Movement and Habitat Use of Juvenile Lake Sturgeon (Acipenser Fulvescens , Rafinesque, 1817) in a Large Hydroelectric Reservoir (Nelson River, Canada)

Received: 2 October 2016 | Accepted: 15 January 2017 DOI: 10.1111/jai.13378

ORIGINAL ARTICLE

Movement and habitat use of juvenile Lake Sturgeon (Acipenser fulvescens , Rafinesque, 1817) in a large hydroelectric reservoir (Nelson River, Canada)

C. L. Hrenchuk | C. A. McDougall | P. A. Nelson | C. C. Barth

North/South Consultants Inc. , Winnipeg , MB , Canada Summary Movement and habitat utilization of juvenile Lake Sturgeon (Acipenser fulvescens) were Correspondence Claire L. Hrenchuk, North/South Consultants examined in Stephens Lake, a large hydroelectric reservoir on the Nelson River, Inc., Winnipeg, MB, Canada. Manitoba, Canada, between 21 June 2011, and 15 October 2012. Stephens Lake is Email: [email protected] defined by a sharp hydraulic gradient at the upstream end (Gull Rapids) and a pro- Funding information nounced reservoir transition zone (RTZ ), characterized by a change in substrate com- Keeyask Hydropower Limited Partnership ; Manitoba Hydro’ s Lake Sturgeon Stewardship position from coarse to fine. Twenty juvenile Lake Sturgeon <600 mm fork length and Enhancement Program were captured in the RTZ , implanted with acoustic transmitters, and tracked using stationary receivers. Our primary hypothesis considered that, if foraging behaviour was contingent on sand substrate, these fish would spend the majority of the open- water season foraging in the relatively small area where hydraulic gradients dictate sand deposition. Data indicated that tracked individuals were highly bottom oriented, and utilized deeper thalweg habitats exclusively during the first open-water season. On average, juveniles spent only 22% of their open-water time in the RTZ (river kilo- meter [rkm] 4.5–7.0). Most fish spent more time upstream as opposed to downstream, but a few individuals did utilize backwatered thalweg areas, suggesting that silt-overlay habitats may be suitable for foraging. A seasonal spatial shift in distribution was also observed. Juveniles vacated the RTZ as winter progressed, moving further downstream and occasionally laterally into backwatered shallows, potentially avoiding extreme ice conditions and a large hanging ice dam that develops downstream of Gull Rapids. After ice break-up, most individuals with active tags returned to the upstream end of Stephens Lake. The results add to the growing body of evidence that suggests factors other than habitat suitability influence Lake Sturgeon movement and utilization patterns, raising questions about the mechanisms for core-area affinity in this species.

1 | INTRODUCTION have been cited as the most important factors in population declines of the species observed over the past 150 years (Beamesderfer & Farr, The Lake Sturgeon (Acipenser fulvescens) was once abundant in many of 1997; Birstein, 1993 ; Haxton, Whelan, & Bruch, 2014 ). Assessments the lakes and rivers throughout their North American range (Harkness made during the past 30 years have considered the Lake Sturgeon & Dymond, 1961 ; Scott & Crossman, 1973 ). Over-exploitation, habitat to be threatened throughout most of its extant range in the United alterations and migratory impediments caused by dams, as well as pol- States (Billard & Lecointre, 2001 ; Peterson, Vecsei, & Jennings, 2007 ; lution in the Great Lakes, Mississippi, and Hudson Bay drainage basins, Williams et al., 1989 ), and populations in Western Canada were

(c. 2006) recommended to be listed as endangered under the Species varies with geomorphology (e.g., Boreal Shield, Prairie, etc.), across the at Risk Act (COSEWIC, 2006 ). Over the past several decades, com- species’ range and needs to be considered. Many authors have empha- mercial fisheries have been closed (Bogue, 2000 ; Haxton et al., 2014 ; sized the importance of sand or a combination of sand/gravel substrate Stewart, 2009 ) and tighter environmental regulations appear to have as foraging habitat for young Lake Sturgeon (Benson et al., 2005 ; Boase allowed several systems, particularly those on which pulp and paper et al., 2014 ; Chiasson et al., 1997 ; Holtgren & Auer, 2004 ; Kempinger, mills were built, to recover from pollution (Rusak & Mosindy, 1997 ; D. 1996; Peake, 1999 ; Smith & King, 2005 ; Werner & Hayes, 2004 ), so Gibson, Ontario Power Generation, pers. comm.), which bodes well for the predicted near-absence of this substrate in the reservoir for the the recovery of Lake Sturgeon populations in these areas. However, Keeyask Generating Station (GS; currently under construction) on the the demand for sustainable and renewable energy is increasing across Nelson River, Manitoba was flagged as potentially problematic during North America and many of the larger river systems in northern pre-Project planning in the late 2000’ s (Keeyask Hydropower Limited Manitoba, Ontario, and Québec, which have existing or are favoured Partnership, 2012 ). However, juvenile Lake Sturgeon had recently (c. for future hydroelectric development, are inhabited by Lake Sturgeon. ~2010) been found to forage extensively over non-sand/gravel sub- Large dams can dramatically alter aquatic habitat in the rivers they strates such as clay and silt in the Winnipeg River, Manitoba (Barth are constructed on, in part due to physical and chemical changes as- et al., 2009 ), and the Grasse River, New York (Trested et al., 2011 ) sug- sociated with the reservoirs created for energy storage (Magilligan & gesting that the rarity of sand might not be problematic to fulfill juve- Nislow, 2005 ; Rosenberg, Bodaly, & Usher, 1995 ; Rosenberg, McCully, nile life history requirements. Still, given the possibility of compromised & Pringle, 2000 ; Rosenberg et al., 2005 ; Yi, Tang, Yang, & Chen, 2014 ; recruitment, it was deemed prudent to assess juvenile Lake Sturgeon Zhou, Zhao, Song, Bi, & Zhang, 2014 ). Whereas the historical riverine movement and habitat use patterns in a Nelson River reservoir charac- habitat may have been relatively homogenous, within a mature im- terized by a pronounced RTZ and a scarcity of sand substrate. poundment habitat characteristics tend to vary considerably from the In 2011 and 2012, 20 juvenile Lake Sturgeon were tracked using upstream extent of backwatering downstream to the lower end. As a stationary acoustic telemetry in Stephens Lake, a large impoundment general rule, water depth in the thalweg tends to increase with prox- created following the construction of the Kettle GS. Our primary hy- imity to the downstream dam and velocities tend to decrease (Baxter, pothesis considered that, should the foraging ability of juvenile Lake 1977). As a result, sediment transport and deposition processes are Sturgeon in Stephens Lake be negatively impacted by non-sand sub- altered and fines settle out in areas of the thalweg where they for- strates, acoustically tagged fish would spend the majority of their merly did not (Baxter, 1977 ; Bogen & Bonsnes, 2001 ; Gore & Shields, open-water time foraging in the relatively small area where sand oc- 1995; Hjulström, 1935 ; Wohl, 2015 ). While the specifics are driven by curs. More generally, the study objectives were to improve the under- channel morphology, the physical characteristics of the surrounding standing of both diel and seasonal influence on movement patterns landscape (overburden, terrestrial vegetation, etc.), and infrastructure and habitat use by juvenile Lake Sturgeon in large impoundments. engineering, a river to Reservoir Transition Zone (RTZ) tends to develop between the shallower, higher velocity, and coarser substrate 2 | METHODS habitat in the upstream section of the impoundment and the deeper, lower-velocity, and finer substrate habitat of the downstream section 2.1 | Study area of the impoundment. Habitat alterations resulting from impoundment of large rivers The Nelson River drains an area of ~1,060,000 km2 , spread across the by large dams can dramatically affect aquatic communities, which is provinces of Alberta, Saskatchewan, and Manitoba (Rosenberg et al., particularly important for species of conservation concern. Given that 2005). It flows 644 km from its Lake Winnipeg outlet to Hudson Bay. hydroelectric development on large rivers is likely to continue for the Hydroelectric development on the Nelson River began in 1961 with foreseeable future, an improved understanding of Lake Sturgeon hab- construction of the Kelsey GS. Subsequently, four additional GS’ s itat use in altered environments could help to predict and mitigate were built; Kettle (1974), Jenpeg (1979), Long Spruce (1979), and any potential negative impacts on populations. While movement and Limestone (1990). Construction of the Keeyask GS began in 2014. habitat use patterns of juvenile Lake Sturgeon have been studied in Since 1976, Nelson River base flow has been regulated at the outlet numerous locations within the Great Lakes (Altenritter, Wieten, Ruetz, of Lake Winnipeg to maximize generating capacity during the winter & Smith, 2013 ; Benson, Sutton, Elliott, & Meronek, 2005 ; Boase et al., months. The Nelson River hydrograph has also been altered by the 2014; Holtgren & Auer, 2004 ; Kempinger, 1996 ; Smith & King, 2005 ; Churchill River Diversion Project (CRD; 1978), which increased inflow Trested, Chan, Bridges, & Isely, 2011 ), Mississippi (Knights, Vallazza, via the Burntwood River tributary, which joins the Nelson at Split Lake Zigler, & Dewey, 2002 ) and Hudson Bay (Barth, Anderson, Henderson, (Newbury, McCullough, & Hecky, 1984 ). & Peake, 2011 ; Barth, Peake, Allen, & Anderson, 2009 ; Chiasson, This study was conducted in Stephens Lake, a large hydroelectric Noakes, & Beamish, 1997 ; McDougall, Anderson, & Peake, 2014 ; reservoir situated between Gull Rapids (56°20ʹ32ʺN, 95°12ʹ8ʺW) McDougall, Blanchfield, & Anderson, 2014 ; McDougall, Blanchfield, and the Kettle GS (56°23ʹ03ʺN, 94°38ʹ06ʺW; Figure 1 ). Stephens Peake, & Anderson, 2013 ; Shaw, Chipps, Windels, Webb, & McLeod, Lake has a surface area of 29,930 ha (excluding islands) and a total 2013; Welsh & McLeod, 2010 ; Wishingrad, Carr, Pollock, Ferrari, & shoreline length (including islands) of 740.8 km (Manitoba Hydro, un- Chivers, 2014 ) drainage basins, the spatial configuration of habitat published data). HRENCHUK ET AL. | 667

FIGURE 1 Stephens Lake study area, a section of the Nelson River bound by Gull Rapids (upstream) and the Kettle Generating Station (downstream). Locations of stationary VR 2W receivers used to monitor movements of juvenile Lake Sturgeon Acipenser fulvescens between 2011 and 2012 are indicated. Pre-impoundment Nelson River thalweg and tributaries depicted in dark blue

Including CRD flow, mean annual discharge at Gull Rapids is (45 × 13 mm, 12 g mass in air, 485 day life; Vemco, Halifax, Nova 3,100 m3 /s (Manitoba Hydro, unpublished data). At the base of the Scotia). Transmitters pinged at 130–230 s intervals, and were rapids, aquatic habitat is shallow and high-velocity, but due mainly equipped with a 0–50 m (±2.5 m accuracy, 0.22 m resolution) pres- to the influence of backwatering from the Kettle GS, depth in the sure (depth) sensor. Transmitters were applied to Lake Sturgeon thalweg increases and water velocities decrease with distance down- <600 mm fork length (FL), assumed to be juveniles in this population stream. Along the hydraulic gradient, substrates transition from coarse (Manitoba Hydro, unpublished data). (boulder/cobble) to fine (silt). Previous modeling suggests that the Lake Sturgeon were captured in ~24 hr bottom-set gill nets, com- homogenous silt overlay begins ~5.5 rkm downstream of Gull Rapids prised of panels of 38, 51, 76, 95, 108, and 127 mm stretched mesh. (Manitoba Hydro, unpublished data). The lower ~40 rkm of the thal- Netting focussed on deepwater habitat (>15 m) to efficiently cap- weg running through Stephens Lake is deep (up to 45 m immediately ture juvenile Lake Sturgeon, as described by McDougall, Barth et al. upstream of the Kettle GS), low velocity, and overlaid by silt. Large ( 2014). Each fish was measured for FL (mm) and total length (TL; mm), expanses of flooded terrestrial habitat (~22,055 ha of land was in- weighed (g), and anaesthetized using a solution of clove oil and etha- undated following construction of the Kettle GS) line the periphery nol (adapted from Anderson, McKinley, & Colavecchia, 1997 ). When a (Figure 1 ). fish lost equilibrium, it was placed ventral side up in a surgery cradle, and its gills were irrigated with river water. An acoustic transmitter was inserted into the body cavity through a small incision (~2.5 cm in 2.2 | Acoustic transmitters and application length) made in the ventral body wall. The incision was closed using Two models of 69 kHz coded acoustic transmitters were used in this three polydioxanone violet monofilament sutures (#3–0), and fish were study: V9P-1H (40 × 9 mm, 5.3 g in air, 140 day life), and V13P-1H placed in a 400 L recovery tank until equilibrium was regained. Tagged 668 | HRENCHUK ET AL. fish were released in off-current areas adjacent to the site of initial Open- water 2012 capture. In total, 12 Lake Sturgeon (322–500 mm) received V9 tags, The open-water 2012 (1 May to 15 October 2012) coarse-scale array and eight (350–570 mm) received V13 tags. Acoustic tags were a max- consisted of 20 receivers (Figure 1 ). A VPS array was not deployed. imum of 3.0% of body weight, below the maximum recommendations of 5.5%–8.0% (Brown, Geist, Deters, & Grassell, 2006 ; Chittenden et al., 2009 ; Lacroix, Knox, & McCurdy, 2004 ; Snobl, Koenigs, Bruch, 2.4 | Physical data & Binkowski, 2015 ). All tagging was conducted between 21 June and Water temperature was measured at 6 hr intervals with a HOBO 10 July 2011. Water Temperature Pro data logger (±0.2°C) deployed 1.5 km downstream of Gull Rapids from 8 June to 20 October 2011, and 1 June 2.3 | Acoustic receivers to 15 October 2012. Discharge and water-surface elevation data for Stephens Lake (hourly averages, measured at the Kettle GS) were Vemco VR2 (wired download) and VR2W (wireless download) omni- acquired from Manitoba Hydro. To validate previous modeling, sub- directional hydrophone receivers were used to monitor movements of strate composition was assessed using Petite Ponar® (WILDCO, tagged Lake Sturgeon from 21 June 2011, to 15 October 2012. The Jacksonville, Florida) grabs collected on 22 and 23 August 2011. number and locations of deployed receivers varied with study period (Figure 1 ). Receivers were affixed to a custom mooring (consisting of a 30 kg square concrete pad with a vertical rebar rod for receiver attach- 2.5 | Data analysis ment and two rebar handles) designed to maintain stability in the current and eliminate receiver sway. From an anchored boat, the receiver/ 2.5.1 | Coarse- scale movement and utilization mooring was lowered to the river bottom using rope so as to ensure Data were exported from Vemco VUE software into Microsoft Excel proper orientation, with the receiver ~1 m above the bottom and hy- 2010 for processing. The complete data set was filtered so that an indi- drophone pointed towards the water surface. A surface buoy was tied vidual fish needed to be detected at least twice by a given receiver during to each mooring to facilitate retrieval during both open-water periods. a 30-min interval for detections to be deemed valid, as suggested by the Receivers were retrieved periodically during each open-water season, manufacturer (Pincock, 2012 ). In addition, data from the first 48 hr after downloaded using Vemco VUE software, and redeployed. Prior to ice tagging were excluded from all analyses, to account for potential tagging/ up, the surface buoy was removed and a sub-surface buoy was added. capture induced behaviour alterations. Coarse-scale movements were Retrieval of submerged receivers deployed during winter followed the investigated in terms of rkm distance relative to the Nelson River thal- methods described in McDougall, Blanchfield et al. (2013 ). weg. The rkm distance of each receiver from Gull Rapids was measured using ArcGIS 10 (Environmental Systems Research Institute, Redlands, 2.3.1 | Deployment California), and these values were then assigned to corresponding detections. The positioning algorithm of McDougall, Blanchfield et al. (2013 ), Open- water 2011 previously adapted from Simpfendorfer, Heupel, and Hueter (2002 ), was The open-water 2011 (21 June to 19 October, 2011) coarse-scale array used to calculate the average detection distance of each individual fish consisted of 47 VR2 and VR2W receivers (Figure 1 ). A subset of these re- based on a 4-hr interval, according to the equation: ceivers was also used to form a Vemco Positioning System (VPS), which relies on signal time-to- arrival methods to triangulate fish positions (see ∑n R D Espinoza, Farrugia, Webber, Smith, & Lowe, 2011 ; Steel, Coates, Hearn, i i D = i=1 & Klimley, 2014 ). In the current study, the VPS array was used to deter- Δt ∑n Ri mine fine-scale locations of fish between 4.5 and 7.0 rkm downstream i=1 of Gull Rapids (i.e., the upstream end of Stephens Lake) which, based on hydraulic modeling, encompassed the theoretical RTZ (Figure 1 ). The where n is the number of receivers in the array, R i is the number of Δ array consisted of 20 receivers and 19 synchronization transmitters detections at the i th receiver during the t time period, and, D i is the (600–800 s ping rate), initially deployed on 23 June 2011 (Figure 1 ). linear rkm distance of the i th receiver from Gull Rapids (rkm 0). Detection ranges were calculated by season (open-water 2011, Winter 2011/2012 winter 2011/2012, and open-water 2012) by subtracting the minimum The winter (20 October 2011 to 30 April 2012) coarse-scale array (upstream) from the maximum (downstream) detection distance. During consisted of 22 receivers (Figure 1 ). Fourteen of these were deployed the 2011 open-water season only, proportion of time spent upstream between rkm 5.0 and 8.0 in a gridded alignment that was designed to of the VPS array (rkm 0–4.5), within the VPS array (rkm 4.5–7.0), also allow for VPS triangulation of fine-scale movement. As hydraulic and downstream of the VPS array (rkm 7.0–46.0) was calculated and and ice process modeling indicated ice scouring was likely to occur plotted. When fish were undetected during a given 4-hr interval due downstream of Gull Rapids (J. Malenchak, M. Hydro, pers. comm.), no to gaps in receiver coverage, assumed general locations (i.e., upstream receivers were deployed upstream of rkm 4.5. Four receivers were or downstream of the VPS array) were inferred based on all spatiotem- deployed downstream of rkm 10.0 (Figure 1 ). poral data available. HRENCHUK ET AL. | 669

For the 2011 open-water season, the effect of fish size (FL, as a con- and <100 mm), modified from Wentworth (1922 ). Sampling location and tinuous variable) on minimum and maximum detection distances, pro- substrate type were overlaid on the 95th percentile flow scenario model portion of time spent within the VPS array (arcsine transformed), and derived substrate map, generated based on Quester Tangent Corporation total movement range was examined using ANOVA. For subsequent acoustic classification and substrate samples collected between 2007 and intervals (winter 2011/2012, open-water 2012), data were summarized 2009 (Keeyask Hydropower Limited Partnership, 2012 ). for descriptive purposes but no statistical analysis was conducted. An ANOVA based on hourly water-surface elevation data from open-water 2011, with 24 hr periods (i.e., 3:00–4:00, 4:00–5:00, etc.) entered as factors was run to determine if water-surface elevation var- 2.5.2 | Fine- scale movement and utilization ied consistently on a daily basis, and if water-level variations caused by Triangulated Lake Sturgeon position data generated from the VPS array operations at the Kettle GS necessitated a correction factor for verti- by Vemco technicians using proprietary methods were imported into cal movement and utilization analyses. Statistical analyses were con- ArcGIS 10 and filtered so the final data set only included positions lo- ducted using JMP 10 (SAS Software, Cary, North Carolina) at α = .05. cated within the array that had a horizontal positional accuracy estimate of <30 m (Smith, 2013 ). Detection yield in the array was used to assess 3 | RESULTS the ability of the array to position tags by dividing the number of valid positions by the amount of time a fish was located in the array, divided 3.1 | Physical data by the nominal ping interval (180 s). Unfortunately, apparent spatial detection bias within the VPS array in combination with the post-field 3.1.1 | 2011 revelation that substrate overlays in the RTZ are highly dynamic precluded meaningful spatial analysis in relation to fine-scale substrate use. Water temperature ranged from 14.5°C on 21 June and 5.7°C on 20 October, reaching a plateau of 20.0°C on 18 July (Figure 2 ). Flow fluctu- ated between 5,000 and 7,000 m3 /s, (approximately 92–100 percen- 2.5.3 | Vertical movement and utilization tile) with extensive variation on a short-term scale due to peaking and During the 2011 open-water season, vertical depth utilization distri- ponding operations at the Kettle GS (Figure 2 ). Water-surface elevation bution histograms (1 m bins) were generated for each fish using data of Stephens Lake (measured at the Kettle GS) varied from 140.88 to from the coarse-scale array. To test for the prevalence of diel verti- 141.12 m (0.24 m difference), but analysis did not suggest a consistent cal migration, the effect of time of day (morning [3:00–9:00], noon daily pattern to water-level fluctuation (ANOVA, F 23 = 0.69, p = .86). [9:00–15:00], afternoon [15:00–21:00], and midnight [21:00–3:00]) The maximum difference in hourly means was 0.008 m (Figure 2 ). It on detection depth was assessed using ANOVA, with individual fish should be noted that relative to the gauging location (the Kettle GS im- entered as a random effect. To eliminate the potentially confound- mediate forebay), variation in water levels would be muted in the upper ing influence of spatiotemporal autocorrelation, the coarse-scale data portion of Stephens Lake (J. Malenchak, M. Hydro, pers. comm.), where set was randomly sub-sampled (n = 5,000 data points) a total of 20 the majority of biological data were collected. Based on the aforemen- times. The statistical test was run for each iteration and a synthesis of tioned reasons, no correction factor was applied in subsequent vertical these results was used to assess significance. The effects of body size movement and utilization analyses. (<400 mm FL, >400 mm FL), and tag type (V13P-1H, V9P-1H) on ver- Substrate grabs were not consistent with the modeled sub- tical utilization (i.e., mean depth) were analyzed in the same manner. strate distributions based on the 95 percentile flow scenario (i.e., Vertical utilization of the water column was assessed by comparing 5,520 m3 /s); most notably, relatively coarse substrates (gravel/cobble, tag depths within the VPS array (as determined via pressure sensors) and sand/gravel) were found up to 0.75 km downstream of the model to total water column depth. An ArcGIS 10 water depth raster based derived boundary of sand and silt (Figure 3 ). on a 95th percentile flow scenario bathymetric model generated by Manitoba Hydro (Keeyask Hydropower Limited Partnership, 2012 ) 3.1.2 | 2012 was used. For each VPS calculated fish location, the relevant “modeled depth” value was extracted from the raster using ArcGIS 10 “Extract” Water temperature measured as 10.1°C on 1 June and 5.2°C on 15 feature. For each valid position, “tag (sensor) depth” was subtracted October 2012, reaching a plateau of 21.3°C on 13 July 2012 (Figure 2 ). from “model depth”, yielding a “depth off bottom” value. Individual and Water flow ranged from 880 to 5,800 m3 /s, and water-surface eleva- population level means were calculated for descriptive purposes. tion ranged from 139.10 to 141.13 m (Figure 2 ).

2.5.4 | Physical data 3.2 | Coarse- scale movement and utilization

Substrates collected via Petite Ponar® grabs in 2011 were qualitatively as- 3.2.1 | Open- water 2011 sessed for content (i.e., cobble, gravel, sand, silt, etc.). Substrate classifica- tions were identified based on particle size: clay/silt (particles < 0.063 mm); All 20 juvenile Lake Sturgeon implanted with acoustic transmit- sand (particles > 0.063 mm and <2 mm); gravel/cobble (particles > 2 mm ters were detected during the 2011 open-water period. In total 670 | HRENCHUK ET AL.

FIGURE 2 Water surface elevation, flow, and water temperature during the study. Dotted lines = delineates study periods (open-water 2011, winter 2011/2012, and open-water 2012). Red line = 95th percentile flow scenario (i.e., 5,520 m3 /s)

190,191 valid detections (i.e., those logged after the 48 hr post- downstream of rkm 10.0 during early winter (Table 1 ); one was de- tagging period, and passing the two detections logged by a given tected as far downstream as rkm 36.1, and the other at rkm 18.7 receiver within a 30 min interval criterion) were logged, ranging (Figure 1 ). In addition, two fish were repeatedly detected (15 days from 391 to 24,955 detections per individual fish (Table 1 ). Eleven each) during January and February by a receiver (assigned a distance fish (55%) were detected as far upstream as rkm 1.3, while three of 7.7 rkm) located approx. 3 km from the Nelson River thalweg (see (15%) were detected further downstream than rkm 10 (Table 1 ). Figure 1 for location). Mean total detection range was 6.8 rkm (SD = 6.7, range: 1.1– 30.6). No detections were logged at receivers deployed in back- 3.2.3 | Open- water 2012 watered shallows. On average, tracked fish spent 22% (SD = 18.0%; range: 0.0%– Five of eight Lake Sturgeon with theoretically active tags were de- 54.2%) of their time within the RTZ (rkm 4.5–7.0; Figure 4 ). In gen- tected during the 2012 open-water period. In total, 11,010 valid eral, they spent more time upstream of rkm 4.5 (mean = 57.3%, detections were logged, ranging from 94 to 3,813 detections per in- SD = 36.8%, range: 0.4%–100%), than downstream of rkm 7.0 dividual. All five fish were located, at least briefly, between rkm 0.7 (mean = 17.1%, SD = 24.9%, range: 0%–90.0%); however, four (20%) and 1.2, while only one (20%) was detected further downstream than fish spent more time downstream of rkm 7.0 than they did upstream rkm 10.0 (Table 1 ). Mean total detection range was 8.4 rkm (SD = 4.0, of rkm 4.5 (Figure 4 ). Fish size was positively related to maximum range: 3.5–14.4; Table 1 ). No detections were logged at receivers de-

(downstream) detection distance (ANOVA, F 1,18 = 15.7, p = .0009), ployed in backwater shallows. and range (ANOVA, F 1,18 = 21.6, p = .0002), but not related to minimum (upstream) detection distance (ANOVA, F = 0.035, p = .56) or 1,18 3.3 | Fine- scale movement and utilization proportion of time (arc sine transformed) spent between rkm 4.5 and 7.0 ( F = 0.23, p = .63; Figure 5 ). 1,18 3.3.1 | Open- water 2011

A total of 22,859 valid positions (i.e., those with horizontal po- 3.2.2 | Winter 2011/2012 sitional accuracy estimate of <30 m) were generated during the Six of the eight Lake Sturgeon with active tags (V13) were detected 2011 open-water period. In general, there was much variation during the winter 2011/2012 period. In total, 59,872 valid detec- in the distribution of VPS generated positions across individuals, tions were logged, ranging from 343 to 41,298 detections per in- and there was no evidence of a core area of movement within the dividual. Analysis of winter data was complicated because receiver array that was consistently preferred by the majority of individuals coverage downstream of the RTZ was sparse (Figure 1 ). However, (Figure 6 ). as winter progressed, tagged juveniles were seldom located within VPS yield was generally low, as only 9.6% of the total number the RTZ. Data indicated that at least two tagged individuals moved of theoretical acoustic transmissions resulted in valid positions. HRENCHUK ET AL. | 671

FIGURE 3 Substrate verification results based on Petite Ponar sampling conducted in August 2011, overlaid on 95th percentile flow scenario (i.e., 5,520 m3 /s) substrate map. The 2011 open-water VPS receiver array coverage also shown

Notably, two fish (FL 570 and 362 mm) had positional yields of were logged. Given these issues, analysis of fine-scale movement 31.7% and 36.9%, respectively. Given the spatial proximity of po- data was not conducted. sitions recorded for these two fish, and partial spatial overlap with some of the other relatively high yield individuals (10.5%–15.9%), 3.4 | Vertical movement and utilization spatial variation in the ability of the array to accurately position tagged juvenile Lake Sturgeon was inferred. This type of bias would 3.4.1 | Open- water 2011 confound the results of habitat selection ratio analyses, which as- sume that detection probability is equal regardless of location. As Based on coarse-scale array data, vertical distributions varied be- such, further quantitative analysis of fine-scale habitat utilization tween individuals; however, deepwater usage was consistent was not conducted. (Figure 7 ). Overall mean (i.e., all fish pooled) detection depth was 15.1 m (SD = 2.0 m; range: 10.4–17.0 m), and 90% of detections occurred between 12.7 and 17.4 m. 3.3.2 | Winter 2011/2012 There was minimal evidence of a population level pattern of diel A total of 1,605 valid position estimates were generated during vertical migration, as only four of 20 iterations (20%) conducted winter 2011/2012, of which 1,340 (83%) were generated by a on 5,000 data point subsets yielded statistically significant results single fish (FL 330 mm). All positions were generated prior to 18 (Table 2 ). The largest difference between means of the four time peri- December 2011. The rate of sync-tag detections (critical to the VPS ods was 0.13 m (mean of means = 0.07 m). Additionally, there was no positioning methodology) began to decline in late November, and evidence to suggest that size class or tag type influenced detection from 25 December 2011 to 28 May 2012, no sync-tag transmissions depth (Table 2 ). 672 | HRENCHUK ET AL.

1H 1H 1H 1H 1H 1H 1H 1H 1H 1H 1H 1H V13P-1H V9P- Tag type V9P- V9P- V13P-1H V13P-1H V13P-1H V9P- V9P- V13P-1H V9P- V9P- V9P- V13P-1H V9P- V13P-1H V9P- V9P- V13P-1H V9P-

9.2 8.9 6.5 3.5 — — — — — — — — — — 17.5 — — — — — water 2011 season.

9.9 9.9 7.2 4.7 — — — — — — — — — — 18.7 — — — — —

0.7 1 1.2 1.2 0.7 — — — — — — — — — — — — — — —

0 0 0 95 — Open- water 2012 No. of scale coarse- Min (U/S, rkm) Max (D/S, rkm) Range (rkm) — — — 3,080 3,813 — — 2,271 — — — — 1,550 — — 1H tags only active during the open-

3.1 4.5 3.1 4.5 — — — — — — — 14.1 — — — — — — 31.5 — water 2011 (21 June to 19 October 2011), winter 2011/2012 (20

7.7 9.9 7.7 9.9 — — — — — — 18.7 — — — — — — 36.1 — —

4.6 5.4 4.6 4.6 5.4 4.6 — — — — — — — — — — — — — —

0 0 343 2,242 3,250 2,552 41,298 No. of scale coarse- Min (U/S, rkm) Max (D/S, rkm) Range (rkm) Winter 2011/2012 — — — — — — — — — — 10,187 — —

0 77 69 15 131 104 203 248 723 487 791 280 1,383 2,813 No. of fine- scale 2,844 5,259 1,675 2,124 1,140 2,493

5.6 8.6 2.3 5.3 3.7 1.1 1.1 2.3 4.4 5.6 2.3 8.6 8.6 5.6 5.6 5.6 2.3 14.4 30.6 13.3 1H tags (theoretically active through the entire study period); all other fish received V9-

6.9 9.9 6.9 9.9 5.0 5.7 5.7 6.9 5.7 6.9 6.9 9.9 9.9 6.9 6.9 6.9 6.9 18.7 35.2 14.6

water 2012 (1 May to 15 October 2012) 4.6 4.6 1.3 1.3 1.3 4.6 4.6 4.6 4.6 4.6 1.3 1.3 1.3 1.3 1.3 4.6 1.3 1.3 1.3 4.6

391 Detection summary, juvenile Lake Sturgeon tagged and monitored in Stephens during open- 1,262 4,155 5,539 5,624 5,076 1,308 2,688 4,358 3,870 9,617

12,175 Open- water 2011 17,486 No. of scale coarse- Min (U/S, rkm) Max (D/S, rkm) Range (rkm) 17,366 11,271 18,926 24,955 16,941 12,651 14,532

350.1 353 381 FL (mm) 322 330 335 362 570 338 355 405 340 350 451 370 360 495 373 374 500 30 April 2012), and open- TABLE 1 Highlighted in bold: eight fish implanted with V13- HRENCHUK ET AL. | 673

FIGURE 4 Proportion of time spent by juvenile Lake Sturgeon Acipenser fulvescens in various sections of Stephens Lake during 2011 open-water season, based on algorithm calculations and assumed locations based on interpretation of all spatiotemporal data. Category % in VPS = area covered by the Vemco Positioning System, between rkm 4.5 and 7.0 (the RTZ ), “US ” = upstream of that area, “DS ” = downstream of that area. Fish listed in order of fork length

FIGURE 5 Juvenile Lake Sturgeon Acipenser fulvescens fork length versus minimum (upstream) and maximum (downstream) detection distance (a), and detection range (b) for 20 fish tagged during 2011 open-water season. Hatched lines = location of RTZ (rkm 4.5–7.0); shading = 95% confidence intervals of calculated linear relationships

Based on fine-scale array data, juvenile Lake Sturgeon were predom- 3.4.2 | Winter 2011/2012 inantly positioned at depths >10 m. An overall mean tag depth of 14.9 m ( SD = 1.3 m) was observed, and 90% of positions were associated with Based on the coarse-scale array data, the overall mean detection tag depths between 13.0 and 17.4 m. Across individuals, mean tag depth depth was 12.4 m (SD = 3.2 m). Across individuals, mean detection ranged from 13.0 to 17.1 m (SD range: 0.6–1.7). On average, fish were depth ranged from 9.0 to 18.1 m (SD range: 1.8–5.3 m). While only positioned 1.0 m above the river bottom (SD = 0.9 m) and 90% of the two fish were detected at receivers deployed downstream of rkm 10, detections occurred between −0.4 and 2.3 m off the bottom (negative vertical utilization distributions were markedly different from that of values likely reflect slight data imperfections, i.e., horizontal positioning, fish detected on receivers deployed further upstream; mean detection pressure sensor, or bathymetric model error). Across individuals, mean depths associated with receivers deployed at rkm 18.7, 35.2 and 36.1 depth off the bottom ranged from 0.3 to 2.0 m (SD range: 0.5–1.3). were 6.9, 4.1, and 4.5 m, respectively. 674 | HRENCHUK ET AL.

FIGURE 6 Graphical summary of valid VPS detections (<30 m error, located within the array) of acoustically tagged Lake Sturgeon Acipenser fulvescens, upstream end of Stephens Lake, 4.5–7.0 rkm downstream of Gull Rapids during 2011 open-water period

thalweg habitat during the open-water season, to the exclusion of the 3.4.3 | Open- water 2012 shallow, non-thalweg habitat that dominates Stephens Lake. Deepwater Based on the coarse-scale array data, the overall mean detection preference by juvenile Lake Sturgeon has been observed in several large depth was 13.9 m (SD = 2.8 m). Across individuals, mean detection riverine systems, including the Winnipeg (Manitoba/Ontario, Can.) and depth ranged from 12.7 to 16.1 m (SD range: 1.5–3.9 m). St. Clair (Ontario, Can./Michigan, USA) rivers (Barth et al., 2009 , 2011 ; Boase et al., 2014 ; McDougall, Anderson et al., 2014 ; McDougall, Barth et al., 2014 ; McDougall, Blanchfield et al., 2013 ) as well as other areas 4 | DISCUSSION of the Nelson River (McDougall, Barth et al., 2014 ), thus the finding that juveniles behaved similarly in Stephens Lake was not unexpected. Coarse- and fine-scale acoustic receiver arrays were used to monitor Indeed, assuming this pattern allowed receiver deployment to focus on juvenile Lake Sturgeon movement and habitat use in a large hydro- the thalweg, yielding a considerable amount of detection data (particu- electric reservoir. Data collection issues precluded some of the more larly during the open-water season) despite the large size and logistical subtle analyses initially planned (e.g., fine-scale habitat selection ratios challenges associated with the study area. in Stephens Lake RTZ). Nevertheless, the results of the study improve Our primary hypothesis was that, if juvenile Lake Sturgeon from the understanding of juvenile Lake Sturgeon ecology in this type of the Nelson River required sand substrates to forage, fish tagged in system. Stephens Lake would spend the majority of their open-water time in Based on the frequency of coarse-scale detections by receivers de- the RTZ (the relatively small area in which sand substrate is expected ployed in the upper 10 km of Stephens Lake and the vertical (depth) to occur). All 20 tracked juveniles were captured and released in distributions, juvenile Lake Sturgeon occupied the deepwater (>10 m) this area, and results derived from the coarse-scale algorithm (2011 HRENCHUK ET AL. | 675

It is not clear why only three individuals (15%) moved into the area downstream of the RTZ during the open-water season. Juvenile Lake Sturgeon are known to exhibit restricted movement patterns in large riverine systems, attributable to a general unwillingness to pass upstream or downstream through shallow river narrows (both natural and inundated falls and rapids) that occur along the flow axes (Barth et al., 2011; McDougall, Blanchfield et al., 2013 ; McDougall, Anderson et al., 2014; McDougall, Blanchfield et al., 2014 ); however, no movement- restricting features are evident in the current study area between Gull Rapids and the Kettle GS. Further, juvenile Lake Sturgeon vacated the RTZ as winter progressed, and therefore it seems unlikely to be a mat- ter of individuals simply being resistant to downstream redistribution (McDougall, Hrenchuk, Anderson, & Peake, 2013 ), which incidentally would be a favourable trait in the context of historical upstream population persistence in rivers subdivided by impassable barriers. Several possible explanations for the apparent preference towards the upstream portion of Stephens Lake (i.e., the RTZ and above) for foraging seem worthy of discussion. Juvenile Lake Sturgeon are benthic generalists, foraging on a diversity of macroinvertebrates found on/ FIGURE 7 Vertical utilization distribution summary for in the substrate and drifting near the river-bottom (Barth, Anderson, acoustically tagged juvenile Lake Sturgeon Sturgeon Acipenser Peake, & Nelson, 2013 ; Beamish, Noakes, & Rossiter, 1998 ; Chiasson fulvescens detected in Stephens Lake during 2011 open-water season. Figure reflects entire post-filtered data set (n = 190,191) with et al., 1997 ; Guilbard, Munro, Dumont, Hatin, & Fortin, 2007 ; Jackson, individual fish in order of fork length. Each histogram is proportional VanDeValk, Brooking, vanKeeken, & Rudstam, 2002 ; Kempinger, to the number of total detections 1996; Nilo et al., 2006 ; Smith & King, 2005 ). It is possible that low- velocity, depositional habitats offer lower productivity and foraging open-water) indicated that these individuals were positioned within resources suitable to Lake Sturgeon relative to those located further the RTZ an average of 22% of the time. Considerable variation was upstream; however, benthic invertebrate sampling in Stephens Lake observed among individuals, but no evidence of a size-related utili- was conducted in offshore habitats during autumn (2013 and 2014) at zation pattern was observed. These results suggest that juvenile Lake distances of 3, 11, and 25 km downstream of Gull Rapids using Ponar Sturgeon are capable of foraging in deepwater habitats with non-sand grabs. Macroinvertebrate density increased with downstream distance substrates. On average, tagged individuals spent 57.3% of their 2011 from Gull Rapids, with the highest mean densities occurring at sam- open-water time upstream of the RTZ, where the predominant sub- pling locations 25 km downstream (> 2,700 individuals/m2 ), and the strates are gravel, cobble, and boulder. The use of coarse substrates lowest mean densities (~1,100 individuals/m2 ) at sampling locations by juvenile Lake Sturgeon foraging in large river systems has been 3 km downstream of Gull Rapids (Zrum & Gill, 2015 ). More specifically, observed previously. In the Winnipeg River, which is highly hetero- mean density of ephemeropterans (mayflies), which have been identi- geneous along its length, juvenile Lake Sturgeon have been captured fied as a primary food item (Beamish et al., 1998 ), were found to be an in high densities over all of the aforementioned substrates, as well as order of magnitude higher 11 and 25 km downstream of Gull Rapids bedrock, clay, and silt (Barth et al., 2009 ; Manitoba Fisheries Branch, relative to the area 3 km downstream of Gull Rapids (Zrum & Gill, unpublished data; Manitoba Hydro, unpublished data). In the context 2015). Given the low density of both adult and juvenile Lake Sturgeon of Lake Sturgeon compatibility with future hydroelectric development present in Stephens Lake (Manitoba Hydro, unpublished data), it seems on large riverine systems, the area downstream of the RTZ (from rkm unlikely that grazing behaviour by the species is suppressing the ben- 7.0–46.0 [Kettle GS]) was seldom used for foraging; despite a large thic community. Still, macroinvertebrate densities may not tell the en- quantity of thalweg habitat, juvenile Lake Sturgeon spent only an av- tire story, as juvenile Lake Sturgeon have been previously observed to erage of 17.1% of their 2011 open-water time within this area. There exhibit a preference for drifting prey items (Chiasson et al., 1997 ; Nilo was evidence of size-related variation; larger individuals tended to be et al., 2006 ) and therefore the total accessible food resources might detected further downstream than were smaller fish. Still, the pro- better be defined by a combination of drifting and benthic inverte- portion of variation in downstream detection distance explained by brates. It is expected that the quantity of drifting invertebrates would size was low, and one individual only 350 mm FL was detected as far be much higher in upstream portions of reservoirs due to higher water downstream as rkm 18.7. Overall, only three fish (15%) were detected velocities, but we are unaware of an appropriate method for synthesiz- further downstream than rkm 10 during the 2011 open-water period; ing benthic with drifting macroinvertebrate abundance to yield spatial based on detection logs of individual fish (data not shown), these re- estimates of accessible food resources for juvenile Lake Sturgeon. sults were not confounded by the relatively sparse receiver coverage Utilization of silt-overlay habitats in other river systems (Barth in downstream areas. et al., 2009 ; Trested et al., 2011 ; Manitoba Hydro, unpublished 676 | HRENCHUK ET AL. .039 .050 .239 — 0.057 0.053 0.050 0.054 0.049 — —

.269 .435 .210 — 0.07 — — 15.06 15.15 15.08 Mean StErr Mean 15.16 sig. 0% 0% — — — — — — — — 20%

.29 .42 Yes 0.13 .029 15.15 No 15.10 15.02 No 15.21

.35 .45 .061 No 0.08 No 15.05 15.13 No 15.23 15.19

.25 .46 .119 No 0.03 No 15.09 15.12 No 15.22 15.22

.25 .40 .479 No 0.06 No 15.10 15.03 No 15.12 15.13

.24 .53 .202 No 0.11 No 15.15 15.04 No 15.16 15.16

.26 .31 No .787 0.01 No 15.08 15.09 No 15.14 15.08

of day (morning, noon, afternoon, and midnight periods), with individual fish .22 .43 .127 No 0.10 No 15.11 15.01 No 15.10 15.17

an values by period for each iteration. The influence of fork length class and tag type .20 .45 .852 No 0.02 No 15.10 15.08 No 15.14 15.11

.28 .45 .060 No 0.08 No 15.13 15.05 No 15.23 15.14 scale telemetry data set to account for autocorrelation

.37 .47 .187 No 0.01 No 15.01 15.00 No 15.10 15.13

.26 .47 .274 No 0.02 No 15.18 15.10 15.08 No 15.05

= 20) of the coarse- .29 .41 n

No .094 0.02 No 15.07 14.99 14.97 No 15.12

.27 .52 No .257 0.07 No 15.11 15.10 15.17 No 15.22

.27 .41 .128 No 0.07 No 15.23 15.08 15.15 No 15.20

.25 .35 .001 Yes 0.06 No 15.14 15.06 No 15.00 15.22

.30 .44 .050 No 0.12 No 15.10 15.11 No 14.98 15.17

.26 .45 .022 Yes 0.12 No 15.08 14.95 No 1H) 15.15 15.06

.26 .40 .007 Yes 0.08 No 15.21 15.09 No 15.22 15.01 1H, V9P-

.27 .43 .230 0.03 No 15.19 15.17 15.08 No 15.11 No

.26 .46 No 0.08 .230 No No Tag type (V13P- 15.16 15.12 15.10 15.03 Fork length class (<400 mm FL, >400 FL) Period (morning [3:00–9:00], noon [9:00–15:00], afternoon [15:00–21:00], and midnight [21:00–3:00]) < .05) < .05) < .05) Summary, statistical analyses conducted on 5,000 data point subsets ( α α α

Morning Noon Evening Midnight Max diff. Probability Significance ( Probability Significance ( Probability Data subset 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 % Period mean Significance ( entered as a random effect. Statistical significance was found for 4 of 20 iterations. Italic and bold values = high low me on detection depth was also investigated, but all iterations lacked statistical significance. TABLE 2 The hypothesized pattern of population level diel vertical migration was investigated by comparing detection depth versus time HRENCHUK ET AL. | 677 data) suggests that at the species-level, these types of habitats are detection range. When bathymetric features obstruct line of sight, suitable for juvenile foraging; however, it is possible that different a fish will not be detected. Fine-scale VPS arrays would be more populations have adapted to exploiting slightly different habitat sensitive to this, since positioning requires triangulation of acoustic types and food resources. The silt-overlay that now lines the thal- tag signals from at least three receivers, all of which need to have weg downstream of the RTZ in Stephens Lake (i.e., downstream of line of sight to the tagged fish. While receivers were deployed ~1 m rkm 10) is almost certainly a contemporary phenomenon, as prior off the bottom, a greater VPS yield in the upstream portion of the to hydroelectric development this stretch of the lower Nelson array could likely have been achieved had receivers been deployed River was confined, highly-graded, and swiftly flowing (Denis & mid-water column. Challies, 1916 ), resulting in negligible main- stem deposition within Lake Sturgeon from several river systems have been found to ex- the Stephens Lake study area. Therefore, it is conceivable that hibit diel shifts in activity rate (Chiasson et al., 1997 ) and movement/ use of silt-overlay habitat is a contemporary foraging option, and utilization patterns (Holtgren & Auer, 2004 ). For example, juvenile that some individuals are adaptively exploiting the food resources Lake Sturgeon in Portage Lake, Michigan, exhibited vertical shifts in present. depth, tending to be located several meters shallower during night It may also be worth considering that Lake Sturgeon in numerous hours (Holtgren & Auer, 2004 ). Similarly, in the Winnipeg River, systems exhibit individual-level core area affinity (Borkholder et al., Manitoba, movements into the vicinity of Slave Falls GS spillway in- 2002; Haxton, 2003 ; Knights et al., 2002 ), which implies habitual frastructure at depths of 6–9 m only occurred during night, whereas movement patterns. While the previously cited studies focused on movements via deeper water (9–13 m) occurred during both day and adults, recent studies in the Winnipeg River suggested that both night (McDougall, Anderson et al., 2014 ). During the current study, juveniles and subadults exhibit these patterns (Barth et al., 2011 ; there was no strong statistical evidence to suggest a population-level McDougall, Blanchfield et al., 2013 ). It is possible that these patterns diel swing in vertical utilization. These results are similar to those develop very early in life, and are related to where individuals estab- in Muskegon Lake, Michigan, and in the Namakan River, Ontario/ lish following larval drift. In a large reservoir, larvae might consis- Minnesota, where acoustic telemetry revealed no significant diel in- tently settle out in the same general area as a function of hydraulic fluence on movement patterns or depths occupied (Altenritter et al., processes. These same processes would also influence sediment 2013; Trembath, 2013 ). Our results add to the growing body of evi- transport and deposition patterns and lead to the development of a dence that suggests behavioural discrepancies among Lake Sturgeon pronounced substrate gradient in the RTZ. The settling out of drifting populations. macroinvertebrates might also occur in the same area Conversely, This study marks the first attempt to collect acoustic telemetry on a system such as the Winnipeg River, the numerous natural lacus- data from juvenile Lake Sturgeon in the Nelson River during winter, trine widenings and hydroelectric reservoirs are considerably smaller, and several general observations might help to guide study design and tend to shift between lotic and lentic environments depending of researchers attempting to conduct studies in similar (extreme) on the year (flow). Substrate deposition patterns in the Winnipeg environments. Prior to initiation of the study, it was anticipated that River likely reflect a cumulative average of hydraulic processes with data collection would be challenging due to the annual develop- some temporal variation in substrate boundaries (similar to the ob- ment of a large hanging ice dam and resulting scouring to depths served variation in deposition within Stephens Lake), but the influ- of 16–18 m in the area 2.0–4.5 rkm downstream of Gull Rapids (J. ence of inter-annual variation in spring flows on where larvae settle Malenchak, M. Hydro, pers. comm.). To prevent damage or loss of out might be more pronounced. In combination with juvenile move- acoustic receivers moved by ice, receivers were not deployed be- ments being restricted due to the presence of river narrows, this may tween rkm 0.0 and 4.5 during the ice-covered period. Predictions partially explain why juveniles exist, but at generally lower densities, proved accurate, and winter data collection was hampered by ice in downstream basins of Winnipeg River reaches, where silt-overlay movement, scouring and the resulting environmental noise. For ex- habitat is prevalent (Barth & Anderson, 2015 ; Barth et al., 2011 ; ample, a receiver set at rkm 4.6 in ~17 m of water was retrieved McDougall, Barth et al., 2014 ). with a mooring bent at a 90° angle, which would necessitate consid- Fine-scale analysis of habitat use within the RTZ (i.e., habitat erable downward pressure. Further, sync tag reception rate by the selection ratios) was abandoned due to a low yield of triangulated VPS array declined to zero by 25 December 2011, and remained at VPS positions and an inferred bias associated with positioning fish zero until 28 May 2012. This suggests that the ability of the receiv- within the RTZ. Detection probability was unequal along the length ers to detect fish transmitters was also compromised by environ- of the RTZ, as tagged fish were more likely to be detected in the mental noise caused by moving ice pans and suspended frazil ice, as downstream portion of the array versus the upstream portion. This far downstream as rkm 7.2. can likely be attributed to a combination of greater detection range Despite the problems associated with winter data collection in this for receivers in the downstream portion of the array, due to lower study area, and a limited sample size (n = 6 fish detected), results sug- water velocities and reduced environmental noise, and bathymetric gest that juvenile Lake Sturgeon moved downstream into the lower features in the upstream portion of the RTZ that blocked transmitter portion of the reservoir, or laterally out of the former river channel signals. Acoustic telemetry relies on the premise of line of site be- into backwatered shallows during winter. Given observations suggest- tween tagged fish and any stationary receivers within the theoretical ing extensive ice build-up and bottom scouring, it seems likely that 678 | HRENCHUK ET AL. the RTZ is uninhabitable during winter, necessitating a spatial shift in Beamesderfer, R. C. P. , & Farr, R. A. ( 1997). Alternatives for the protection population-level utilization. and restoration of sturgeons and their habitat. Environmental Biology of Fishes, 48, 407 – 417 . Overall, our results show a clear population-level preference for Beamish, F. W. H. , Noakes, D. L. G. , & Rossiter, A. ( 1998). Feeding ecology habitats at or upstream of the RTZ during the open-water season; of juvenile lake sturgeon, Acipenser fulvescens, in Northern Ontario. however, this preference does not appear to be related to the pres- Canadian Field Naturalist, 112 , 459 – 568 . ence of sand substrate, and considerable inter-individual variation was Benson, A. C. , Sutton, T. M. , Elliott, R. F. , & Meronek, T. G. ( 2005). Seasonal movement patterns and habitat preferences of age-0 lake sturgeon observed. Indeed, a few tagged fish used backwater thalweg areas, in the Lower Peshtigo River, Wisconsin. Transactions of the American suggesting that silt-overlay habitats may also be suitable for foraging. Fisheries Society, 134 , 1400 – 1409. Most generally, these results speak to the need of Lake Sturgeon re- Billard, R. , & Lecointre, G. (2001 ). Biology and conservation of sturgeon and searchers to consider appropriate sample sizes to adequately capture paddlefish. Review in Fish Biology and Fisheries, 10, 355 – 392 . Birstein, V. J. ( 1993). Sturgeons and paddlefishes: Threatened fishes in individual-level variation in movement and utilization patterns within need of conservation. Conservation Biology, 7 , 773– 787 . a given population. Boase, J. C. , Manny, B. A. , Donald, K. A. L. , Kennedy, G. W. , Diana, J. S. , Thomas, M. V. , & Chiotti, J. A. ( 2014). Habitat used by juvenile lake sturgeon ( Acipenser fuvlescens) in the North Channel of the St. Clair River ACKNOWLEDGEMENTS (Michigan, USA). Journal of Great Lakes Research, 40 , 81– 88 . Bogen, J. , & Bonsnes, T. E. ( 2001). The impact of a hydroelectric power Funding for the field component of this research was provided by plant on the sediment load in downstream water bodies, Svartisen, the Keeyask Hydropower Limited Partnership, as part of the envi- northern Norway. Science of the Total Environment, 266 , 273– 280 . ronmental studies program for the Keeyask GS (under construction). Bogue, M. B. ( 2000). Fishing the Great Lakes: And environmental history, Manuscript production was supported by Manitoba Hydro’ s Lake 1783–1933 ( 444 pp.). Madison, WI: The University of Wisconsin Press. Borkholder, B. D. , Morse, S. D. , Weaver, H. T. , Hugill, R. A. , Linder, A. T. , Sturgeon Stewardship and Enhancement Program. The following Schwarzkopf, L. M. , … Frank, J. A. ( 2002). Evidence of a year-round resi- members of Tataskweeyak Cree Nation, York Factory First Nation, dent population of Lake Sturgeon in the Kettle River, Minnesota, based Fox Lake Cree Nation and War Lake First Nation are thanked for on radiotelemetry and tagging. North American Journal of Fisheries their local expertise and assistance in conducting the field work: J. Management, 22 , 888– 894 . Brown, R. S. , Geist, D. R. , Deters, K. A. , & Grassell, A. ( 2006). Effects of Beardy, K. Bignell, R. Henderson, J. Lockhart Jr., K. Kitchekeesik, P. surgically implanted acoustic transmitters >2% of body mass on the Massan, S. Mayham, J. Redhead, C. Saunders, D. Saunders, and J. swimming performance, survival and growth of juvenile sockeye and Saunders. Thanked for their logistical assistance are: D. Kitchekeesik, Chinook salmon. Journal of Fish Biology, 69 , 1626 – 1638. P. Morris, E. Beardy, R. Mayhem, S. Backhouse, M. Kullman and S. Chiasson , W. B. , Noakes, D. L. G. , & Beamish, F. W. H. (1997 ). Habitat, benthic prey and distribution of juvenile lake sturgeon Acipenser fulvescens Matkowski. The collection of biological samples described in this in northern Ontario rivers. Canadian Journal of Fisheries and Aquatic report was authorized by Manitoba Water Stewardship, Fisheries Science, 54, 2866– 2871. Branch, under terms of the Scientific Collection permit # 38-11. Chittenden, C. M. , Butterworth, K. G. , Cubitt, K. F. , Jacobs, M. C. , Ladouceur, A. , Welch, D. W. , & McKinley, R. S. (2009 ). 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