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Capture, Marking, and Enumeration of Juvenile Bull Trout and Cutthroat Trou Smalln Ti , Low-Conductivity Streams JOSEPH L

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Capture, Marking, and Enumeration of Juvenile Bull Trout and Cutthroat Trou Smalln Ti , Low-Conductivity Streams JOSEPH L 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 Trout and Cutthroat Trou Smalln ti , Low-Conductivity Streams JOSEPH L. BONNEAU Department of Fish and Wildlife Resources. University of Idaho 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 cutthroat trout Oncorhynchus 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 Salvelinus 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 salmo- 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 rainbow trout 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 Washington 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 salmon 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 .
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