North American Journal f Fisherieso Management 15:563-568. 1995 <£> Copyrigh e Americath y b t n Fisheries Society 1995

Capture, Marking, and Enumeration of Juvenile Bull and Cutthroat Trou Smalln ti , Low-Conductivity Streams JOSEPH L. BONNEAU Department of Fish and Wildlife Resources. University of Moscow, Idaho 83844,USA RUSSEL . THUROF L W

U.S. Forest Servicet Jntermountain Research Station 3/6 East Myrtle Street, Boise, Idaho 83702.USA DENNIS L. SCARNECCHIA Department of Fish and Wildlife Resources, University of Idaho

Abstract.—Relative efficiencies of sampling methods were evaluated for bull trout Salvefinus confluentus and clarki in small, high-gradient streams with low con- ductivities comparee d nighttimW .an y da d e observation snorkelery b s enumerato t s e bull trout and cutthroa tt nigha trout e d alsw tan o, use a band k observer. Methods were developer fo d capturing juvenile bull trou arean i t s where traditional methods suc s electrofishinha g were inef- fective. Juvenile salmonids were counte reacheo d nightw an dn i ty s durin da (20 e 0gth mf o ) Trestle Creek, Idaho, in August 1991. In July 1992, juvenile salmonids were counted during the f threo reache) 0 nighd dae1 m an y Idah n 5 i t (7 s o streams: Trestle, Rattle Granitd an , e creeks. Night count juvenilf so e bull trout exceede county dda aln i sl reach comparisons; differences were significant (P < 0.05) in 1992 but not in 1991. In contrast, summer day counts of cutthroat trout were significantly higher (P < 0.05) than night counts when reaches were pooled in 1991, but no differences were found in 1992. Observations from the bank sometimes improved the accuracy of the population estimates; more than one-third of the juvenile bull trout observed in Trestle Cree 199n ki 2 were observed fro banke mth , whereas bank observer fewew ssa r fish (both species) than snorkler Granitn i s e Creek. Both snorkeler band san k observers effectively captured juvenile bull trout with specially designed net t nighta s e snorkeleTh . juvenile rth capturef o e% buld71 l trout observed, wherea bane th s k observer captured 86%. Visible polymer implants alloweo t s u d identify marked fish at night without the need for recapture.

Bull trout confluentus, onle th y native suc s electrofishinha snorkeliny da e d b gy an gma e intermountaith cha n i r n West s sustaineha , - re dineffectiv r impracticao e r samplinfo l g juvenile ductions in distribution and abundance in this cen- bull trout (Fraley and Shepard 1988). tury. Ratliff and Howell (1992) estimated that two- Preliminary attempts to enumerate and capture third5 bul6 lf o strou t populations they studie n i djuvenil e bull trout with electrofishing gear were Oregot leasa d moderata t nha e ris f extinctionko , unsuccessful. Water conductivitie r studou yn i s Factors responsibl decline th r fo e include habitat stream (<5w s lo wer 0o jxS/cm)eto juvenild an , e degradation, interactions with introduced - bull trout were too elusive for effective sampling nids, overharvest, and climatic change (Goetz with a backpack electrofisher. Fish were observed 1989). avoidin electricae gth l field. o Moreovert d ha e w , e AmericaTh n Fisheries Societ s classifieha y carefue injuro b t dt large no eth l e- (>40ad ) 0mm bull trouspeciea s a t f speciaso l concern (Williams fluvial adult bul l stude trouth n yi t streams (Shar- et al. 1989), and the species is listed as a Category ber and Carothers 1988). 2 candidate under the U.S. Endangered Species Act. The primary objective of our study was to de- In October 1992 U.Se th , . FisWildlifd han e Service velo effectivn pa e sampling metho r bulfo dl trout petitiones wa asseso dt statue sth f bul o scutthroad l an trout.t trout Oncorhynchus clarki. evale W - The inventory of bull trout in small, high-gra- uated underwater counts of both species during the dient streams poses problems Idahon I . ,nighd juvenilalsd an otan y compareda e d summe wind ran - bull trout are typically found in cold (<15°C) ter counts. Additionally, we developed a technique streams witconductivitw hlo y jjiS/cm) 0 (<10 , genr capturinfo - g juvenile bull trout with speciall- yde erall closn yi e association wit e substrathth d r markinsignean e fo netp d di dsan g them wit imn ha - woody debrichannee th n i s l (Pratt 1984). Methods plante t visibldbu e fluorescent polymer polye Th . - 563 564 BONNEAU ET AL.

mer implants were used as part of another study under the fish. The fish was then easily transferred but are described here because of their applica- containea o t r temporarfo r y retention. bilit fiso yt h enumeration. Bank observers use t wit ne a n dsmala hp di l attached encirclin o capturt t ne g e fishe conW . - Study Area structe encircline dth - attachiny 60 b t X gne 6 1 ga Trestl d Granitan e e creeks flow directly into cm piec f 3-mm-meseo I6-cX h3 1 mnylo a o t n Lake Pend Oreille. Rattle Cree tributara s ki o yt dip-net frame. The bottom of the encircling net Lightning Creek and the Clark Fork River, the weightes wa d with lead. Whe observed s nfisa hwa , principal inle Lako t t e Pend Oreille e streamTh . s the encircling net was lowered around it with the drain steep watersheds vegetated by coniferou downstreae th s n o t dipne m end. Onc s fise eth wa h forest. Stream gradients ranged from 1-8d %an surroundedd an s t chasene wa t p i d, di inte th o canopy coverage fronearlo t m0 y 100% aquato N . - removed from the stream. The observers wore a ic vegetation was observed within sampled reach- head-mounted ligh freo t t e both hand r nettingsfo . . Watees rt limiclaritno td underwateydi r obser- Efficiencies of both types of nets were evaluated vation summen i s r wintero r . Highest n flowi e ar s during both day and night sampling. We attempted wintee th sprind an r g when rai snon no s wcomi - to capture every age-1 and older bull trout and mon. Fish species present were bull trout, wests- cutthroat trout observed r eacFo .h attempt- re e w , lope cutthroat . lewisi,trouc . O t On- corded fish species and success or failure of the corhynchus mykiss, mountain whitefish Prosopium capture attempt. williamsoni, and one or more species of sculpins Marking.—We sought a method of marking that Cottus spp. would enabl o identift s u e y bull trou t nighta t , preferably withou neee th tf recaptur do withd ean - Methods out increasing mortality of the fish. We used flu- Fish capture.—Many method f underwateo s r orescent polymer implants, develope y Northdb - capture such as the zap gun or spear gun (Ivanovic west Marine Technology, Inc.1, Shaw Island, 1955) e kiltargeth l t fish e ,unac b whic y - ma h e implanTh . t appear a smal s a s l flu- ceptable for rare or endangered species. Other orescent line visible to the naked eye. methods such as the slurp gun, which captures fish implane Th t consiste two-componena f do t poly- alive, were used effectively for fry of Atlantic mer that we combined immediately before use. The Salmo salar but were less effective on larg- polymer was injected beneath the skin or between r fise h (Morant t alze . 1987). Smal netp di ls have fin rays wit 28-gaugha e syringe. Fish were marked shown promise for sampling juvenile salmonids. in one of the following locations: top of head, DeGraaf and Bain (1986) used a small net to cap- adipose tissue behin eyee dth , adipose fin, dorsal ture more tha juvenilne halth f o f e Atlantic salmon fin, pectoral fin, or caudal fin. We used different they observed t largebu , r fish were more difficult marking locations to distinguish fish from different to capture. Morantz et al. (1987) used a similar stream sections as part of another study. Tagged capturo t t ne e small Atlantic salmon par fount rbu d fish were relocated at night by a diver or bank that larger parr avoided the net. observer using a fluorescent light. We constructed two nets, one used by a snor- To test tag retention times, we tagged 85 juve- keler and the other by a bank observer. The snor- nile bull trou tSandpoin e oncth t ea t Hatcher- yop keler use dsmala l dome-shape 3-mm-mesf o t dne h Idaheratee th y odb Departmen f FisGamd o t han e nylon equipped with a drawstring closing mech- in Sandpoint, Idaho. Fish were checkeg ta r fo d anism. The narrow, rectangular frame of this net retention afte mont2 r agaid han n afte months4 r . longeo n s rwa tha longese nth capturee t b fis o ht d Enumeration test I, underwater counts.—We (12 X 27 cm) and could be placed over a fish lying compared underwater counts of fish during day on an irregular substrate without leaving escape and night within two reaches of Trestle Creek in routes beneath the net. The snorkeler proceeded lat) werB e d o ereachesummeran tw e A ( s Th . upstream until a trout was observed. The snorkeler about 200 m long and contained 6 pocket-water approached the fish (without shining the light di- habitats riffles0 pools1 9 , d . an , Water tempera- rectl t durini n yo g night sampling), slowly moved tures, recorded continuousl a thermograph n o y , the net until it was directly above the fish, then swiftly loweret ove pressed fise ne th an rhe dth d 1 The use of trade or firm names in this paper is for it firmly agains substratee th t drawstrine Th . s gwa reader information and does not imply endorsement by then pulled, which t closene e bottoe dth th f mo the U.S. Forest Service of any product or service. TROUT SAMPLIN LOW-CONDUCTIVITN GI Y STREAMS 565

ranged from o 112.5°t 1 C durin e snorkelinth g g TABLE 1.—Capture frequencies for juvenile bull trout period, with minimal diel fluctuation. and cutthroat trou snorkelery b t band san k observers using Two snorkelers completed night counts on Au- dip nets at night. Capture frequencies during daylight hours were less than 10%. , 199120 d , an betweegus 9 1 t n 230 d 0230an 0 hours. Each snorkeler, equipped wit a wetsuith , Numbef o r Capture mask, snorkel, recording sleeve, and underwater Technique frequency light, counted in one reach. The snorkeler entered and species Attempts Captures (%) watee th r downstream fro lowermose mth t habitat Snorkelers unit and proceeded slowly upstream through each Bull trout 91 65 71 unit, countin l salmonidal g d recordinan s g them Cutthrout trout 60 13 22 Bank observers in 100-mm size-classes assistann A . shorn o t e fol- Bull trout 50 43 86 lowed the snorkeler and transferred counts to a Cutlhrout trout 40 12 30 t attempdatno ad couno sheedi t t t bu t fishy Da . counts were complete n Auguso d 0 betwee2 t n 110 d 140an 0 0 e samhourth en i s reaches with counted fis shallon i h w stream margin backd an s - identical procedures. water areas inaccessible to the snorkeler. The bank We categorized bull trout as small juveniles observer counted fish along both banks. Com- (<100 mm total length), large juveniles (100-400 munication betwee e banth n k observee th d an r mm), and adults (>400 mm), and westslope cut- snorkeler ensured that fish were counted only once. throat trou s juvenilea t d adults an (<20 ) s 0mm We plotted day and night counts by species for (>200 mm). Day and night counts of each species each reach. Counts were pooled for the 2 reaches in each reach were compared e examineW . e th d in winter and 10 reaches in summer, and differ- effect of fish size on day versus night counts by ences were tested wit paireha d /-test (Dowdd yan pooling fisy specieb h d size-clasan s r eacfo s h Wearden 1983). Percentages of fish counted with reach e difference useth W .o a d tesr tw fo t n i e each method (bank observe snorkelerd an r ) were proportions to examine differences in day versus compared betweenightd an y . nda night counts (Zar 1974). Results Enumeration text 2, underwater plus bank counts.—We compare d nighan ty snorkelindda g Fish Capture counts during winte reache2 n ri Trestln si e Creek Both snorkeler band san k observers successfully and during summe 1n ri 0 reache Trestlef so , Rattle, captured juvenile bull trout wit netp ht di night sa . and Granite creeks. Reache f eacso h stream were Capture frequencies were 71% for snorkelers and selected between the mouth and the uppermos r banfo tk % observer86 s (Tabl . Succes1) e s wa s limi bulo t t l trout migratio werd nan e abou m5 7 t lower for cutthroat trout: 22% for snorkelers and long wit wida h e rang f temperatureeo grad an s- 30% for bank observers. Capture efficiencies did dients. Each reach contained several pools and rif- not exceed 10% for either species during the day. flesmeasuree W . d water temperature e timth et sa of snorkeling with a hand-held thermometer. Fish Marking counts in winter were completed from January 15 After 2 months, all 85 fish had retained their to February 10, 1991; in summer counts were made injected fluorescent tags. By the end of 4 months, July 10-25, 1992. Fish were counted during winter only one fish had lost its tag, and all fish survived. days between 1000 and 1300 hours and during Marks on the head, , adipose fin, and winter nights between 170 200d 0an 0 hourse W . caudal fin were easily observed by snorkelers with- completed counts during summer days between out recapturing the fish. Marks on the pectoral fins 1000 and 1500 hours and during summer nights r behino e eyeth d s were more difficul o locatt t e between 2300 and 0200 hours. because the diver had to see both sides of the fish. observerso Tw shoresnorkeline n o ,on e ,on d gan counted agaid fisan h n y durinthada e t gth night . Enumeration snorkelee Th r entere streae lowee dth th d t ma ren Test /, underwater counts.—When counts in in- of the reach and proceeded slowly upstream. Num- dividual habitat units were pooled into two reaches bers of bull trout and cutthroat trout were recorded (A and B), night counts were greater than or equal and periodically reported to the bank observer county l thre.al da r eo t sfo size-classe f bulso l trout Age-0 fish wer t countedeno e banTh . k observer in both reaches (Figurt night-dabu , 1) e y differ- walked upstream parallel to the snorkeler and ences were not significant (P > 0.08). In contrast, 566 BONNEAU ET AL.

120

100 -

I

<100 100-400 Adult <100 100-400 Adult Size of bull trout (mm) FIGURE I.—Da nighd yan t count juvenilf so aduld ean t Reach 1 Reach 2 bull trout pooled by size-class in two reaches of Trestle FIGURE 3.—Day and night counts of bull trout (BT) Creek. August 1991. and cutthroat trout (CT) in two reaches of Trestle Creek in winter (January-February), 1991. day counts were greater tha r equao n o night l t counts for both size-classes of cutthroat trout in both reaches y count(FigurDa f juvenil. o s 2) e e fer significantly from the number counted during cutthroat trout were significantly larger than night the day (Figure 5). During winter, however, night count 0.025)< P reache ( n 0.001 si < B . P d ( )san A counts of cutthroat trout were significantly larger Text 2, underwater plus bank counts.—Juvenile thacounty 0.01< nda P ( s; Figur. e3) bull and cutthroat trout were observed in the 2 During night surveys observerso tw , snore on , - reaches sample l 1winten d0i al reached ran s sam- keling and one on the bank, were necessary to ple summern di numbere .Th juvenilf so e bull trout observe fish in stream margins and backwater ar- counted at night were significantly greater than the eas. A large percentage of the fish were located by numbers counted during the day for the combined e banth k observe Trestln i r e Creek, whereaw fe s reache botn i s h winte < 0.001 P summed ( r an ) r fish were located by the bank observer in Granite (< 0.001)P . Night counts exceede county da d s Creek (Figur banA . ke6) observe s alswa or used within each reach (Figure. 4) , s3 t nevebu y r durincounteda e th g d age- r oldeo 1 r During summer, in contrast, the number of ju- bull trout or cutthroat trout. venile cutthroat trout counte t dif t nighno d-a d di t

Cutthroat trout 10 FIGURE 2.—Day and night counts of juvenile and adult cutthroat trout (pooled reacheo tw n i )f Trestl so e Creek, FIGURE 4.—Da d nighyan t count f bulso l trou n 1i t0 August 1991. reache f threso e stream summern si , 1992. TROUT SAMPLING IN LOW-CONDUCTIVITY STREAMS 567

80 60 Day I bank observer % snorkeler Night 50 60 | 40

40 £30

Z 20 20 10

1234567 9 10 1 23456789 10 Reach Reach FIGURE 5,—Da nighd yan t count f cutthroaso t troun i t FIGURE 6.—Numbers of bull trout and cutthroat trout 10 reaches of three streams in summer, 1992. observe snorkelee th y db band ran k observe 1n ri 0 reach- es of three streams.

Discussion The ease of capturing juvenile bull trout at night Althoug foune hw d visual count snorkelea y sb r with nets allowe colleco t s du t fish without relying and bank observe superioe b o t r electrofishino t r g electrofishingn o arean I . s where juvenile bull trout for samplin enumeratind gan g bull trout, othe- rre are scarce or access is poor, a diver may find cap- searchers have found the opposite. In the Flathead turing bull trout with nets at night is easier and River drainage, electrofishing estimates of juvenile more efficient than electrofishing. We captured all bull trout consistently exceeded estimates derived size juvenilf so e bull trout effectively because their from day snorkeling (Fraley and Shepard 1988). resting behavior at night made them susceptible to r studInou y streams foune w , d electrofishing gear capture with nets. Attempts to net bull trout and ineffective for capture and enumeration, and fish cutthroat trou t wery durinda ee unsuccessfulgth . were observed avoidin electricae gth l fieldw Lo . f neto t nigha e y sals Us ma ot have application water conductivities (<50 |xS/cm) and low water when injury to fish such as adult bull trout must temperatures (

bull trout counted in 1992 (63) were higher than trouw western bo i t n Washington Cascade Mountain in 1991 (32) e actuaTh . l differenc s probablwa e y streams. Pages 39-48 in F. W. Olson, R. G. White, even greater because age-0 bull trout were includ- and R. H. Hamre, editors. Symposium on small hy- dropower and fisheries. American Fisheries Society, e 199 th e 199 2n th i count1t n i counno d t e . bu t Western Division and Bioengineering Section, Be- The differential day-night observability of ju- thesda, Maryland. venile bull trout appeared to be greater for smaller . BainDeGraafH . L . . d A.1986D ,an , . Habitay b e us t fish than for larger ones, perhaps because smaller and preferences of juvenile Atlantic salmon in two fish hide more effectively than large fish during Newfoundland rivers. Transaction Americae th f so n daye th f largI . e bull trou e lesar ts susceptiblo et Fisheries Society 115:671-681. Dowdy, S., and S. Wearden. 1983. Statistics for re- predation than smaller bull trout, they may not search. Wiley Yorkw Ne , . seek cove oftens a r . Fraley, J.T and B. Shepard. 1988. Life history, ecology, Compare bulo dt l trout, cutthroat trout were less d populatioan n statu f migratorso y bull trout (Sal- readily observe t nigha d t than durin e dayth g . velinus confluentus) in the and River When counts were poole reacy db comparedd han , system, . Montana Department of Fish, y countda s were significantly higher than night Wildlif Parksd an e , Kalispcll. summeo tw count e th r n si 199 1 reache f Trestlso e Goeiz, F. 1989. Biology of the bull trout Salvelinus con- fluenta literatur : us e review. Willamette National t e diffe10th no reache n d i Creekr di d f threso an , e Forest, Eugene, . creek 1992n si oftee W . n foun difficult di obtaio t t n Goetz . 1991F , . Bull trout life histor habitad yan t study. accurate counts of cutthroat trout at night because Final report (Contract 43-04GG-9-1371) to U.S. the dive lights usually caused aggregations of fish Forest Service, Deschules National Forest, Bend, scattero t , thus lowerin countsr gou comparisonn I . , Oregon. cutthroat trout typically faced upstrea could man d Ivanovic . 1955V , . Modern spearfishing . BarnesS . A . , New York. e approacheb divea y daytimedb n i r . Morantz . SweeneyK . L.. . D ,ShirvellR , S . . D C , d an , If cutthroat trout shift from the water column to . LongardA . 1987. Selectio f microhabitao n n i t cover, the shift may be influenced by predators summe y juvenilb r e Atlantic salmon. Canadian (Bugert and Bjornn 1991; Tabor and Wurtsbaugh Journal of Fisheries and Aquatic Sciences 44:120- 1991). Within Trestle Creek, the presence of large 129. (>400 mm) bull trout may have influenced the . Pratt1984P . K , . specied Habitaan e sus t interactions of juvenile cutthroat and bull trout in the Upper cover-seeking behavio f cutthroao r t trou t nighta t . Flathead River basin. Master's thesis. University of Idaho, Moscow. Acknowledgments Ratliff, D. E., and P. J. Howell. 1992. The status of bull Danny Lee, Pat Saffel, and Alane Bonneau as- trout population Oregonn i s . Pages. J 10-1. P n 7i sisted with study desig field nan d data collection. Howell and D. V. Buchanan, editors. Proceedings Funding for this study was provided by the Inter- of the Gearhart Mountain bull trout workshop. American Fisheries Society, Oregon Chapter, Cor- mountain Research Station, U.S. Forest Service, vallis. Boise, Idaho, and by the Department of Fish and . CarothersSharberW . S . G.d N , an ,. 1988. Influencf eo Wildlife Resources, Universit f Idahoyo , Moscow, clectrofishing pulse shap spinan eo l injurie aduln si t through a Research Joint Venture Agreement. rainbow trout. North American Journal of Fisheries Management 8:117-122. References . WurtsbaughA . TaborW . d A.R ,an , . 1991. Predation importance th risd kan f coveeo juvenilr fo r e rain- Bugert, R. M., and T. C. Bjornn. 1991. Habitat use by bow trout in lentic systems. Transactions of the steelhea cohd dan o salmo theid an n r responses to American Fisheries Society 120:728-738. predators and cover in laboratory streams. Trans- Williams, J. E., and seven coauthors. 1989. Fishes of actions of the American Fisheries Society 120:486- endangered, threatened, or of special 493. concern: 1989. Fisheries 14(6):2-20. . NeunerH . J Campbelld . an 1985, F. . .R , Seasonad an l Zar, J. E. 1974. Biostatistical analysis. Prentice-Hall, diurnal shifts in habitat utilization by resident rain- Englewood Cliffs Jerseyw Ne , .