Stat. of Ca lifornia The Resour ces Agency DEPAA::'!'{Eh'T Of fISH AND GAME

Et:L RIVER SURVEY 1

By :

Lar::"'1 R. Br own .0' Pet er B. Hoyle

Oepa rt~ent of Wildlife and Fisheries Biology University of California Davis, Calitor:till. 95616 I I , !hi. ?roject ~a. ~uppor:ed ~y Feder.t Aid in Spor: Fi~h R~~ : or.t~on Ae: funds (C.lifornia Project F·51·~. Subprojec: IX, SCtldy 8, Job. 2.6) f or I ~~. periOd Jul y 1. 1986 through June 30. 1990. I I I I z I EXECUTIVB SUMMARY This !'eport contains the I"nults ot four years of WO!"K in the Eel River draina&"e. Durinlr this time "''' conducted [ish surveys of the mainatem Eel I Rive!", Middle Fork Eel River, North Fo .. k Eel River, South Fork Eel River, Van Duzen Riv .. r, and many smaller tributaries. We conducted studie" of the microhabitat use of squ.aW"fillh and oth". resident fishes in the South Pod: E"l River and van Duzen River. These s tudies ""ere designed to detect effecls of I squII.",[ish on the microhabi18l use ot the other [ishe". We conduct.. d "tucie! in ar~i!icill.l stream t.!!nks to determine it the habitllt and microhabitat shifts observed during the microhabitat studies "'ere the result of behsvioral I r"!lpons'"'' of the prey. \"e calc:ulated len&"tb at SI''' of squllwf;sh using 9"!lle analysis and analyzed feeding habit" tor squa .... (ish collected from a variety of aI"eas .. nd times durin&" our studies. Finally, .... e !lnalyzed OUI" popUlation I e!lti.mate data to establish the level of natural variation present in Eel River rainho", trout (steelhead) popUlations Rainho.... trout (steelhead) .... as the most .... idespread speciea in the su,veys. Rainbo", trout ",ere 1P0st abundant in cool, hi&'h &"adient, 10'" order I stream!;. California roac!"!, Sacramento sucker, Sacramento squa.... tish, threespine stickleback, and prickly aculpin "'ere most abundant in .... armer, 10'" i'radient, hia:h order streams. Divenity of the fish assembla&"es varied I bet .... een rivers. The mainl'ltem Eel River "'''s most diverse (19 species) bec!luae ot the presence ot estuarine and introduced fresh ....ater fishes. The Van Duzen River and South Fork Eel River .... ere nen in diversity (10 species). I The Middle Fork Eel Rive" NOI"th Fork Eel River, Black Butte River, and Rice FOI"k Eel River ",eI"e least diveI"lse ...·ith only 4 to 5 species ohser"Ved. Principal components analysia of species relative abundances yielded th.-­ p,incipsl components. The firat indicated that squaW'iil'lh snd roach were I positi"ely associated with each other !lnd both "'ere ne&,atively correlate d .... ith ,ainho'" trout. These re18tionships are primarily due to the relponaea of these species to physical conditiona, particularly temperl'lture. The second I princ;pI'I1 compone nt indicsted s positive associstion amon&" threespine stickle back, prickly aculpin, and sucker. All three were ne&"atively a8aocisted '-"ith r"OlIch. Theae a"sociations are the result of the first three 8pecies an I rellchin&" their peak abundance in the 10.... e I" part of the drainall"e .... hue roach became le~s important. Tbe third principle component describe a positive a6socistion b .. t ..... een "ucker and squa.... tis!! and s nell"ative relationship bet"'ee n these t ..... o species and rosch and stickleback. The positive associstion or I sucker and aqua.... fi"h .... II.S relsted to the utilization of large deep pools by the adults of both species. The ne&,ative respon".. to the pres.. nce of these t""O other "pecies l!III.y he the re"ult ot the pre"ence of the predatory squoW'iish. I Similar re"ulh were obtBined .... hen species densities '""ere used in place of ,elati~'e abundances. The I"an &"e of squll..... fi"h in the Eel River drainsll"e eEplUlded aigniticantly I OVer the CaUl's .. of our studies. SqulI.....-tish are continuing to move upstream in the Van Duzen Riv.. r and South Fork Eel River. Natural harriers bave halted the upstream movement ot aqull. .... fish in the upper mainstem Eel River c:!rainll.lI"e !!Ind Middle Fork Eel River draim.&"e. The North Fork Eel River and I Black Butte Riv"r have not been colonized to any si&"niticant e;rtent. This may b .. due to the rarity of appropriste habitat. There were no IIpparent barriers to invasion. Invasion mill' occur in .... etter years it hi&"her !lo.... s increase the I IIvailability ot appropriate habitat. Squa.... rish ha\'e still !lot invaded the cool, I .J 3 hiI'll e:-!l.dient t:-ibuta.r: Itre!lms ",h"!'e lare .. numbers of 1OUn~ I~lhe!l~ overlumme!'. The invasion of _ueh tributarie.. may .. till occur, but eVen in lU"eas ...... here .quawfish have been abundant for .. ever!ll year .. , they ha.. e IKlt colonh:ed these tyPes of streams. Younl'-of-year _qu!l.w!ish were prese:'!t !.n aom.. tributaries that w.. ra too ... srm to provide I'ocd trout habitat. Microhabitat It:.ldlu sho..... d that the preaence of squa ... fillh does affect the habitat ami micrOlnabitat uae of juvenile steelhead trout a nd the othe!' ,. .. sident fishes. Juvenile !'!llnbow trout and auekeu d ..creued ule of pool habitat \Jhen squaw!;sh ..... re pres.. nt.. Fiah found in pooll used shsUo,",e!' ",ater closer to the ec!ee of the strellm "'hen IIqusw1'ish "'ere ?!'esent. ;oh e n squaw1'i .. h were p !'esent, niche overlaps fOlr the various microhabitat va,;"'b!e s .. enerally declined. Thu., the presence of squa",fi.h relulted in l"reate!' sea-rel'ation amonl' the memberl of the flsh alsemblaa-e. E..:rpe:"iment .. in Imall IU"tificial Itrea", tanks !.ndicated that rainbo,,' t :'Qut r!lpidly detected the presence of 'qua",fish and IIIQved into riffle habitat to avoid them. This il the lame reapenae obs.. rved in the above fi.. ld studies. Similarly, wa-e and , mall C!I..li!ornia roach exhibit.. d Itronl' r .... ponl... to the pre.ence of .. qusvfish, ",ovinl' into shaUo", .till"'ater habitat .... hen squllw1'i .. h "'ere pres.. nt. Stiekleback did not .. ho.... a I tronl' behavioral responle to the presence of aqua"'fish "ul'l' .. stlnl' thllt stickleback Clay be the speelel that vi1I be mo.t affected by the .qua"'fish introduetion. Feedinl' habih and lice and .t="'th of aquaw{illh from th" Eel River .... ere .imilar to tho.e of populations of .quawfi.h trom the SlIc:-lIment..o River drainal'e. Fiah appeared in the diet of Eel River aquavfi.h at 51-100 mm SL and be<;.&me dOQlinlint at lOl-150 ' Clm SL. Similarity of .qua...t"i .. h feedinlil h.bits and rainbov lrQUt f ....dinl[ habits .... u Irener!l..lly low indlca.tlnl' little pot.entia.! for competition. Squllwflsh did conlUme salmonldl ...... hen the opportunity eti.ted. The potential. for sil'nificant predation i. hia-he.t in the arell betveen Pill.bury !lnd Van Andale re.ervolrs, where wa-e population. of adult "qu.",fi .. h and over.uQlmerinl" juvenile lteelhead o:o-oceur , Ind in the = .. a belo", Van Aradale where late emil[rlltina- salmonid. encounter Iquaw1'i.h "'hen the \Jater i" clear a nd "'lU"m, condition" which favor Iquavfl.ah predation. Juvenile rainbow trout (Iteelhead ) lind Sacramento squavflah are wl'ely ~epar.ted by habitat. Juvenile "uelhead occupy the cool tributary Itreaml lind .quaw1'ilh occupy the warmer do"'n.. tream portion" ot the larlile streams and the ...·ar'" tribulL...;e... A natural barrier to the upltrellm :nil"rlltion of squa",fl.h on the Middle ::'ork gel Riv.. r .nd the failure of aqua.... fi.h to invade the North Fork Eel River lind Black Butte River provide further protection tor up"tream rearine habitat. Bovever, the latur tyo Ilream .. InIlY be invllded durin&" ...... tter yearll, if incre .....d no... . meke appropriate h.sbitat . vailable. Rellrinlil hllbitat for youna--of-,.eer It.eelhelld '-'"ill be r educed in reoehe!! w here !ldult Iqu"wfi.h oc<;:ur; hovever, the effect this vill h"ve on the production of adult. will depend on the relative i ... portance of tMbutari... and ",ain.t:-ell:ll reoch... to production. Rellrin. habitat probahly vill not be reduced. for 1+ and Jar.er JUVenile .teelhead, which IICcount for the I'resu.t return of IIdulu. Th" e:red of aquawfi.. h On the microhabitat Ulle of .t.... lhead mllY be one res""n tor the abeenee of .. teelhead from the cool dovnstream areas of the mllinstem Eel River but the IIb ... nce of larl".. r trou.t =Iill'".tl that other factor. "ueh a. t ..... perature mI.,. also be important. Density by nu ... ber of rllinbo", trout fluctuated from year to year lit our permanent electrof;"hinl' stelionl. The It.andard deviationa of mean trout d ..nslties '-'"ithin litea and within .t.... a"'. '"'ere larlile and .there .,a. a poliUve •

4 correlation beh;een the mean and the standard de-villtian. Thul, larce populations "'ere mor e variltble than small popu illtion a. The lIIa&"nitude of variation 11.I1"&:e61. that only very eubllt3nlial chan .... in responae to hUllllln manipulation, will be detectable. The patter n of c hll na-e wall eonsi.tent acl"Ose ltalionl in some .lr".. ms but not In others. The p"tter n of Incr",''''''. and dedin". "'''s not eonsi.te nt scroSI str.. llml. Ov er the lour ye=s 01 OUf uudy the . tmera\ trend h ..a been one ot decline in trout numbera. This .. ,,"eral decline i. likely related to the conaistent1y lo w r ainfan t.otals over the courn of the study. ThUG, the numbers we observed probably r epresent low population levels lind increases may occur in wetter ,..,ors. The phYlical variables collected durin, the eleetrot is hln~ u.mplin ...... ere not stron,. predictol"B of trout abundance. Multiple re~rea .. ion modela baaed on thue variable. explained lesa than 50" of the variance in tl"Out denaitl'. Includin ~ variables impor tan t durin~ the .pa..... nin.. season a nd dur in .. the hot aummer IOOnth. would improve p r adictability. Lon .. term environmental monitorin,., use of habitat specific samplln~ methodolo~iea, a nd lon~ time aeri.... of data .... iII probably be neceau.ry to diltin ..uiah human ind uced c h an ~e. fr om natural fluctuations, except in extre me caae ... Beeause the aquawfllih Is nO ...... idely distributed in t he draina,.e and its ra n~e is still expandina:, it aeems extr emely unlill:ely that squawfiah control ...it hin the Eel River draina~e "" ould be aconomically feuible or affective for the draina"" a. a .... hole. Control meaSUrU that are not selective for squa"" fish could affect other fish populationa that an economically valuable, s uch as juve nile steelhead and American ahad. Conuol etror t. could alao affect apecies luch a. Sacramento Buckers and California roach that form part of the foraa:e ba!le for bird s, such aa ~reat blue herona and otIpreya, or mammals, such a" otters. Thue possible community level eftech indicate that a drainaa:e wide 8q u.a ••: fish control prol(l"sm may not be environmentany feasible. Within these major conltrain19, our .tudie. su~~est the foUow in~:

1. The best ...·ay to promote production 01 juvenile ateelhead Is to increaae the amount ot cold, tributary atr eam habitat available th r ou~ h atream restoration and habitat Improvement efforts.

2. Control of adult Iquawtlsb mi~ht be useful in the limited area between Pillabury Reaervoir and Van Aradale Reser voir. The deneity of lar,.e squa... · fish appears to be especiany hi.ih in thia area and the area between the dams haa tradltionany been important rearin .. habitat for juvenile steelhead. Squsvflsh control In the area downstr eam of Van Arsdale to Outlet Creek milCht be usetul in i ncreasin~ sur vival of outllli"rant.. , thou.ih ..... ithout dala on lones due to p r edation r elative to other fae tors s uch lIB t hermal atress and disetule, a n objective d ecision iln' t possible. Effo rta could be restricud to spot t r eatm ents of heavily u tilized pooll in the Van Andale to Outlet Cr eek area. Further .. tudles are ne<:es ..... r,. to deterllline if aquawf;sh predation r ates on salmon amoln and ateelhead juveniles and smolts are hi,.h enou,,!>. to make squa ..."fiah removal desirttble. It the tn.ditional chemical treatmen t .... it h rotenone .... a. uaed, t reatme nt .... ould also r esult in the 10•• of several yea r classes of ateelhead. ; 3. Natural variability il'\ trout populations ""ss bleh in all of the Itre8I11S atudied. Lon&, term environmental monitorinll, Ule of habitat apeocitie "mplinc methodoloCie.. and Ion&' time serie .. of data. IJjll probablY ~ nece'''('7 to di.8tincuish human induced chanaea from natural fiuctuationa, except in e.rtr eme CUeS.

I u

, INTRODUCTION

Th., Eel River a the third we-e.t drain.. , .. in California with .. m"l'\:1.

'''1011./111 diadu,rt" of 5.4 million aCre feel. Anadromoua fi .. h". uti..ll:tinl[ the river indud ...teelh""d (9ncorhynehua m,.ki ... j , chinook ..u.mon (0. uh ...... "t""h,,), coho u.lmon (0. kisut<;;h ), Allleri"an IIh ..d (Alan "pldj"i",.. l,

Pacitlc lamprey (Lampet:'.. tl"identatua), cOIIILaI cutthroat trout (2.:. ch.rki clarki), and Itreen aturzeon IA-eipen."r medko.tris). The nativ" enident lpec:iu indude SaC:r8l11ento sucker (9,tp.tpIAUI oc:eidentalis), threeapine

.tickleback (Gnteroaleu. ,liul.. atua), pricklY IIculpin (Cottus !!1!:!r.J, CO&lIt",n,,,

.culpin (C. aleutlcuII), and Pacific brook lamprey (L. pacifica). Caiitot"nia rosch

(La"';n;a s"",,,metric:ua) "'aI introduced to the I),stem around 1970 and lir e no",­

.:emmOn lb.9Ul'hout the drainlll'l! (...... Brown 198j for" revie.... ). A popUlation of speckled dace (Rhinichth .... ' osculus) hss been discovend in the VAn Du:en

River dr&naze (Bro.... n and Mo"le 1988). This population aleo appears to be the result of an introdUCtion. Larlremouth bsn (Micropteru, lalmoides), bJuelrill (Leuom;s ",,,croc:hirua), green sunfish (Lepo"'i~ 9Y8nellu8), brown bullhead (Ictaluru, nebule!us), tbreadfin ah"d (Doro!tOm"8 petenense), and colden shiner motem/gonus crysoleur::"j have alllO been introc:iur::ed but neVe not established !arKe populations, ell:r::ept in Pillsbur" Reaervolr. Sacr amento squawfish (?tvchocbejl!.. s n"ndiaj waa illelran" introduced into the upper reaches ot the mainltem (Pmsbur y Reservoir) in 1979 or 1980 lind an now rspidly invadin, other areas of the draina,e (8m.... n et al. 1987, Brown and

Mo,,!e 1988, 1989, and 1990). The expandin, aquawfi6h population lIL!Iy pose a threat to the production of anadmmous fishel in the draina,e.

De8pi~ its lize and importance to Inadmmoull fiBhes, the Eel River bas not been systematically surveyed to determine the distribution, abundance and -

, habitat requirem",nts at it$ fifthes since the work of Shapovalov (1939) .. nd

Snyder (1907). The ID.lljorityof 9ubaequent studies WeX"e 1'tJ!I1Iociated with various wllter development schemes propelled for the ""ell C!lee Brown 1987 fo, a !'evie""). The upp.. r Eel River drsiIlllge is the most intensiv"ly studied ar.. " b ecaus" of Cape Horn and Scott Dams, the only major dam" in the syste m (". 10: .

VTN 1982, BEAK 1986, SEC 1986, 1987, 1988, 1989, 1990). Sam .. work has be e ~ done on the .. nadromau,. fish"s by the Cali!ornia DeplI.rtment of Fish and Game and the U.S. Fish and wildlife Service (e.g. Puckett 1975. 1976, Jones 1980,

Jone s and Ekman 1980) but :11091 of this work i. unpubllllhed. Ther.. are ,,]so

" few unpublished th.. ses on the Eel River fishes (".11:. Fit.. 1973, Ashley 19741.

This r"port p~e""'ntll the final ~esults of fou~ yeM'S of wo~k on the fishes of the Eel River and includes a numb,,~ of studie" intended to aseesa the dfects of squawtish on the resident fishes and to desc,..ibe th" biology of aqua,dish in the system.

Th" most fundamental I'Oal of tbe project ..... as to examin" tbe distribution and a bundance of the fishes in the Eel River drainage. We pre sent spec,es maps and narr!ltives ..... hich qualitatively describe the distribution of the species in the dr"3inage. We pre"ent quantitative results on the relationship' of sp""ie" abundance" to phy"ical variables and the interrelationships among • the msjor species present. We summsrize the results of our micrQhabitat work and present r e suits • trQm experimental studies in small artificial stream tanks. The purpoae ot the micrQhabitat studie ...... as to determine if the presence of aquawfish affected the spatial rel.etionships of the resident fishell and, if 90, ho...... We pre sent a summary of these results (full de"cription8 in Bro.... n and Moyle, 1988, 1989.

1990, and in pre ss). We also pre sent the ,.."suits ot our .... ork in M'titiewl Itream llI.nk.. Thi. work "·al intended to deterllline if the apatw.l Ihift" detected in the microhabilll.t Itudies were the result of active behavioral ,hift" on the part of the r esident Cishes Or rellloval of fish by IQuawfilh predation.

we pre",nt the result. of squswfi.h age .nd gro'"'th atu di...... d studies at the feeding of the resident fishes. These reaults are bllsed on samples collected st various times and places throughout the are. and time .-pan of our .tudies. We ",ere especially interelted in determinin, if the ,rowth or diet of this Introduced population ot squa"'fiah differed from populations in its notive ranl'e or l! there were dl!ferences amone arees within the Eel River d rsins,e. we also wanted to sness the potentw.i for competition for food all>On. the 'pec,e ...

We also pr",sent more detailed analy"e" of our dllll. from the permanent population "''''pline IllI.tion.. we include information on the variability at rainbow trout popul.tion" amone year. both for lpecili<:: .ite. and tor 8treaml.

The purpose at this work ..... s to determine the n.atural v.riability in r!linbow trout populations.

METBODS

Di.tributian and Abundance

we ... mpled nah by electro,hockin. ....inin,. snorkeiinl'. or lOme combination depend in. on the physicsl conditions lit each alll.tion. We sampled a iencth of .tr.-m which we felt included all IvailBble habilll.t types. The majority at slll.tions were II I least 50 m Ion.. All fish cau.ht .... ere counted and measured (Btandard len.th. SL. :!: I mUlJ. Salllple. of fi.fthe. ""ere preserved in 10% formalin lor ltom"ch cont ent. analYli,. Visual count! at small fish Or those .... hich ev"ded capture Io'ere aleo r ecQ rded. lOh,n

.norkelin., one Or two researcherB """"m in a n upBtream direction "nd counted ..• • individuals of all sped"s pre.ent and estimated their len&"th (SL, :!: 5 mm). An • abundance code (1-5) wa. a !I!Iicned. to each aped... and to total f lah abundance where l : rare. 2=uncollllDOn, 3=common, 4=ahundant, and

5=auperllhundant.

In addition to the fiah ""mplin.. , we measur ed or estimated a number of environmental variables Inc1udin.: water temperature ("C) , mea n and waximum depth (em), melln wid t h 1m), fio,", (cfa), turbidity (1- 5 leale: l =crynal c:leu to

5=edremely turbid), conduct;v;ty, " rooted aquatic v",etation, " neatin .. aquatic " ,""etation and/or alell.l mats, " pool- rittle-run, " ahod e (estimated" of the ,",,,ter'. Burface .... hich ..'a. apparently shaded !!lost of the day), covel"

(.. "timated " of ares "" jth: no cover, object cover (<150 111111 in a;".. , 150-300 mm in lin a n d) 300 mm in .i::eJ. overhan"in" "'",,,etation ••urface turbulence. rooted ve"etation. root .... ads. and undercut bank.. ), a nd .ub.tr-ate com position in % of mu d . sand. "ravel. rubble. boulder . and bedrock.

We record ed the diatribution oJ e ach lpecies on I draill8"e map. For sitel sampled more than OnCe durin" the year or in Beveral yeau, the number of specieli recorded at each "ite includ .. s all speeies CSUl[ht in at lee.t on! of the samples. Sample aitea are shown in Fia:ure I and li.ted in Appendix A.

Specie. tha t were obser ved dur inl[ qualitative Sprin l[ semplinlir (rut ele<:t:'Qfishin" in April and May 1989 and anorkelinl[ in May 1990) wer e Dated at the nearelil quantitative .tation.

In contrast to p r evious yeara we snalyzed 'peciel ranks. relative abundanCel of apeeie,.. and density oJ .peeie. (fiah per hectare) rat her t han s peciea renks or nmka and relative abundance. only. The area for calculation of density wal o btained by multipl,.inl[ the station lenl[th by t he avera"e

,,·idth. These analyses ..·ere conducted uilin" the combined data aet f rom all •

10

)Tear- s. The mOOna- of oamphn, te chnique s a t many stations reduced our

confidence In the absolute numbe rs and theretor e densities. Also, the snorke l

surveys '-'ere condu,,~ e d ".. ;th varying numbers of ohservers .... hieh may have

affe"t .. d the total area surveyed e nd thus the tot"l !ish count. The se c"v e!lt~

should be kept in mind ""hen interpreting rMults,

"',, e xplored the rellltionships bet"'·.... n [ish ",bundan" .. !llld the physical

variables measured in the foilowing :nann.. :. First we calculated Pearson

p::-oduct-moroent cor::"elations b ..t"' .... n fish species ranks, reu..tiv," abundances,

!lod densitie s lind each of the physical variables measured. Spec;.. " which

=c:lrr e d in more than lOX of the s"mples .... ere included. PhYllical variables

havinll sillnificllnt "o,"::-elations ,.-jth b. o or more species wer.. retained for the

:lext step of analysis. When mor.. than One v a riable within II nonin depende nt

&"!"oup of variables (e.g . h .. bitat percentages of pool, ritfie and run are

nec essarily highly cor!"elated) were correlated with abundance, we chose th~

va!"iabl~ "'ithin t hat z r oup "'hich had t h e highest number of correlations or

the hi&,hest a~'er a ge correl .. tion, in the c ..s e of ties. Since many of the

p h ysical variable" are intercorr elated, '\ol e then conducted a principal

components analysis of th ~ variables r .,tain.,d for analY8ee. For species rsnks,

these we r e stream order, stream gradient, elevation, wate r tempe!"ature,

"ye!"ai'e depth, maximum depth, average loI;dth, flow, turbidity, shade, ali'al I .na t s, cobble, pool, small cover, snd surface turbulence . For relative II.bundsnces, the variables retained ",.,re "lr.,1UD order, stream vadient, I ele vation, wa te r temperature, average de p th, ma;rimum depth, aversge v:idth, fio'W, turbidity, shade, roote d "ei'etstion, attached alE"e, algal mats, sand, pool,

small cover, snd Burfac., turbulence . For d ensities the variables 'We!"" stream I order, g r a die nt, ele vstion, wa te r temperature, a vera g e de pth, ll>II..rimum depth, I • .. I I " I mean width, turbidity, shade, algal mats, attached ali'''''' cobble, pool, large cover, and surface turbulence. Scores tor "ach sit ...... ere calculated for each I principal component ,,,;hieh had an eige nvalue &"r ealer than 1. Finally, correlations be t"" .. e n total fiBh a bundance 0-5 .. cale ) and principal compone nt I scores a nd be t ....· e .. n species ranks, relative "bundanc.. ", and densitie s and I principal component scor .. s .... ere calcul.!tted. Principal components analysis ""811 ..Iso used to explore the I interrela tionships emon&, sp"",i"". Species which occur red in more than 10% of the samples wer e included. Analyses were conducted for ..11 three "bundance

I !!lettSUre",.

I Microhabitat Stu dies I We conducted studies of microhabitat of Eel River fish .. " in 1987, 1988, a nd 1989. The se studies .... ere de scribe d in de tail in the Annual Reporta

I {Bro.... n .. nd Moyle, 1988, 1989, .. nd 1990). As II. summary ot this .... ork .... e h a ve included a ma nuscript .... hich has been acce pted tor pUblication in the Canadian

I Journal of Fisheries and Aquatic Science s. This manuscript is include d as I Appendix C. The results ot these studies are briefly summariz ed in t he results s ection. The implications of these studies tor the management of I anadromous fishes are included in the discuasion.

I Artificial Stream Tflnk Rxperimenl.B I Artificial stream8 The experimental stream8 consisted of 4 recl8.ng umr, fibergms8 umks r located belo'" s small galmonid rearinll' facility on Little Spro.... el Creek, II tributary to the South Fork Eel Rive r near Garberville , Califor'nia. The t.anks 12 ..... ere fitted ""';th a ply",ood inurt to create t"'o parallel .hallo", "'ate.

compartment. (l.8 mione:, O.S m "'ide) at the up.tream end of the tank and a

sin&,le deep ",ater compartment 0.75 m lon&" 1.1 m wide) at the do..... n.tream end. Water ..... a. ~upplied to the tank~ trell! the re.rine: facility by "r!wity flo ..... , throu&'h 4 em PVC pipe. In each tank a spray bar "'as directed at the

~urface of the up~tream end of o ne of the shallow compartmenlB. W.ter e;til ed throue:h a Itandpipe in the downstream dl!

remainin&, compartment reprelented pool ede:e habitat. The sub.trate in all habitats con~isted of ..ravel appro:timately 2.5 cm in du..me~r. Mean depth I I:

SD) In the de-ep ..... ater compartmentll vas 58 I: 2 cm and in the .h.llo..... compartmentl wal 24 I: 4 cm.

SqUl.wtilh "'ere excluded frem the Ihal1o", "'ater habitats by 2.5 c m . ted

"creen ov er o penine:s cut in the do",n.trealll end. 01 the ahallow coClpart ..... n· ..

The comp"rtmenlB in ""ch tank could be i/JOllIted lilllultaneou.ly ulln&, plexi ..lalls drep ....te.. The lIlnk. "'ere fitted vith 0.6 cm hard ...·"re cJo:..i:: be:&.

Shada ...... provided by a 60 em wide atrlp of nylon .unlcreen !"unnin&" the lenl'th of the c enter o f the tank and faltened to the hard ...· are clot b lid .

Experime ntal dellign

The purpo.e of tbe !ir9\ .et of uperiment. wu to dete<:l dif!er""'''''''' amon&, pre y &,roupa in habilB! uae and the efte<:t of the presence Oil ~ !Ii on habitat ule. Theae experiments ua.d rainbow trout, small roach 1< • lI:Il

SL) and larl'e roach (} 40 mill SL) and "'ere run in the !ollo ...i.nc _n placed t ...·o .qua.... fi9h (ca. 300 mill SL) in the pool habilllt compartJw:l.l d __ of the st..,sm tanks. With the drep e:a\el do.... n, we placed ,iI Pr"e7 ... __ •

.hallow .... aler compartments fo~ .. totAl of 12: prey per tank (3 pre,.... :.').

Thes" prey denaities were within the !"anl'e of naturel variability for the Eel

Rh'"'' drll.inal'l!, except for rainbow trout which did not eJlceed 2.4 {iah'Ult in

30 III .tream sections. However, the total fieh dena;ti... in thes" section. otten exceeded 3 tish-m! and the trout ",ere a:eoerelly concentrated in particuUor

habitat paLche. vithin the uction ",hidl probably resulted in local d,msitiel

exceedinl' 3 fish'tll'• (Brown and Moyle, 1988, 1989, 1990).

were then covered and the drop ,,,tes ra1aed. W" left the Itream tanka

ove:-nia-ht tor the two roach &,roup" and for two n;l'ht8 for the .... inho'" trout.

Pr"liminary data for roach collected in 1989 indicated that the r" .. ults obtained

in the t ..·o tim" period, were not statistically differen\... In tbe IDOrrunr the

ratee were dropped and the number at tiah in each habitat type counted. In

aeveral at the e:rperiments .... Ith IImall roeeh, we noted tiah with funll'll.i

infection.. The"e fillh were not included in the distributional eounts because

we "'ere not aure ~ the intectiona affected habitat lIelection. We ",ere also

UnSure if the infections .... ere due to handlinr streaa or the reault at

Iquawfish attack". We a ..umed tiah that "'era not recovered "'ere eaten

becau .... > 99" of the control tillh weI"! r ecovered. The experiment waa

repeated 4 lime. tor e"ch prey cmsa reaultinr in t .... o r e plicate" per atr$Bm

tank (8 replkatea totaJ) tor each squawfiah treatment (presence or "bsence).

These data "'ere analyzed uainr II. three-way II.l1II.l,."iII 01 variance (pr ey,

aqul!lwfillh, atream tank) of the arcsine trenelormed proportion of fiah uain,

pool hebltat.

A t .... o-prey experiment wa. run uain.. Iar,e rosch and .... inbo.... trout ...

prey eimultaneoualy. Since the intent ot the e:lperiA>ent ... aa to aimulate the

eft...,t of tiah beinr crowded to,eth"r due to the pre"ence ot "qua... !i"h, we used 12 fiah of ..a"h specie. in the trials tor" total of 24 prey fillh per tank"

16 preY'!III). We ra" thea.. experiment. for 24 hour". Qualitative obaerYlltio"s

of the ain&,le-pre)' trout trial. indicated that the cupon.. " of r ainbow trQUt to

the presence of aqulI,.,,[iah .... a .. rapid, ,,~ tor roach, ",akin&, the 24 hour period

appropriate (A. Braaher, personal observation). The dal!!. "'ere analyzed In .eve .. ,,] ways. The reaponse variable in all ca".. a W,," the arcaine transformed

proportion of fi"h using deep "'ater. Habitat use of the prey ",ere compared

",Ith " three-way analysi. of variance (prey, _qulI,diah, strealll tank). Habitat

USe of aaeh apedes waS ""lOpseed to the results obtained in the aingla- prey

trial tor that aped.. s usin. II thr«-"'"y analyaill of variance (presence of

other prey, squ"",tish, atream tank).

A tau sea.on stor ... in June 19'90 deslroyed almo.t the entire 1990 year

class of aticklebecka; thuefore, We only have data from 1989 f or thiJl lpecies.

The protoc:oi for It!ckleback. differed from the 1990 e:tperimenta in tbe

foliow;n, ways. The be&innin&" denaity was 24 pr ey (6 prey.".·).• ThiJl prey

density wal within tbe rana:e of natural variability for thiA lpec:iell (Brown

and Moyle, unpublisbed data). The dilitribution of prey waa checked every 12

hours for 2 days. Rather than beina: directed at the surface ot the rUne

habitat, the apray bar waa auhmer,ed and produced much leu surface

turbulence. Treatments we r e not evenly dlltributed amon&" the str_m tanks

.0 the tank effect could not be teated. Finally, eo number of fiah diacovered

,ap" lead In, to the are" underne"th the plywood insert, so predation rate could not be elti... ated. The effftCt of squeowfish prelence on Ule of deep

water "'al tellted uaing a repeated meaeuree .nalYBis of varience of the

arcsine tranllformed proportion of eticklebackl recovered from t he pool

habitat. 15 All prey eJ[o;e pt rainbo" trou t ",ere captu r e d "';tll seine.. Rainbow trout

.... ere captured ,,;ilh ,. blleki'lI.ck .. \e<:tro.hocker. All [ish 'Were held overni'ht in II holdin, tank (3 III lon, J: O.S '" "";de or 3.3 '" diameter) belor e beloit uaed

in II t rial. Prey f~h " ere only uaed once. The pr ey den~liel we ulled we re

within the ran&"e of natuu.l variability to r the Eel River d r ain•• " (Brown a nd

Moyle, unpublished data).

4.. &nd Grovtb

We collected Bcaln trom aquawfish whenever pollsibl". Scal" ...... re

removed from the a .. e" below the tip of the lell pectoral fin and be10w the lau::-aJ line. Sca]ell "'ert! cleaned a nd mounted bet.... een tvo II..... lide •.

Selll". w .. re viewed uainl' II aeale re.der (23X ma&,nilication]. Distance. from focus to ed,e lind from focUI to annuli were measured to the neareat lIIillimeler with a plastic ruler. B!ll;).-caJC\llated lenl'ths at each a l'e .... ere calcula ted usin" Fraser'. 0916) proportionality forlllula:

In L, :: a + (In SI/ln S,) .t (In L, - a),

.... her e: L. = lenl'th of the fish at annulus torlllation, S. = distance from f ocus

1.0 annul\ls, Sf = distance frolll f oc\ls to e-dl'e, and Lc :: lenl'th at captur .. , a :: t he intercept v al\le of a rel'reaaion of the nat\lrai lol'arithm of nsh lenl'th o n the ""t\lra) 10l'arithm of ,cal.. radiu • .

We calc:ulate-d mean backcslculaled I .. nl't h and .t.andard d .. viation f or 1 each al'O I'ro\Ip f rom each aroa for each ,.ear in which a collection VIla made. w.. al80 c ombined data acros. year . and compared mean backcalclllated l.m,th at al'e alllon, arellS usinl' one-wilY analysis of variance. The area" used we r ..

Rice Fork Eel River, Eel Rh'''r bet...... n Cape Horn and Scott dams , Eel River belo... · Van Andale Re"ervoir 1.0 O!..ttlet Creek, and the South Fork Eel Riv.. r.

• • 16 • Only aeinina: and hook and line "'er e used to c:ollect fi.h in the South Fork Eel River. Raft a nd backpack eleetroshockinl' .... ere the primary method, of • coll,,<;t!on in the other ar.. a •.

F ....din. Babita

Throulthout the study we pres e rved Ampl"" of fish"a in 10% formalin for analy.is 01 feed In .. habits. In the laboratory, each flsb was measur ed to the nearest mill Sl and "" eil'hed to the nearest 0.01 I'calll (If). The contents of the I'ut .... ere then removed and ...... i.hed on an electronic: balance to th" nearest 0.00011" Itelu in the &,ut "'ere identified to tbe Iow"st taxon poesibJe and the percentsI''' of ....eh t.&lIon present estimated. Percenta&,es of each t.aJ[on for each species were ... limated by calculatina: the "8tim.ted man of

..:leh taxon in individual stomachs (measur ed total lI\.ft.1S X esti:n&t"d proportion), lIumminl' over all individu"ls ot the lpecies, and calcua.tina: an overall percen tal'e. Frequenc:iel ot occurrence (percental'e ot stomachs in whkh s pllrtkular taxon occurred) were alllO calculftted. Most species were broken into two eize clft~8es (J ; younl'-ot-year tish e nd A = older nih) tor

"n"lyael. The breakpoints were based on lenl'th-frequencies but ... ere l'eneraUy 50 mm SL tor roach snd 100 mm SL to r rsinbo... trout snd suckers.

Squ"wfish were !leparated into 50 mill SL lize CU.SRe!!. Speckled dace snd three'pine atickleback were not b roken into cate ,ories.

We calcua.ted dietary similarity smon, the species and sil:e c:.u. ..ee present in " 98mple usina: Schoener'. formula (Schoener 1970),

S = 1 - (0.5 X (E :P1, i - P',i:)' where t he P . and P , are the proportioni o r each taxo n i used b y apecie s x I ,I t, and y. Value. rana'e from 0 (no similarity) to 1 (comp lete s imilarity). I

Similariti.. s ..... r .. clllculat.. d on th .. basis of combin.. d cat.. gori.. s of I.a%.a,

I usually at the level at order. &ceptions includ.. d fiah, which "" .. re combined I into a ajnlile ateliory, and allia.. , ... hich included fil:tm .. ntou8 ala:a.. and diatoms. I Population Betimates I We conducted three-pass depletion estimates a t 28 sites in 1988- 1989 and 1989-1990. Twenty-five eites "'ere sampled in 1987-1988 and only 2 in 1986-

I 1987 (sites sampled were th.. upper Rice Fork Eel River site and lo.... er Be .. r I Creek site)...... 0 rites "'ere located on the Van Duzen River. An additional t wo sites ",e re locat.. d On Grizzly Creek, a tributary. Three lIitell were located I on the South Fork Eel River at the Nature Conservancy CoaJot Ran.e P ....senoe I (NCCRP). Additional sites in the South Fork Eel River dnoinage "'ere located on Elder Creek (3), Canoe Cr.. ek (3), and Bull Creek (10, only 7 aampled in I 1987). Two sites "'ere located on the Rke Fork Eel River and an additional three ... ere located on Bear Creek, a tributary to the Rice Fork Eel River. At

I each site, a s=tion "'as blocked of( using blocknets. The ae"tion "'as then shocked three or four time" uaina: a Smith-Root Type Xl, XII Or VII

I e l=troshocker. All fiah captured ",ere measured I! 1 mm SL). Lara:er I individuals "'e re "'ejghed with Pesola llealea. Smaller fishes "'ere "'eia:hed by ...... ter disp\&cement usina: .. a:radu.. ted cylinder. P ..ciIk a:iant sa\&msnders I (Dicsmptodon ensstus) "'ere also me ..sured (anout-vent length) and "'eighe d. Exce pt for specimens pre .. er,·ed for gut contents analysia, all fish ",ere

I returne d to the stream. In addition to the fiBh datz., the B.. m .. physical I parameters de scribed in th.. diBlribution and abundanc.. section, except cover, ...·ere measured at each site. I I 18 We calculated population estimate.. , standard deviations a nd 95" confidence in ter-vels by the me thod of Carle and Strub (1918 ). lo'e estimated both number! o f tish and biomass. The estimated numbers and biom... " e=-f:' converted 1.0 numbers and &rtllU ~r IIquare meier by dividinl' by the area slImpled (8V",""&,,, width (m) lI: len.(th (ro)).

The primal":> pl,lrpose of the pop ulation estimate. wall to eltablish the amount of variabillty Over time of rainbow trout populationa in the dr-aiMi'''' w" calculated mesnS lind standard deviation. across years for rainbo..... trout populations "t each aite and for each stream. We determined the percental''' chllna:e in popuJ.e,tion between auccess;ve yesr. at each aite. .... alltO c.alcuh.ted P"al"8Qn product-moment correlntions betw"en ""!lms lind standa:-d d eviations to determine if they were r elated.

We alao ",anted to determine if the physical data routinel,. collected durin&" population surveys "'ere useful predictora ot rainbow trout abundance.

We calculated Pearson product-moment correlation s between the physical v arlable. mea .. ured and r ainbow trout denaitiea. We alao constructed multiple re&,reuion modela r etatin&, fiah abundance to physical hllbitat l or r ainbo... trout. The multiple re&,reasion "'"" calc:ulated Ullin&, data f rom all ,.ellu combined. Rel'reaaiona ... e re calculllted tor an aites, including rites ",her e rainbo", trout were IIbsent, lind tor all aites ",here r ain~ trout Qc;curred.

RES ULTS

Distrib u tion and Ab undanc:e

We .ampled a total of 412 aite" durin&, the four ,.ea u 01 the atud,. (Fill" '

1). we e;.;c:luded aile. in the estuary and ait.. mi"". in. physical da ta from tbe quantitative analyaes le avin.r 40] site" for q uantitative analysis. We captured :

19 or ohse,"ved 22 specIes 01 fiah (Table 1). Eight of the species have been

introduced to the system and 5 of the specie .....ere only obllerved in the

estullry. We obll"rved 19 specie s in the lDainlltem Ee l River , 10 apede .. in the

South Fork Eel River !l od V ~m Duze n Rive r, 6 species in the Rice Fork Eel

River,S apecies in the Middle For k Ee l Rive r, and 4 species in the North Fork

Eel Rive r and Black Butte River. The locations of the sample "ites and apecie s

ceptured at each site are &"ive n in Appendu. A. The r 81o' data for fiah and

physical variable s ar .. pre sented 8.10 Appendix B and have been IlUpplied to the

California De partmen t of Fish " nd Game as " Lotus 1- 2-3 file (r ele8se 2.0).

Re sults for a.nalyses conducted wHh specie s ranks lind specie s r elat ive

a bundances were similar IiO only the r e sults tor r e lative abundance s and

d ensitie s lire discusse d be low. I PrincipIII compone nts d erive d trom the physical vllriables ret.. ined tor ana lyse s of r elative abundances and densities are ~iven in Tables 2 snd 3. I For the vari.!tble s r etaine d for u .. e with r e lative abundance .. , principal I compo nents analysi .. produce d'; principal component .. which explained 61% of th e vari.!tnce . PC 1 describes a g radient rangin~ from sman, clesr, cool, I s hs ded, hi ~ h ~rsdient, low order streams to Iar~e, turbid, "'.. rm, 10", ~radi"nt, hi~h orde r atresms. PC 2 sep.. . a t es open, warro, sh.. now site. with attached

I alg.. " from sh.. ded, cool, deep sites without s l~se. PC 3 separates low flo ... s ite s dominated by poola from sites with hilfhe r nolo's and more rifne are".

I PC 4 s e parate s hilfh ele vation site .. with surface turbule nce ..nd little shade I from heavily sha ded, calm, low elev.. tion sites. Four principal compone nts, which e xplaine d 6411: of the variance, we re obtained from the ..nalysis of the

p h ysic .. l v ..riabl e s a ssociated with fish de nsity. The interpretation of PCs 1 I a nd 2 ..re the ssme .... those above. PC 3 r e llemble s PC 4 a bove a nd s e par.. te s 20 bleh elevation, open, turbulent (riffle- like) sites with little abaci!! trom 10"'"

"lev.tion, shaded, atill waler habitat. PC 4 a"po>rates sites with pools and alrae from run.. &rella.

Total. f iJIh abu ndance

Total fiah abundance 0-5 sCIlle) "'..... potIitivel,. correlated with PC 1 and nel'stiveiy cor related with PC 2 of both dille Bet. (Tabl!,. 4 and 5). Total fiah abundan"e "'lUI n",ativ"iy correlated with PC 3 of the relative abundance data set and positivel,. correlated vith PC 4 of the demlity data set. All the correlations ",ere 10,"" The positiVI! con"elation with PC 1 indicate. t hat fish were mOrl! abundant in larter, warmer, hi,h order IItr"1I1II8 than in smaller, cooler, 10,", or der str"aIDS. The ne,ative cor relation .... ith PC 2 reinforce. " positive relationahip of abundance with increas:in, telllpo!utur e, and attached al,ae. The cor relationl with PC 3 (relative abund~nce) ~nd PC 4 (denaity) reinlorce ~ poaitivlI ,..,laUonship bllt"'een abundance and pool habitat.

The cor:-eilltiolls 01 total fish abundance vith the p r incipal COlllponents derived {rolll the phY8ical variables "'ere lo"'er than t hose obtained in thll

1987 au!"veYI 01 the Van Duzen Riv er lind South Fork Eel River (Brown and

Mo"le 1988), but "'lire lillln"r to the valUlI1I obtained tor the 1988 aurvey. of the Middle Fork and North Fork Eel River (Bra"'n and Moyle 1989). The 10 ...· correilltions in the 1988 and 1989 analyalls ",ere due primarily to differances amona" the subdrainlla"1I8. Each of the main forka la uniqulI f r OM thll others hath in physical upecta and the aped.... 01 fiah p r e ... nt. For "Dlllple, in 1988 we lurveyed the No rth Fork and Middlll Fork Eel Rivero "'her ll cool ",ater in the up"t,..,alD areal supported lar&"e popuilltionl of juvllnil" st,,"lhe~d. Mo ..~ downstream, trout .... "re rllpillced hy juv enile roach and luck e r l ",jt h little chan&"e in overall abundance. In the V~n Duzen River lind South Fork Eel •

" River fish were more abundant in the do"'n.tre~"n r"ach"s due to iar&e

populations of :rou nl'-of-Y"lIr tmlch ""rl elickleback snd lar." I' rou p~ of adult

Buck ers and a qu8",(ish. Thull , the correlat ion of lara''' num~r. of fillh " -' t h

lo..... " r elevations "'a. atr on .. in ths1 II.naIYlli. . The lDainstelll Eel River

surveyed in 1990 "" lUI &imilar to the North Ilnd Middle Forks .ho.... inl" little

ehanl''' in overall abundance In an upstream-do .... n.tream direction. Upatream­

rlo'oo'na trellm chan"" .....er e primarily in the presence and abundance of

individual ape<;ies. Combininl' th" data frolll all of t h e drailUll'es obscur ed the

Itronicr r ewtionshlp ob... rved in the SOI.I th Fork Eel River and Van Duzen

Rive... In aUID"", ry. fiah were l'enel"lI.l1y IDo .. e abundant in t he tarl'l!r, .... armer,

10'" elevation portiona of the drainsr"a, but the relationship was v e ry weak.

RainbQ.... trout .... as the IIKlst videllpread speeiu. It .... a& present a t 314

ot the 412 aites ...mpled (Fil". 2). Abunda n ce ot r..mbo.... trout ,"""II ""I"atively

correlatad .... ith PC 1 ot the physical d ata (r elative abundance) and positively

correlated with PC 2 snd PC 4 (Table 4 ). Theae relationships in dicate that

rainbo .... trout became Ie .. abundant vith increaain... tream order and the

other associat ed variable. 00 ...... radient, .... arm te ll>peratu r e., hi.. h turbidity).

Abundance 01 rainbo.... trout .... a. also nel"alively corr elated .... ith PC 1 of the

physical data troll> the de nsity d.ta alit and pollitively correlated with PC 4

(Table 5). The Interpretation of thelle correlations i!l the lIall>1I a s above.

Although rainbow t rout ...... re pre s ent at the I"rHtelt numhllr of etations,

nUlI>bers Wllre otten low. In the lI>a;nlltem Eel River, ...... ob.ery"d trout at 84

ot 161 stations but they .... "r" (I n ly abundant in the extreme headwaters, in the

area bet .... een Scott lind C.. pe Horn dall>s, and in c ool tributary streaMII. The

p!lttern wal .III>Har lor Middle Fork Eel River, Black Butte River, Nor th Fo r k 22 Eel River, and South Fork Eel River. Trout "'er" most abundant in the \o.Jer part 01 the Vtln Duzen River drainll&"e and In the edrem" headWllter.. T:-Ou t

.... e r e Ie.. abundant In the middle reaches.

The distribution of trout in the Eel River drainal'e appear. IQ be IIlrI"!" controlled by temperature. In II.U branches of th.. river, trout were abundant in the cool headwaters and became len abundant ..s we moved downstream and tempenUul""" increased. Ail the ",ater became "'.. rmer, trout incre.. aintiy exploited cool",,,t,,r r .. l up suc h all apr-inil' inflow, cool tMbutariell, and shade.

We la ...· an extreme example or thi' in the South Fork Eel River in 1988. On 25

July 1988 we observed Il "ummer die-olf of trout near Garberville. ;.; .. me ..sured II muimufIl w"ter temperature of 28.S' C on this date !lnd temperatures had probably bHn similar for teveral daya praviou aly. In addition to many d ead and dying trout "'e observed concentrationll o n the o rder of thounnda of fish around .pdng inflows.

The IlbllenCe of trout f rom tha lower rellch"s of the malnste ll! Eel River

..·a s une;tpected. Brown (1980) reported that IO.1n: of the fi,h obHrved in atatlonll below Eel Reek "'e r e young steelhead and s"veral Iliu-cl".se. were pre.ent. We o bBerved very few .... llIIo nid. in t h e area between Eel Rock and the estuary, even in areas ... here cool inlio... wall available. BrO\o" n (1980) repor te d trout present in pools, rif1'1es snd near cool wate r intIo .... in thi. area. The rarity of trout in ou r Ilurvey. ma,. ha'·e reaulted fr<>1II difference. in physical condition, bet ... een the two ,tudi"., differences in the aites Or habitat tyPes aurveyed, the prellence of .quawfish, or a combination of t.he t hr ee. In particular, the eUc-etll at ongoing drought (low 1'10ws end pre'UlDably hifl"h tempe ratures) may have reduced the ability of aalmo nids to s urvive In the lower river Or more likely lIIay have reduced the lIu r vival of •

!i.sh ",ovil'll" down.tres", from areaa hieher in the drains"e. Predation by "

.qulI",fi.h may be a contrihu tini' factor hut is unlikely to be the only One

llinee aalll'onida Went not obser ved in riffle habitat ",h"re they lU'e sale from

Iqua",ri,h pred"tion.

Califor nia rooeh

" e found California roach at 230 of the .itu .empled (Fill'_ 3). The

relalive abundance of r oach "'115 po.itiv!!ly correillted with PC 1 of the

phy,;"a) data indklltln. II positive reaponlle to nrca", order lind the

uaociated physical variables (Table 4). Roech relative abundance .... a. alao

nel'at;ve!,. correlated ",jth ?C 2 and ?C 3 indica tin&" an incr eaae in e.bundance

....;th incr "a.in&, temperature, attach.d alca", and d&Crea.lna: "pool. The lame

p"ttern "'1l1I found for correlation. of roach den,it,. with pC 1 lind PC 2 ot the

appr opriate phy.kal data (Tllble 5). The lle&IItive relationship with pool arell

reflects the obeervation thllt roach tend to favor sbaUov, "'a rlll pools and use

wa-e deep pool. less intenaively, lend ina- to concentn.te arOl,lnd the ed&es.

Also, squa"'fish tend to be found in the Jar&er, deeper pools ",hloch affects

habitat use by roach.

Roach "'as by far the most abundant apecie. "'e observed and ita

abund"nce "'U complelDentar y to that of rainbow trout. As trout abundance

decr eaaed at 1D0re do",natr ealD atationa, the abundance of roach increaled. In

the cool tributariel the IIbundsnce of roach "'as "enerally len thlln thllt of

trout. Thia relationahip ia at least partially a result of the different

responaes of the t ....o species to physical conditions, especiall,. telDperature.

Ro..ch ",ould probably alao be the IDOSt "'ideapread speci.,. in the draina.. e if

not for the preaence of barriers to upatrealll 1II1&",lion. o..borne Roui'hB

prevents the diapersal of roach into the upp<>r re80Chea of the Middle Fork Eo,I " Ri"..... There is II. barrier in the Black Sutte River located bet'W&en Whiteh"""k

Creek and Mi ..iaslppi Creek (ca. 3 kill b.!lo .... '.ihit"h"..... k Creek). Roach .... ere

abient trom the Van Duzen River above the confluence of South Fork Van

Duzen River where there i" .. barrier. ROllCh were pr".'! .. nt throuthout the

South Fork Eel River which doe. not bave anJ' barriera. The presence o f

roach in the North Fork :Eel River above Split Roek I. curiou. be.. "u"" of "­

very aleep cascade. area located at Split Rock. Thi" area baa been modified

(bl.a"ted ) In recent years be<;llus" it "". ;mpedinlt the up_tream lIlilfration of

f>8. imon and ateelhead (W. Jonn, CDFG. pen. comm.). The prea"n"e ot roach

""lf8'"st" that the aped". ma)," have been lntrt>d1,1ced sbove the barrier bl' humans. The upstream limit of roach in the draln.,e ",all located at the confluence of the Eaat and 10iut forkll of the North Fork gel River. Tbe~ 'W1lS no phy.ical barrier to upatream mirration at that point. we eaptured a ori."lc!e roach in the Rica Fork Eel River in 1986 but .... e bsve not captur ed any in aubsequent year.. Roach ... ere al"o pre..,nt in a nu",be~ of tributary .t:"~ throughout the Eel River drainare but .... ere ,anerally restricted to the k>ve~ reache •.

Sacramento IlUcker

We observed Sacramento sucker at 174 of the 4lZ aample sites (FiC. 4).

Sucker relative ahundance .... aI poeith-el,. corr elated with PC 3 of the ph,.P:aJ data_ No other airnificant correlationa .... ere found. This correlation Indicl!l:es decre&sinc abundance .... ith decrezurinr !Iov and increaainc S pool {Table 41.

For the denaity data set suckars "'ere po_itively corralated v:ith PC 1 and neratively correlated .... ith PC Z. Theile correlations indicate that aucker density Increased .... Ith .. tream order but tended to be I"", io larlr" =ldvata" pool". The laHer pattern probably r eaulled primarily from the ab_nee oL \

,uchrs frOID the head ..... ter area of the Middle fork Bel Riv"r and North Fork

Eel River.

The diltribulion aho.... n in Pil1.lre 4 ia IJOIDe .... hat IDaleadIn .. because a dult aucken were re.tricted to anI,. the deepest pool. throou ..hout much of the area ... here the,. a r e sho.... n as being abundant. We rarel,. obaerved young-of~ year lucker" in large numbers. The largut concllntrsUon. of luckers ... ue in the lo... er reache. of South Fork Eel River, Van Duzen River, snd mainalem Eel

River .... he,e lar.. e deep pools .... ere comIDon. Suitable pool, be<::aIDe progreuively rarer In IDOre up"treaID Irees and large .ucker~ (>150 ID'" S l. )

"'ere reatricted to tho"e pools. We alae ob.erved large Ncker . bet...... n Scott

Da

Despite tbe ablence of large IIdult~ theee populat;on~ we r e IIpparently llelt­ supporting. Young-of-year lucker. were found in th.. lower roches of a number of tributaries but adult. were primaril,. nltricted to the IDain r iverll.

10' .. found II stron .. corr elation at aucker rank abundance ..,th physical variablea in 1988 when the South Fork Eel River and Van Dur-en Riv ..r ...... re

.urve,.ed (Brown lind Mo),l .. 1989). The relationship waa not ver,. atrong in

!JIe other drainages 10 eomblning the data f«lID the different drainaa:el obscured the .trona: relatlon.hlp lleen in the South fork Eel and Van Duzen

Rivers.

5ac:r'amento squavfish

\o'e observed squllvtish lit 156 of th.. 412 sample sites (Fig. 5). Squa..-tilh abundance waa pO.itlvel,.. correlated with PC 1 ..nd n!! ..lltively "

correlated wi t h PC ;:: of tha phylical data from bot h analy .. e. (Table 4 and 5).

Th ..e corr elations indie... te that .qu... ..-ti.h were IIIoat abundant in the WllTme r ,

Iarl:er, hi&,her ordar .tr e ... ",. with hi&'h percenw&,eI of all:.....

The upatraam limit! at Iquawfiah in the drainalt'e chanlt'ed .i&,nificantly

durinit' our study. Squawfi.h emibited tha I:r e ..te.t r anl:e exten.ion. in the

Van Du~en River and South Fork Bel River. A Iarlt'e nu",ber of adult

"qua ...·fi.h IIIoved above Goat Rock in 1989 on the Van Out-en River and are no ....

preaent above Bridl:e\'ille tor an unk nown di.tance. At the beginninlt' at our

study the upstream limit at .qu.. ..-ti~b ... a. located at Grinl,. Cnek State P ..rk .

In 1989, we captur ed youn&,-of-yellI" aquawtiah at our perme.nent atation

located above Brldlt'eville and in tbe lower por tion 01 Yalt'er Creek indicatin&,

that tha population in the Van Duzen River ia reproducinlt' within the Van

Duzan River. In the South !'ork Eel River, the upatream li.mit of aqua.... fish

"'''-I located n!.lar Quber ville, California, balow Benbow Reservoir. We obaerved

a linlt'le "dull .qu".... fiGh at the Bi&' Bend Lod&,e located belo.... the confluenca

of Rattleanake Creek in 1989. The next aqua.... tis-h wa obaerved .... aa

do.... n.tre.. m at Wlt'lt'ett, where tbe Hilt'h ...... y 10! bridlt'e cl'Ol!aea the South Fork

Eel River. Younlt'-ot-yellT squawfiah and juvenile .quawfiab "'ere pusent in

10 .... numbers do.... n.lream to Benbo.... Reservoir. Juvenile Gqua ...·fi.h ware slso

cault'ht in a do.... n.tream milt'ro!I.nt trap located in the Eaat Branch of the South

Fork Eel River in the Sprin&, of 1989 (Scott Do .... nie, perl. comlll.). Squ... ..,fiah have not ext ended their range in the Black Butte Rivar or in the Middle For k • Eel Rh·er. Younli:-of- yaar !lquawfi.h dominated the aquawfi.h population in tbe • middle re .. ches 01 the mainmtelll Eel River from aoout eel Rock to tha • "------.. --.. ------~• 27 confluence ot the Middle Fork Eel River. Lere" adu\t" .... ere pre .. "nt in hil'ller proportions both upstrea", lind down.. trelllll of this tll"eO !Fil'lI. SA-SRI. The dom.inance of youn.!l-of- year IQulI ...'fillh in the ",iddle reachel h". many possible ""panlltion... Adl.llh "'ere not particularly abundant in the II.rell- The tarze adult. we did lIee "'ere r" .. tricted to the large"t, deepest poola in tile area and only tbe pools which o fferlld 80me .art of COver .ueh ,u, large boulde .. pile .. , ralle n tr .. ea, or tare" arelll! of aquatic veKetalion (primarily

Elodea apl. Squllwfish from dovn .. tr.. "", areas l!I8y mia-ralll to thi" ar.. a for

• .,..... ·nlnll and then only" limit"d number OV" .. Rummel" where appropriate habitat .. .tin.. A tar.. " number of "pawner. "'''Y mi&"ral" into th" are" lind then remain but only thOle that find appropriate habitat eecape from p.-edaton durinl' the aummer period. Ponibly. larvae trom upstream areas teal' collect In this area for .ome r eason or younl'-of-year fieh may move ...... ,

!rom hahltatl wh e ~ predatory adult squawfiJ

Qualitative snorkel surveys made in April and May 1990 aua-guted t hat adult aquawfish we r e much more diaperaed in the Sprinlr than in the SUllimer .

10'11 'fU.r v!lred pools in the lo.... er South Fork Eel River and mainlltem Eel River

"'here larl'e concentrationa of adult squalolfilh .... e re found durinl' the aUllllller and f ound only small number. (1-4 fish ) remaininl'. Lar.e concentraUonl ot adult suc ken which were .lso found durinl' the summer .... ere IItill p~.ent all

... e~ smaller Iqua""fiah «ISO mm SL). Thill movement 01 adulh may be related to .pa .... nin. behavior Or a behavionll relponse to hi.h flo"'s and cold temper.. tures during the ... inter. Given this apparent mobility. it _mil that the absence of adult II qua... tish from the middJ!I reach ...... aa probably the •

28 • rnull of activ., movement out of an area .... hieh did not orte r III hiS" h

probability o f aurviva}. • The Iqu" ... fish population. in the SQuth Fork Eel River and Van Du z.e n • River .... .,re domina ted by small and ",edlum sized nah (Fitre. SI and SJ). The lack of larj'er individual .. (>300 IIUII SL) indicates that the initial invasion ot • theae systems "'as 8Ccolllplished by emaller fllh.

The atr .. "", reach between Pmsbur,. and Van Aradale Reaervoir. Seem!! to • be aQmewhat atypical in compariaon to the ~lIt of the Eel River drain.... _ • Adult aqua,dish a ppear to be much lDore abundant in tbi. reach in comparison to the rest of the d r ain8a:e. "'e d o not have the quantitative data to • Bubstantiate this statement because the Wilier wae too turbid for accurate

.norke! lurvel'''; however, the eaae witb which lari''' numbe~ 1I of la~ge adult

IIqulI",Ci.h ... "~,, cau&ht ",ith a nIt " J ectro.hocke ~ in AU&'>lIt 1989 and Ma y 1990

(ulllplin& in a9socilltion ",ith Steine ~ Environmental Con!luit.a.ntl Inc.) indi<:ate&

thlt Cilh "'e~e abundant. In addition, dudn& a qualitative .norkel .urvey of a portion of thi. reach in AU l'ult 1989, la~l'e IIqua",fillh "'ere t he o n ly lar"e fish identified. The turbidity of the "'ate~ "'aa e xtremely high dudn" the

.u~vey lu&&elltin& that only a !llllIlll portion of the fillh p~eaen t we~e lIeen.

Theae ob.e~vatio nll 6U I'I'''8t that larl'e I quawfish were common, perhaps

because the relatively constant hll'h flo ... . du~inl' the aumm e ~ .... ere favorable for Iqua .... ri.h aurvival. The conatant flow probably provided a more abundant and Ie .. va~iable reROUrce balle, e.pecially II Jar.e population of c raytllh, thlln il 1I"ailable in the r emainder of thll drainal'e. Also, t he constant hi&'h turbidity may provide protection from predlltors.

Threespine stickleback

W" found threespine stickleback at 93 or the 148 sample sites (Fi". 6 ). • I " • S~kkl"back .dative abundance .... tli poaitlvely corr elllted with PC I !lnd PC 3 of t b .. physical dats and negatively corre\e.ted wit h PC 4 (Table 4). This

indicates lh"t atleklebac k were !!>Ore abundant in t he warm, low a-radien t

.t.ream, of hi&"her order. Stickleback denaity waR negativel,. cor rebited with

PC Z and PC 3 of lhe appropriate phylicai d"ta {T"ble 5). Thele correlations

indiclI.te higher denaltl"l in .... a r m pooll at low elevation •.

Stickleback "'ere pre s ent in the lower reach .. " of the Van Duzen River

Illld main.te", Eel Ri ver, throu&,hout the South Fork Eel River, a nd in the

estuary (Eel River below Fe:-nbrida:e). They werl! 11180 pre.ent in low number.

in tr ibutary IItr"!lml in these area.> An apparently isolated population of

atickleback was present in th .. "tre!lms around Willita and dovnatraam of

w'illitl near the confluence of Lon&" Valley Cr eek and Outle t Creek. Th e

population around Willits ... as characteri:;ed by r educed plate count.. Six f lah

f rom Eaehl Cr eek "'ere examined, all of "'hich ver e unarmored poaterior to the

pech;c &"irdle. A 'in&"le stickleback "'III eo!leded Irom the Rice Fork Eel River

belov the confluence 01 Be"<. Cr..... k in 19B6. Sticklebac k ha.ye not b ..... n

oburved in this ares since. Sticklebac k vere eBpeda!ly abundant in the Salt

River .... hich i. tr ibutary to tbe e"tuary. The only other species Iound with

Lbem at thia location VI!I8 prickly s culpin.

Sticklebackl have b ..... n reporte d from both tbe North Fork Eel Rive r and

Middle Fork Eel River, In the North For k Eel River, Borton et al. (1968)

obee ..... ed .ticklebllcks trom the contluence ",ith the main.t.. m E .. l River ,

IlpIIUe8.lD to Soldier Creek. In the Middle Fork Eel River ?> .tkkleback e have

been re por~ u p8tr eam to Beaver Creek (SlIIith and Elvell 1959, JonII''' 1980,

-'caoe. a ..::d Eckman 19BO). These populationl may have been t he re.ult of

~ental introduction. durin&" fish re.cue o~ration8 in the d r ainage (10'. 30 Jones, CDFG, pers. eOIDm.). Such prol"rams oper a ted In the Eel River drain"li:"

from 1938 Into the 1960.. Flood "vents or other environmental perturbations

subsequent to these introductions could havl' extirpated thel .. pQp",lations.

Prickly sculpin

\0'" obsl!I"ved prickly sculpin lit 47 of 412 sites (Fill"' 1). Prickly ."",Ipin

relative II.b\lndan<::e was nel"atively correlated with PC 2 and positively

correlated ,",ith PC 3 of the physical data (Table 4 ). These correlations

indicate that prickly sculpin abundance ",a8 ,r"atest In open, wsrll> riffle.

with bil'h fiow and surface turbulence at mainstreslII .iles. Prickly sculpin

",'ere nea-atively cor:-eiated ,... ith PC 2, 3, and 4 of the density phT'leal data

set (Table 5). Thea.. correlations indicate the same relationships as abeve.

We oblerved prickly RCu lpln in ~he mainstem Eel River upnream to Fort

Seward, in the South Fork Eel River to Garberville, lind in the Van Du~en

River to the area where Golden Gate Drive crones the river. Prickl,. aculpin

were most common in ths lower reaches of the Van Duzen River wher .. suitable

habitat wae common. Other"";8e, they were restricted to patches of 8uitable h.!tbitat. The upstrellIll limit in the South Fork Eel River was determined by a aini'le individual captured n ..ar Garberville. Prickly sculpin were found in many ot the cool tributary streams, thoui'h they were not noticeabl,. mor-e abundant there. One exception iii Bear Creek, a tributar,. to the mainatem Ee]

River, which contained many Jar"e adultl.

Pacific ].aJI)pr-ey

We found Pacific lamprey at 42 of 412 lites (Fir. 8). Lamprey! were almoet certainly mOre abundant than this. The apparent scarcit,. of lamprey in the samples wal due to the fact that lamprey OImmocoetea burrow in the substrate makinr them jmpouibJe to oblerve durin&, Inor kel surveY8. They • • can be collected with "leclroahockerK but eve" this method ie not very

e!!icient. WI! eb.e ....'eel apa..... nin' "dults, dead adultll and lamprey neata .t "

numbe!" of locationll durin, boat I!lectrofiahin&' in April and May 1989 and

lnorkelinl' in April and May 1990. Th ...e oblervations indicate that edena;ve

spa'.-r.in, tak ... place in the South Pork Eel River upltrellm to Garberville, in

lCe main_tell! Eel River both above and below the con!1uence of the South Fork

Eel River, and in the upper ",a;nstelll Eel River both above and below Cape

Be.. " Da", al Van Andale. We did not incll,lde lamprey in the quantitativI!

a!:!.alyaes because WI! knew W I! did not .ample th"m e!ficienliy.

"'hile the major ity of lampreys we oblerved durinj[ our .ummer Burvey.

werl! ammocoetes, WI! captured adult lampreys in the upper South Fork Eel

River in September and in Elder Creook in July and September. Theae

ho.::!preY8 were full-aized adults in good condition and Indicate the prelence of

a -summer rUn- race of la.mprey in the South Fork Eel River.

Coaat.ra!la-e 6Culpin

t,;e captur ed cOllatrana-e Iculpin at 3Z of 412 sample litea (Fii'. 9).

Coaat:ana:e Iculpin we ~ not numerous enou"h to be included in the

quantitative analyees. Their distribution W51 similar to that of prickly Iculpin

but was not quite al extensive. In the Van Duzen River the ranges of the

t"-'O sculpins were identical with the upatream limit located at the Golden Gate

Orive location. In the mainltem Eel River we did not capture COOBl.rani'e

-.::ulpi.... in the estuary but they "'ere found &I far upstream es prickly

sculpin. The upltream limit in the South Fork Eel River "'al located noar the

c::onfluence of Bridae Creek. a consider able diltance downsl.reem from

c.rberville. Similar to prickly sculpin. coastranae aculpin were often found in

cool tributary s treams but were neVer very abundant there. Again, an e:rceptio n ""ss Bear Creek, 8 tributary to the Eel River, where wle adult "

sculpinl were coromon.

Green aunfish

we obs e rved ,r.. .. " 8l.lnfi,h at 25 ,ilea, 21 in the mainslem Eel Riv e r snd

4 in the South Fork Ee l River (Fl,. 10). In the main. tem Eel River we

obaerved Ir~n sunfish from below Cape liorn Dam to the srea around Eel

Rock; how.,ver, the mojo!;'ity of the obllervlltions were concentrated trom belo",'

ClI.pe Horn Dam to the confluence of the Middle Fork Eel River &nd in the

Outlet Creek d:-sinsCI!. In the South Fork Eel River we observed Ireen

Bunfish crom the confluence of Canoe Creek t.o iust above Benbow Reservoir.

Green sunfish were a\so present in Salmon Creek. Green luniilh wer e found

in BlJIsll, .... Ilrm pool. or slonl' the edt" .. of IarceT pool.. They we re usually

associated ",-:ltb eover In the tor

American ah.. d

I.'e observed A

m"in.le

number. but ..1"0 ob.erved adults-near the confiuem:e of the Middle Fork Eel

River, near Bell Sprlnas Station, and ..t Alderpoint. Shad ""ere aenerally

"slIOCiated vith the Iara'".. t, deepeat pool. pre.. ent in an &rea. The one

exception v .... at Alde rpoint .... here ve observed a Iara'e IIchool of "dult ahad

(ca. 200 fiah estimate d at 300 m

.h"llO'W rUne .. at both end •.

Coho lIalmon

We conected coho .. "Imon at 10 !rite., 3 in the Van Duzen Rivltr drainaEe.

6 in the South Fork Eel River d rainaae, and 1 in Lona Valle;!' Creek a

tributary to the

• I

33

for coho Willen becaule it w"a ao rarel,. collected. In the Van Du:.. m River

drain,aze we collected coho _lmon in the lo",.. r p8rt of the !!lain rivllr, in

Gr'.zzly Cr eek, and in CU IDIDinCIl Creek. In the lower South Pork Eel River .....

c:apl\lred s almon at 2: ,It.. " on Canoe Creek. In the upper p,art of the drllin',e

We captured salmon in Elde r Creek, Red",ood Creek, Jack of Hearts Creek, and

in the South Pork Eel River pJ;'Qper. In the "'Mns tem E .. l River we c:ollected

R~·"ra.I In Lon. Valley Creek, II tributarl" to Outlet Creek. Except for Red",ood

Creek and Je.ck of Hearts Cre"k in the upper South Fork Eel River drainll.&"e,

coho ulmon ",ere \ .. "" abundant than rainbow trout lit the atat;on" where they

oc:eurred. Coho salmon wer e ,ener81}y round In the deeper poola available and

ill auociation ",Ith cOVer in the form of undercut bank., rootll, or fallen tr.... s.

Brown bullhead

...·e o bser"ved br"own bullhead at 7 sample stations all vilhin the msinatem

Eel River" dn1nal'e (Fii" 13). All of the aitea "'er"e loc:ated bet""ef:n Alder"point

and aellr"lIt vith 2 located in Outlet Cr"eek.

Spe<::tled dace

Speckled dace "'en obeen-ed at 5 stationl all located in the Van Duzen

Rive:- (Fii" 14 ). we firat captured apeckled dac e in the Van Duzen River near

the to.... n of Brld,eville durinl' the summer of 1987. At that t.lme they ""ere

only found do"'natr-eam to just belo"" the bridlle at Golden Gale Dr ive.• he

limited r"anlre of thia fJlh and the la.ck of previous recor"da ot ita pnaence in

the drainai'e indicate that it ""U introduce d, probably only aeveral yean

previaull,.. As of 1989 they bad extended their r ..nll" levual kilomllten

downstream to the Silvio Botchi" Santl bridlle .. t the eastern boundary of

Grizzly Creek St.. te Park. Chinook -tmon

We ob.erved wlIlOn at 3 eites during our Bummertime .urv ey" 2 in the main.tem Eel River and 1 in the Middle Fork Eel River (Fi&" . 15). The salmon obser ved in the Middle Fork Eel waa an adult, prl!lum... bly ... apring-run adult.

In SOlDe years one or two .almon have been observed holdin&" ,,"ith .ummer

.t.... lhead in tbe upper part of th" draina&"" (Jone. and Ekman 1980). AU the other saimon we observed were youn&"-ot-year fish. We observed a ain&"le salmon in Benmore Cr eek in the upper part of the mainetem and also captured

. everal ""lmon while seinin&" in the e stuary. We alltO observed nUllleroul youn&"-ot-year .allllon in the area between Outlet Cr..... k and Van Arsdale Dam during April and May bo..t electro.hockin, in 1989.

Pacific brook \.a.mprey

We have captured Pacific brook lamprey only frolll Be ... r Creek, • tributary to the Rice Fork Eel River (Fi&". 16). The .pecies !!I.). be !!lore widespread in the areas a bove Pillsbury Reservoir than these u.mpi". indicate, eiven the difficulty in collectin&" lamprey ammocoete.; ho"·ever, our failure to locate the", ... t other eilee de.pite increased effort may indicate II relatively

.mall population.

Blue&"ill

"·e ob.erved blue&"iU at 3 litel, all located between Pillabury Relervoir and Beaut (Fi&". 17).

Lar&,emoutb bas..

We observed lareemouth baae at only one site in the ",ainste", Ee l River draina&,e (Fi&,. 181. We captured the flah durin&" IprinC electrolhockin&" in the plunge pool below Cape Horn dam. I

g,rtuarine species

w. observed or clI.ptured 5 species which we r e found e:rclusive!,' in the

enu&:'y: lurf smelt (Hvpom... ",. preHofluM) (F;&,. 19), lltachorn IIculpin

{LeDtocottUI UlM1u1' (Fi&,. 201. starry flounder (Plalisihlhn stellatus' (Fig.

21). top.",elt (Atherinop. arlini.) (Fi&,. 22), and red tail .",rfperch (Arnphjslicus

rhodot![u.) (Fi,. 23). Starry fiounder wa. the moat widespread species in the

.IItuary and "'all found in the main la&"oon near the bench in the .and bar, at

Fernbrid&,e (conBidered the upslrell.lD limit of the eatuary), and in Mor a'sn

SlouCh a Rmllll tributary to the estuary. Surf IImelt, I t.a&,horn Hculpin, and

.... dtaO .urfperch "'ere only captured in the main body 01 the estuary in

proximity I.e the breach in the sand bar. Topsmelt were found in the

mainstem Eel River at Cockrobin bland and in Mora-an Slou&,h.

Species reiaooDabipll

Since principal components anal"sil at species rIInk ..nd relative

abundance data &,ave aimilar result", only the analYllis usin&, reiativs

abundance d .. ta will be prelented (Table 6). The anal"si, yielded 3 princip.. 1

componentll "";th ei&,env ..lues &,realer than one, ",hich accounted tor 70~ ot the

variance. The tint p r incipal COlDponent separated rainbow trout from rOftch

and squawfish. The second principal =mponent separated roach from prickly

sculpin, Itickleback, and to a le ..er eJttenl lucker. The final component

showed a positive a."ociation bet"'een squavfish and sucker and a nea-alive

aa.aciation at theee species vith roach !lJ1d stickleback.

The resultl obtained "";th density data diftered aome",hat. The analyaill

relJUlted in three principal cOlDponentll wbich exp1zlined 67~ of the variance

(Tabl" 7). The first principal component separated rainbow trout f r OID

thr~"plne stickleback and Sacralllento sucker in addition to 'qua",fiah and

J 36 rm.ch. The second principal component separ ated aqua"'fiah from all species e Icept roach. The third principal component s eparate d prickly Bculpin from

,ainbow trout and to a le sser extent roach and sucker.

Microhabitat Studies

Habitat UII"

In the South Fork Eel River, "'e tound si~nificant difference s in habitat use for a dult roach, , ainbo'" trout, Bnd Buckers. In the presence of squavfish, adult r oach use d run habitat less ofte n and used riffle !lnd pool hebitat more often. Juvenile trout and sucker s used pool habitat leas often and riffle habitat more often.

In the Van Duzen River, we found s i~nificant difference s in the availability of habitat types betv""n years, 190 v e did not compare habitat u"e directly. Instead we examine d c h anges in selection betveen y ears by comparing habitst us., of .,sch group to habitst availability uRin~ cbi-Rquare tests and comparlna: tb., r e sults betwee n years. I n 1987, all specie" groups u ,"ed habit"t in proportion to availability except juvenile suck.,rs, Which selected pool habitat. In 1989, whe n squswfish were present, juvenile suck.,rs used habitat in proportion t.o availability, a d ecrease in use of pools compared to 1987. Rainbow trout juve niles avoided pool habitat in 1989. Juvenile r oach selected pool habitst in 1989.

Microhabitat use

In the Soutb Fork Rei River, we found differences in microhabitat use be tween areas with a nd witbout IIqullwfillh for all species. In the Van Duzen

River, all species eIcept adult and juvenile rainbow trout exhibited differ snces between years. In the South Fork Eel River, sticklebacks and juvenile roach •

were found in .)"illa"'er ""ater in both h"bitat type_, .... h .. re aquawfiah "'ere

?reu:ll. The 811m .. relationship we .. observed [or adult roach in riffle/run

habit.!lt and juvenile lIuck'ns (pool and riftle/run hll.bit.'ltll combined). Theile

=lIUlts were lIupported by count. of fishes in quadrat. 11 IIh loeated at 25,

500, ,-"d 100 em. In the Van DU'I'en River, juvenile roach and juvenile lIuck ers

~re found in sh .. llov"r "'at"r in botb poOl. lind riffle/runa, when IIqua,.,.fiah

_r-e prellent. In the South Fork Eel River, juvenile luckerll, adult n:)IIch, and

ju,",enile rainbow trout were found at lIi&nilkantly rusher veiocitiu where

.qua,di.h "'ere pr!!lent, refiectinll' incrl!lIl1ed use of rif!!es. In the Van Duzen

River. adult roach in riffles uud lover veiocitil!lI "'hen Hquawfi.h "'en

~"t but the dilf".... n.::" was .mall lind the chana''' ....a" in the direction

expee:ed, baud On the small difference in availability of mean velocity. In

tlle South Fork Eel River, sticlr.leb!l.clr.s (pools only), juvenile rOllch, and adult

n.cb (ritfle/ r un only) were found closer to the eda-e of the IItream where

.....:a .. -:iah "'ere present.

Spatial overlaps

!n both Itreams, hi.h overlaps in microhabita t USe were mare common

vben squa"rfish "'ere absent. The chana-'" in IpatiaJ overlap amana- the

~. pairs reflected chana:es in hsbitat uSe. The 1ara:est declines in spatial

arerlap oecurred when one member of a pair Ihowed a stronl' habitat shift or

vt.e.. memberl at a pair exhibited opposite responses in the prelence of

~i.ah. For eumple. overlap of juvenile rainbow trout with juvenile roach

decHned for all variables In both streams because of the stronl' .hift of trout

!:ltD r1flea ...,hen Iqua"'filh "'ers present. ConVersely, the lara-elt increasel in

~ overlap oc<:urred when habitat use became more similar in the presence

d. IlqUSvfillh. For eltllmple, overlap in d epth increased tor juvenile luckera 38 and juvenile trout because both shifted into riffle/run in the presence of

IQuawfish. Species which primerily chanzed microhabit3t use within h"bita\s in the presence of IIQuawfiah, auch as juvenile r08.ch .. nd .. tickleb8ck in the

South Fo.k Eel Rive., exhibited the sm"Uest difference s.

ArtificW Stream Tank Experiments

Data on the sizes of pred"tors and prey, dates of trials, and ",ater temperatures for all the expe riments "re ziven in T"ble 8. The prese nce of sQuawtish had a "tronZ errect on ho", sm"U ro8ch, wze roach, a nd rainbow trout u s ed deep ",ate. in the single-prey triAls ( FI,lI= 129.0, P<0.OO1). AU prey r educed their use of deep "'a ter in the prellence of "Qua",fi"h (FiZ. 24 ).

Both sizes of roach used primarily edZe h"bitat when sQu"wtish were p.esent.

Rainbow trout used primarily riffle habitat.

Among tbe two lizes of ro8ch and r"inbow trout, the prey used deep water differently (FiZ. 24), independe nt or the prese nce of sQuaw!ish (F Ul= 6.7, P=0.OO5). Bonferroni comparisons indicated that juvenile roach used deep water ailtnificantiy less often than " dull roach (P

The analysis "'as complicate d by the extreme response ot juvenile ro8ch.

No rosch. use d deep water in the presence ot aQuawfish resultinlt in all valu e s being ° (i.e. no variance) tor this treatment level. Variances were equai amona' the other treatment Itroups (Bartlett's test, all l.8nka combined).

Subatitutina' a proportion corresponding to the presence of one fiah [or one at the zero values for e"ch t"nk (4 non-zero values) resulted in equal ""riances

"monS' all tre"tment levels (B"rtiett'll tellt, all tanks combined) and the effect or squewfieh r em"ined sia'nific"nt (F!.!,:: 93.0, P

Th r ~lIpine stickleback d id not .ho,", II "'''PO''''' to the pre• .,nce of

aqu.a"'filh (repeated measUrel ANOVA , aU P ) 0.05), Threeapine Itickleback

ued both pool habitat and edl'e habitat in r oue-hly equal proportion a .... hen

Iqua"'fiah .... ere elb ... "t (Fi&,. 2 ~ ) . When aquawfillh .... er e p resent there "'ttl an

iccr~ed t .. "de n"y to ulle pool habilJot but the difference "'II., not slll'nificant.

The pre • .,nce of IIqu ..wfish had " atron, effeet on the Ulle of deep .... ater

m the two-pr ey e"'periment for both large roach (FI.I=13.2, P=O.OO7) and

rainbow trout (F],,= 40.9, P

different f rom t hat obaerved in the one- prey expeI"imenta tor both prey

(p>Q.(5). As in the one-prey eXJH'rimena, roach ",aed edll'e habitat and

:-ainbo.... trout "'lIed rUOe habitat in the pre . enc e 01 aquawfi"h (Fi&,. 25 ).

All of the prey typea were <;onsumed by IIqullwfi6h In th .. artificial

str.. a m tanks. The m.... n number I!atl!n per tank vari.. d from 2.4 rainbo.... trout

In th" two-pr.. y experiml! nt to 4.5 Iar." roac h in th ...in&,ie-prey experiment

(table 9) . The total numbe r of lI,h conaumed In t h .. two-prey experiment was

nQt ai&,nilicantly diff"rl!nt from thl! numbl!r of prey con"umed in t he one-pre,.

I!xperim .. nts (one-"'a,. A."OVA P>0 .05, Table 9 ).

Al(e and G:rowth

The old ... t squawfish "'e collected "'.... ace 6 (T"ble 10). Bac k calcuiated ien&'ths for squawfiah collected from I!a ch site for each year ara vven .n

Appendu D. Ther e ",,,re "I'nificant differenc e. ,ullon&, areaa ",hen

beekcalculaled len&'th. at al'e "'ere compared. On e-year-Qld fish from the

So\Ilh Fork E .. l River "'e r e ai&'niflcantly Iar&, er than flah trom other areas of

th.. d r a.ina &,e . The difference bet... een un.a ...... no loo&,er apparent at s&, e 2. 40 No fish older than a&"e 3 were collect.. d from the South Fork Eel River.

Lar&"er fish were present but could not be collected by seininlt Or hook and

line. The lenltth frequency hilltoltram of squawfish observed durinz OUr

surveys of tbe South Fork Eel River indicates that Iarlter fi,h were reiali\'ely

rare (FiZ. 5I ). Dillerencea bet.... een area .. occurred a,ain at alte 4. Fish

collec ted b .. t .... "'''n the t .... o daOl. were h'r,er than fi,h from the Rice Fork Eel

River. This dilference ""all no lonlter apparent at aze .. 5 and S, but our

sample sizes were small.

F .... dinlt Habita

Feed!n&" habits varied zreatly amon, the spedes and to SOme extent

.... ithin specie.!! dependinz on Jo,;a.tion (Appendix E); ho.... ever, the 'peciea are relath'e!y euy to characterize. Calilor nia roach, and Sacramento sucker of a ll sizea con,umed primarily filamentoua alltae and diatoms in varyinlt proportions, with small aquatic insecta makin, up the remainder. There appeared to be a tendency for roach to include a hilrher proportion of insecta in the diet in the

Sprinz .... hen al,ae "'U reh.tjveiy rare. Sculpin. of both apede•• speckled dace, three'pine stickleback. small snd Iarlre rainbow trout {)Ioo mm SL), and aqus""fish <100 mm SL comrumed mostly insectll beloniln, to the orden

Ephemeropterll. Trichoplerll, Diptera. and Hemipter a. Thrll'e.pine stickleback

Wall the only apecies to COnSUme ei,niticllnt proportions of smllli Crustac"l1 such a!l dadocerans and os tracods. Larlre rainbow trout induded fro&",. tAdpoles. and small fish in the diet in amall p r oportiona. Pish appeared In the I diel of aquawfish 51-100 mm SL and became proeresaively lI'ore important In I larcer size dasaes. Crayfish .... ere importAnt in the diet of Iqu,wfish >200 mill SL in the river reach between Scott and Cape Horn Dalila "nd trolts and I I " ~dpol". '"'ere important in the Hi!;e Fork Eel River. Salmonid fi.h", '"'ere not an important item in the diet of aquawfish eollected durina: th" .ulllmer period.

In April 1989, "mall aqu"",fish 51-100 mID SL thllt were collected from 8 fiah rescue trap at Tomki Creek contained primarily s",.n ... lmcnids, but the hiZh concentration of f r y in the t r ap undoubtably IIl8de prey capture easier (Table

Ii in AppendL' E). Salmonids were en important item for IIqua'offish 51 111111 SL and lar"er (loa); at diet) in the ",,,instem Eel River at the confluence of Outlet

Creek in May 1989 IT,,bl,, 16 in Appendix E). The situation \oI1UI "specially inter .. ",tinr becaus.. the Outlet Creek water waa clear and the Eel River wllter

..... turbid cr.. aUn a: " turbidity gradient at the confluence. SevenoJ. of the aqulI."'1'ilh we collected ware located where the clear and turbid .... al.. r joined, indicatin&" that th.. y .... ere " hidinZ" in the tur bid .... ater and attackinz the

.a.\:!Ionid. as they approached.

Dietary similarity bet .... een llpe<;iell .... 1/11 zenerall)' 10.... lTable 11, lIimilarities calculated by location and time &re in Appendix F). The averaze

.imilllrity of the 204 comparieonll calculated .... all 0.25 (SD = 0.25) with a ranze of 0 to 1.0. Many of the.e aimilarities .... ere balled on dietary proportlona from very small llample. and should be interpreted with ctoution.

Similarity valuell llmonz lIize Clallllell of .qua.... n.h .... nl'ed from 0 to 1.0.

The similaritieB of 1.0 occurr.. d lit th .. Outl.. t Cre.. k .ite discuaaed abov .. , .... h .. n all of th.. Wl'er .qu.a....ti.ah .... e r .. feedinz on f ilh. Mean Iimilarity between .ize c ws... varied from 0, .... h .. n younl'-of-y.. ar .qua.... fi.h .... ere compared with larz.. r aize cialJsea, to 0.95. SimiJaritie. tended to be hil'her amonz th .. larl' .. r me claSiel.

Dietary similarity between juvenile rainbo.... t.rou.t and oth .. r llpeei... ranl'ed from 0.01 to 0.65. Th .. hi,helt mean similarity value. Wllre obtained tor stickleback and speckled dace. Similarity between juvenile rainbo.... trout"

and various size c1asaee at aquaw{iah ranled from 0 to 0.33. There .... er e tot'"

opportunities to ",eke trout-aquswfillh comparillClns because of the

complementary '&OI'r1lphic distributions of the t ....o "peciee.

t.arjl''' rainbo",' trout exhibited hil'her aimi\aritie. to IIqUAwfillh with

values rancinl' (rolD 0.03 to 0.60. The ran,,, of aimil.uitiell w !IS 0.01 to O.SO

whe n all comparisons we re con sidered. The hia:h"at overlaps (0. 43 and 0.601

occurred bet .... een lere" rainbow trout and IqU3",fi"h 51-100 mm SL. In the

first caBe the hi,h ovulsp ....a. caused by a hleh propor tion of unidentified

insects in the diet of both .p"'ciea in the South Fork Eel River. In the

second case, both ape';:!",,, h"d consumed " high proportion of fiah, trolts, snd

tadpole. in the Rice Fork Eel River (Tables 9 and 20 in Ap~ndix E).

Compar;'lOns yieldin. hi.b similaritiu occurred amon. the speciee

con:sumin. IarKe proportions 01 al.ae includin. sm.all and Jar,.e roach and

lar,.e and IImall .u~kers. Hi,.h overlap also oc~urred bet.... een eoa"tran.e &Dd

pri~kly sculpin (Table 11) which <;on"umed the .ame types of inlle<;11 when

t hey oc<;urnd torether.

Population Batiaaat.ea

The density oC tiah populations by number and biomass at eaeh . ite

varied acro .. yean, sometimes substantially (Table 12). We only di.cuss tbe

result. for rainbo... trout because trout oc<;urred .at all but one of the sa.ti

and were the principal llpec;je .. of interest in this part of the IItud".. A1->._ only diac:uas den.ity by number rather than biomasa. Biomaall III more liIu.l".

to hav" been infiuenc;ed by dilferinll' .rowth periods c;aulled by dit1'erences iD

.amplin,. dates between years. More detailed location inform"tion ean be fou.Dd. ,

in Fizure 1 Appendu A. Raw data, population estimates and confidence "

irlte:-vala for each station are contained in ~he Annual Reports.

Sitas on ~ID" _treams .howed II consi.tent pattern of chance in denility

01 rainbow trout. Rainbo.... trout populations in Grizzly Creek decre.aed from

1987 to 1988 then increased frolll 1988 to 1989 (Tables 12 and 13). Trout

population. declined durin,: both time periode for station. on Elder Cnek.

Population estimates from ltationl on Canoe Creek all incre8.8ed from 1987 to

1988 then d eclined from 1988 to 1989. Rainbow trout population "stimetea frolll

s tations on the Van Duzan River, South Pork Eel River and BuU Creek and ita

trIbul.arin '"'ere not a. conlisteot. Rainbo... trout population density declined

froID 1987 to 1988 in both the Van Duzan River and Soutb Fork Eel River.

Oo:nIit:y tben increaaed at 1 of 2 stations on the Van Ouzen River and at 2 of

3 ,lations on th~ SOl,l th ForI< E~l Riv~r. Popl,llation deneit)' increased at all

three nations on Bear Cree k from 1987 to 1988 and al.., increased at 2

stations from 1988 to 1989. The resulte from Sull Creek were much more

varied, ahO"";n, no overall pattern. There "'$01 no o v~rall .imilarlty in pattern

of fluctuation amon, Itreaml.

Tbe ov~rall trend in trout abundllne~ bllll beion downward deapite the

mixture of positive and n~'lItive eban,es in yearl,.. eomparilKlnl. Both ataUona

sampled aine~ 1986 hllv~ ahown net declinell from hi,hs in 1986. or the

atations sempled ..inee 1987, 14 Mve exhibited declines f rom 1987 value., 1 did

not ehan,.e, and 6 e:o:hibited net iner.. a.e.. The 4 ltationl sampJ~d for th~

!i:lt time in 1988 sho"'ed decline. in 1989.

The standard deviation of th~ d~nait,.. estimatea """ poBiUvel,. eor r elat~ d

""';th the me"n of denaity ~atimlltes at • lite (Pi,.. 26, r =O.62, P

:-elationlhip between the meSn and ltandard deviation ..,al also si,.nil;eant

L ______44 .... he" sites within II etre8m w" .... pooled {Fi". 21, .. =0.72, P

1988 (Tabl" 13); ho.... "ve,. thl! act1,1al chan".. in denaity of trout W8S only 0.16 , lieh/III" which is smaU .... than """'Y of the other chan"es tbat "'ere recorded

(Tabie 12J.

The variation amon" years waa .ubetantial. Por example, 95" confidence intervals constructed tor the atation vith the hiehest mean density (middle

Elder Creek), lowest mean denaity (upper Rice Fork Eel River), and an intermediate deneil)' Clower Elder Creek) were 11817-26579, 0-1073, and 0-20151

{Ish/hectar e , reapectively. Theee confidence Intervala cover a ranee of value. much "'ider than lhose actually obeerved (Table 13).

Combinine litel from the Ame stream did not have a laree e!teel on the

.landard deviation even thoul'h poolinl' increases the Ample size and mil'ht be e"peeled to ~duce the variance (Table 13 and Fla •. 26 and 27). However, pooling: aleo combine. .iles with ditfe~nt physical characteristics and thul d.iffe rent potential popu1elion sizes. The lack of chanl'e repre.ente s balance between these two factors, thoul'h in I'ener.. l sn Increase Or deerease are equally likely dependinlf On the characteristics of the sample Site,.

Rainbow trout density ws, significantly positive!,' cor~lat"d (P<0.05) with averll&'e width, averalfe d.epth, shade, boulder, and bedrock and neptlvely cor~lated with SIInd snd I'",vel. when all stationa ""ere included in • • 45 the anal"'''is. When aLations .... h ..re trout wer e not found .... e re excluded f rom

the dll.ta oet , the correlation ... ith avera,,, depth .... ".. no loncer . il"nificant. We

ealculated multiple recrellllion llIad"l. tor both set. ot data hilled on avenge

width, 8ver"I''' depth, maximUlD depth, Bhad .. , now, ... "tel' telllpe"'t"r e, BlInd,

erllve!, boulder, and bedrock. ~IDU!D depth, no.... , and water temper ature "'ere included because the simple correlation Bnaly,,;. mirhl not detect

important inte ractions amon&, variable.. that may be import.ant in th" mu ltiple

re&,realliona. The recre8llion lor aU date .... a ••ienitiesn t IF11,11 : 7.4, P

.... u the .. ",renion lor !lutionl with trout (F1f •., =6.8. P

The relre88ion equation. "'er e;

All .ite"

RT :: 695Z - 89(j'AW - 293'AD + 64ffD + 19'5H + Z16"f'L + 115'WT + 33'S _

68

Site .....ith trout anly

RT = 7044 - 100Z',AW - 327'AD + 70ffD + I1'SH + 246'FL + 188,WT + 4005 -

91«; + li3 'BO + 24713£

where AW;.avera,e .... idth, AD:averaa'e depth, MD=maximulll. depth, SB =ehade,

FL=fiaw, WT:: .... llter temperature, S=aand, G=c:ravel, BO=boulder , and BE= bedrock.

DISCUSSION

Diatribution and Abundance

Rainbo.... \.roI.It waa clearly the ~t wld""pread spoeiaa. Alt houc:h 1r Ol.lt

'Were p r esent at a Jar,e nUlDbe. of aitea the,. we. e often not ve.,. abundant.

The ne,,,tive correlation of rainbo'W trout abundance with the firlt principal

component (incI'elUin, atream orde. and the cor related variablea) of the t hr1!'f! I I

.el..l of physical variables (r ank, relative abundance, a nd denaity) indicates

that rain bow trout " ere the molt abundant fiah in smaller streama and hesd"ate r. o f the IarCer stresms. Thi. pattern was primarily due to hia-h

.... ater temperatures in the lo .... er rea<:hes of the streams. Tempersture9 often rea<:h levela stressful to trout a nd rea <:he d lethal l.. v .. 1s dur inc the hotter

period. of the s ummer (Kubi<:ek 197;). On 25 July 1988, we ob.erved It tar,-e die-off of trout in the South Fork Eel River above B.. nbow Re.er voir, The hl,he"t water temperature we meuured durina- the die-otf vas 28.s"C.

Kubi<:ek (l977) rated thi. area as reachln, temperature' lethal lor trout. ;;e observed Iara-e concentrations of trout in aprinI outno..... durin, this period.

The water temperature in one of these axe"",, was 27'C. We ob.erved similar lar,.e conc.. ntrations of fllh around th .. confluences of cooler t r ibutary Itreama or aprina- inflo.... 1 in other !U"eal durinI thi .. period. Similar behavior W!l.S noted in the North Fork Eel River and Black Butte River. A. "e sample-d farther d o .... n.tr eam from the cool head ....at erl trout be,.an to con,.repte around the confluencel! of tr ibutary stresllls a nd when poasible moved into the

factor innuencin&" the di.tribution of trout in th.. system,

We did not obse rve IarIe numbers of trout in the lower reachel 01 the msinstem Eel River, .... here they- .... ere obse rved by Brown (1980) in Aucu.t and Septemb.. r. Trout 01 a .. veral lize CIa8S .. S accounted for 10.8% of th .. !i.h.... h .. observed in snorkel survey, of th.. main.t .. m Eel Riv .. r belo.... Eel Rock, "'"e never encount.. red that h i&"h of a perCentaI" in the sam.. ar.. a, even when electro.hockin&" rittle., ""e a lto did not observe any trout around cool tributary intlows .... here they would be expected to eOna-reIate Civen the .... arm tempera tur" s, The discrepancy bet.... een the Btudies msy be due to aeveral factors. \" e may not have aampled the lame loc.. tionl or tYPei of habitat.

Our oblervations in 1989 .... ere conducted in a year of 10 .... flow lfl conjunction with leveral previO\la yearl ot low flow. The warmer temperature. earlier in the ye!lI" mey have affected tba behavior of the trout. The pre.. ence of lara-e aqual.'fiah in the pOOl' mar allO be a factor . Mlcroh.. bitat Itudie .. in the

Soutb Fork Sel River lind the Van Duzen River ( .. ea below) demonstrated tha t juvenile rainbow trout ail"nilicanlly decrea.. e their uae of pOOla when aqual.ofiah are preaent; ho... ..ver, larl"er aize clasae .. are unaffected. The a baence of wa-er aiza claSSei as .....11 as (i.. h .. mall enoua-h to be vulnerable to squa" ""!ish pr.. d ation aU l"l"ests that other factors !lI"e at leaat partially involved..

Tha fish fauna of e .. <:b of the !lUbdrainal"e .. "'''S unique trom the others

Crable 1). Th.. mainatem EeJ River waa mOl t diverse, containinlC 19 lpecies.

F.ve of these apecies ..... re found only in the ..stuary. Th.. ma.in .. tem Eel River d.rairuoa-.. also contain.. d the lara-.... t number ot introduced speciel includinl"

A:>erican Ihad, lireen sunfish, bro"",,, bullh.. ad, hluelill, ..nd wi"emouth baaa.

"!b .. occur renc .. of t he later t ... o speci.. s in the areas dov nltrellm of Pilliburr

Reser voir indie ..t e the rese r voir aa the IIOU r ee tor thue .. peclo~s. Green

....nfish and bravn buUbe.. d ... ere IIlOre ... idespread and hllva aatablished per!:lllJ1ent popui.. tions in .. everal are ..s.

The Van Duzen River and SO\Ith Fork Bel River both supported 10

.peci.. a of filh. Green !lUnfilh va .. the only introduced speci.1 pre.ent (South

Fork ~ l River only), other than rotIcb and Iqu..... fi.. h, The Van DWlen River

..... the only r iver ... here apeckled dace ..... pre .. ent, thoulih tbi .. "peeiel ..-ill likely continue to spread throulih a WI"" portion of the Eel River ..nd tributariel. The rewnder ot the apeeiel list ia Identical.

The rem.. inie, Itre.. m a vere ver y almilar in diver.. ily, containinl" 4 to 6 .. species. Chinook salmon "'as onl,. r~orded from the Middle Fork Eel RiVer and upper main.tern Eel River, slthouch all of the IItrel!l.m, except the Rice

Fork Eel River a re known to support populations of chinook n.lmon. DUpile the difference. in specie. lish, the ISIDe species tended to be abundant in all of the rivers. The cool head"",tel"R were dominated by rainbow trout. A, the weter ....ellled downstream. trout WeTe .. eplaced by California roach lind

Sacramento squllwfish. Sacramento sucker were present alon" ....-jth the roach and .qua .... ti.h but were not abundsnl except in the deep pools of the most downstream areas. In the most downnream areas, stickleback, prick),. SCl.llpin,

.. nd coastr"n.... SCUlpin a1ao oct:urred in sicniticant numbers.

Principal components anelysi. of species relative abundance" tended to empha.i:te relationship. between individu.l apeeles. thoulfh eo-oc:currin,

,roup. of apeeie. .... e .... alao identified (Table 6). The fint principal component indicated that rainbow trout .... ere ne,alively 51l1ociated ..n.th

California roach and Sacr.mento .qUll..... ti.h ••lthou,h the relationRhip ,..ith squ..... fj.h ..... 81 not as stron£". A strona-er relation.hip rna,. develop in the f uture all the dietribution of aquawfi.h continues to e.pand. These aRsociationa .... ere probablY a r esult of the dilferent temperature preferencea of the apecies. Temperature differencea have been Iho.... n to influence habitat selection in a similar California Rlream flah aasembla,e !BaH:t e t .1. 1987).

ROBch and aqu., ..fish tend to be more abundant .t .... armer temperaturea than trout. The second principal component indic.ted th.t prickly ""ulpin and atickleb.ck .... ere IItron,ly .nociated ..n.th each other and to a le"aer extent

.... ith sucker. This r elation.hip renect. the fact that all of the"e apc.eiel .... ere lI>Oat abundant in the downltream areaa. The"e "peeie. were n"lfatively aS90cialed ..... ith California roach. The third principal component described a •

49 ?Osit;v", relationll hip between Sacramento IIuc:ke .. and Sacra ..... nta squa w1iah, II

l"eS1.l1t of the tendency for the adults of the two .pee/es to inha bit lart.. poOls

in tbe lower river. The n",ative relationahip of California roach and

threespine stickleback with aqua"'!i.h and Bucker may indi""te the etl=ta of

squllw1i11h predation on theae species.

The reBults obtained vith denaity dftte were ditfel"ent in sever al way.

from the results obtained with .. ellltiv", abundan<;:eI /Table 7). The liut

principal component separ ated I;'llinbow trout from all of tbe other spedu

except prickly Hculpin which often occurred vith trout in the low elevatkm

tributary Itreams. All wilh the fir st component of the relative abundance

a.'Ullysis, this component 8tl"e86ell differin&' Ullponaell to temperature. Th"

RC<:lnd principal component separated .qua.... f!sh from all .pecie" except roBch.

Thia component probablY include" the ertecu of tempenture (trout) and

e J e~'ation (other apecie.,. Moat of the other .pede .... ere only preaent at

Io\.. er elevation. or .... ere mo.t abundant there. The third pr incipal component

sepanted prickly K:ulpin from roainbo .... trout and to a lesser edent roach and

. ucker. This component streaeee the dominance ot pr ickly sculpin in the

Iarze, .... arlD riffles of the mainstem.

The difference bet.... een the analyse. i. due to the different propertiea

of the dsta. Relative abundances muat .um to 1 110 • larZe percentaze of one

.pedes results in s."all percentares of the other species rere.rdle .. of the

actual numbera present. The density data sre independent amon& speciee but

are .ub,;ect to other erron such as incomplete count. Or unequlll ettorta

amon, counts. Despite these differences in data properties, the overall

penerns .... ere very similar, atressinr the effects of tempersture, .tream or der,

and elevation. ;0

The ranee of aquawfi"h i. continuin .. to expand in the Van Duzen River and South Fork Eel River. Squa",nah no" occupy the Van Duzen River an unknown dlatance above Brida-evill'" They...m prob.bly reach the barrier located jUlt above the South Fork V,,-" Duzen River within aeve",l yeara at

1II0gt. In the So... th Fork Eel River s cattered individuals ..... re present upstream to about Rattlesnak e Creek. Squ ...... ri.h ""ill probably reach the head"'!!t.. ,.. o f the South Fork Eel River in ...veral yell.rll. The ranr" of

.qUlO .... !illb in the Middle Fork Eel River h ... reached tbe baae ot the Osborne

Routh. and IIhould not expand farther upstream. On the mainatem Eel River it" rane" has r eached ita maximum. Further dispersal is prevented by the bllrri"r at Bloody Rock. Squawfillh have not invaded the Black Butte Rive .. Or the North Fork Eel River to !lny !lppreciable extent, even thou&"h there !Ire nO physiclll barrien to upstre!lm disperso!l!. Durin&" our survey.. , ... e noted th!lt lar&"e, d_p pools ... ere r are in both systems. Also, the iar&"er poola ,"'merally d id not have much COv ..r. It il po.. ible thst aqua"'1'iah that do attempt to inv!lde these areas can't lind sdequatll COVer to escape predators (e.&". ottera, mer&"ansen, herons). If appropriate habitat is mOl'" .vailabl.. durin&" ..... tter yean, aqua ... tish may eventually inv!lde theae stre...... durin&" yean of hi&"h rainfall. It is ai&"njJicant that iar&"e Sac ramento s ucken were Illao rare in the!!e atream!!. The habitat requirement' of the larl'a reproductive .dulU of these t wo species are similar; thus, thll low numben of sucker. in thelle atreams may indicRta thst squawfish will never become abundBnt iI thllY do eventulllly invRde theae stre!lms.

New RreaS CRn be colonized by either adult or Juvenile ,quawfi.h. The individuals we obaerved invading the Middle Fork Eel River were moat likely one-year-old fish. In the South Fork Eel River, We obaerved a iar&"e !ldult 51

. "I!:-al kilo::le tera upstream ot the nearest juvenile nsh. In the Van Duzan

Rlve:" an area of hi"h a:radient apparently neeeillitated inv.. ion by lar.". lb'. The d ominance of youna:-ol- year squ"""fiah in the middle reach at t he

~ I m'-er b et ....e n Ee l Rock and the confluence of the Middlll' Fork Eel River

a:>d the a pparent diapersal of adull. durin" the Sprina: mllY indicate tluot a

por tion of t he population i. mil'r&tina: to particular are.. _ to epawn. ,,'., know

tha t fia b mia-ra te out 01 Pillsbury Reservoir to apavn in the Ric .. Fork and

::>tinst,,!!! Eel River. Adult squlI.w!ish have also been obllerved leapina: at the

~ of Scott Dam apparently tryina: to lIIove I1pstrealll to apawn (Park Steine r,

per ... camlll. ). ~h . ther the fillh are r"turnin, to traditional. are". to epawn ia

uakno"'n bu t leelllS unlikely. The fiEh which invaded the upper Van Ouzen

Rive!' we re o b~;oualy reproduc tive aince younE-of-year were observed in the

invaded area. It seem!! more likely that ther!' is a gene ral upstream moveme nt o! fish to . pa.... n , followed by 0 downl'ltream moveme nt durin, whleh fi.h

dlatributa them!elves amon, oppropriate poole:. A portion of the population

.,robably .pawn. in the 10Clill area aa well aince youn,-ot-year, thou,h not alway. obundant, .eemed to be d!.tributed throuEhout the adult ran,e . The dO"'l!ltrealD lIIov ement ot adults seelDs likely becaule ot the rllrity of pools with .ood COVer. An alternative explanation !a that adulta move into the area to Sp""'n, lllay in the area, and lire then relDoved by predators from pools

"'hie h do not ofter adequate eover. The latter axplanation aeelDll Unlikely aine e "'ater depths are adequate tor .quawfiah to IDlErate all ,.ear and it s eema doubtfu l they would .tay in an area .... here predator rilk .... a. hi,h.

L.arEe sd .. lt IIquawti.h .... ere atill relatively rare in the IIK>IIt recently invaded a trelllDa , the South Fo rk Eel RiVer and Van Duzen River at the end of •

the study (FiC O>. 51 and 5J). Larc" adult fiah vill probobJy accumulate •• the"

population continue" to mature. Both .,.'le,,,. apPflar to contain adequate

habitat for larc" adu iu.

Adult .qu8\dish have not invaded the cooler, hilt! "r&di.. nt tributarje.!J

01 the main forks 01 the Eel River to • , reat extent, but may be ... ain&, IIOme

or the small, ",,,rm tributariu for IIpewninr. Our permanent electrotlhockinll'

sites on Grizzly Creek In the Van Dunn River drainlll'e , and Canoe Creek in

the South Fork Eel River drain""" ~tiU do not contain Iqu• .....tillh. 10'" aL.o did

not o baer ve squ8wtiah in the tributariu to the m.!linstem of the Eel Ri ver

between PiUsbury a nd Van Andale Ruervoira or in the tributaries to the

lower mainstew Eel River around Scotia. Theee cool, lower order streams .~

thoe-.. in which ralnbo..... trout we r e the dominant fiah . Squawtish invadad Bull

Creek in 1990 after our atud y e nded (Brown and Moyla, unpublished data).

I'e alao fou nd juvenile squawfiah in Williams Creek a tributary to the Middle

Fork Eel River !l.nd younl-of-yeZl.I' were abundllnl in Tomki Creek, a tributary

to the mamstem Eel River below Va n Aradale Reservoir (SEC 1987). Younl'-o!­

ye ar Iquawfiah we re also pre"ent in Blue Rock Cref!k, Jewett Creek and

BurZe r Creek which are tributariel to the mainatem Eel River in the area

be tween Alderpoint and Dol Rios. Larle numbers o! younl'-of- year .quawfish

bave alltO been reportad from Dean Creek in the South Fork Eel Rival"

dnlinale (Scott Downie, pers. comm.). All of theae c reeke are warm, low

Zradient, otten intermittent durinz the aummer, and do not provide I'ood

habitat tor younz Iteelhead. The continued failure ot squaw1ish to invad e the

cooler Eel Riv e r tributaries between Van M sdllle and Pillsbur y :Re...,rvoir l

"ince their appeZl.I'ance In 1981 a nd 1982 (SEC 1987, 1988, 1989, 1990), su"nia

that this trend may hold over time throul'hout the Eel River dreillaze. I Kicruhabltat Studie..

Tb~ prelence of Iqua>or(i ..h had • definite e ffect on the habitat and

microh.bitat Ule of the "Slident {;shu. All apedes 1l: e-c;Ia.ll,u'l! e:o;cep~ .IIdult

rllinbo.... trout .... hicb were too Wire to be eaten by squ.ll .... fi.h exhibited

diffe r ence.ll in h.llbit.at or microhabitat use bet.... een yeara (V. n DUllen River) or arelUl (South Fork Eel River ). For juvenile rllinbow trout .nd juvenile lucker ,

th.. microhsbitat shiftl .... ere very clear. In area s .... here Iqua.. ofiah we r e

pr.. s ent, these speciel! uled pool habita~ len often. Roach juveniles .nd adulh, lltickleback, and l u c ker juvenilel all uhibiled microhahitat .hiltl .... hen

Iqua.. ofilh .... ere p r ellent. Juvenile roach, ltickle back, and lucke:- moved Inl.o

Ihallower water whe n Iquawfisb were preaen!.

Th~ ditterem:e8 in the r .... ponee. of [iehes to Iqulwfi.. h bet.... een the Vlln

Duzen River and Soutb Fork Eel River mill' be due to differencel in habitat structure .nd recentne.. ot inva.. ion. At the South Fork Eel River lite,

juvenile rainbow trout and .uckers were complelely abient trom pools .... her"

SqU8wtilh .... ere present, .... hile in th .. Van Duzen River, th~:r wer .. found in

.. educed numb.. rs in "hallo.... are.. ". Th~ pooll in the Van Duzen River "' ~re much more h ..teroir .. nou., with boulder COver pr...... n! in IIOme Iballow .real.

AlIIO, th ~ deep water uled by adult .qu.wfi8h con8lllted or i.olated pocketa around boulder and b~drock o utcrop., thul Jar.:.. ar.. aa of the pool. were probably not e88ily acc~ •• ible to .qu.wfilh. In .ddition, the Van Outen River

. tudy wal conducted. durin.: the firlt .um ... e .. aquawfilh were pr""ent at the lite, whlle the South Fork Eel River wa. oecupied a mlnl/ll.um DIone lull yesr before the Itudy and had probably been oc:eupied tor aeveral year,.. Thu I, more lub8tantial differencea may .till d evelop in the Van DU%en River.

The maa-n.itude of the reapon.e to aquawfilb ""a. 8iz.e nltaled. Adult I

rainbow trout did no t .ho.... any difference. in hllbit..!lt or mlcrohllbitat u.e in " the preaence of .qu..... filh. We often sa.... adult trout .choolinC .... ith .qua""ri.h of .imilar size. Adult roIlch (South Fork Eel River oniy) and juvenile rainbo... , trout .... ere similar in lize (50-120 111111 SL) and both inereased their ule ot lhallower and/or .witter .... ea. in the p reRnee of .qua... · fi.h. The amalle l t fish es, juvenile roach, juvenile suckeCG and threeapine aticklebackl (in the

Sout h Fork Eel River only) all exhibited diffeceneel in u.e of microhabit..!lt,

Ulin&" .hallow, ed&"e h.bitat mOre often in the preaence of squs .... fi.h.

Althou&"h size wSll dearly s factor In!luencin&" the re.ponae to

.qua .... !iah, .... e also oblecved 'pec:iel .pecific difference.. The IIIOlt eztcelrle d iffer ence. in hllbil.at and/or mieroh .. bitat use occurred in stickleb"ckl, juven ile suekers, .. n d juvenile rainbow trout, l u&"Ce stin&" thllt these 'peciel were 1II0st vulnerable to predation. Other I tudie. auppoet thie hypothesis for stick lebaeks and suekers. Smith (1982) obaer ved that lhre-eapine aticklebllCkl and .qua .... !i.h .... e re not found to&"eth er in pool. In the absence of he.vy cover

.. nd suc&"e sted t hat the .tiekle baeks .... era eliminated from open pooll by

Iquawfl.h predatio n. Schiosaer (19871 found that juvenile whila sue kel"ll

(Cato"tomu. eommer lonl), which ace extremely limilar to Sacramento eueke r. in baha'·'o r and morphoio&"y , .... ere the IIIOst lu.ceptible fi.h to predation by

.mallmoulh bus (Micropterus dolomieuil at any be teated. In the Eel River, the local populstiona of sticklebacks, euckere and trout may be eepacially vulnerable to predation bee.. uae the,. have not e:q>erienced equaw1i.ah, or any other freehwater piacivoroue fiRh, in their r e cent evolutionary history. The diatr ibutions of theae epeei" BUCC est that they may have low avoidanc e of

.qua.... fillh and that the eurvivo... just happen to be li vinjf in are....

Ina cce~eible to the predators. In the preeence of equaw1i.h, we found " juvenile rainbow trout restricted almost exclusively to riffl.. s, the only habltllt ty;>e not used exten.i""ly by adult aquawfiah. In Van Duzen River pools,

!arlle sql.lswfiah used depths >50 em .....bieb corresponds to the greatest depth .. uud by juvenile suckers_ In the South Fork Eel River, adult aqua'-'flah used depths >70 em, which ",a. the upper limit of depths .. t which we observed

.tic:klebac ks_

In the ahsence of squawfiah, the fiahes of the Eel Rivltr show wide overlap in their use of "pace, .. uentiall:y rao&,inl' throl.l&h all habit.llta. Larl'e numbers of trout, stickleback, sucken and roach can be ob.erved ..... im min.: lI.!ld foraa"inl' throurhout the pools and riffl.... In the presence of squawfish, these fishes are found primarily in riffle. or along pool edl'eI, .... here they have reduced overlap. in their use ot microhabitat space. Thus, the presence of .qua.... rl.h reduces the amount of habitat .vailable to .maller n.hes .

...·hether this .... ill affect production of Iteelhead in the Eel River drainace depends on the effect the reduction in habitat area hal on production of l+ and older trout ..... hlch account for the createst return of adulta. The overall effeet of 3qua .... {ish will alao depend on the ilJlportance of tributarlee in tbe production 01 trout in compari.on to the ma.in.tream are...... here .qua...-fiah and trout CO-OCCur. Even in the arel!la .... h ..re they co-occur, the lJI.a.inatr"am ar.... can .till act a. nuraery area. for y ..arlinc and older fiah. The production of theae main.tream area. ... ill depend on the aurvival of younc-ol­ year fiah in th" tributariel and riffle areas.

Artificial Stream Ta.ak Brperimenl8

There .... ere dit!erenc". amonc the specie" in r""ponge to the pr".encB of .qua... flah in the artificial Itrlllllll; however, the fj,,}d !'lata lu&"cealed that 56

the introduced roach responded to the presence of .qu...... n"h much lua

dramatically than the netive ruident li.he. inciudinlC thrHaplne Itickleback,

juvenile rainbow trout, and juvenile SacrlllDento suckers. The .".~riment.al

data indicates that both }aI'S"" and BI:".n roech .... sponded ,lronlr1y to the

presence of squB",fish. in artificial atreams, ". did juvenile r ll.inbow trout.

Three.pine stickleback exhibited larl"e differences in microhabitat \,III!! in th"

field in the p r .....nce of aquB,dish, but showed nO respon.e to the pre.. ence o!

IIqul!I,..tish in the experimental situation. ThUll, the field and ellperimental

results appear to provide conflictinr information eoncernin;: the effect of the

pre.ence of aqua,dish on the behavior of the r"aident fishes.

Both California roach lind Sacramento .qua.... fi.h were introd\lced from

the S.cr.mento-San Joaq\lin draina ,e where they h.ve .hared a lon,

evol\ll;onary hillOry (Moyle 1976), It .eem. likely tha t over evolutionary time,

roach wO\lld develop the ability to lUae.s the de,ree of threat po.ed by

.qUllwfillh in pllrticular ,aituations and thus develop behaviors that would

decrelllle their v\l!nerability to attack by .q\lllwfis h, compar ed to fishel from

sYlltems that did not include .quawfiah, Geo,raphic variation in behavioral

response, to predatora amon, pop ulationa of II ,in,le apeciu have been found

that coincide with differences in p redation pressure (Se,hers 1974, GUn and

HunUnvord 1984 , Fraser and GUliam 1987), The .tron, ef:ect of Iquswn.h on

habitat 1,1." by roach in the experiments Wall. probably due 10 th" stron, thr eat poe"d by the .quawfiah in the eonfined ap"'ce of the e:r;periiDental

atreams, The confined nature of the Itream. lIIi,ht alec have _de elcape

behaviorl lei. effeetiv", placin, the e"lphalil on avoidance behavior s. The

ability to a811.e81 predation riak and adjuat behavior acco...:!in,ly hall. been

esta1:liahed for a number of fiahea (Cerd and Fruer 1983, Milln.lli and SaUer - I

57

1978, FrllBer and Iluntinl"!ord 1986). In the field .... h .. re eq\la.,tfiah are 1II0ce

.w.per."d and the thnat to an individual prey reduced, the emphui. llIay

IIl:U!t to... ard utili~in, a. much of the habitat as pcBSible resultlnl[ in the lesl

d.."lO-Cl8tic diffl!~nces obaerved In the field.

LarKe roach consiatently uaed ahallo.... ed,e habitat in the atream tanh

.... hen aqui!I,... rlsh "'ere pr.. sent but n.rely did ItO in the field. The difference

bet.... ~n the field and e)[pe rimentai responses is probably the r"sult of the

p~."nce of fuh-eat!n, bird. in the field, particulM-ly heron., "creta and

lrinr-i.hers. Lar,.. roach and (",he. COlllparable in II;ZI! are bia:bly vulne:-eble

to ,rest blue her-ona lArd .. " herodi... ) In .hallow edCI! habitat (Bra_her and

Brown, unpublillhed data). In the elre8m tanks, the hardware cloth lids and

_nllec""n may have been perceived a. overhead cover from bird pre

re...,ltina: in the unexpected habitat ehift.

Threesplne .ticklebllCk did not .ho... a r .... pons.. to .qua1odl.h in the

erpe"';.!!Ien!.al. tank.. TheB.. ",suit.. are tome... hal mialead;nl' beocause the !i.h

that utili z ~d pool habitat when aquawfilh ... ere prea,mt ... ere often obllerved

bo'o'erina: clo.e to the scre.. ns separatinl' the d~p and IIhallow compartment.

(A. Brasher, perianal observation ). Ho ... ever, it ie clear that stickleback ... eu

Ie•• re.ponsive to the presence of aquawfish in the e xperimental tanka than

roach or trout. Thus, it appears that atickleback mal" be the iDOIIt vuln.. rable

of the prey tested. Smith (1982) noted that stickleback and .qua""fi.h ..... r ..

onl:r found tol'.. ther In poolll ""ith denae cover. Stickleback ... ere absent from

pool. wher.. aquawfi.h were prellent and cov.. r ... as "pal"'"' Thua, the larl'e

ehanl'eS in microhabitat Ulle noted in the field .. tudy IIlaY have been due, in

80me part, to removal of stickleback b:r .quawfish, rather than behaviorel

response,. of tha prey. Previous IItudia& have demonstrated the ahility of 58

Btiekleback to adjust behavior in response to p~dato ra (Milinaki and Heller

1978, Gile ~ ,md Huntlngford 1984, Frailer lind Iluntingford 1986). However, aticklebacka .... hich have not previously experienced predatory fiahea beeome

habituated to their preaence {Huntingford and Coulter 1989) and would be

hirhly vulnerable until obt.aininr enourh experience to avoid the predator.

Perhapa the stickleback~ which avoided the initial pradation epiaode were

better able to aaaeas the threat of predation in the presence of Iqullwfish in

subaequent encounten and adjullted habilat \lSe accordingly.

Juvenile rainbow trout shO'Wed the same r e sponse to the presence of

Iquawli"h in the lield lind in the experimental IItrell"'s. increalling their utilj"ation of riffiel whe n sq\lllwli'h were prellent. Rainbow trout wera the only prey to elthlbit similar patterna in both lIituationa. Since Eel River rainbow trout have not had previous experience with IIquawfish, we would eltpect the reaults for trout to be 8imilar to tholle for sticklebllck; however, this u.pectation ignore!! the selective prellures which OCCur durin,J the ocean dwelling pha~e of this species. Considering the rlln,e of predatora lacing juvenile steelhead rainbow trout in the ocean environment, a IItron, reaponae to larger fishel 'eft",a likely_

The reaulta of the two-prey eltperimenta aU,J,Jllltad that neither roach nor trout strongly &flected hahitat selection by the other. Thia indicate" t hat competition for apace aman,J these two fishes ia not an important interaction, at lealt In the .hort term. ThuI, the prelence of roach does not &fleet lurvival of rainbow trout when ~quawfi.h Invade an area. In effect, it appeara thet the two prey .~ie. re.ponded independently to the invasion a! the predator, rather than the invaJ'lion tri,J,Jerina- a aerie. of interactive rellpon,es_ Longer-term studiea u.in,J lingle- and multi-llpecies triall are 59 need ed to address this question for this a nd other prey combinations.

In summary, the changes in hs bitat a nd microhabitat use obssrved for juvenile r ainbow trout a nd large a nd 11"",11 roach we r e the r!!!lult in chanK' e ~ in b e ha ~-jor. Th .. change s observe d for th " ""spine stickleback 1D8y be due to

:, .. 11>0,'.1 of s tickleback rather than chanlre s in b ehavior. We did not collec t data On juvenile suckers, 110 the nature of t h eir response is unknown. It seems likely that stickle back will be the s pecies mOl!t affe cted by the in t :,oduction of squlI ",·fish.

A&:I! and Growth

The backcalculate d lengths a t . iC" for Eel Riv e r squawfi8h feU well within the ranI''' of value s found for Sacramento River drainage populations

{Br o",n 1990). Thus, the r e is no "" ide ne" that squs,..fi"h were growinll" raster or lar ger in the Eel River d raimlll'e . The larger size at age 1 in the South

Fork Eel Riv e r compared to other areas of the dra inllge luggests that young­ of- yea r fish in ne wly e stllblished popUlations IIl8y grow faste r than in more

IIl8ture popula tions. Howeve r, the difference di,.,.ppeared hy a g e 2 sho'.ring t ha t whate ver advantall'e may e xist does not exte nd 8crooo ..n "lI'e s. At 8i'e 4 s q uawfish from the Rice Fork Ee l Riv er we re .. maller than those f rom the re!lch b etween the d!lms but this difference disappeared a t a g e 5. The lack of consistent diffe r e nce s in le ngth at age among t h e differe nt areas indicstes t hat condition... for growth 8re relatively aimila r t hroughout the drainal(e.

Feeding liabits

The feeding habit ... of .. qu8 .... !ish in t he Eel River drain8ge are "imils,. to t hoie of squ!l .... fis h from the Sacramento River draina ge. In Bear Cre ek "

60 (Sacramento drainage), squavfish beil'"n consuming fllfh at 51-100 mm SL and

fish made up more than 50"' of the die t in squawfish 101- 150 mm SL (Brown

1990). This Bam e pattern was evident in the Eel River draim.&,e (Appendix EI.

The Eel River results were some.... hat unusual because of the consumption o!

lamprey ammocoet.. s. frogs and tadpoles. These items have not been re<:orded

in "tudi"s 01 squ"wfish feeding from other areal!

The potential for competition for rood between squ8wfi8h IlrId rainbow

trout see ms r e18tiv.,ly low. Juvenile trout showed hill"her similarity to

speckled dace and stickleback than smali equawfieh. Larger trout showed

r e mtiv.. ly high'similB.rity to squawfish on " couple ot occasions but iltrge trout

are r e latively rare in the drain"e" b""8uoe of the anadro!!>oull natur e of the

population. Also, the sep..ration of rainbow trout and squawfiBh on the basi..

of physical habitat te nds to keep interactions bctw.... n the two species to a minimu!!>. FinaUy, there ia no evidence that food i8 a limiting factor in the I a ystem.

Squawfish do eat salmonids when they have the opportunity, auch as I durin&" the sprini\" outmii\"ration. A.l80, aquaw!ish do consume .. almonida dUring I the Hummer in the area between Pillsbury Reaervoir and Van Arsdale Reservoir (P. Ste iner, pers. comm.). It 8eemS po8sible that the hi&"h 1088 of marke d I amolts between Van Ar8dale and Outlet Creek noted during outmigrant studies

by Steiner Environmental Consultantll (SEC 1987, 1988, 1989) ill at least I p..rtially due to squawfillh predation. The potential for 10Bses to squaw!illh I predation i8 higbellt in the ..rell downstream of Pillsbury Re8ervoir. The!irea between the dams a ppears to support a large population ot predator)' I squawrish as dot!s the area directly downstream ot Van Aradale Reservoir.

The area be tween the dama is the one ..rea in the drainage where large I I I I 61 tw:::!;)erl of predatory aqu,.,.,fiah CO-OCC1.Ir wit h abundant j uvenile salmonid •.

AJ.o. dO'lolnltru.m mi~rll.tion of I mo1t. from this II.rea e J;tend8 ",eU into the

...rin~ '.;hen the "'8ter i .. warm and clear, conditionll whi"h "'Quid ravor

equewfilh predation.

Populatiol> B.timat.ea

The overall tre nd Wll8 de.:!"ea!"in&, abundance at trout Over the course of

0t,1!" study. This overall decline W88 probably linked vith the d r ou&'ht

C'Qnditionl which exillted throu&"hout our study period. The numbers we

o baen'ed probably r epeelent 10"'- population levels and incr .."""" a r e likely in

wetter years. The trout popul..tiona in the differe nt Itr " .. ",... tudied did not

!luctust.. in .. conaistent pattern serau .treemll. Thr. lack of coordination i.

DOt really Burpris;n&, .-iven the d ifferent physical. characteristics and locat ion.

o! the study streams. The tact that situ within utream. tended to re.pon d in

parallel indicated th8t within II stream, the population tended to r eact to t h e

e nvl.."'Onm ent in the SlIme way at difterent site.. The dltterent responaes of

sites within stresms, in some c ases, implies that multiple .ite. are required to

adequately monitor chflnl"ea In fish population',

The standard deviation ot d e n51ty wa, sil"nifica.ntly and positively

correlated with the mean. Thus, wIe populations n uctuated more than .mall

pop ulationa. Thi. aUl"l"eau t hat it will be harder to detect .i&"nificant chanl"'"

in iar&"" populations b"cause of naturally hl&"h v .... iabllity. This could be

especially impor18nt when attemptin&" to a ..ells chanI'" in population. due to

human induced chanl"ea .uch a. habi18t improvement proje<;ts. PoolinI _mple

lit"s within streams t ailed to decrease t he variance due to the ofhettln&"

eftects or increasinll" ssmple siz"" and combinin&" sl.8tions with differe nt mesn 62

population ai:.u. po.nb},. due to different ph:rsical condition.. The use of

aamplin&, ~tr.te.lies that stratify .... mpHn. by h"bi~t type" (e .•. pool, riffle,

run) rather than by representative r .. ache. can reduce thi" t)"pe at varu.billty

(Hankin 1985). Thea.. """"'plinl' .tr"te~e" aleC> avoid problem. caueed 0,.

chane;n&, phy.ieal conditions within representative reach site". The IarZe

variation. between l'e""8 indicate that \onl' time aeries ",ill be n"c"Slary to

a<::curalely ....us chan.". in trou.t poP\llationa.

Multiple .. " ...eulon ana]ya"s explained le8" than SOX of the vllrianc!! In

the population data on th" baai" of the physleal variabl... mealured. Thus,

these measUrement" have limited predictive value. Thi. "'a. not really

surprl,ln. sinc:e the s uitability of " stream tor rainbow trout i" pro~bly 1II0rl!

a fundlon of habitat condition. durin, the .p".... ninr aeaaon and dllrln, the

pre~·iou. "everaJ months of the rearinr period than of condition. on •

particular d.y. We uSllally ."lIlpJed Ollr !lites in late Septelllber after the

hottest .... eather .... a. over ..nd several tim .. s .... e BlllIlpled dllrin, rainy period a

.... hen temper.. tllre15 "'ere .ubstantially lo"'er than normal for tha time of ,.ear.

Thua, Our measurement. ot ...... ter temperature and fio'" "'ere not

repressntalive of earlier condition". Lonr term environmental IlIOnitorinr

,hollid be ineluded in future "tudie. 110 the relation.hips bet"'''n rainbo",

trout popul.. tiona and environlllentai chanee15 can be more IICClIretelT useaaed.

MANAGEMENT RBCOMKBNDATIONS

Be<:au8e the aqu.. ",fi.h is no'" .... idely distriblltsd in the drainare and Itl

ranre is still eXp"ndln&" It ..... m. extrem.. ly lInlikel,. that sqWlwfah control

.... ithin th.. Eel River d r aina&,e would be economically feaaible or effective for

the dralnaI" ss .. ",hole. Control m..... ures that ..r .. not seleclive fo r

• 63 IqulI",-fisb could .!fect other fiab populations that ace economicall,. valuable,

lIu.;1I .. II juvenile ateelhe8d lind American shad. Control aftach could alea affect llpe<'iell .ueh II. Sacramento suckeu and Calilornia roach tbat fo<"'" part of the tor",,, baSil tor birds, Buch .1 &,reat blue herons lind alpre,.., Or

aaamma!s, such as otters. These ponibJe communit y level ettecta indkste lh.t

II drainsge wide squllwfiah control proi:ram 11111.1 not be anvironment.ally feasible. \o"ilbin these major eonltrainl., our atudiea 8U"IISt the follo";I'I':

1. The mOllt dtective .... ay to promote production of steelbead ia to

emphasize the ditlerences in ph,..iclIl habitat preferred by trout and

Iqua",fiah. The availability of ,mall. cold, tributarl' atrefUII habitat

.hould be Increased throua:h stream :-...locatlon and habitat improvement.

2. Control ot adult 'qulI.wfi.h mi.ht be uaeful in the limited area bet.... een

Pill, bury Reservoir and Van Msdale Reaer'VQir. The density of wee

Iqua",fiah appeara t.o be especially high in this erea and th.. area

bet .... een the daws hss traditionally been important rearinlt habitat tor

juvenile uaeihesd. Squawfish control in the are" do.... n.trell1ll at Van

Ar.dale t.o Outlet Creek wight be useful in increa.lnl" aurvival ot

outmil"rant., thoulth without data on lo.aes due t.o predation r daUv" to

olher factors auch aa thermal stnu and di.seaae an objective deei.ion

I.n't poaaible. Ellort. could be reatricted to .pot treatment. 01 haavily

utili:ted pools in the Van Aradale to Outlet Creek area. Further atudie!

are nllce."ary to dalllrmine if Iqu.w1ish pr edation rate. on wmon

slllOlta and .teelhead juvenilea and amolta are hia-h enoul"b to make

squawfi.h control delllr8ble. 11 the traditional chemical treatment ,",ith

rotenone ....a. used, treatment ,",ould also result In the lola at leveral

:rear clanel 01 steelhead. 3. Monitorin. studies or evaluations of habitat improvements which utili:ce

population estimates from e1ectronshin&, stations abould include multip le

site... &bitat related variance can be r educed by Ullin. habitat

aamplin&' methodoloeiel. Lone term environmental monitorin&, should be

included a .. part 01 ion&, term atudle... Lon&, time .eriel will be

necessary to dtsUn&"ullh natural nuet_lionll from human induced

nUctuationa, except in the caSe of edreme dlaturbances.

SUMMARY

We eurveyed the Iiahel pre,ent tbrouehoul the Eel River drainaJ:e.

Rainbow trout "'as the most "";de.pre!ld .pecies in the .urvey.. Rainbo....

"'ere !DOlt abundant in cool, hl&"h &radient. 10'" order streams. ~orn.ia roach, Sacr amento Sucker, thr eespine stickleback, and Sacralllento .qu a....-f"aJo

.... ere moat abundant in "'arlller, 10'" cradient, hi&h order atreaml. DlverlC!J' of the lisb s ..emb la&e. varied bet.... ""n riven. The mainstelll Eel River .....

1II0st diver.e (19 species, becsuse 01 the presence 01 estuarine and non­ ealitornia Insh ..... ter fishes. The Vsn Duzen River and South Fork Eel Rive were next in diversity (10 species). The Middle Fork Eel River, North For k

Eel River, Black BUUe River, snd Rice Fork Eel River were least diverse ..;t!t only 4 to 6 species obaerved. Principal cOlllponents &na.I.yaia 01 apecie. relative abundances and denlities both Btre.. ed the importance of ph,.a<.cal conditiona, particular!,. telllperature , in determinine the distribution of ",.;._

Rainbow trout "'ere meet cOlllman in cool headwater and tributaI",. .trealllB and the other specie" were mor e common in the lar&er, warlller, dOW1\lt~ac:t ...­ ot the rivers.

The rsn&,e ot squs"'filh continued to expend in the Eel River drainal'e •

65 over t he course or our atudy, primarily in the Van Duzen River and Soutb

Fork Eel River. Barriers have halted tbe upslream movement of aquawfiah in

the upper mainst.em Eel River draim'&,e and Middle Fork Eel River drains&"e.

The North Fork Eel River and Black Butte River have not been colonized to

any .il:nificant edent. This rna,. be due to the rarity of appropriate h ... bit.t. There ""ere no apparent barl'iers to invasion. Squaw!iah may atill invade

these streams it hleh !lows durin&" wet years increan the availability of

appropriate habitat. Squswfish have etill not invaded the cool, hia'h gradient

tributary streama where lara''' numbers of youn&" steelhead ov"numm"r ;

thou,h, the in vasion of such tributaries may still occur. However, eve" in

areas where squawfillh have been abundant l or H"veral :yearll, they hllve not

colonized the.e t:ypes of IItream.. Youn&"-of-year ~q\lawfillh were prellent in

some tr ibutaries that wer e too warm to provide &"ood tro\lt hahltat.

Microhabitat studiu II howed that sq\lawfiah affected both the habitat

and microhabitat \lSe of the .... Iilident fishe.. J\lvenile rainbo.... tro\ll and

suckers \l"ed pool habitat less often when aq\lawfish were pre.ent. J\lvenile

roach, stickleback and j\lvenile a\lckera \lIed 8haUower water when Iq\lawtish

were present. Whe n aq\lawfish were present, rucbe overlap. fo r the vario\l.

microhabitat veriable. &"enerally declined. Thu&, the presence of IIQ\lalodlsh

re.\l!led in ,realer _,re,stion amon, the member. of the fish aaaembla&"e.

Experiment. in ertifidal Itre"", tanka indicated that the chan,es in habitat

and llOicrohabitat ule o bserved for roeeh and juvenile rainbow trout were the

rel\llt of .tron .. behaviorel rellpon8e8 to the presence of aquawfi8h.

Threelpine stickleback did nat ahow a lIi,nitic:ant behavioral re8ponlle to the

pre,enee of IIquawfilh indicatin, that the obeerved chanles in habitat and

mlcrghabitat ulle wer e the result of removal of sticklebacks by the predator. -_. " Life history charactenstic" of "qu"wfiah lrom the Eel River draina ..e

.... ere lilllllar to thoae of Iqua""fi.. h from the SacMlmento River draine .. e.

Backcalculated len .. th at a ..e of squawfiBh from t he Eel River drllina.. e .... ere

""ithin the ran .. e observed in the Sacramento River dralna ..e. Feedln .. habit~ of .qua .... lI.h from the Eel River draina.. e .... ere .imilar to thoee of equawfish from the Sacramento River draina,e. Squawfish from the Eal River be,an consulllin ...mall fish at a size of 51-100 mill SL and fiah became the dominant item in the diet at 101-150 eUII SL. The posaibility of competition tor food bet""een squs",ofiah and juvenile sleelhelld is unlikely, civen the 10"" dle~ry

.imihrities ob~ined tor IIIOSt comparisons. Squawfish did consume IJIIlmonldl durin .. the aprin, outmi,ration period. The potential tor li,nificant pradatory effectt of Iqua""fi.9h on aalmonid .. is hl,heat durin.. the outmi.. r ation period and in the area bet""een Pillsbury Reaervoir and Van Aradale Re.ervoir .... here hu .. e populations of adult squawfiah and juvenile steelhead co-occur.

Density by nUlllber of rainbo.... trout nuctuated from year to year. The

.. ~ndard deviation. of mesn trout den .. itie. within sites and within streams were Jar,e and there ""atI a po,,'t"'e correlation het""een the mean and tha standard deviation. Thul, lar ..e populatlonl ""e .... IIIOre variable than slllall populationa. The ma .. nllude of variation lu .... est. that only very 8'Ubs~ntial chan.. e" in reaponle to hUllllln lIIanipulaUons ""ill he detectable. The p"ttern of chan ..e ""118 con.. iatent acro.. " .. tations in some atreaml but not in other".

The pattern of incre".e. "nd declines .... a. not conlli.tant across IItreama.

Over tbe four year .. of our .. tudy the I'eneral trend ha' been one of decline in trout nUlllbers. Thl... eneral decline ia likely .... lated. to the consistently

10 .... rainfall totals Over the COurae of tha study. Tbe nUlllbere we observed probably represent 10 .... populations for the.e stream. and incre""e. may occur ,; in "" .. Her years.

The physical variablu colle<:ted durin&" the ele-c:troliahina: -.mplinr "'ere

not IItron, predictors of trout abundance. Multiple rel're ••ion models based

On these variables explained I..... than 50" of the vlIl"ience in trout d eneity.

Includina: '"ariables important duMna: the IIpawnina: season and durin .. the bot

SUmmer month .. would improve predictability_ Lon& term envir onmental

monitorin&", use of habitat epecitic MmpUn&, methodolo.. i"., and long thlle lenes of datil .... ill probllbly be ne<:en.llry to diatin&,uieh hUlllan induced chan&"U from

natural nuctuationa, .,;teept in !!:dr-em" eatea.

Because the aquaw!ish ia now ",idel,. diatrihuted in the drain"." and its ran." is .. till expand in&', it seems extremely unlikely that aquawii8h control

.... ithin the Eel Rlver draina&,,, ,",QuId be economically fea.ible Or effective for the drainage as a "'hole. Control mea lUres that are not selective lor squa.. i'iah could alle"t other fi.h populations that are e"onomic:ally valuable. such u juvenile steelhead and American .had. Contr<:>l e!lorts could a1ao afleet a~clel .uch u Sacramento sucker l and California roach that form part of the fora,e bale lor birds. lIuch al ,reat blue herona and ospreys, or mammals. such as otterl. Theile ponible community level eflects indicate that a draina,e wide IIqua .... tI.h control pro,nm mlly not be environmentally feaaible. Within tbese major constr aints, our studiea s u"eat the follovin,:

1. Our studies indicate that the best way to promote production of juvenile

steelhead is to increSlle the amount ot cold, tributary .tream habitat

a~'ailable through .tream restoration and habitat improvement efforts.

2. Control of adult squawfish mi,ht be ",aeful in the limited area between

Pillsbury Reservoir and Van Aredale Reeervoir. The density of !ar,e

Iquaw!iah appe"u to be e"peci.ally hi,h in this ares end the areEi betwee n the dams has traditionally been important re!U'ing habitat fo,

juvenile 9teelhelld. Squaw!ish control in the area downlltream of v ......

Arsdllie to OuUet Creek mil'ht be ulleful in in<:reallinl' survival of

outmil'rant6, thoul'h ",itbout data on 109ses due to predation relative to

oth .. r factors such all thermal IItreall and dis .. as.. an objectiv.. d .. c illion

isn't possible. Efforts could be restricted to spot tr.. stm .. nts of heaV":!y

utiliz.. d pooIII in the Van Arsdal .. to Outlet Cr .... k ~s . Furth .. r studies

are necessary to det.. rmine if squawfish predation rate s on salmon

smolts and steelh.. ad juveniles and smolts are high enoul'h to make

squswfish control desirable. It the traditional chemical trealme"t '-ith

rotenon.. wa s us .. d, tre atment ",auld also regult in the loss of seve,.,.}

y .. a r class.. s of gteelhead.

3. Natural Vllriability in trout populations "'liS hil'h in all of th.. 9tr"""'5

IItudied. Long term environmental monitorinl', ulle of habitat apecific

sampling methodololfies, and long time lIe r ie8 or data will probably be

necessary to distinguish human induced changes from natural I

fluctuations, e:oo;cept in extreme cases.

I I I I I • 69 ACKNOWLBDGBMENTS

!'!an,. thanks to Bill Bennatt, Anne Brasher, William Coles, Lury 0.'-;8,

3::"t.>c:e Ee::-bold, TOlD Kennedy, Derek Kuda, Laura Rod~erll-Benn .. tt, Keith

~"b.1tene r . and Erie Wikramanayake tor help in collectin£" IJU rvey, microhabitat,

~ ~t data. I. .... MenK belped input and ana.lyze the survey and population esti=ale data In 1988. An ne Brasher conducted th" artificial s tream tank LITBRA TURB CITED

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