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 ...