Freshwater movement patterns by juvenile Pacific salmon Oncorhynchus spp. before they migrate to the ocean: Oh the places you ll go!

Transcription

1 Journal of Fish Biology (2014) 85, doi: /jfb.12468, available online at wileyonlinelibrary.com Freshwater movement patterns by juvenile Pacific salmon Oncorhynchus spp. before they migrate to the ocean: Oh the places you ll go! J. M. Shrimpton*, K. D. Warren*, N. L. Todd, C. J. McRae*, G. J. Glova, K. H. Telmer** and A. D. Clarke *Ecosystem Science and Management (Biology) Program, University of Northern British Columbia, 3333 University Way, Prince George, BC, V2N 4Z9 Canada, Nicola Tribal Association, Nicola Watershed Stewardship and Fisheries Authority, Coutlee Avenue, Merritt, BC, V1K 1B8 Canada, LGL Limited Environmental Research Associates, 9768 Second Street, Sidney, BC, V8L 3Y8 Canada, **School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Rd, Victoria, BC, V8P 5C2 Canada and Freshwater Fisheries Society of British Columbia, 80 Regatta Landing, Suite 101, Victoria, BC, V9A 7S2 Canada Juvenile movement patterns for coho salmon Oncorhynchus kisutch and Chinook salmon Oncorhynchus tshawytscha from two large interior rivers of British Columbia, Canada, were examined. Otoliths from post-spawned fishes were collected on spawning grounds and elemental signatures were determined through transects from sectioned otoliths using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Large variations in otolith elemental signatures were found during the freshwater life stage indicative of movement downstream to rivers and tributaries that differed in elemental signature. This study highlights that downstream movements occur before migration to the ocean during the parr smolt transformation. Extensive downstream movements of parr appear to be a successful life-history strategy based on variations observed in the otolith elemental signatures of spawners. Movements downstream in parr and the remarkable homing ability of adults also suggest that imprinting to natal streams must occur prior to the parr smolt transformation The Fisheries Society of the British Isles Key words: anadromy; elemental signatures; migration; otolith. INTRODUCTION The parr smolt transformation is a complex set of physiological, morphological and behavioural changes that are preparatory for downstream migration and seawater entry. Anadromous salmonids have evolved to respond to natural seasonal changes in environment that stimulate migration in the spring (Zydlewski et al., 2005; Sykes & Shrimpton, Author to whom correspondence should be addressed. Tel.: ; Mark.Shrimpton@unbc.ca Present Address: ERM Consultants Canada Ltd, 3790 Alfred Avenue, Smithers, BC, V0J 2N0 Canada Present Address: Natural Resources and Environmental Studies, National Dong Hwa University, No. 1, Sec. 2, Da Hsueh Road, Shoufeng, Hualien, Taiwan The Fisheries Society of the British Isles

2 988 J. M. SHRIMPTON ET AL. 2010). Endocrine changes associated with smolting have also been shown to be important for the remarkable ability in adult anadromous salmonids to make extensive migrations and locate their natal freshwater streams. Juvenile anadromous salmonids imprint on odours associated with their natal site prior to migrating downstream, and as adults use the olfactory signals for homing on their return journey (Dittman & Quinn, 1996). The process of imprinting as smolts requires exposure for at least 14 days (Yamamoto et al., 2010). As a result of this imprinting process, fidelity to spawning sites is high (Dittman & Quinn, 1996), while the specific habitat used is dependent on the physical characteristics of the stream and intragravel environment (McRae et al., 2012). Selection of a suitable site for spawning is crucial because the highest rates of mortality in salmonids generally occur during the incubation period and this mortality is closely related to the features of the spawning and incubation site (Quinn, 2005). Movement downstream in large catchments, however, has also been documented at times of the year not associated with the spring parr smolt transformation. Juvenile coho salmon Oncorhynchus kisutch (Walbaum 1792) from interior British Columbia use off-channel ponds for overwintering habitat and to avoid periods of high flow (Swales & Levings, 1989). In Chinook salmon Oncorhynchus tshawytscha (Walbaum 1792), movement downstream occurs in the summer and autumn in populations from the upper Fraser River in British Columbia (Bradford & Taylor, 1997; Sykes et al., 2009) and from the Snake River in Idaho (Bjornn, 1971; Achord et al., 2007), a movement pattern that is not linked with smolting. Juvenile O. tshawytscha vary in their tendency to move downstream (Bradford & Taylor, 1997) but factors linked to the magnitude of movements downstream are stream discharge, temperature and habitat availability (Bjornn, 1971). Numbers of parr that move downstream before smolting are appreciable in large rivers; the number of migrating smolts past enumeration traps in the Nechako River, an upper Fraser River tributary, is commonly only 2 15% of the number of parr that move downstream (Sykes et al., 2009). The considerable number of juvenile anadromous salmonid parr observed to move downstream before the parr smolt transformation would suggest that there is some benefit to moving away from the natal spawning habitat. If this is the case, it might be expected that the early migrants are more successful and return in greater numbers to spawn. The parr smolt transformation has been demonstrated to be an important stage of development for imprinting to natal spawning streams (Dittman & Quinn, 1996). Movement downstream of juvenile anadromous salmonids prior to the parr smolt transformation raises a number of questions that are important for successful management of interior Pacific salmon Oncorhynchus spp. populations. How far downstream do the fishes move and what habitat is used? Is this life-history strategy more successful than remaining in the natal stream or near the spawning habitat? If the fishes move downstream early in freshwater residence, does this affect fidelity of returning adults to site of origin? Tracking juvenile salmonid movements is not only challenging due to their small size, but also potential for tag loss and difficulty distinguishing individuals (Roussell et al., 2000). Natural tags using the physiological life processes of the fish to trace movements are an attractive alternative (Campana & Thorrold, 2001). Otoliths are metabolically inert structures that grow by the addition of calcium carbonate layers, usually in the form of aragonite but sometimes vaterite will form part of the structure. Trace elements found in the otolith are primarily derived directly from the water, such as calcium (Ca), strontium (Sr) and barium (Ba), but some are under physiological

3 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP. 989 regulation such as zinc (Zn) (Campana, 1999; Clarke et al., 2007a). Analysing these layers allows researchers to estimate the water conditions surrounding a fish during a given period and use that information to identify likely areas of residence (Campana & Thorrold, 2001) or movement if spatial differences exist within a catchment (Clarke et al., 2007b). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used on otoliths from adult O. kisutch and O. tshawytscha collected on spawning grounds of two interior British Columbia rivers, McKinley Creek and Coldwater River. The change in otolith elemental signatures was used to define putative movement patterns based on correlations in element ratios in the otolith and those of the water. STUDY LOCATION MATERIALS AND METHODS This study was conducted within two large tributary catchments of the Fraser River in central British Columbia, the Horsefly and Nicola Rivers (Fig. 1); both systems have important spawning habitat foroncorhynchus spp. populations. In the Horsefly River catchment, McKinley Creek is one of the larger tributaries to the Horsefly River, entering the river downstream of a 10 m waterfall that creates a barrier to upstream fish migration and effectively excludes migratory fishes from moving into the upper half of the Horsefly River. McKinley Creek is a proposed indicator catchment as it is one of the few systems where O. kisutch from the interior Fraser River have been documented to spawn and a long-term enumeration of spawners has been conducted. The Horsefly River flows into the Fraser River by way of Quesnel Lake and the Quesnel River. In the Nicola River catchment, the Coldwater River is an important spawning system that is currently the site of two Oncorhynchus spp. enhancement approaches. Production of O. kisutch and O. tshawytscha in the Coldwater River is supplemented by the Spius Creek hatchery, using brood stock captured in the Coldwater River. Additionally, spawning and juvenile rearing habitat was created in the Coldwater River catchment as compensation following construction of the Coquihalla Highway and the Nicola Tribal Association is implementing further habitat restoration projects. The Coldwater River flows into the Nicola River and then into the Thompson River before joining the Fraser River. SPATIAL HETEROGENEITY OF WATER CHEMISTRY To determine the heterogeneity of chemical signatures in the streams and rivers within the study locations, water samples were collected in duplicate from 45 locations in the McKinley, Horsefly and Quesnel catchments (August 2007) and from 52 locations in the Coldwater, Nicola and Thompson catchments (August 2007 and 2008; 17 sites sampled in both years). Methods for obtaining water samples followed the recommendations outlined by Shiller (2003) for sampling dissolved elements in remote locations, with some minor modifications as outlined by Clarke et al. (2007b). Water analysis was completed with a Leeman Labs PS 1000-UV inductively coupled plasma optical emission spectrometer (ICP-OES) (Teledyne Instruments Leeman Laboratories; The elements measured included Ca, Sr, Ba, magnesium (Mg) and manganese (Mn). Four calibration standards prepared from traceable (NIST) standards were run for every 10 samples analysed. Laboratory blanks and field procedural blanks were also included in the analysis. To provide a visualization of geographical separation using water chemistry data, the Sr:Ca was plotted against Ba:Ca for each water sample location in both catchments. Water chemistries were obtained from multiple sites in all mainstem rivers of each catchment and multiple tributaries where juvenile salmonids had previously been observed (Fig. 1). To define the range of water chemistries characteristic of each sampling catchment, a confidence ellipse was created for each mainstem river and also for tributaries from each mainstem river with similar water

4 Creek 990 J. M. SHRIMPTON ET AL km (a) Quesnel Fraser River River Horsefly River McKinley River (b) Thompson Nicola River Fraser River Spius Coldwater Creek River N Fig. 1. Map of locations where water samples were collected; in each figure closed symbols are main stem water sample sites and open symbols are sample sites from tributaries. (a) McKinley Creek ( ), Horsefly ( ) and Quesnel ( ) River catchments and Fraser River ( ) (b) Coldwater ( ), Nicola ( ) and Thompson ( ) River catchments and Spius Creek Hatchery ( ). Spawners were collected at sites: Oncorhynchus kisutch ( )andoncorhynchus tshawytscha ( ). chemistries. Ellipses were centred on the mean Sr:Ca and Ba:Ca values with boundaries defined by the unbiased s.d. of Sr:Ca and Ba:Ca. The default probability of was used for ellipse creation (SYSTAT 7.0; FISH COLLECTION Sagittal otoliths were collected from post-spawned carcasses. Oncorhynchus kisutch (n = 40) were collected in 2007 from McKinley Creek above an enumeration fence located c. 200 m

5 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP. 991 upstream of the confluence with the Horsefly River. Oncorhynchus tshawytscha (n = 25; 10 collected in 2007 and 15 collected in 2008) and O. kisutch (n = 25; 15 in 2007 and 10 in 2008) that had died on the spawning grounds of the Coldwater River were also used for the study. For the 2007 Coldwater River O. kisutch spawners, three fish were included that were of known Spius Creek hatchery origin, indicated by clipped adipose-fin. For hatchery fishes, the water chemistry during the juvenile phase was known until they were released as smolts into the upper Coldwater River where they generally migrate to the ocean soon after transport. The constant water chemistry of the hatchery environment, therefore, served as a comparison to the wild fishes and helped to assess whether the method was able to determine spatial movements. To determine the relationship between the measured water elemental ratios and the corresponding ratios in the otoliths, juvenile O. kisutch were collected from four locations in the Horsefly River catchment (McKinley Creek, n = 4; Horsefly River, n = 4; Patenaude Creek, n = 4; Woodjam Creek, n = 4) and an additional four locations in the Coldwater River catchment (Juliet Creek side channel, n = 3; Flynn ponds outlet, n = 3; Zulton Kunn ponds outlet, n = 3; lower Coldwater River, n = 1). OTOLITH PREPARATION Sagittal otoliths were removed from fishes and sonicated for 5 min in ultra pure water. Otoliths were then embedded in epoxy resin (Allied High Tech; and ground in the transverse plane with 1200 μm silicon carbide paper until the core was reached. Ultra pure water was used during wet grinding to prevent external contamination of the samples. Otoliths were then sequentially polished with 6, 1 and finally 0 05 μm diamond suspension to ensure an adequate surface for ablation with the laser. LA-ICP-MS analysis was conducted following the protocol outlined in the study of Sanborn & Telmer (2003). Material was extracted from the otolith with a VG Elemental PQ II S + high sensitivity ICP-MS (Thermo Electron Corporation; coupled to a Merchantek UV laser ablation system (New Wave Research; The laser system was operated with an output of 266 nm that had a maximum energy output of 4 mj. Optimization was conducted using standard reference material (SRM) 613 NIST glass which contains c. 50 μg g 1 of total trace elements. The width of the laser scan was measured after analysis with a microscope-mounted micrometre and determined to be μm. All otoliths scans were completed by tracking the laser across the otoliths at 5 3 μm s 1. The isotopes measured in the otoliths were 25 Mg, 43 Ca, 55 Mn, 65 Zn, 86 Sr and 137 Ba. Calcium was used as the internal standard due to the otoliths aragonite (CaCO 3 ) composition, which has a known and consistent Ca content (40% molar mass). An internal standard was used to account for variations in aerosol production caused by the variation in the amount of material being extracted from the otolith by the laser. Background intensities were collected for 30 s prior to turning on the laser. Data collection and reduction were completed using VG Thermo Electron PlasmaLab Software, version (Thermo Electron Corporation). The fully quantitative analysis option was chosen and an SRM 613 NIST glass was selected as the known standard. Two SRM 613 NIST glasses were analysed at the start and end of each run. These certified standards were used to complete an external drift correction to compensate for any changes in machine sensitivity. Five otoliths were analysed between each set of standards. An SRM 611 NIST glass was analysed after every five otolith samples to determine accuracy from how close the measured composition was to the true composition and precision by assessing the amount of variation in repeat analysis of the same material. The relationship between water elemental signatures and otolith microchemistry was determined by linear regression of the chemical signature at the outer edge of the otolith as a function of water chemistry from the location of capture. The outer 30 μm of each otolith from juvenile O. kisutch was used as it represents the most recent time period experienced by the fish before capture. Putative movement patterns for fish during the freshwater phase were then calculated by using coefficients from the otolith to water linear regression. Laser line scans were initiated at one edge of the otolith, run through the core and continued to the other edge. As a consequence, the marine signature of the adult is at either edge, and the maternal signature is in the middle of the line scan. Water Sr:Ca is high in seawater and generally lower in fresh water and Ba:Ca

6 992 J. M. SHRIMPTON ET AL. Otolith Sr:Ca (mmol mol 1 ) Marine Fresh water Maternal Fresh water Marine Distance (μm) Otolith Ba:Ca (mmol mol 1 ) Fig. 2. Representative otolith laser ablation-linescans for an Oncorhynchus kisutch spawner from the Coldwater River (co674)., changes in strontium to calcium;, changes in barium to calcium from outer edge through the core to the other edge., marine, freshwater and maternal regions. is low in seawater and generally higher in fresh water. This relationship was used to define the freshwater portion of the otolith line scans. Water elemental chemistry signatures were then calculated for every 20 μm of the otolith elemental line scans from the decline in Sr:Ca (and corresponding increase in Ba:Ca) to the portion of the otolith line scan that showed a marked increase in Sr:Ca (and corresponding decrease in Ba:Ca) for each fish (Fig. 2). The relationship between otolith elemental signatures and water elemental chemistry determined for juvenile O. kisutch was also used for interpretation of movement patterns in O. tshawytscha. It is likely that elemental uptake is consistent within related species as the relationship for O. kisutch was found to be similar to that of Arctic grayling Thymallus arcticus (Pallas 1776) from a previous study (Clarke et al., 2007b). To determine the number of distinct water chemistry signatures each fish encountered throughout their juvenile freshwater residence, changes in otolith elemental ratios were determined using a change-point analysis, a technique to assess whether a change has occurred in time-ordered data. The technique is flexible and robust to issues of non-normality and outliers within the data set. Change-point analysis determined whether there had been a change in the underlying process that generates the sequence of events and identified where the change occurred. The test assumes that the observations form an ordered sequence and that initially the distribution of responses has one median. The change-point analysis determined if and at what point there was a shift in the median of the distribution. The commercial software Change-Point Analyzer (version 2.3; Taylor, 2000) was used. The average number of water chemistry signatures determined from the change-point analysis was then determined for each catchment and for each species within a catchment. Movement patterns were further characterized as to whether or not fishes stayed within their natal river system until they smolted and migrated to the ocean. Fishes with otolith elemental ratios that remained within the range of elemental signatures bounded by the confidence ellipses of either McKinley Creek or the Coldwater River were considered natal stream residents as juveniles. Otolith Sr:Ca and Ba:Ca values that overlapped with elemental signatures for river systems other than the natal stream were considered not to have remained within their natal river systems as juveniles. The number of natal stream residents was expressed as a percentage of the total number of fishes sampled for each year. Fishes of hatchery origin from the Coldwater River were not included in the analysis.

7 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP. 993 RESULTS SPATIAL HETEROGENEITY OF WATER CHEMISTRY Considerable differences existed in chemical signatures among the tributaries and rivers sampled in the two study catchments (Fig. 3). Although variation in elemental signatures is evident within each river system, differences in elemental ratios for either Sr:Ca, Ba:Ca or both resulted in little overlap in chemical signature among rivers. Generally, it was possible to discriminate water chemistries among the larger rivers and their tributaries. Variation in elemental signature for the two rivers where spawning fishes were collected, however, made it possible to discriminate water chemistries within these two rivers. The upper McKinley had a greater range of Sr:Ca values compared to the lower McKinley [Fig. 3(a)]. The upper Coldwater had higher Sr:Ca 1 0 (a) Water Ba:Ca (mmol mol 1 ) (b) Water Sr:Ca (mmol mol 1 ) Fig. 3. Mean ratios for Sr and Ba relative to Ca for duplicate samples collected in (a) the Horsefly River catchment [McKinley Creek ( ), Horsefly River ( ), Quesnel River ( ) and Fraser River ( )] and (b) the Nicola River catchment [Coldwater River ( ), Nicola River ( ), Spius Creek ( ) and Thompson River ( )] (see Fig. 1). Open symbols, mainstems; closed symbols, tributaries; darker coloured symbols, sample sites further upstream. Confidence ellipses were drawn to define water chemistries for mainstem rivers ( ) and tributaries with similar elemental signatures ( ).

8 994 J. M. SHRIMPTON ET AL. and Ba:Ca levels than the lower Coldwater [Fig. 3(b)]. There were also substantial differences in water chemistry within each catchment and the water chemistry of most tributaries showed considerable differences from the mainstem rivers. OTOLITH ELEMENTAL SIGNATURE AND WATER CHEMISTRY Otolith elemental signatures for juvenile O. kisutch captured in the Horsefly catchment (n = 16; four locations) and Coldwater catchment (n = 10; four locations) were compared with that of the water elemental signatures for locations of capture. LA-ICP-MS revealed substantial differences in otolith chemistry among rivers and tributaries where juvenile O. kisutch were captured. Highly significant relationships between otolith chemical ratios and the chemical ratios found in the water were found for Sr:Ca (F 1,24 = 132, P < 0 001) and Ba:Ca (F 1,24 = 838, P < 0 001) (Fig. 4). A significant relationship was found for Mn:Ca (F 1,24 = 45 6, P < 0 001) for the two catchments combined, but there was no relationship for samples collected in the Nicola River catchment (F 1,8 = 0 266, P > 0 05). No relationship existed for Mg:Ca (F 1,24 = 0 032, P = 0 86). Mn and Mg, therefore, were not included in further analysis. PATTERNS OF CHANGE IN OTOLITH ELEMENTAL SIGNATURES Changes in otolith elemental signature indicate that fishes are experiencing different water chemistries that reflect movement. Using the relationships between otolith Otolith Sr:Ca (mmol mol 1 ) Otolith Ba:Ca (mmol mol 1 ) (a) (b) Water element:ca (mmol mol 1 ) Fig. 4. Linear regressions for elemental concentration in otoliths from juvenile Oncorhynchus kisutch as a function of the water element to calcium ratios for (a) strontium and (b) barium. Horsefly River catchment ( ; n = 16) and Coldwater River catchment ( ; n = 10) fish were used in the analysis. The curves were fitted by: (a) y = 162x 156 (r 2 = 0 86) and (b) y = 9 79x (r 2 = 0 97).,, mean ± s.e.;, individual fish.

9 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP. 995 elemental signature and water chemistry (Fig. 4), potential water chemistries for juvenile O. kisutch were calculated from emergence until capture (Fig. 5). Two juvenile O. kisutch from the Horsefly catchment caught in McKinley Creek (M2; blue solid line) and Patenaude Creek (P1; red dashed line) demonstrate the variation in putative movement patterns [Fig. 5(a)]. Both fish appear to have come from spawning sites in 1 0 (a) FR 0 8 HR HT 0 6 UM LM B AA Water Ba:Ca (mmol mol 1 ) QR HT B (b) UC A NT NR B LC A B SP TR Water Sr:Ca (mmol mol 1 ) Fig. 5. Elemental water signatures for Sr:Ca and Ba:Ca calculated from otolith laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data based on relationships in Fig. 4. (a) Two juvenile Oncorhynchus kisutch from the Horsefly catchment caught in McKinley Creek (M2; ) and Patenaude Creek (P1; ). (b) Two juvenile O. kisutch from the Nicola catchment caught in Juliet Creek side channel (J1; ) and a fish caught in the Flynn Beaver pond outlet (F2; ). Open symbols on the elemental line traces for each fish represent averages across 5 μm of otolith. A, elemental signatures after emergence; outside the zone influenced by maternally inherited marine signatures. B, the elemental signature when the fish were caught. Confidence ellipses were drawn to define water chemistries for mainstem rivers ( ) and tributaries with similar elemental signatures ( ). Individual tributaries that did not cluster with other tributaries from a given catchment are shown as single points as in Fig. 3. (a) UM, upper McKinley; LM, lower McKinley; HR, Horsefly River; HT, Horsefly tributaries; QR, Quesnel River; FR, Fraser River. (b) UC, upper Coldwater; LC, lower Coldwater; NR, Nicola River; NT, Nicola tributary; SP, Spius Creek; TR, Thompson River.

10 996 J. M. SHRIMPTON ET AL. an upper McKinley Creek tributary (marked A) and then spent time in a second upper McKinley tributary. Fish M2 then moved to the lower portion of McKinley Creek where it was caught (marked B). After moving downstream from the upper McKinley, fish P1 appears to have moved directly to tributary habitat in the Horsefly River, Patenaude Creek where it was caught (marked B). Juvenile O. kisutch from the Coldwater catchment also showed considerable differences in patterns of movement; a fish caught in Juliet Creek side channel (J1; blue dashed line) and a fish caught in the Flynn Beaver pond outlet (F2; red solid line) are shown in Fig. 5(b). Fish J1 moved from upper Coldwater [Fig. 5(b); dashed blue line, marked A] to Juliet Creek side channel where it was caught (marked B). Fish F2 moved from water chemistry indicative of Juliet Creek soon after emergence (solid red line, marked A), spent time in the upper Coldwater River and was captured in the outlet from the lower Flynn Beaver pond (marked B). Potential water chemistries experienced during freshwater residence for spawning fishes were also assessed, water elemental chemistry signatures that are high in Sr:Ca (and low in Ba:Ca) are indicative of maternal signature and marine signature. The intervening signatures that were low in Sr:Ca (and high in Ba:Ca), therefore, were considered to be juvenile freshwater signatures (Fig. 2). Five fishes were excluded from the analysis as the core was missed during laser ablation; two McKinley Creek O. kisutch, two Coldwater River O. tshawytscha and one Coldwater River O. kisutch. For the remaining fishes, examination of the freshwater portion of otoliths showed considerable variation in elemental signatures indicative of movement among waters with different elemental chemistries from both catchments. Elemental chemistries are shown in Fig. 6 for O. kisutch spawners that demonstrate the variation in putative movement patterns of the fish as juveniles. Two McKinley Creek spawners appeared to have used habitat in the upper McKinley before moving through the lake to the lower McKinley [Fig. 6(a)]. One of the fish remained in the lower McKinley until the rapid increase in otolith Sr:Ca suggested migration to the ocean (blue solid line), while the second used habitat in at least two tributaries to the Horsefly River before migrating to the ocean (red dashed line). In the Nicola River catchment, two Coldwater River O. kisutch spawners had otolith elemental signatures that suggested early freshwater rearing in the upper Coldwater (marked A) and then moved downstream [Fig. 6(b)]. One fish used enhancement habitat and also habitat in the lower Coldwater before migrating to the ocean (red solid line). The other fish appears to have used tributary habitat in the upper Coldwater with a similar elemental signature to the lower Coldwater prior to moving downstream and residing in the Nicola River before migrating to the ocean (blue dashed line). The third Coldwater River spawner shown in Fig. 6(b) (green dotted line) was a hatchery fish. Elemental signatures for Sr:Ca and Ba:Ca varied little for most of the freshwater portion of the otolith and remained within the range of values bounded by the confidence ellipse for Spius Creek water chemistry. An increase in Ba:Ca was observed in the otolith consistent with transport from the hatchery to the upper Coldwater River where Ba:Ca is higher. Other hatchery fishes also showed little variation in Sr:Ca and Ba:Ca until Ba:Ca increased, which was observed in five of the eight hatchery fishes. The high Ba:Ca levels declined just before levels of Sr:Ca in the otolith became very high and indicated ocean entry. Otolith microchemistry suggests that some juvenile fishes spend most of the freshwater phase in their natal river system, while others move downstream into the larger river systems such as the Horsefly or Nicola River before smolting. Fishes with otolith Sr:Ca and Ba:Ca signatures that remained within the range of elemental signatures

11 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP (a) FR 0 8 HR A HT Water Ba:Ca (mmol mol 1 ) UM LM HT (b) UC A QR B B 4 A 3 LC A NT NR B A B Water Sr:Ca (mmol mol 1 ) B SP TR Fig. 6. Elemental water signatures for Sr:Ca and Ba:Ca calculated from otolith laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data based on relationships in Fig. 4. (a) Two Oncorhynchus kisutch spawners from McKinley Creek (Q3, ; Q16, ). (b) Two wild origin O. kisutch spawners from the Coldwater River (co690, ; co466, ) and one hatchery origin O. kisutch spawner from the Coldwater River (co480, ). Open symbols on the elemental line traces for each fish represent elemental averages across 20 μm of otolith. A, elemental signatures after emergence; outside the zone influenced by maternally inherited marine signatures. B, the elemental signature for fish before the large increase in Sr indicative of migration and entry into seawater when the fish smolted. Confidence ellipses and symbols defined in Fig. 5. bounded by the confidence ellipses of either McKinley Creek or the Coldwater River (Fig. 6) were considered natal stream residents as juveniles. Otolith Sr:Ca and Ba:Ca values that overlapped with elemental signatures for river systems other than the natal stream were considered not to have remained within their natal river systems as juveniles. The percentage of natal stream residents for all the fish examined in this study was 47% indicating considerable movement downstream prior to smolting for interior British Columbia wild juvenile anadromous salmonids (Table I). Evidence for one Coldwater O. kisutch spawner sampled in 2007 with otolith elemental signatures that did not overlap with that of the Coldwater River was also found; this fish appears to have been in the Nicola River and tributaries throughout the juvenile freshwater phase, but spawned in the Coldwater River.

12 998 J. M. SHRIMPTON ET AL. Table I. The number of different water chemistry signatures experienced during the juvenile freshwater life stage of wild spawning Oncorhynchus kisutch and Oncorhynchus tshawytscha in the Coldwater River and McKinley Creek. Changes in Sr:Ca and Ba:Ca were determined using a change-point analysis (Taylor, 2000). Natal stream residents were fishes that only exhibited otolith elemental signatures from the system where they were retrieved as spawners. Values are mean ± s.d. and ranges given in parentheses Number of movements in fresh water Year Sr:Ca Ba:Ca n % Natal resident O. kisutch Coldwater River ± 2 0(2 6) 5 0 ± 2 5(2 8) 9 78 Coldwater River ± 1 5(2 5) 2 4 ± 1 1(2 4) 6 50 McKinley Creek ± 1 4(2 8) 4 4 ± 1 5 (2 9) O. tshawytscha Coldwater River ± 1 2(3 6) 4 1 ± 1 7(2 7) 9 44 Coldwater River ± 1 8(3 9) 5 3 ± 1 8 (3 9) n, sample size. Otoliths were analysed from both wild spawned and hatchery origin fishes collected in the Coldwater River. Otoliths from Spius Creek hatchery O. kisutch (four collected in 2007 and three collected in 2008) and O. tshawytscha (one collected in 2008) showed little change in Sr:Ca or Ba:Ca [Fig. 6(b)]. For wild spawned O. kisutch and O. tshawytscha, however, multiple distinct elemental chemistry signatures were found for the freshwater portion of the otolith suggesting considerable movement of wild juvenile fishes before they smolted (Table I). The number of movements in wild fishes as juveniles was highly variable for both species, in both years and also between the two catchments; only wild O. kisutch were present in McKinley Creek. Interestingly, potential movements for fishes from the Coldwater River were greater when fishes remained within their natal river system than for fishes that appeared to move downstream to the Nicola River. Probably, this does not reflect a difference in movement patterns, but rather the greater similarity of elemental signatures in water samples collected throughout the Nicola River. Analysis from this study suggests that considerable downstream movements occur before fishes smolt and migrate to the ocean. DISCUSSION Previous studies have used otolith microchemistry to demonstrate habitat shifts for fishes at the individual level (Veinott et al., 1999; Zimmerman & Reeves, 2002) or discriminate among fish populations (Kennedy et al., 1997; Clarke et al., 2007b); however, this study has used changes in elemental composition to track specific habitat use by Oncorhynchus spp. during the freshwater life-history stage. Spatial differences in water chemistry must exist to use otolith microchemistry for determining movements of fishes. The Horsefly and Nicola River catchments and tributaries showed substantial spatial differences in water chemistry enabling discrimination among rivers and streams. Data presented in this study support earlier work by Wells et al. (2003) and Clarke et al. (2007b) who were successful in discriminating geographical locations

13 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP. 999 using chemical signatures measured in freshwater environments. Spatial differences in the chemistry of fresh waters largely reflect differences in age and composition of the underlying bedrock. These differences result in variation among stream chemistries within a catchment. Consistency within river systems has been well described by Taylor & Hamilton (1994) who examined 25 years of water chemistry data on the Saskatchewan River system and found that elemental ratios remained fairly constant over time. Monthly measurements over a 2 year period from the Adour Basin in France, however, found that Sr:Ca ratios fluctuated seasonally (Martin et al., 2013). Fluctuations in water elemental chemistry were mainly driven by water flow regimes, but interestingly were not reflected in the otoliths of juvenile Atlantic salmon Salmo salar L Otolith Sr:Ca ratios during freshwater residency for these fish were stable for each site and were related to water Sr:Ca ratios during low flow periods. While interannual differences in otolith elemental composition among rivers were observed, this variability was minor compared to spatial differences and did not limit classification of juveniles to their natal stream (Martin et al., 2013). Further support for consistency in elements incorporated into otoliths from water with different chemistry signatures has been shown in the stability of Sr:Ca and Ba:Ca measured across otoliths of slimy sculpins Cottus cognatus Richardson 1836 (Clarke et al., 2004). Cottus cognatus are considered to be non-migratory, with their otolith elemental concentrations maintaining a flat profile for 2 5 years depending on the age of the fish. Lack of changes in elemental signature across much of the otolith for the fish examined indicates that chemical signatures are quite stable. Changes in elemental signatures from the otoliths used in this study, therefore, should represent movement to locations within the catchment where the elemental ratios differ. EXTENT OF DOWNSTREAM MOVEMENT AND HABITAT USE There was considerable variation in Sr:Ca and Ba:Ca in otoliths for both species during the freshwater rearing phase in the Horsefly and Nicola catchments. The simple interpretation of this finding is that the fishes did not remain in the same habitat throughout their juvenile freshwater stage. The variation in elemental signatures for Sr:Ca and Ba:Ca reflects movements of fishes among freshwater habitats with differing concentrations of these elements. Among individuals from each species, however, there were no common patterns, indicating tremendous diversity of movement patterns and consequently freshwater habitat occupied. It was not always possible to identify location within a mainstem river, although it was possible at the catchment scale to differentiate between tributaries and rivers. The analysis indicates that O. tshawytscha and O. kisutch juveniles do not remain in the upper Coldwater River catchment, but move down into the lower Coldwater River. Some fishes also moved into the Nicola; 27% of O. kisutch and 36% of O. tshawytscha from the two brood years combined moved out of the Coldwater River. A greater proportion of juvenile O. kisutch moved out of McKinley Creek; 68% of the fish exhibited otolith elemental signatures characteristic of the Horsefly River or Horsefly tributaries before smolting and migrating to the ocean. The difference in emigration from the two natal rivers systems is probably due to size of the rivers; the Coldwater River is approximately three times longer than McKinley Creek. Enhancement features constructed in the Coldwater River system as rearing habitat for juvenile anadromous salmonids may

14 1000 J. M. SHRIMPTON ET AL. also contribute to the difference as no such habitat modifications have been built in McKinley Creek. The analysis of the otoliths removed from spawning adult fishes by LA-ICP-MS suggests that juvenile O. kisutch and O. tshawytscha exhibit highly variable movement downstream from spawning areas, with some fishes moving considerable distances downstream into larger river systems. Variation in O. tshawytscha fry dispersal behaviours has been found among individuals from populations throughout the Upper Fraser River (Bradford & Taylor, 1997). There is also evidence that O. kisutch move downstream to larger pool habitat (Peterson, 1982) or into tributaries and side channels (Swales & Levings, 1989) when mainstem rivers increase in flow and decrease in temperature in late autumn. Downstream movements of juvenile anadromous salmonids in this study did not appear to extend beyond either the Horsefly or Nicola Rivers until the spring smolt migration and seawater entry. Elemental signatures distinctive of fish rearing in the Quesnel River or Thompson River were not found during the freshwater portion of the otolith. It would appear, therefore, that the Quesnel River, the Thompson River and also the Fraser River are probably only used as migration corridors by juvenile anadromous salmonids from McKinley Creek and the Coldwater River. Consequently, larger river systems do not have an appreciable contribution to rearing habitat for O. kisutch or O. tshawytscha from the two study catchments. MOVEMENT PATTERNS AND SURVIVAL POTENTIAL The use of otoliths as natural tags provided insight into habitat use for juvenile anadromous salmonids spawned in two interior Fraser River catchments. The change-point analysis indicated that fishes moved between areas that differed in chemical signature, from two to eight and on average more than four different water elemental chemistry signatures before seaward migration. Previous work has indicated that coastal anadromous Oncorhynchus spp. juveniles are fairly stationary during the juvenile life stage (Bell et al., 2001) and it is often assumed that deviations from strict site-fidelity in juvenile O. kisutch are caused by forced migration (Bell et al., 2001; Minakawa & Kraft, 2005). The results of this study indicate that variability in habitat use during emigration may be a normal characteristic of interior anadromous Oncorhynchus spp. life history. It has been suggested that migratory juvenile salmonids have higher growth and survival rates than do stationary juveniles (Swales & Levings, 1989; Kahler et al., 2001). A positive effect on growth rate and survival suggests that movement carries few penalties and confers benefits to individuals. The reason for emigration from natal interior streams by anadromous juvenile salmonids is probably due to a difference in habitat requirements for incubation compared to requirements for juvenile rearing; cold, low productivity streams benefit incubating eggs, but are ill-suited for rearing juveniles (Quinn, 2005). Emigrating from natal areas may allow juvenile anadromous salmonids to find more suitable habitat and increase their survival. DOWNSTREAM MOVEMENT AND EFFECT ON HOMING Previous studies have shown that the sensitive period for olfactory imprinting in anadromous salmonids is during the parr smolt transformation (Dittman & Quinn,

15 MOVEMENT PATTERNS IN JUVENILE ONCORHYNCHUS SPP ; Yamamoto et al., 2010). Evidence from otolith elemental signatures from Spius Creek hatchery-reared anadromous salmonids in this study supports that the parr smolt transformation is important for imprinting. Smolts are transported from Spius Creek hatchery to the upper Coldwater River in the spring. The upper Coldwater River has much higher Ba:Ca than Spius Creek hatchery water and a spike in Ba:Ca was observed in most of the hatchery spawners. The increase in Ba:Ca suggests that the fishes resided long enough to incorporate elements from and imprint on the water of the upper Coldwater River. Otolith elemental signatures for wild spawning anadromous salmonids in this study not only had signatures during the juvenile portion of the life cycle distinctive of their natal stream, but also had elemental signatures that represented considerable movement downstream from spawning locations into non-natal tributaries and larger river systems. If the imprinting period only occurs during the parr smolt transformation, greater straying might be expected in populations where individual fishes move downstream before smolting. Evidence of straying into the Coldwater River was found; one O. kisutch had no evidence of juvenile history in the Coldwater River, but was found as an adult in the Coldwater River where it went to spawn. It is likely that this individual was spawned in the Nicola River, where it stayed as a juvenile until smolting. Low levels of gene flow associated with straying have been documented in interior British Columbia catchments and may elevate effective population size and preserve genetic variability (Walter et al., 2009). In this study, with the exception of one spawning fish, the rest of the wild spawned fishes returned to their natal river system to spawn as adults, demonstrating a remarkable capacity to return to their natal spawning area. It is suggested that the sensitive period for olfactory imprinting occurs before the parr smolt transformation. Elevated thyroid hormone levels enhance olfactory sensitivity during the parr smolt transformation (Dickhoff & Sullivan, 1987; Dittman & Quinn, 1996). In hatchery-reared fishes, increases in thyroid hormone have been documented at other stages of development, notably at emergence and during rapid summer growth (Dickhoff & Sullivan, 1987). Migration patterns of wild juvenile anadromous salmonids from interior British Columbia streams suggest that long-term memories of odours important for homing develop before the parr smolt transformation, potentially as early as emergence. SIGNIFICANCE Freshwater life histories of juvenile anadromous salmonids in rivers from the interior of British Columbia may involve substantial movement between tributaries, side channels and mainstem river areas for rearing. No pattern of freshwater movement was consistent among the adult spawners that returned to McKinley Creek or the Coldwater River, suggesting tremendous variation within both catchments. Variability in juvenile movement is probably important for population sustainability. Diversity of movement patterns in juveniles may provide resilience for the populations against perturbations or stochastic events. Salmonid habitat requirements, however, are often examined with the assumption that juveniles are relatively stationary and therefore usually refer to a single natal reach or stream. The elemental signatures from otoliths of McKinley and Coldwater adult spawning anadromous salmonids suggest that a

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