Distinguishing between juvenile anadromous and resident brook trout (Salvelinus fontinalis) using morphology

Transcription

1 Environ Biol Fish (2008) 81: DOI /s FULL PAPER Distinguishing etween juvenile ndromous nd resident rook trout (Slvelinus fontinlis) using morphology Geneviève R. Morinville Æ Joseph B. Rsmussen Received: 24 My 2005 / Accepted: 17 Decemer 2006 / Pulished online: 1 Ferury 2007 Ó Springer Science+Business Medi B.V Astrct Phenotypic vrition linked to hitt use hs een oserved in fish, oth etween nd within species. In mny river systems, migrtory nd resident forms of slmonids coexist, including ndromous (migrnt) nd resident rook trout, Slvelinus fontinlis. In such popultions, juvenile ndromous (migrnt) rook trout, prior to migrtion, inhit regions of higher current velocity thn residents. Becuse it is more costly to occupy fst currents thn slow currents, differences in morphology minimizing the effects of drg were expected etween the two forms. As predicted, migrnt rook trout were found to e more stremlined (nrrower nd shllower Contriution to the progrm of CIRSA (Centre Interuniversitire de Recherche sur le Sumon Atlntique). G. R. Morinville J. B. Rsmussen Deprtment of Biology, McGill University, 1205 Dr. Penfield Ave., Montrel, QC, Cnd H3A 1B1 G. R. Morinville (&) Rescn Environmentl Services, Sixth Floor, 1111 West Hstings, Vncouver, BC, Cnd V6E 2J3 e-mil: genevieve.morinville@mil.mcgill.c J. B. Rsmussen Deprtment of Biologicl Sciences, Wter Institute for Semi-Arid Ecosystems (WISE), University of Lethridge, 4401 University Dr. West, Lethridge, AB, Cnd T1K 3M4 odies) thn resident rook trout, nd these differences persisted into the mrine life of the fish. Migrnts lso exhiited shorter pectorl fins, which fcilitte pelgic swimming, indicting tht migrnts, prior to their migrtion to the se, possess the pproprite morphology for swimming in open wter hitts. The reported differences etween migrnts nd residents were powerful enough to derive discriminnt functions, using only five of the seven mesured trits, llowing for ccurte clssifiction of rook trout s either migrnts or residents with n overll correct clssifiction rte of 87%. Importntly, this study contriutes to the notion tht link exists etween morphology, hitt use, metolic costs nd life-history strtegies. Keywords Fish shpe Hitt use Coexistence Slmonid Metolic costs Energetics Se trout Migrtion Andromy Introduction Phenotypic vrition in morphologicl trits implicted in predtor evsion, feeding nd hitt use hve een commonly reported in the literture. For exmple, crucin crp, Crssius crssius, increse their ody depth s defense mechnism ginst gpe-limited piscivores (Holopinen et l. 1997; Pettersson & Brönmrk

2 172 Environ Biol Fish (2008) 81: ) nd Arctic chrr hve evolved morphologicl dpttions in mouth nd snout shpe ccording to their enthivorous or plnktivorous piscivorous feeding ehviors leding to four symptric morphs in n Icelndic lke (Skúlson et l. 1989). Phenotypic vrition linked to hitt use hs een oserved, oth in wrm-wter strem fishes including cyprinids nd percids (Wood nd Bin 1995), nd in slmonids, oth within nd etween species (Riddell nd Leggett 1981; Bisson et l. 1988; Swin nd Blir 1989). It hs een consistently demonstrted tht fish inhiting fster currents re more stremlined (shllow-odied versus deep-odied) thn those inhiting slow currents. A more stremlined morphology in fst wter reduces swimming costs y minimizing the effects of drg (Pettersson nd Brönmrk 1999). Drg is influenced y fish shpe, the squre of the current speed nd the Reynolds numer (Re) of the fish (Vogel 1994). Re is positively relted to fish size, the undistured velocity, nd wter temperture (kinemtic viscosity). Pressure drg predomintes t high velocities such tht chnges to more stremlined ody morphology, s indicted y the fineness rtio (rtio of stndrd length to ody depth), leds to reduction in the drg coefficient (We 1975; Blke 1983). A high rtio etween spn nd length of their cudl fin ( spect rtio ) lso reduces the effects of drg (We 1984, 1988). Using field oservtions, Bisson et l. (1988) demonstrted tht differences in fin size nd ody shpe could predict the strem chnnel loctions utilized y juvenile slmonids. Coho slmon, Oncorhynchus kisutch, prefering pools, possess deep nd lterlly compressed ody with lrge medin nd pired fins, fcilitting trnsitory mneuvering ility. In contrst, steelhed trout, Oncorhynchus mykiss, possess fusiform ody shpe with short medin fins nd lrge pired fins, llowing for efficient swimming in fst wter, wheres cutthrot trout, Slmo clrki, morphology is intermedite to these species, consistent with its hitt preferences. Within-species vritions in morphology hve lso een reported. In Atlntic slmon, individuls inhiting river with higher verge flow velocities were more stremlined in shpe nd hd lrger pired fins thn those inhiting river with lower verge flows (Riddell nd Leggett 1981). Similrly, Tylor nd McPhil (1985) found heritle morphologicl differences etween interior nd costl popultions of juvenile coho slmon. Interior popultions were more stremlined in shpe nd possessed smller medin fins thn costl popultions, most likely the result of their greter need for efficient swimming during migrtions, ecuse these interior popultions originted from loctions tht were further wy from the se. Interestingly, ndromous (migrnt) nd non-ndromous counterprts hve lso een oserved to differ morphologiclly such tht the former is etter suited for prolonged swimming (Tylor nd McPhil 1986; Tylor nd Foote 1991). Fish my thus evolve morphologicl dptions specific to their life-history strtegy nd exhiit these dpttions throughout their life stges. In certin rivers, rook trout popultions comprise mixture of ndromous (migrtory) nd resident forms (Thériult nd Dodson 2003; Morinville nd Rsmussen 2003, 2006). It hs een suggested through vrious lines of support including ioenergetic nd stle isotope nlyses tht in such popultions, juvenile ndromous (migrnt) rook trout, prior to migrtion, inhit regions of higher current velocity in freshwter thn residents (Morinville nd Rsmusen 2003). A recent comprtive study lso tends to supports this fst hitts were occupied more frequently in strems contining migrtory rook trout (migrnt-resident strems) reltive to riffle hitts of strems comprising only resident trout (resident-only strems) (Morinville nd Rsmussen 2006). In the wild, rook trout tend to swim ctively nd feed in the wter column nd continue to swim ginst the current even in fst wters (Keenleyside 1962). As for other slmonids, trout occupying fst currents re expected to possess more stremlined morphology in order to minimize the costs ssocited with swimming. Such oservtions hve een reported for rook trout s erly s in their first yer of life (McLughlin nd Grnt 1994), lthough the differences my not necessrily persist over time (Imre et l. 2001). Becuse rook trout migrte s erly s t ge 1+ (Thériult nd Dodson 2003), it is likely

3 Environ Biol Fish (2008) 81: tht morphologicl differences exist etween juvenile ndromous (prior to migrtion) nd resident rook trout. Distinguishing etween the two forms t erly life stges will llow for future studies investigting coexistence nd ultimtely, the underlying mechnisms of ndromy. The min ojectives of this study were thus to (1) determine whether coexisting ndromous (migrnt) nd resident rook trout differ in ody morphology, (2) whether the oserved differences coincide with hitt use expecttions, nd (3) whether ny oserved differences cn e used s tool for future field identifiction. It is predicted tht within migrnt-resident strems (strems with resident nd ndromous forms), migrnt rook trout will e more stremlined thn residents. Specificlly, it is predicted tht resident rook trout will hve wider nd deeper odies (higher drg morphology) compred to migrnt rook trout. Fin sizes including cudl, pelvic nd pectorl re lso expected to differ etween migrnts nd residents. Furthermore, it is predicted tht resident fish from migrnt-resident strems will e less stremlined thn those of resident-only strems ecuse of their previously reported differences in hitt use. We lso predicted tht ny oserved pre-migrtory morphologicl differences etween migrnts nd residents would persist (crry over) into the mrine life of the fish. Tht is, se trout migrnts were expected to continue to differ morphologiclly from residents throughout their life stges. Study site nd methods Study site This study ws conducted in the Ste. Mrguerite River (SMR) system in the Sgueny region of Queec, Cnd (48 27 N, W). The SMR flows into the esturine Sgueny River tht further empties into the St. Lwrence River. The SMR system is home to the lrgest ndromous rook trout popultion of the Sgueny River sin (Lesueur 1993). Popultions of ndromous Atlntic slmon nd rook trout, s well s resident rook trout, co-occur in the region. Strems contining such popultions of coexisting rook trout nd Atlntic slmon will e referred s migrnt-resident strems. Andromous rook trout down-migrte from mid-my to erly-june, s erly s ge 1+ to the esturine Sgueny River (Thériult nd Dodson 2003). Strem reches ove mn-mde rriers, such s poorly constructed culverts nd nturl rriers, such s wterflls, will e referred s resident-only strems s these only contin resident rook trout. Fish collection The genus Slvelinus exhiits the lest pronounced ndromy of slmonids (Power 1980). No ovious smoltifiction occurs in migrnt rook trout (McCormick et l. 1985) mking it very difficult to differentite migrnt from resident until the moment of migrtion. In migrnt-resident strems, we distinguished migrnts s trout cptured in trp nets during the downstrem migrtion period, wheres those cptured in strems following the migrtion period were defined s residents. Tgging studies confirmed tht this method ws effective in seprting migrnts from residents (Thériult nd Dodson 2003). Although the trout remining in the system fter migrtion re considered residents, n unknown proportion of these trout my ctully consist of future migrnts. Migrnts were cptured from two migrntresident strems, Morin (spring ) nd Portge (spring 2002). Migrnts were lso cptured upon se entry in the Sgueny River estury every 2 4 weeks from the Ste. Mrguerite By or from nery Anse-de-Roche (oth sites re locted in the Sgueny River) etween My nd Octoer of These trout will e referred to s se trout. All resident rook trout were cptured eginning mid-june using ckpck electro-fisher (Smith-Root, Inc. model 12A), following the migrtion period. Residents were smpled in three migrnt-resident strems including Morin (summer ), Portge (summer 2002) nd Édourd (summer 2002), nd in two resident-only strems including Épinette (summer 2002) nd L Pririe (summer 2002).

4 174 Environ Biol Fish (2008) 81: Morphologicl trit mesurements All fish morphologicl trit mesurements were performed in the field. Both fork (FL; to the nerest mm) nd stndrd length (SL; to the nerest mm) were mesured for ll rook trout. Previously reported empiricl evidence nd theory, in ddition to logisticl constrints, guided the selection of morphologicl trits to e mesured. Morphologicl trits included mximum ody depth (tken s distnce from strt of dorsl fin to strt of pelvic fin), mximum ody width (tken t front of dorsl fin), peduncle depth, cudl fin height, pectorl fin length nd pelvic fin length (Imre et l. 2001; Peres-Neto nd Mgnn 2004). A needlepointed divider ws employed to mesure the length of ech ody trit. This involved stretching the divider to the desired length, susequently plcing the divider on field ook pper, nd trcing the distnce etween the two needle ends. These lines were then susequently mesured using clipers (to the nerest 0.05 mm). All fish were relesed live. This procedure ws done in order to minimize fish hndling time nd ny susequent stress on the fish ecuse of the numerous mesurements eing tken in the field. The sme person (G.R. Morinville) took ll mesurements. Morphologicl comprisons In order to detect morphologicl differences etween migrnts nd residents, ll morphologicl trits were ln-trnsformed nd regressed upon ln-trnsformed stndrd length for pooled migrnts nd residents of migrnt-resident strem (Morin) for yers Residuls otined from these regressions were retined for further nlyses. Individul t-tests were susequently conducted for ech morphologicl trit using the residuls to compre migrnts nd residents within strem over the 3 yers of study. Comprisons etween residents of migrntresident nd resident-only strems were lso conducted ecuse of their previously reported hitt use differences (Morinville nd Rsmussen 2006). Liner regressions of ech ln-trnsformed morphologicl trit upon were conducted for pooled residents cptured in migrnt-resident strems (Édourd, Morin nd Portge) nd resident-only strems (Épinett nd L Pririe) in Residuls were retined from ech morphologicl trit for susequent t-tests compring the two types of strems. Discriminnt function nlysis (DFA) ws conducted on 2002 dt to ssess whether the overll differences oserved etween (1) pooled migrnts (Morin nd Portge), (2) pooled residents of migrnt-resident strems (Édourd, Morin nd Portge), nd (3) pooled residents of resident-only strems (Épinette nd L Pririe) using ll mesured trits were powerful enough to ccurtely predict the life-history group to which n individul fish elonged. Residuls otined from group-specific ln-trnsformed liner regressions of ech morphologicl trit s function of fish size (stndrd length) were retined for DFA, nd ll fish were reclssified ccording to the model generted y DFA to otin the correct reclssifiction rte. Finlly, comprisons etween residents of migrnt-resident strems nd se trout were lso conducted in order to determine whether ny oserved differences etween migrnts nd residents persist post-migrtion, tht is, whether the differences persist into the mrine life of se trout. Liner regressions of ech ln-trnsformed morphologicl trit upon ln-trnsformed stndrd length were conducted for pooled residents cptured in migrnt-resident strems (Édourd, Morin nd Portge) nd for se trout cptured in the Sgueny River in Residuls were retined from ech morphologicl trit for susequent t-tests compring residents nd se trout. All sttisticl nlyses were conducted using SYSTAT (Version 10.2). Comprisons of form drg etween life-history forms Form drg ws estimted for the different lifehistory forms including migrnt-resident migrnts nd residents, resident-only residents nd se trout cptured in 2002 using two surrogte mesures: (1) fineness rtio (rtio of stndrd length to mximum ody depth, nd (2) circulr rtio (rtio of mximum ody depth to mximum ody width)

5 Environ Biol Fish (2008) 81: indictive of prolonged swimming (We 1975; Siing nd Ngelkerke 2001). A higher fineness rtio indictes more elongted ody shpe with rtio of out 5 indicting low drg. A lower circulr rtio indictes more circulr shped ody with rtio of 1 indicting perfect circle. Both the fineness nd circulr rtio were compred etween residents from migrnt-resident nd resident only strems, migrnts nd se trout using one-wy nlysis-of-vrince (ANOVA) nd susequent pirwise Tukey comprisons. Field identifiction nd vlidtion An interctive stepping DFA (Alfonso 2004) ws conducted using ll possile size-free rtios of morphologicl trits of migrnt nd resident dt from Morin 2002 in order to select the vriles tht est clssified migrnts nd residents. The purpose of this ws to develop simple method, using the fewest numer of size-free rtios, for discriminting etween future migrnts nd residents well efore the spring outmigrtion (i.e., during the previous summer when fish could e esily cught y electrofishing). Vriles were selected using oth sttisticl nd iologicl informtion until n overll clssifiction rte of t lest 85% ws chieved. The model incorported size-free rtios rther thn residuls (in comprison to tht presented in erlier section) in order to simplify the model, nd thus in the process, mking it ccessile to ll field workers nd fishery mngers. The resultnt function ws then pplied to fish cptured in Morin in 2001 nd 2003, in ddition to trout cptured in 2002 resident-only strems in order to ssess the vlidity of the model. Results Fish collection In totl, 2561 fish were mesured in the field cross ll sites nd yers. Migrnts cptured in trps instlled on Morin Strem nd Portge Strem nd mesured rnged in size etween 93.3 mm nd mm (Tle 1). Residents cptured in migrnt-resident strems (Édourd, Morin nd Portge strems) rnged in length from 96.4 mm to mm, while those from resident-only strems (Épinette nd L Pririe strems) rnged in length from mm to mm. Se trout cptured in the Sgueny River, including sites in the Ste. Mrguerite By nd Anse-de-Roche, were lrger, rnging in length from mm to mm. Morphologicl comprisons Migrnts versus residents Significnt regressions were detected for pooled migrnts nd residents from Morin Strem for ll ln-trnsformed morphologicl trits cross ll 3 yers of study (Tle 2). Residuls from these regressions consistently indicted tht Morin Strem migrnts were more stremlined thn residents, possessing shllower mximum ody depths nd smller ody widths (Fig. 1). In ddition, Morin migrnts consistently hd shorter pelvic nd pectorl fins thn residents, suggesting temporl persistence for these trits. In contrst, vritions cross yers existed for oth peduncle depth nd cudl height. Peduncle depths of migrnts were shllower thn residents in two of the 3 yers (2001 nd 2003). Cudl heights were lso shorter in two of the 3 yers (2001 nd 2002). Migrnt-resident strem residents versus resident-only strem residents Significnt regressions were detected for pooled residents from migrnt-resident nd resident-only strems for ll ln-trnsformed morphologicl trits cross ll yers (Tle 3). Residuls from these regressions indicted tht residents from migrnt-resident strems were more stremlined thn residents from resident-only strems, possessing shllower ody depths nd peduncle depths, nd smller ody widths. In ddition, migrnt-resident strem residents hd shorter cudl, pelvic nd pectorl fins. Migrnts versus migrnt-resident nd resident-only strem residents A complete DFA ws used with the known priori seprtion of migrnts, migrnt-resident

6 176 Environ Biol Fish (2008) 81: Tle 1 Numer nd men fork length (±1 SE) of smpled resident, migrnt nd young-of-the-yer (YOY) rook trout from resident-only (res-only) nd migrnt-resident strems, nd Sgueny River (se) smpling sites Site Site type Fish type Yer Men fork length (mm) Rnge (mm) N Épinette Resident-only Resident ± L Pririe Resident-only Resident ± Édourd Migrnt-resident Resident ± Morin Migrnt-resident Migrnt ± Resident ± Migrnt ± Resident 98.2 ± Migrnt ± Resident 96.4 ± Portge Migrnt-resident Migrnt ± Resident ± Sgueny River Se Se trout ± ± nd resident-only strem residents. Residents from oth strem types showed the most overlp in multivrite spce, ut were distinct from migrnts, with resident-only trout eing most distinct from migrnts (U = 0.365, F 6,12 = 112.7, P < 0.005; Fig. 2). The DFA model correctly reclssified (jckknifed clssifiction) 91% of migrnts, 74% of resident-only residents nd 65% migrnt-resident residents for n overll correct clssifiction of 74%. Only 2.3% of migrnts were misclssified s resident-only fish nd 6.5% s residents from migrnt-resident strems. The lower clssifiction rte of residents from resident-only strems stems mostly from misclssifying 24.5% of fish s migrnt-resident residents; only 1.9% of resident-only fish were misclssified s migrnts. A higher proportion of residents from migrnt-resident strems were misclssified s migrnts (11.7%) nd n even lrger proportion s residents from resident-only strems (23.8%), leding to the lowest clssifiction rte overll. Migrnt-resident strems versus Sgueny River se trout Significnt regressions were detected for pooled residents from migrnt-resident strems nd se trout from the Sgueny River for ll ln-trnsformed morphologicl trits (Tle 4). Residuls from these regressions indicted tht se trout were more stremlined thn residents from migrnt-resident strems, possessing shllower ody depths nd peduncle depths, in ddition to smller ody widths. Se trout lso hd shorter cudl, pelvic nd pectorl fins. Comprisons of form drg etween life-history forms Fineness rtios (stndrd length to mximum ody depth) vried significntly (ANOVA: F 3,1354 = 291.9, P < 0.001) etween 2002 resident-only strem residents, migrnt-resident strem residents, migrnts nd se trout (ll t P < 0.001; Fig. 3). Similrly, the odies of migrnts nd se trout were significntly more circulr (rtio of mximum ody depth to mximum ody width is closest to 1) thn those of residents from migrnt-resident nd resident-only strems (ANOVA: F 3,1354 = 61.7 P < 0.001; Fig. 3). Although no sttisticlly significnt differences existed etween migrnts nd se trout (P = 0.062), significnt differences were found etween residents from migrnt-resident nd resident-only strems (oth hve P < 0.001). Overll, migrnts nd se trout hd the most elongted nd circulr ody form, nd thus possessed drg-efficient morphology compred to residents from resident-only strems tht possessed less elongted nd circulr ody form. Field identifiction nd vlidtion Using n interctive forwrd stepping DFA with Morin 2002 dt, three size-free rtios

7 Environ Biol Fish (2008) 81: Tle 2 Regression sttistics from ln-trnsformed morphologicl trit length s function of ln-trnsformed stndrd length, residuls nd sttisticl comprisons using t-tests etween rook trout migrnts (M) nd residents (R) of Morin Strem from 2001 to 2003 for six morphologicl trits Yer Trit n Pooled regression Life-history Residuls form P R 2 Men SE t P 2001 Depth 197 < M P < R Width 186 < M P < R Peduncle 175 < M P < R Cudl 168 < M P < R Pelvic 172 < M P < R Pectorl 173 < M P < R Depth 285 < M P < R Width 285 < M P < R Peduncle 285 < M P = R Cudl 248 < M P < R Pelvic 285 < M P < R Pectorl 285 < M P < R Depth 222 < M P < R Width 222 < M P < R Peduncle 223 < M P < R Cudl 195 < M P = R Pelvic 225 < M P < R Pectorl 225 < M P < R were selected using oth sttisticl nd iologicl informtion, including depth to stndrd length rtio (DEP_LTH), peduncle to cudl height rtio (PED_CAUD) nd pectorl to stndrd length rtio (PECT_LTH). The following function ws derived for Morin 2002 using the stndrdized within vrince cnonicl discriminnt functions, within smple mens (m yer ) nd stndrd devitions (SD yer ; Tle 5) to clssify rook trout s either migrnt or resident: F ¼ (0.728)(DEP LTH m yer )(SD yer Þ 1 +( 0.719)(PED CAUD m yer )(SD yer Þ 1 + (0.386)(PECT LTH m yer )(SD yer Þ 1 ð1þ If F < 0, trout re clssified s migrnt, nd if F > 0, trout re clssified s resident. This function correctly clssified 94.3% of migrnts nd 81.8% of residents from Morin 2002 rook trout

8 178 Environ Biol Fish (2008) 81: () () (2) 0.6 Residul (c) (d) Fctor (e) migrnt (f) resident migrnt resident Life-History Type Fig. 1 Men residuls (roken lines) of ln-trnsformed () ody depth; () ody width; (c) peduncle depth; (d) cudl fin height; (e) pelvic fin length; nd (f) pectorl fin length regressed on ln-trnformed stndrd length for 2002 Morin Strem rook trout migrnts nd residents. Different letters indicte significnt differences t P < 0.05 etween life-history types Fctor (1) Fig. 2 Bivrite plot of the first two cnonicl vriles of the liner discriminnt function performed using migrnts (circles, dotted line), resident-only strem residents (digonl crosses; dshed line) nd migrnt-resident strem residents (crosses; solid line). Confidence ellipses re centred on the centroid of ech life-history form. The first cnonicl vrile (eigenvlue = 1.486) cptured 94% of the difference mong the groups. Significnt differences existed etween the three groups (U = 0.365, F 6,12 = 112.7, P < 0.005). The model otined correctly reclssified 91% of migrnts, 74% of resident-only residents nd 65% migrnt-resident residents for n overll correct clssifiction of 74% Tle 3 Regression sttistics from ln-trnsformed morphologicl trit length s function of ln-trnsformed stndrd length, residuls nd sttisticl comprisons using t-tests etween rook trout residents from 2002 pooled migrnt-resident (Édourd, Morin nd Portge strems; R) nd pooled resident-only strems (Épinette nd L Pririe strems; RO) for six morphologicl trits Trit Life-history form n Pooled regression Men SE t P P R 2 Depth RO 163 < P < R Width RO 162 < P < R Peduncle RO 163 < P < R Cudl RO 160 < P < R Pelvic RO 163 < P = 0.15 R Pectorl RO 163 < P=0.008 R

9 Environ Biol Fish (2008) 81: Tle 4 Regression sttistics from ln-trnsformed morphologicl trit length s function of ln-trnsformed stndrd length, residuls nd sttisticl comprisons using t-tests etween rook trout residents from 2002 pooled migrnt-resident (Édourd, Morin nd Portge strems; R) nd Sgueny River se trout (Se) for six morphologicl trits Trit Life-history form n Pooled regression Men Residuls P P R 2 SE t Depth Se 192 < P < R Width Se 192 < P < R Peduncle Se 192 < P < R Cudl Se 184 < P < R Pelvic Se 192 < P < R Pectorl Se 192 < P < R leding to n overll correct clssifiction rte of 86.6% (U = 0.42, F 3,649 = 298.8, P < 0.001). The ove function ws employed to ssess its vlidity for other smpling yers, using the sme cnonicl discriminnt functions s ove ut using smple mens nd stndrd devitions specific to 2001 nd 2003 smples (Tle 5). In 2001, the function ccurtely clssified 92.2% of migrnts nd 89.6% of residents, for n overll clssifiction of 90.8%. Similrly in the yer 2003, the function ccurtely clssified 90.8% of migrnts nd 83.7% of residents, for n overll correct clssifiction of 87.2%. The sme function ws lso pplied to 2002 resident-only strems, using the function ove, nd the 2002 mens nd stndrd devitions. The function correctly predicted 96.3% of the pure residents s eing residents (n = 160). The function thus ppers to work well cross yers nd sites. Discussion Morphologicl differences etween ndromous nd resident rook trout The present study compres morphologicl chrcteristics of ndromous (migrnt) nd resident rook trout of the Ste. Mrguerite River system, Queec, Cnd in order to estlish link etween morphology, hitt use, ioenergetics nd life-history strtegies. Migrnt rook trout from Morin Strem, migrnt-resident strem, were found to e more stremlined thn resident rook trout; they were oth slimmer nd less deeply-odied indicting tht migrnts re etter suited for swimming in fst wters thn residents. Importntly, these differences persisted cross yers, suggesting tht these chrcteristics my e selected for in mixed popultions (i.e., those comprised of oth migrtory nd resident individuls). Morphologicl differences mong rook trout using different hitts hve een detected s erly s ge 0+ in resident popultions (McLughlin nd Grnt 1994). Young-of-the-yer (YOY) rook trout using fster current velocities hd shllower ody depths compred to those using slower currents, giving support to the morphologicl differences oserved in older trout (older thn 0+) in this study. However, contrry to our findings, YOY utilizing fst currents in the wild (McLughlin nd Grnt 1994) nd YOY rised in fst wters (Imre et l. 2002) hd lrger cudl fin heights thn those using slow currents. Moreover, such oservtions did not persist over time (Imre et l. 2001), suggesting the presence of other mechnisms. Other mechnisms could include differences in developmentl rtes (Mrtin 1949), physiology (such s stndrd metolic rtes) or ehviour, wherey certin

10 180 Environ Biol Fish (2008) 81: SL:BD BD:BW () () RO R M Life-history form dpttions my e importnt t smll sizes ut not necessrily so t lrge sizes. In ddition, provided there is genetic sis to the differences, selection mechnisms in resident popultions my differ from mixed popultions such tht the sme morphologicl chrcteristics re not selected for or tht the trits re present ut selection is wek. In ddition to possessing stremlined morphology tht is etter dpted for swimming, migrnts were found to hve shorter pectorl fins nd shorter pelvic fins compred to residents. No Fig. 3 Rtios of () stndrd length to mximum ody depth (SL:BD; fineness rtio), nd () mximum ody depth to mximum ody width (BD:BW; circulr rtio) for 2002 resident rook trout from resident-only (RO) nd migrnt-resident strems (R), migrnt rook trout (M) nd se trout (ST). Different letters ove rs indicte significnt differences t p < etween life-history forms. Numers in rs indicte smple size c c d c ST Tle 5 Within yer mens, stndrd devitions nd smple sizes for depth to stndrd length rtio (DEP_LTH), peduncle to cudl height rtio (PED_CAUD) nd pectorl to stndrd length rtios (PECT_LTH) selected in field identifiction for Morin 2001 to 2003 rook trout Rtio Yer Men SD N DEP_LTH PED_CAUD PECT_LTH such differences were oserved in YOY rook trout (lke strin) rered under slow nd fst flow conditions (Imre et l. 2002). Slower growth of pelvic nd pectorl fins my e selected for migrnts in order to llow for immedite dpttion to pelgic swimming upon se entry, since se trout continue to exhiit short pelvic nd pectorl fins throughout their ontogeny. Pectorl fins of lcustrine enthic-feeding rook trout were longer thn those of pelgic-feeding ones (Bourke et l. 1997), the former fcilitting slow nd precise mneuvering (We 1984). Short pectorl fins, importnt for cruising, re required for serching efficiently for prey in open wter hitts (Ehlinger 1990). Shorter pectorl fins lso reduce drg (Drucker nd Luder 2003). Similrly, enthic feeding Arctic chrr, chrcterized y stocky odies, lso possessed longer fins thn stremlined piscivorous plnktivorous feeders (Skúlson et l. 1989, nd references therein). Se trout lso continued to e more stremlined in shpe thn residents, possessing slimmer nd shllower ody depths, s well s shllower peduncle depths. Similr differences were oserved in Nov Scoti popultion of migrnt nd resident rook trout where newly returning se trout to freshwter hd more cylindricl odies nd shorter fins thn freshwter trout (Wilder 1952). This sme pttern ws oserved even though the trout were lrger (verge size of 170 mm) nd older thn SMR fish (80% of migrnts were t ge 3+ compred to SMR system where lmost 100% migrte efore the ge of 3+). The dpttions leding to ndromy

11 Environ Biol Fish (2008) 81: thus seem consistent cross popultions, regrdless of the ge or size t migrtion. Efficient prolonged swimming requires stremlined ody shpe of out equl depth nd width, nd length/depth rtio round 5 to minimize drg (Siing nd Ngelkerke 2001). Thus rook trout exhiiting ll life-history forms hve hydrodynmiclly efficient ody forms, lthough trout cptured during outmigrtion nd t se hd the highest fineness rtio (rtio of stndrd length to mximum ody depth), in ddition to hving the most circulr ody shpe compred to residents from migrnt-resident nd resident-only strems. The morphology of migrnts nd se trout thus produces the lowest drg. Thus overll, the vritions in ody shpe reported here re consistent with previously reported studies regrding morphology nd hitt use. It should e noted tht differentil smpling periods my hve contriuted to the oserved differences in ody condition (ody depth nd width) ecuse migrnts were smpled in erly spring following winter, period ssocited with low feeding nd growth. However, our results showed tht residents from migrnt-resident strems were lso more stremlined thn residents from resident-only strems, possessing nrrower nd shllower odies, nd therey supporting initil predictions. The oservtion tht the morphologicl differences mong residents ecome less pprent t lrge sizes, which results in steeper reltionship etween trit length nd size, is logicl s the older nd lrger rook trout of migrnt-resident strems re most likely true residents, ecuse the mjority of trout tht migrte leve y the ge of 2+. In ddition, differences in ody condition were not likely due to smoltifiction ecuse rook trout do not experience physiologicl trnsformtions prior to migrtion (Hor 1976; McCormick et l. 1985; Beemn et l. 1995). Liner discriminnt function nlysis reveled significnt discernle nd predictle morphologicl differences etween migrnts nd residents from oth migrnt-resident nd resident-only strems. The model ccurtely clssified over 90% of migrnts s migrnts, wheres residents from migrnt-resident nd resident-only strems were correctly clssified t 65% nd 74%, respectively. The misclssifiction ws mostly the result of residents from migrnt-resident strems eing misclssified s residents from resident-only strems, nd vice-vers. Only 1.9% of residentonly residents were misclssified s migrnts while 11.6% of residents were misclssified s migrnts. Given the high correct clssifiction rte, nd the presence of future migrnts within the rook trout popultion of migrnt-resident strems we interpret this to men tht the migrnt-resident residents tht were misclssified s migrnts, were proly fish tht would migrte in future yers (i.e., future migrnts). Lrger fish, older thn >3+ (the oldest ge of migrtion), would e expected to e true residents, while mny of the smller fish, younger thn 2+, could likely e future migrnts. Interestingly, the migrnt-resident strem residents misclssified s migrnts were smller (82.6 mm ± 16.4 SD) thn those misclssified s resident-only strem residents (106.8 mm ± 30.9 mm SD). Even so, the misclssifiction hypothesis remins to e confirmed. Given the mesurle differences etween migrnts nd residents, function with high clssifiction rte using three size-free rtios including depth to stndrd length rtio (DEP_LTH), peduncle to cudl height rtio (PED_CAUD) nd pectorl to stndrd length rtio (PECT_LTH) could e derived from 2002 Morin Strem rook trout. Only five morphologicl trit mesurements were required for ccurte clssifiction of migrnts nd residents. Cross-vlidtion further lso indicted tht the function could e employed to ccurtely clssify fish from other smpling yers, nd tht misclssified residents were possily future migrnts. Although this function remins to e pplied s predictive tool in the field nd confirmed, it indictes potentilly useful tool for distinguishing etween migrnts nd residents in mixed popultions. This tool would e very eneficil for fishery mngers needing to estimte the yerly se trout popultion in order to estimte nd set fishing quots. Importntly, the oserved morphologicl vritions concurred with inferred ndromous nd resident rook trout hitt use nd ioenergetics

12 182 Environ Biol Fish (2008) 81: (Morinville nd Rsmussen 2003, 2006), such tht migrnts, y possessing more stremlined morphology, re more efficient swimmers (lower energetic costs) in fst wters thn residents (Sgnes et l. 2000; Boily & Mgnn 2002). Tylor nd McPhil (1986) lso found tht ndromous three spine sticklecks, Gsterosteus culetus, hd less roust odies (nrrower odies nd heds, nd shorter cudl peduncle depths) nd ftigued less quickly thn resident ones, coinciding with their hitt use. Erly morphologicl development nd the doption of ndromy Overll, this study demonstrtes tht morphologicl differences cn e detected within species exhiiting two life-history strtegies, residency nd ndromy. Importntly, these differences re powerful enough to develop predictive models for discriminting trout s either migrnt or resident y mesuring only few morphologicl trits. Furthermore, the results gree with the expected hitt use of ndromous nd resident rook trout, where the former exploits fster hitts nd is more morphologiclly dpted for doing so thn the ltter. Although morphologicl vritions relted to hitt use hve een oserved in the wild, uncertinties remin s to how these rise. In prticulr, it is still not fully understood whether fish tht re morphologiclly pre-dpted for swimming in fst wter prefer nd select fster hitts or whether fish modify (phenotypic plsticity) their shpe ccording to the hitt in which they experience. In ddition, it hs not een estlished whether erly differences in physiologicl trits (such s higher eroic metolism) contriute to initil hitt preference nd selection, lthough morphologicl vritions etween morphs hve een found to e oth heritle nd relted to physiologicl performnce (Proulx nd Mgnn 2002, 2004). Erly vritions in metolism nd morphology thus suggest the presence of mechnisms involving oth environmentl nd genetic fctors. Perry et l. (2004) found tht mternl genetic effects were high for emryonic length, ut quickly decresed for post-resorption length in rook trout red from ndromous nd resident prents. They in turn detected low ut significnt heritility for rook trout length t the levin (fter yolk sc resorption) stge. In ddition, it ws lso found tht mternl genetic differentition etween emryonic ndromous nd resident rook trout ws high (Qst > 0.5) nd ws greter thn neutrl genetic divergence in their study for specific emryonic trits including length nd growth rte for length (Perry et l. 2005). Mternl Qst for post-resorption morphologicl trits ws lmost zero (Perry et l. 2005). This work suggests tht post-emergence stges re more susceptile to developmentl chnges induced y erly vritions in environmentl conditions, ecuse mternl effects re gretly wekened. It is thus possile tht immeditely fter emergence, size segregtions occur in strems ccording to hitt. The lrger posthtch individuls (specificlly those with n intrinsiclly high metolic scope), possessing the competitive dvntge for otining etter feeding territories (Johnsson et l. 1999), could exploit the fster velocities chrcterized y high food delivery rtes sooner, leding to susequent morphologicl dpttions. Such predictions re likely ecuse ody shpe my e ltered under different current regimes (Pkksm nd Piironen 2001; Imre et l. 2002; Peres-Neto nd Mgnn 2004). Sgnes et l. (2000) demonstrted shift in ody shpe nd swimming potentil during gryling, Thymllus thymllus, ontogenesis in reltion with hitt use. Gryling, over their ontogeny, developed towrds more hydrodynmiclly efficient shpe for swimming t high velocities. Similrly, comprisons etween older migrnts nd residents with pooled YOY reveled tht YOY were intermedite oth in mximum ody depths nd cudl fin heights, suggesting tht the morphologicl differences oserved etween the two forms diverge with incresing size (dt not shown). Differentil hitt use my thus influence fish morphology t young stges, leding to lrger nd more mesurle chnges over time. Such erly size differences could result in the development of divergent ody forms in prllel with the susequent ioenergetic consequences of hitt use nd ultimtely to the presence of

13 Environ Biol Fish (2008) 81: migrnt nd resident phenotypes. However with the evidence t hnd, it cn only e concluded tht rook trout dopting the migrtory lifehistory strtegy (prior to migrtion) hve higher consumption rtes, exhiit more elevted metolic costs, utilize fster current velocities (Morinville nd Rsmussen 2003, 2006) nd re more stremlined in shpe thn those dopting the resident life-history. Further studies re needed to gin etter understnding of the link etween erly morphologicl development, hitt use nd the dopted life-history strtegy. Acknowledgements We thnk M. Bélnger, S. Bodmer- Roy, A. Boivin, J-F. Bourque, A. DuCp, L. Hrris, G. Krmer, S. Lenormnd nd V. Thériult for field ssistnce nd lortory work. We re grteful to D. Browne for his helpful comments on erlier versions of this mnuscript nd to N. Alfonso for his ssistnce with the liner discriminnt nlyses. This study is contriution to the progrm of CIRSA (Centre Interuniversitire sur le Sumon Atlntique). Funding for this project ws provided to J.B.R. y the Nturl Sciences nd Engineering Reserch Council of Cnd (NSERC; Strtegic Grnt nd Collortive Specil Projects), the Foundtion de l Fune du Quéec, the Government of Quéec (FAPAQ), the Government of Cnd (Economic development), the finncil prtners of CIRSA Inc., nd Grdute Fellowships to G.R.M. from McGill s Deprtment of Biology nd the McConnell Fmily McGill Mjor. References Alfonso NR (2004) Evidence for two morphotypes of lke chrr, Slvelinus nmycush, from Gret Ber Lke, Northwest Territories, Cnd. Environ Biol Fishes 71:21 32 Beemn JW, Rondorf DW, Tilson ME, Venditti DA (1995) Nonlethl mesure of smolt sttus of juvenile steelhed sed on ody morphology. Trns Am Fish Soc 124: Bisson PA, Sullivn K, Nielsen JL (1988) Chnnel hydrulics, hitt use, nd ody form of juvenile coho Slmon, steelhed, nd cutthrot trout in strems. Am Fish Soc 117: Blke RW (1983) Fish locomotion. Cmridge ; New York, Cmridge University Press Boily P, Mgnn P (2002) Reltionship etween individul vrition in morphologicl chrcters nd swimming costs in rook chrr (Slvelinus fontinlis) nd yellow perch (Perc flvescens). J Exp Biol 205: Bourke P, Mgnn P, Rodriguez MA (1997) Individul vritions in hitt use nd morphology in rook chrr. J Fish Biol 51: Drucker EG, Luder GV (2003) Function of pectorl fins in rinow trout: ehviorl repertoire nd hydrodynmic forces. J Exp Biol 206: Ehlinger TJ (1990) Hitt choice nd phenotype-limited feeding efficiency in luegill: individul differences nd trophic polymorphism. Ecology 7: Hor WS (1976) Smolt trnsformtion. J Fish Res Bord Cn 33: Holopinen IJ, Aho J, Vornnen M, Huuskonen H (1997) Phenotypic plsticity nd predtor effects on morphology nd physiology of crucin crp in nture nd in the lortory. J Fish Biol 50: Imre I, McLughlin R, Nokes DLG (2001) Temporl persistence of resource polymorphism in rook chrr, Slvelinus fontinlis. Environ Biol Fish 60: Imre I, McLughlin RL, Nokes DLG (2002) Phenotypic plsticity in rook chrr: chnges in cudl fin induced y wter flow. J Fish Biol 61: Johnsson JI, Noelin F, Bohlin T (1999) Territoril competition mong wild rown trout fry: effects of ownership nd ody size. J Fish Biol 54: Keenleyside MHA (1962) Skin-diving oservtions of Atlntic slmon nd rook trout in the Mirmichi River, New Brunswick. J Fish Res Bord Cn 19: Lesueur C (1993) Compte rendu des résultts otenus lors de l étude de l omle de fontine ndrome de l rivière Ste-Mrguerite (Sgueny) en Assocition de l rivière Ste-Mrguerite, Scré-Coeur, Quéec Mrtin WR (1949) The mechnics of environmentl control of ody form in fishes. Pulictions of the Ontrio Fisheries Reserch Lortory 70:5 76 McCormick SD, Nimn RJ, Montgomery ET (1985) Physiologicl smolt chrcteristics of ndromous nd non-ndromous rook trout (Slvelinus fontinlis) nd Atlntic slmon (Slmo slr). Cn J Fish Aqut Sci 42: McLughlin RL, Grnt JWA (1994) Morphologicl nd ehviourl differences mong recently-emerged rook chrr, Slvelinus fontinlis, forging in slowvs. fst-running wter. Envion Biol Fishes 39: Morinville GR, Rsmussen JB (2003) Erly juvenile ioenergetic differences etween ndromous nd resident rook trout (Slvelinus fontinlis). Cn J Fish Aqut Sci 60: Morinville GR, Rsmussen JB (2006) Does life-history vriility in slmonids ffect hitt use y juveniles? A comprison mong strems open nd closed to ndromy. J Animl Ecol 75: Pkksm S, Piironen J (2001) Wter velocity shpes juvenile slmonids. Evol Ecol 14: Peres-Neto PR, Mgnn P (2004) The influence of swimming demnd on phenotypic plsticity nd morphologicl integrtion: comprison of two polymorphic chrr species. Oecologi 140:36 45 Perry GML, Audet C, Berntchez L (2005) Mternl genetic effects on dptive divergence etween ndromous nd resident rook chrr during erly life history. J Evol Biol 18:

14 184 Environ Biol Fish (2008) 81: Perry GML, Audet C, Lpltte B, Berntchez L (2004) Shifting ptterns in genetic control t the emryolevin oundry in rook chrr. Evolution 58: Pettersson LB, Brönmrk C (1999) Energetic consequences of n inducile morphologicl defence in crucin crp. Oecologi 121:12 18 Power G (1980) The rook chrr, Slvelinus fontinlis. In: Blon EK (ed) Chrrs, slmonid fishes of the genus Slvelinus. The Hgue, Netherlnds, W. Junk, pp Proulx R, Mgnn P (2002) Physiologicl performnce of two forms of lcustrine rook chrr, Slvelinus fontinlis, in the open-wter hitt. Environ Biol Fishes 64: Proulx R, Mgnn P (2004) Contriution of phenotypic plsticity nd heredity to the trophic polymorphism of lcustrine rook chrr (Slvelinus fontinlis M.). Evol Ecol Res 6: Riddell BE, Leggett WC (1981) Evidence of n dptive sis for geogrphic vrition in ody morphology nd time of downstrem migrtion of juvenile Atlntic slmon (Slmo slr). Cn J Fish Aqut Sci 38: Sgnes P, Chmpgne J-Y, Morel R (2000) Shifts in drg nd swimming potentil during gryling ontogenesis: reltions with hitt use. J Fish Biol 57:52 68 Siing FA, Ngelkerke LAJ (2001) Resource prtitioning y Lke Tn rs predicted from fish morphometrics nd prey chrcteristics. Rev Fish Biol Fish 10: Skúlson S, Nokes DLG, Snorrson SS (1989) Ontogeny of trophic morphology in four symptric morphs of Arctic chrr Slvelinus lpinus in Thingvllvtin, Icelnd. Biol J Linn Soc 38: Swin D, Blir HL (1989) Differences in morphology nd ehviour etween juvenile Coho slmon (Oncorhynchus kisutch) rering in lke nd in its triutry strem. Cn J Fish Aqut Sci 46: Tylor EB, Foote CJ (1991) Criticl swimming velocities of juvenile sockeye slmon nd koknee, the ndromous nd non-ndromous forms of Oncorhynchus nerk (Wlum). J Fish Biol 38: Tylor EB, McPhil JD (1985) Burst swimming nd sizerelted predtion of newly emerged Coho slmon, Oncorhynchus kisutch. Am Fish Soc 114: Tylor EB, McPhil JD (1986) Prolonged nd urst swimming in ndromous nd fresh-wter threespine stickleck, Gsterosteus culetus. Cn J Zool 64: Thériult V, Dodson JJ (2003) Body size nd the doption of migrtory tctic in rook chrr. J Fish Biol 63:1 16 Vogel S (1994) Life in moving fluids. Princeton University Press, Princeton, N.J We PW (1975) Hydrodynmics nd energetics of fish propulsion. Deprtment of the Environment Fisheries nd Mrine Service: ville from Informtion Cnd, Ottw We PW (1984) Body form, locomotion nd forging in qutic vertertes. Am Zool 24: We PW (1988) Simple physicl principles nd verterte qutic locomotion. Am Zool 28: Wilder DG (1952) A comprtive study of ndromous nd freshwter popultions of rook trout (Slvelinus fontinlis). J Fish Res Bord Cn 9: Wood BM, Bin MB (1995) Morphology nd microhitt use in strem fish. Cn J Fish Aqut Sci 52: