Duncan Reservoir Fish Habitat Use Monitoring Year 2 (2009) Data Report

Transcription

1 Duncan Dam Project Water Use Plan Duncan Reservoir Fish Habitat Use Monitoring Reference: DDMMON#10 Study Period: May 2009 March 2010 Ico de Zwart 1, Greg Andrusak 2, Joe Thorley 3, Robyn Irvine 3, Sylvie Masse 3 1 Masse Environmental Consultants Ltd. 513 Victoria St, Nelson, BC V1L 4K7 2 Redfish Consulting Ltd Highway 3A, Nelson, BC V1L 6N6 3 Poisson Consulting Ltd Shasheen Road, Nelson, BC V1L 6X1 April 9, 2010

2 EXECUTIVE SUMMARY This report summarizes the results of the first year of sampling for the Duncan Reservoir Fish Habitat Use Monitoring program (DDMMON#10) conducted on behalf of BC Hydro. Seasonal habitat use surveys were conducted on the reservoir and selected tributaries in spring, late summer and early winter. Reservoir sampling consisted of gill netting in pelagic habitat, and gill netting and minnow trapping in littoral habitats, at four stations. Tributaries were surveyed with night snorkels (or daytime electrofishing) and night minnow trapping was conducted at up to twelve sites in the drawdown zone and the first 100 m above the high water mark. Kokanee were the most abundant species captured during the reservoir surveys, with a mean CPUE over the year of fish/100m/hr of gill netting. Based on scale samples, and length frequency distributions, age-1 kokanee typically ranged from mm, age-2 from mm, and age-3 were likely >210 mm in length. Several age-4 fish were also observed. Bull trout were also relatively abundant, with a mean CPUE of fish/100m 2 /hr of gill netting. Bull trout showed a strong seasonal change in abundance with very few present during September, when mature bull trout migrate into tributaries to spawn. During November, several large bull trout kelts were captured, some of which are likely fish returning to Kootenay Lake. Just four rainbow trout were captured by gill netting (0.002 fish/100m 2 /hr) over the entire sampling period, indicating that the reservoir population is likely small. One of the rainbow was a mature female (age 5+), which suggests that some natural reproduction does occur. It is unclear if the other three rainbow trout were of natural or hatchery origin. Tributary surveys documented two or more of the s pecies of interest in all five of the tributaries surveyed with the exception of Howser Creek. Bull trout were the most abundant species of interest, with the highest densities found in Little Glacier Creek. Spawning kokanee were also observed in Little Glacier Creek, Glacier Creek and the upper Duncan River. Low numbers of rainbow trout were documented in all the tributaries except Howser Creek. Most fish observations were made above the reservoir high water mark. Water sampling and temperature data were also collected in the reservoir and tributaries. Strong gradients in turbidity, secchi depth, phytoplankton and zooplankton were observed between stations and between seasons. These are associated with the re-suspension of sediments of the upper Duncan River floodplain during the spring as stream discharge increases and the reservoir fills. Phosphorus continues to be the limiting nutrient in the reservoir. The current study addresses several of the management questions outlined in the Terms of Reference. The lake and tributary surveys address questions regarding physical habitat use and fish distribution. Spawner surveys commencing in April 2010 will provide information regarding i

3 life history timing. The study is limited in its ability to address questions regarding fish-food abundance and distribution due to the limited limnological sampling. Several changes to the study plan are proposed. The length of gillnet sets will be reduced, and daytime sets will be eliminated. This will reduce mortality rates, particularly of mature bull trout, while still providing sufficient information to address questions regarding relative fish abundance and distribution. Minnow trapping will be eliminated from both lake and tributary surveys due to extremely low catch rates for the species of interest. Additional electrofishing is proposed as an alternative method in tributaries to collect additional information of early life stages of the species of interest. Analysis of the existing limnological information in Year 3 (2010), rather than Year 4 (2011), along with postponing the Year 3 water sampling, is also recommended. This will highlight uncertainties regarding reservoir productivity and will be used to inform future limnological sampling. Postponing the Year 3 water sampling regime will allow for a more thorough limnological sampling program in Year 4 of the study. ii

4 TABLE OF CONTENTS Executive Summary... i Table of Contents... iii List of Figures... iv List of Tables... vi List of Appendices... vi Acknowledgements... vii 1 Introduction Background Duncan Reservoir Fish Species-Composition and Distribution Methods Overview Digital Elevation Model Substrate Mapping Lake Surveys Fish Surveys Gillnet Surveys Minnow Trap Surveys Statistical analyses Tributary Surveys Fish Surveys Water Sampling Lake Sampling Physicochemical Zooplankton Tributary Sampling Results Lake Surveys Fish Sampling Gillnet Surveys Trap Surveys Stomach Contents Tributary Surveys Fish Sampling Overview Bull Trout Rainbow Trout Kokanee Water Sampling iii

5 4.3.1 Lake Sampling Physicochemical Tributary Sampling Water Temperature Discussion Lake Sampling Kokanee Bull trout Rainbow Trout Non Target Species Tributary Sampling Seasonal Habitat Use Life History Timing Reservoir Limnology Conclusion and Recommendations Lake Sampling Tributary Surveys Spawner Surveys Limnology References LIST OF FIGURES Figure 1. Duncan Reservoir sampling locations in Figure 2. An example of a pelagic mid-water net set (91.2 m x 2.4 m) using a sinking variable mesh gill nets (RIC 1997) Figure 3. Gillnet CPUE demonstrating seasonal distribution, habitat use (pelagic and littoral) and vertical distribution of bull trout, kokanee and rainbow trout at sites on the Duncan Reservoir in Pelagic data separates catches in surface and midwater sets at each pelagic station. Combined data from day and night sets from all sites Figure 4. Gillnet CPUE demonstrating seasonal distribution, habitat use (pelagic and littoral) and vertical distribution of non-target species at sites on the Duncan Reservoir in Pelagic data separates catches in surface and mid-water sets at each pelagic station. Combined data from day and night sets from all sites Figure 5. Length frequency for all species captured in gillnets (pelagic and littoral) on the Duncan Reservoir in Figure 6. Length frequency of kokanee captured in gillnets by season and assigned ages in No age data available for November Figure 7. Length frequency of bull trout captured in gillnets (littoral and pelagic) by season in the Duncan Reservoir in iv

6 Figure 8. Trap CPUE for northern pikeminnow, peamouth and redside shiner demonstrating seasonal distribution by littoral index site on the Duncan Reservoir in Figure 9. Length frequency data from gee traps by species at littoral index site on the Duncan Reservoir in Figure 10. Length frequency histogram of bull trout observed by season in tributaries to the Duncan Reservoir, Figure 11. Temperature profile by station and season for Duncan Reservoir, Figure 12. Oxygen profile by station and season for Duncan Reservoir, Figure 13. Secchi depths (m) by station and season for Duncan Reservoir, Figure 14. Light profile measuring PAR (µmol m -2 s -1 ) by station and season for Duncan Reservoir in The horizontal lines indicate the 1% extinction lines Figure 15. Total suspended solids (TSS) at pelagic stations by season on the Duncan Reservoir in Figure 16. Turbidity (NTU) at pelagic stations by season on the Duncan Reservoir, Figure 17. Conductivity (µs/cm) at pelagic stations by season on the Duncan Reservoir, Figure 18. Total phosphorus (TP) at pelagic stations by season on the Duncan Reservoir in Figure 19. Total dissolved phosphorus (TDP) at pelagic stations by season on the Duncan Reservoir in Figure 20. Total nitrogen (TN) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line Figure 21. Dissolved inorganic nitrogen (DIN) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line Figure 22. Total alkalinity (mg/l CaCO 3 ) at pelagic stations by season on the Duncan Reservoir in Figure 23. Chlorophyll a (μg/l) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line Figure 24. Zooplankton density by season and station in the Duncan Reservoir, Figure 25. Zooplankton biomass by season and station in the Duncan Reservoir, Figure 26. Turbidity in Duncan Reservoir tributaries by season, Figure 27. Total phosphorus in Duncan Reservoir tributaries by season in Detection limit is marked on plot with the solid line (note a higher detection limit (20μg/L) was used in May Figure 28. Dissolved inorganic nitrogen in Duncan Reservoir tributaries by season in Figure 29. Mean daily temperature in tributaries to the Duncan Reservoir (May Nov 2009) v

7 LIST OF TABLES Table 1. Summary of operational constraints on the Duncan Dam Table 2. Duncan Reservoir survey timing (2009)... 5 Table 3. Duncan Reservoir tributary survey timing (2009)... 9 Table 4. Duncan Reservoir limnological stations (2009) Table 5. Summary of total gillnet catch by species and percent composition for Duncan Reservoir in Table 6. Summary of gillnet catch per unit effort (CPUE) by species and zone for Duncan Reservoir in CPUE is measured in number of fish per 100 m 2 of net area per hour Table 7. Gillnet CPUE for comparing daytime and nighttime sets for all species combined on the Duncan Reservoir in 2009 (all sites combined) Table 8. Biological data for target species by season from gillnet (pelagic and littoral) captures on the Duncan Reservoir in Table 9. Biological data for non-target species by season from gillnet (pelagic and littoral) captures on the Duncan Reservoir in Table 10. Kokanee age data from the Duncan Reservoir in Table 11. Rainbow trout age data the Duncan Reservoir in Table 12. Summary of total trap catch by species and percent composition for Duncan Reservoir in Table 13. Summary of trap catch per unit effort (CPUE) by species and zone for Duncan Reservoir in CPUE is measured in number of fish per trap per day Table 14. Summary of stomach contents from selected fish Table 15. Summary of fish observations by tributary and month, Duncan Reservoir Table 16. Bull trout observations by tributary and month, Duncan Reservoir, Table 17. Rainbow trout observations by tributary and season, Table 18. Mean concentrations or measured values by season and year for chemical parameters on the Duncan Reservoir, Table 19. Zooplankton species present during seasonal sample periods in the Duncan Reservoir, Table 20. Life history timings assumed for species of interest Table 21. Summary Table of Results from 2009 with respect to Study Objectives and Management Questions LIST OF APPENDICES Appendix 1. Electronic data (provided on a CD). Appendix 2. Water sampling data. vi

8 ACKNOWLEDGEMENTS Several people have assisted in implementing this project. BC Hydro provided buoys, a Van Dorn sampler, and accommodation in Meadow Creek. Jeff Berdusco (BC Hydro) provided a point of contact with BC Hydro and was invaluable in providing background information and organizing equipment. Alf Leake and Rian Hill of BC Hydro (Castlegar) provided helpful input at the study design and implementation stages of the study program. Jeremy Baxter (Mountain Waters Research) and Paul Seaton (Ingersol Mountain Enterprises) provided and operated boats for the reservoir sampling. Piotr Kuras, Patrick Humphries and Sarah North (Northwest Hydraulic Consultants) prepared the Digital Elevation Model. Kyle Shottanana (Canadian Columbia River Intertribal Fisheries Commission) assisted with the reservoir bathymetric surveys. Lidija Vidmanic (UBC Fisheries) analysed the zooplankton samples. Cantest (Burnaby) performed all the water sample analysis. Carol Lidstone (Birkenhead Scale Analysis) analyzed the scale samples. Eva Schindler (Ministry of Environment) provided technical support and in-kind equipment for lake surveys. vii

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10 1 INTRODUCTION This data report summarizes the results of the first year of sampling for the Duncan Reservoir Fish Habitat Use Monitoring Program (DDMMON#10). This program is required to fulfill requirements ordered by the British Columbia Comptroller of Water Rights, and will specifically address clause 6(f) of BC Hydro s Duncan Dam Conditional Water License The key management question this study aims to address is Will the recommended reservoir operations (Alternative S73) improve fish productivity through habitat and fish-food abundance and distribution? However, it was recognized that very little baseline information was available on the reservoir, and since alternative S73 was implemented in 2005, directly comparing fish productivity in a before/after study design is not possible. As a result, the questions developed for this program were formulated to address uncertainties related to interactions between reservoir management and fish/fish-food: 1. What is the relative abundance and distribution of key fish life histories in the pelagic and littoral zones of the reservoir? 2. What is the relative abundance and distribution of fish-food organisms in the pelagic and littoral zones of the reservoir? 3. What is the life history timing associated with fish species of interest? Once the first three management questions are addressed, the final question can be considered in the context of possible impacts to fish: 4. How are key fish life histories (spawning and rearing) influenced by reservoir management? Two hypotheses were proposed to be tested over the duration of this monitoring program: H o 1: Life history timings of fish species of interest are consistent with those defined during the WUP data collection phase. H o 2: Reservoir operations do not negatively affect fish life history uses of pelagic, littoral or tributary zones. H o 1 was to be evaluated by assessing use throughout (and adjacent to) the assumed life history windows, including spawning and rearing phases, for key fish species in the reservoir and its tributaries. H o 2 was to be tested by analyzing reservoir operations in consideration of observed habitat use, identifying areas of use that are marginalized through reservoir operations, and quantifying those habitats in the context of overall availability. In addition to the biological sampling required to address these questions, the study included the development of a digital elevation model (DEM) for the reservoir, and substrate mapping in the drawdown zone of selected tributaries. 1

11 2 BACKGROUND 2.1 Duncan Reservoir Duncan Reservoir provides water storage for obligations under the Columbia River Treaty (CRT) and downstream flood control on the Duncan River. The reservoir is approximately 44 km long, with a width ranging from km. The Duncan Reservoir has a mean and maximum depth of 52 m and 117 m, respectively (Perrin and Korman 1997). The reservoir has a surface area of 7,350 ha at full pool, declining to 2,190 ha at low pool. As a result, 5,160 ha of reservoir bottom are exposed at drawdown. The current operation of the dam is specified in the Water Use Plan for the Duncan Dam (BC Hydro 2007), which specifies minimum and maximum flow releases for the dam, as well as targets for flows as measured at the Water Survey of Canada (WSC) gauge located below the confluence of the Duncan River and the Lardeau River. The operations are also constrained somewhat by the Columbia River Treaty (CRT), which specifies particular elevations the reservoir should be at various times of the year. Dam operations are summarized in Table 1. Table 1. Summary of operational constraints on the Duncan Dam. Reservoir Elevation Date Reservoir Elevation (m) Comment July Targeted to reach full pool Dec 31 <569.8 Feb 28 <551.0 <564.4 High snow year Average snow year Downstream Flows Date Discharge (m 3 /s) Comment Minimum Daily 3.0 Release from dam Maximum from LLO 1 Continuous Release from dam via LLO Lardeau/Duncan confluence Minimum Continuous 73 Measured at WSC monitoring station Maximum Aug and includes discharge from the Aug 25 Sep Lardeau River Sep 25 Sep Sep 28 Sep Oct 1 Oct Oct 21 Dec Dec 22 Apr Apr 10 May May 16 Jul LLO low level operating gates 2.2 Fish Species-Composition and Distribution There was no quantitative assessment of fish populations completed prior to dam construction and, to date, there has been no comprehensive fish assessment work conducted on Duncan Reservoir. Peterson and Withler (1965) conducted the only assessment of the fish populations in 2

12 the Duncan watershed prior to reservoir formation in Their work was largely descriptive with little quantification of any of the numerous species they identified. Hirst (1991) provides a good summary of impacts due to construction of the Duncan Dam but actual work on the reservoir is notably absent. A bull trout monitoring project has been carried out in the system (O Brien 1999, Olmstead et. al. 2001) but it focused on adfluvial Kootenay Lake bull trout that migrate through the Duncan Dam to access spawning habitat in the upper Duncan River. A burbot monitoring and tracking program is also taking place as a separate WUP study, DDMMON#11 (Neufeld 2006, BC Hydro 2005). Otherwise, most fisheries studies to date have been focused on the lower Duncan River with usually only passing reference to the upstream reservoir. DVH Consulting (2001) provides the most information on Duncan Reservoir fish and their habitat, summarizing the information available at the time, identifying potential impact pathways of the dam, as well as identifying data gaps. The Duncan Reservoir is known to support a number of sport species such as kokanee (O. nerka), mountain whitefish (Prosopium williamsoni), burbot (Lota lota) and bull trout (S. confluentus) (DVH Consulting 2001; FISS 2010). The reservoir is also reported to support a number of non-sport species including pygmy whitefish (P. coulteri), lake chub (Couesisus plumbeus), peamouth chub (Mylocheilus caurinus), northern pike-minnow (Ptychocheilus oregonensis), redside shiner (Richardsonius balteatus), longnose sucker (Catostomus catostomus), largescale sucker (C. macrocheilus) and slimy sculpins (Cottus cognatus) and torrent sculpins (C. rhotheus) (McPhail 2007; FISS 2010). White sturgeon (Acipenser transmontanus), identified as a Species at Risk, are also known to inhabit the reservoir. The present composition of sportfish and non-sportfish species in Duncan Reservoir is unknown but has been surmised by some sources to be similar to that prior to impoundment (BC Hydro 2005, Smith 1988). There is very limited information regarding the distribution, abundance and use of habitat by fish populations within the reservoir, or how this habitat is affected by operations of the dam. A summary of fish captured by a rotary screw trap immediately downstream of the dam is provided by Olmsted et al. (2001) as cited in DVH Consulting (2001). Twelve different species, including juvenile rainbow trout, kokanee and bull trout, were captured during May- November These fish were presumed to be entrained from Duncan Reservoir. The uncertainty regarding fish species composition and distribution in the reservoir was recognized during the WUP process, and as a result the operating decisions made during the WUP were based primarily on recreation, wildlife and riparian interests. This study was recommended by the consultative committee so that future operating decisions could also take into account fish and fish habitat issues. 3

13 3 METHODS 3.1 Overview To address the uncertainties identified during the WUP process, several methods were selected. A digital elevation model of the reservoir, based on existing information and additional bathymetric surveys, was proposed to provide information on how the amount of littoral/pelagic habitat changes as a function of reservoir elevation. Substrate mapping in selected tributaries provides information regarding the availability of potential spawning habitat and how this is affected by changing reservoir elevation through dewatering or inundation. Seasonal gill netting surveys provide information on fish species and distribution in the reservoir, while seasonal tributary surveys provide information on habitat use within tributary streams, particularly within the drawdown zone. Lake and tributary water sampling was chosen to provide additional information on limnological conditions within the reservoir and tributaries. Temperature data loggers were installed in selected tributaries to provide data with which to determine likely periods of fry emergence based on accumulated temperature units (ATUs) and spawning timing. 3.2 Digital Elevation Model A digital elevation model (DEM) for the reservoir was developed by Northwest Hydraulics Consultants (NHC) by combining an existing DEM for the reservoir provided by BC Hydro with data from a bathymetric survey conducted from August 7-14 th, The DEM provided by BC Hydro was compiled from 1:10,000 scale aerial photography collected in May 1993 at a reservoir elevation of approximately 549 m. The bathymetric survey covered the southern half of the reservoir, including the original Duncan Lake basin, and was conducted at a reservoir elevation of approximately m. Survey transects were spaced at ~ 200 m intervals along the reservoir. Positional data was obtained using a real time kinematic global positioning system (RTK-GPS), which broadcasts GPS corrections from a base receiver set up on a known benchmark to the GPS receiver mounted on the boat. This was used in conjunction with an echo sounder to produce 3 dimensional bed profiles at each transect. The final DEM was compiled by removing overlapping data points and obvious outliers. This data was then used to generate a Triangulated Irregular Network (TIN). A 10 m grid was built from the TIN, with the centre of each cell having the value of the TIN. A 200 m grid was subsequently built from this 10 m grid, with the centre of each 200 m cell having the mean value of the input cells (excluding cells with no data). The DEM is provided electronically as point data (.txt file) and in ESRI Grid format (Appendix 1). 4

14 3.3 Substrate Mapping Due to delays in the awarding of the contract, substrate mapping was not completed in Substrate mapping is currently scheduled to occur in late April/ early May of 2010, when the elevation of the reservoir is expected to be at the minimum for the year. 3.4 Lake Surveys Fish Surveys Fish surveys were conducted in spring, late summer and early winter in The timing of sampling, and the approximate reservoir elevation at the time of sampling, is summarized in Table 2. Table 2. Duncan Reservoir survey timing (2009). Season Date Mean Reservoir Elevation (m) Spring June Late Summer/Fall September Winter November Gillnet Surveys To interpret seasonal habitat use of target adult fish species, gillnet surveys were conducted in the pelagic (>14 m) and littoral (<14 m) habitat (as defined in Perrin 2002) in the Duncan Reservoir in A total of four sites were surveyed in June, September and November, representing the spring, summer and winter seasons respectively (Figure 1). Sites were located to represent potential fish use throughout the reservoir, with two littoral and pelagic sampling sites in the original lake basin, and one of each site at the north and south ends of the reservoir in the drawdown zone. The locations of samples sites at the north and south ends of the reservoir varied due to seasonal differences in reservoir elevation. Three net sets were conducted at pelagic and littoral habitats at four stations during each of the three seasons. Net sets at each site included one pelagic floating net (PF), one pelagic sinking net (PS) set at 10 m in depth and one littoral floating net (LF). Net sets were generally deployed and retrieved during the daytime (09:00-16:00h) and night time (17:00-08:00h) to account for potential diel behavioral patterns. The only exception to this diurnal split was site 4 in the upper basin, where only a day set was conducted in the littoral habitat in September and only a night set was conducted in both the pelagic or littoral zones in November. All gill nets were standard 91.2 x 2.4 m floating and sinking variable mesh gill nets (RIC 1997) consisting of 6 panels, each of which were 15.2 m long and consisted of a different mesh size arranged in the following sequence (25, 89, 51, 76, 38, and 64 mm stretched mesh). A net set (floating or sinking) consisted of a combination of six panels strung together termed a "set". Total net area for each set was m 2. 5

15 Figure 1. Duncan Reservoir sampling locations in

16 Pelagic Index sites for the pelagic surveys were located adjacent to, but offshore from, the littoral index sites. Surface and mid-water sets were made at each pelagic sampling station. Surface net sets consisted of a pelagic floating (PF) set that fished at a depth of m. Mid-water net sets consisted of a pelagic sinking (PS) set that fished at a depth of m. Large A4 Scotchman or LD-2 buoys accompanied each net set for flotation and to minimize the hazard to boat traffic. Both types of pelagic nets (floating and sinking) were anchored to the bottom using 3/8 double braided nylon rope and small 3 kg anchors that reached depths between m (Figure 2). Pelagic sets were typically set parallel to the shore to facilitate placement and retrieval in rough, windy conditions. Gillnet location (GPS UTMs), bottom depth, time in and time out were recorded for each pelagic net set. Littoral Index sites for the littoral surveys were located close to shore, adjacent to the pelagic index sites. One littoral floating (LF) net was set perpendicular to shore to sample the upper 2.4 meters of the water column in the littoral zone. One end of the net was secured on shore, while the other end was secured to an anchor at a depth appropriate for littoral sampling (<14 m). One A4 Scotchman or LD-2 buoy accompanied each littoral net set. Gillnet location (GPS UTMs), panel number near shore, end of net bottom depth, time in and time out were recorded for each littoral net set. water surface Experimental Gillnet To anchors m White floats with nylon Cable To anchors m Figure 2. An example of a pelagic mid-water net set (91.2 m x 2.4 m) using a sinking variable mesh gill nets (RIC 1997). Fish Collection For both the littoral and pelagic survey types, captured fish were sorted by the net panel/mesh (#1-6) from which they were extracted during net retrieval. Following net retrieval, all fish were enumerated and fish species, length (±1 mm), sex (U=unknown, M=male and F=female), and 7

17 maturity (U=unknown, MTC=maturing, IM =immature, M=mature, SP=spawning and ST=spent) were recorded. Weight (±1 g) was recorded for all the species of interest, and over 80 % of the remaining fish captured. As well, depending upon the species, appropriate age information was taken from individual fish. In each season, a select number of target species, covering a range of sizes, were retained for analysis. Scale samples were taken from kokanee and rainbow trout and sent to Birkenhead Laboratory for age estimates for each season. Bull trout heads were obtained from each season from mortalities for later removal of the otoliths. In cooperation with another BC Hydro WUP program (DDMMON#5), all bull trout heads were given to Golder Associates Ltd for otolith aging, and to provide otoliths for micro-chemistry analysis. Stomachs, obtained from mortalities, were removed from remaining viscera, washed with formalin and stored in a container with 70% ethanol solution. Stomach contents were extracted in the laboratory and identified to the lowest taxonomic level possible, typically genus for fish, family for invertebrates, and order for zooplankton. In cases of advanced decomposition, heads were used to count individuals Minnow Trap Surveys Gee traps baited with cat food (42 cm length x 21 cm diameter with 0.5 cm rigid square mesh and 2.5 cm diameter opening in the intake cone) (RIC 1997), were set on the bottom at a minimum of 10 sites within each littoral index area. For consistency, five traps were located on either side of the littoral net set in water <1m deep. A variety of habitat types (sand, gravel and cobble) and gradients were sampled within each site to obtain a sample representative of the available habitats. Trap location (GPS UTMs), bottom depth, time in and time out were recorded for each trap set. The fish from each Gee trap were enumerated by species and a minimum sample of 30 individuals of each species was measured for length (± 1 mm) and weight (± 0.1 g) Statistical analyses All data was entered into a Microsoft Access 2007 database developed for this component (Appendix 1). Numbers of fish caught were converted to catch per unit effort (CPUE) by species and station and compared between seasons for Gill netting CPUE was expressed in terms of the number of fish per 100 m 2 of net area per hour and minnow trapping CPUE was expressed as the number of fish per trap per day. 3.5 Tributary Surveys Fish Surveys Tributary surveys were conducted in mid-may, early October and late November (Table 3). Night snorkel surveys and minnow trapping were the primary survey methods. Daytime electrofishing 8

18 was used in Griz Creek in May and October, and in Little Glacier Creek in May, when stream depths were too low to permit snorkeling and water temperatures were greater than 5 C. Table 3. Duncan Reservoir tributary survey timing (2009). Season Date Reservoir Elevation Spring May Late Summer/Fall October Winter November Sample sites were selected during the day, and were chosen to select discrete habitat types or areas of higher quality habitat. Up to 12 sites were selected in each tributary, however this varied by tributary and by season. For example, at higher reservoir elevations (October and November) all of the tributaries, except the upper Duncan River, could be adequately surveyed with fewer sample sites. During the May surveys, when a large amount of tributary habitat in the drawdown zone was exposed, snorkel sites were targeted to areas considered to represent higher quality habitat, in order to maximize the likelihood of observing fish if present. Similarly, due to the length and size of the upper Duncan River, only a relatively small fraction of the total amount of habitat present could be surveyed in each season. Surveys targeted areas where juvenile fish were expected to be present, such as back eddies, large woody debris accumulations and side channels, and sample lengths were selected to encompass an entire habitat unit. With the exception of the upper Duncan River, the high water mark was generally apparent as a distinct change in bank and channel structure, and surveys sites were located either above or below the highwater mark. On the upper Duncan River the change was not readily apparent, as the low gradient meant that this change occurs over a much longer stretch of stream than for the other tributaries. The GPS coordinates (downstream end), length, wetted width (three measurements), maximum depth, presence of woody debris and substrate type of each site were recorded. Photos of each site were taken from an upstream and downstream direction. Snorkel sites were marked with flagging or painted rocks to aid identification at night. Snorkeling was conducted at night, during the period from 0.5 to 4 hours after sunset. Divers used high-intensity dive lights to observe fish, and moved from downstream to upstream directions within a sample site. To reduce double counting errors, one diver surveyed each site, with the other crew member taking notes and spotting fish in the shallow margin areas. In general, snorkel surveys were conducted from a downstream to upstream direction along the tributary. Fish species and length (estimated to the nearest 10 mm) were recorded. Snorkellers calibrated fish lengths by estimating the length of 10 cm and 20 cm cylinders held underwater prior to the start of surveys, by measuring lengths (10, 20, 30 cm) along their glove and forearm to assist in length estimates, or by measuring rocks in close proximity to the observed fish. The majority of fish exhibited little fright response and allowed snorkelers to approach relatively 9

19 close. Visibility was estimated by recording the distance that a secchi disc held ~ 1m underwater could be seen. Within each site, minnow traps baited with cat food were placed in low velocity areas. Typically, one minnow trap was placed per site. The depth, time in and time out of each trap was recorded. Traps were set in the afternoon prior to snorkeling, and retrieved the following morning. Species, length (±1 mm) and weight (±1 g) of captured fish were recorded. Electrofishing was conducted using a Smith Root 12B backpack electrofisher in Griz Creek in May and October and in the drawdown zone of Little Glacier Creek in May. Sample sites were selected using the same methods as for the snorkel surveys, and the same details were recorded, in addition to electrofisher settings (voltage, frequency, pulse and electrofishing seconds). A thorough search of the sample site, focusing on pools, low velocity margins and cover was performed. Sampling proceeded from the downstream end of a site to the upstream end and back (one pass). A downstream net was used during the May surveys, although this was omitted in October in Griz Creek. Species, length (±1 mm) and weight (±1 g) of captured fish were recorded. All data was entered in a Microsoft Access 2007 database developed for this component. The results of stream surveys are provided as an electronic file (Appendix 1). 3.6 Water Sampling Lake Sampling Physicochemical Physical and chemical data were collected at three stations on the Duncan Reservoir in 2009 (Table 4). The three water sampling sites were located within the old basin of the former Duncan/Howser Lake. Sampling was conducted seasonally during the months of June, September and November, representing early spring, late summer and early winter, respectively. Table 4. Duncan Reservoir limnological stations (2009). Site Month Location Easting Northing Bottom Depth (m) P2 June Lower basin P3 June Mid basin P4 June Upper basin P2 September Lower basin P3 September Mid basin P4 September Upper basin P2 November Lower basin P3 November Mid basin P4 November Upper basin

20 At each pelagic station in each season, vertical temperature (ºC) and oxygen (mg/l) profiles were taken in situ with an YSI digital oxygen-temperature meter probe. Profiles were obtained from recording measurements at approximately 1-m intervals from 0 to 20 m and at 2-m intervals from 20 to 60 m. Water transparency was measured at each station using a standard 20-cm Secchi disk. The depth recorded was the mean value of two separate observations of the point where the disk disappeared upon lowering and reappeared upon raising from the shaded side of the boat. As well, light attenuation (extinction, k) and compensation depths (1% of surface intensity) were estimated from vertical light profiles obtained using a Li-Cor submersible quantum sensor ( μm, Model Li 192sa) in September and November. The sensor was not available in June for spring sampling. Water samples were collected seasonally at each pelagic station. At each station, two replicate epilimnion water samples were collected by compositing samples from 2 m, 5 m and 10 m depths using a Van Dorn water sampler. Water samples were placed in 1L polyethylene bottles and shipped within 24 h of collection to Cantest Ltd. in Burnaby, B.C. Samples were analyzed for alkalinity, turbidity, conductivity, total phosphorus (TP), total dissolved phosphorus (TDP), total nitrogen (TN), nitrate, nitrite, ammonia, dissolved inorganic nitrogen (DIN), silica and chlorophyll-a (Chl-a). Dissolved phosphorus samples were filtered through a 0.45 μm filter prior to preserving. Prior to shipping to the lab, Chl-a samples were prepared by filtering a 500 ml portion of the composite water sample through a filter with 0.45-µm pore size. At the lab, the filters were placed in centrifuge tubes with 90% buffered acetone and were sonicated to rupture the algal cells and homogenize the filters. Chl-a concentrations were then calculated from formulae using the absorbance of the supernatant at specific wavelengths. Chl-a samples were only collected during the growing season (late spring and late summer). Data is provided in Appendix 2 and in electronic format Zooplankton Zooplankton samples were collected at the three pelagic sampling sites located within the historical Duncan/Howser lake basin in late spring (June) and late summer (September). This was a change from the original proposal of two replicates at two pelagic stations, and was made based on the strong longitudinal gradient in turbidity observed in June. At each site, one sample was collected using a vertically hauled Wisconsin net (0.5 m diameter mouth, 153 µm mesh) with a straining bucket. The net was lowered to a depth of 30 m and retrieved to the surface at a constant rate. Samples were extracted from the straining bucket using a 125-ml wash bottle and preserved in 70 % ethanol. A replicate sample was collected at one site in late summer to assess variation within a site. The samples were analyzed for species composition, density and biomass at the UBC Fisheries Center. Samples were re-suspended in tap water filtered through a 74 µm mesh and sub- 11

21 sampled using a four-chambered Folsom-type plankton splitter. Splits were placed in gridded plastic Petri dishes and stained with Rose Bengal to facilitate viewing with a Wild M3B stereo microscope. For each replicate, organisms were identified to species level and counted until up to 200 organisms of the predominant species were recorded. If 150 organisms were counted by the end of a split, a new split was not started. The lengths of 30 organisms of each species were measured for use in biomass calculations, using a mouse cursor on a live television image of each organism. Lengths were converted to biomass (µg dry-weight) using empirical lengthweight regression from McCauley (1984). Less common species, e.g., Alona sp. or Alonella sp., were counted and measured as Other Copepods or Other Cladocerans as appropriate. Zooplankton species were identified using taxonomic keys (Sandercock and Scudder 1996, Pennak 1989, Wilson 1959, Brooks 1959). Data is provided as an electronic file (Appendix 1) Tributary Sampling Water temperature, ph, conductivity and turbidity were recorded in the field using handheld instruments. Duplicate water samples were obtained from each tributary once each season. Except for the May sample, water sampling in the tributaries coincided with water sampling on the reservoir. Samples were analyzed for ph, alkalinity, turbidity, conductivity, total and dissolved solids, total phosphorus (TP), total dissolved phosphorus (TDP), total nitrogen (TN), nitrate, nitrite and ammonia. Total phosphorus, ammonia and nitrate-nitrite samples were preserved with sulfuric acid according to laboratory instructions. Total dissolved phosphorus samples were filtered through a 0.45 μm filter prior to preserving with sulfuric acid. Water samples were placed on ice and shipped to Cantest (Burnaby, B.C.) within 24 hours of collection. Data is provided as an electronic file (Appendix 1). Automatic temperature loggers (Onset Tidbit V2) were installed in duplicate in each stream during the May surveys. Two different methods were used to house the dataloggers. Loggers were either installed in a perforated, capped PVC tube which is subsequently secured to the streambed using rebar, or loggers were attached to a 10-pound weight installed in a 4-inch PVC pipe, and anchored to the shore (tree, log or boulder) using a stainless steel cable. Loggers were installed above the full pool level of the reservoir in areas that were shaded, to minimize solar heating. In the upper Duncan River and Howser Creek, 10-pound weight loggers were deployed. In Little Glacier and Griz Creek, perforated PVC tube loggers were used. One of each type of logger installation was used in Glacier Creek. The temperature loggers deployed in the upper Duncan River were moved in September, as one was out of the water and one was near the water s edge. High water levels in May had prevented crews from installing the loggers far enough out in the channel to ensure they would remain wetted at lower flows. These loggers were redeployed to deeper water. The data loggers in Howser Creek were redeployed in November, as both of the cables securing the loggers to the bank had been severed, presumably due to the high sediment load in

22 4 RESULTS 4.1 Lake Surveys Fish Sampling Gillnet Surveys Species Composition The gillnetting data provided important information on species composition in the Duncan Reservoir in During the entire sampling program, eight fish species were encountered: kokanee (KO), rainbow trout (RB), bull trout (BT), mountain whitefish (MW), peamouth chub (PCC), redside shiner (RSC), sucker (Catostomus spp.) (SU), and northern pikeminnow (NSC). A total of 671 fish were captured in the gillnet surveys (Table 5). Of these, 225 fish (34%) were target species (bull trout, kokanee or rainbow trout). Most of the remaining 446 fish of nontarget species were peamouth chub or northern pikeminnow. Kokanee were the most numerous of the target species and peamouth chub were the most numerous of the non-target species, accounting for 25% and 46% of the total catch, respectively. Only four rainbow trout were encountered during gillnetting in 2009, despite the high rate of hatchery introductions from 2007 to 2009 (FISS 2010). CPUE, Distribution and Habitat Use Numbers of fish caught were converted to catch per unit effort (CPUE) by species and littoral or pelagic zone for comparison. Day and night sets for all sites were combined for the following discussion. The overall mean CPUE from gillnetting was individuals per 100 m 2.hr -1 in Individual species CPUE by zone (based on combined data) are tabulated below (Table 6). Kokanee had the highest CPUE at fish per 100 m 2.hr -1 over all stations for the target species (Table 6). In comparison, peamouth had the highest CPUE at fish per 100 m 2.hr -1 over all stations for the non-target species (Table 6). Table 5. Summary of total gillnet catch by species and percent composition on the Duncan Reservoir in Species Number of Fish Percent Composition Kokanee (KO) % Bull Trout (BT) % Mountain Whitefish (MW) % Rainbow Trout (RB) 4 0.6% Peamouth Chub (PCC) % Northern pikeminnow (NSC) % Redside shiner (RSC) % Sucker spp (SU) % Total % 13

23 Table 6. Summary of gillnet catch per unit effort (CPUE) by species and zone for Duncan Reservoir in CPUE is measured in number of fish per 100 m 2 of net area per hour. Zone BT KO MW NSC PCC RB RSC SU Littoral Pelagic Mean CPUE data also provides important information on species distribution and habitat use within the reservoir. Target and non-target species indicated strong seasonal trends (spring, summer and winter) in distribution and habitat use (pelagic and littoral) in the reservoir in For comparison of habitat use, pelagic data combines catches from both surface and mid-water sets at each pelagic station. Capture rates demonstrated that kokanee primarily utilized the pelagic area in the reservoir over all sampling seasons in 2009 (Figure 3). In addition, there was a large increase from the spring to the summer and winter in kokanee CPUE. The data suggest that bull trout utilized both the littoral and pelagic zones in the reservoir in A strong seasonal pattern was evident, with low catch rates for bull trout in September, the period when many of the mature adult bull trout are spawning in the tributaries. The number of rainbow trout captured (n=4) was too low for any seasonal comparison; however, all four individuals were encountered in the littoral area of the reservoir. Of the non-target species, peamouth chub and northern pikeminnow dominated in littoral gillnet catches, and to a lesser extent also appeared to cohabit the pelagic area with kokanee (Figure 4). Further analysis of fish distribution and habitat use revealed a vertical depth distribution and diel migration patterns for several fish species. Although kokanee were consistently captured in the pelagic area, CPUE was highest for mid-water (10 m) pelagic sets in late summer compared to surface sets for the same period (Figure 3). Much of the time kokanee are distributed in the deeper water layers (>10 m), often near the thermocline, when the reservoir is stratified. However, kokanee are only vulnerable near the surface to gillnetting when they vertically migrate to the epilimnion during crepuscular periods. As mentioned previously, although total bull trout catch in late summer was low, data indicated that only the littoral set and the midwater set in the pelagic zone captured bull trout in late summer (Figure 3). Of the non-target species, peamouth chub and northern pikeminnow were mainly encountered in surface gillnet sets at night, with only a small proportion of the catch coming from mid-water sets (Figure 4). Similarly, CPUE from gillnet data demonstrated that night-time sets were consistently higher than daytime sets in 2009 (Table 7). This diurnal pattern was highly evident in late summer sampling when no fish species were encountered in pelagic sets during the daytime. In general, these distribution patterns are consistent with many of the species life history characteristics or known behavioural diel migration patterns (i.e., thermal temperature preferences) and are likely associated with the seasonal variations in reservoir conditions. 14

24 Figure 3. Gillnet CPUE demonstrating seasonal distribution, habitat use (pelagic and littoral) and vertical distribution of bull trout, kokanee and rainbow trout at sites on the Duncan Reservoir in Pelagic data separates catches in surface and mid-water sets at each pelagic station. Combined data from day and night sets from all sites. Figure 4. Gillnet CPUE demonstrating seasonal distribution, habitat use (pelagic and littoral) and vertical distribution of non-target species at sites on the Duncan Reservoir in Pelagic data separates catches in surface and mid-water sets at each pelagic station. Combined data from day and night sets from all sites. 15

25 Table 7. Gillnet CPUE for comparing daytime and nighttime sets for all species combined on the Duncan Reservoir in 2009 (all sites combined). Zone Period June September November Littoral Day Littoral Night Pelagic Day Pelagic Night Gillnet Selectivity Data indicate that fish smaller than 68 mm were not vulnerable to capture in 2009 (Figure 5). The cumulative length frequency from all fish captured in gillnets (pelagic and littoral) showed a wide range of fish sizes were captured ( mm) in 2009, with the most frequently caught size of fish being approximately 190 mm. No fish < 99 mm were captured in the pelagic zone. Based on size, most species encountered in gillnets were either adult or sub-adult life stages (see trap data below). Figure 5. Length frequency for all species captured in gillnets (pelagic and littoral) on the Duncan Reservoir in Fish Data, Age and Growth Kokanee were the most numerous of the target species in gillnet catches (Table 8). Kokanee demonstrated a mean length of 197 mm (n=17), 170 mm (n=71) and 180 mm (n=80) for spring, summer and winter sampling, respectively. Overall, kokanee encountered in gillnetting ranged from 116 to 278 mm in length. Bull trout were the largest fish captured in gillnet surveys, having a mean length of 472 mm (n=19), 309 mm (n=3) and 558 mm (n=31) for spring, summer and winter sampling, respectively. The largest bull trout encountered was a post spawning adult, ~900 mm, caught in November. Only four rainbow trout were captured, two in June (132 mm and 142 mm), and one each in September (540 mm) and November (305 mm). 16

26 Table 8. Biological data for target species by season from gillnet (pelagic and littoral) captures on the Duncan Reservoir in Species Month n Mean Length (mm) Range (mm) SD (mm) Mean Weight (g) KO June KO September KO November BT June BT September BT November RB June RB September RB November Peamouth were the most numerous of the non-target species in gillnet catches in By season, peamouth demonstrated a mean length of 204 mm (n=199), 164 mm (n=78) and 186 mm (n=32) for spring, summer and winter sampling, respectively (Table 9). Overall, peamouth sizes encountered in gillnetting ranged from 94 to 409 mm. Northern pikeminnow, the largest of the non-target species, had a mean length of 256 mm (n=70), 259 mm (n=26) and 347 mm (n=4) for spring, summer and winter sampling, respectively. Mountain whitefish had a mean length of 297 mm (n=1), 162 mm (n=2) and 213 mm (n=7) for spring, summer and winter sampling, respectively. Suckers (Catostomus spp.) had a mean length of 321 mm (n=3) and 322 mm (n=8) for spring and summer sampling, respectively. Table 9. Biological data for non-target species by season from gillnet (pelagic and littoral) captures on the Duncan Reservoir in Species Month n Mean Length (mm) Range (mm) SD (mm) Mean Weight (g) PCC June PCC September PCC November NSC June NSC September NSC November MW June NA 249 MW September MW November SU June SU September RSC June

27 Kokanee A total of 168 kokanee over three seasons were captured in gillnets on the Duncan Reservoir in Scales were taken from samples during each season to determine kokanee age structure in the reservoir at the time of sampling. Age data from spring sampling (n=13) identified three age classes (ages 2, 3 and 4) captured in gillnet sets (Table 10). None of the scales exhibited significant plus growth, which indicates that no, or very little, new growth had occurred since the winter. The laboratory commented that this was considered unusual for June, even for a cold system. Age data from late summer identified 2 age classes (n=34) with all the scales exhibiting plus growth. No age data is available yet for the kokanee captured during winter sampling. Table 10. Kokanee age data from the Duncan Reservoir in Age Plus Growth Season Sample (n) Mean Length (mm) Range (mm) SD (mm) 2 No Spring No Spring No Spring Yes Summer Yes Summer Figure 6. Length frequency of kokanee captured in gillnets by season and assigned ages in No age data available for November. 18

28 Bull Trout A total of 53 bull trout were captured in gillnets on the Duncan Reservoir in Bull trout of all size ranges were captured in littoral and pelagic sets. The lack of larger bull trout in September sampling is consistent with migration to tributaries for spawning for this species. Seasonal length-frequency distributions of bull trout captured in littoral and pelagic sets are provided in Figure 7. Heads were collected from bull trout mortalities to provide otoliths for determining bull trout age structure in the reservoir at the time of sampling. These were provided to Golder Associates, who are carrying out another BC Hydro WUP study (DDMMON#5) utilizing bull trout otoliths. Age data for the bull trout were not available at the time of writing. Figure 7. Length frequency of bull trout captured in gillnets (littoral and pelagic) by season in the Duncan Reservoir in Rainbow Trout A total of 4 rainbow trout over three seasons were captured in gillnets on the Duncan Reservoir in All four were captured in littoral sets in the southern half of the reservoir. Otoliths and scales were collected from rainbow trout to determine rainbow trout age structure in the reservoir at the time of sampling. Age data from spring sampling (n=2) indicated that both rainbow trout, 132 mm and 142 mm in length respectively, were one year olds (Table 11). However, it is unclear whether these juvenile trout were of wild origin or hatchery origin. A total of 20,000 un-marked yearling rainbow were stocked in the Upper and Lower Howser Arm of the reservoir in both 2009 and 2008, and 50,000 were stocked in 2007 (FISS 2010). Stocking of rainbow trout in 2009 occurred on May 26, one 19

29 week prior to the lake surveys. The female rainbow trout (580 mm) captured in September was aged at 5+, and showed signs of having spawned in the spring. The rainbow trout that have been stocked into the reservoir within the past three years have all been triploid, and should be incapable of spawning (FISS 2010). The maturity and age of the rainbow trout, suggests it was of wild origin. Similar to bull trout, adfluvial rainbow trout progeny often rear in tributary streams from ages one to three prior to migration to lakes or reservoirs (McPhail 2007). Age data is not yet available for the rainbow trout captured in November. Table 11. Rainbow trout age data the Duncan Reservoir in Age Season Sample (n) Mean Length (mm) Range (mm) SD (mm) 1+ Spring Summer Trap Surveys Species Composition Baited Gee-traps were set on the bottom at 10 sites within each near shore littoral area during each season. For consistency, five traps were located on either side of the littoral net set in water <1m deep. A variety of habitat types (sand, gravel and cobble) and gradients were sampled within each site. The trap data provided important information on species composition in the littoral zone on the Duncan Reservoir in In all, five fish species were encountered: peamouth chub (PCC), redside shiner (RSC), longnose dace (LNC), sucker (Catostomus spp.) (SU), and northern pikeminnow (NSC). Overall, a total of 3,162 fish, all non-target species, were captured in the trap surveys in 2009 (Table 12). Redside shiner (91.3%) was the dominant species, with sucker spp. (2.9%), northern pikeminnow (2.8 %), longnose dace (2.0%) and peamouth (1.0%) making up the remainder of the catch. Notably, no species of interest were captured in minnow traps set in the littoral zone. Table 12. Summary of total trap catch by species and percent composition for Duncan Reservoir in Species Number of Fish % Percent Composition Redside Shiner (RSC) 2, % Sucker spp. (SU) % Northern pikeminnow (NSC) % Longnose dace (LNC) % Peamouth chub (PCC) % Total 3, % 20

30 CPUE, Distribution and Habitat Use Numbers of fish caught were converted to catch per unit effort (CPUE) by species and littoral index station for comparison. The overall mean CPUE in the Gee traps was individuals per trap per day in CPUE for the most abundant species (RSC, SU, LNC, PCC and NSC) are tabulated below (Table 13). Redside shiners composed the majority of the catch and had the highest CPUE at individuals per trap per day over all stations. CPUE data also provides important information on species distribution and habitat use by season and site within the reservoir in Notably, the lack of juvenile salmonids in the catch indicates that these species are not utilizing the near shore areas (<1 m) of the littoral zone in any of the seasons or habitats sampled. The near shore littoral zone was extensively utilized by many of the non target species, primarily cyprinids. The trap CPUE data demonstrates a seasonal decline in catch rates from spring to winter for redside shiners and northern pikeminnow, suggesting a shift in littoral habitat use with the onset of winter (Figure 8). Table 13. Summary of trap catch per unit effort (CPUE) by species and zone for Duncan Reservoir in CPUE is measured in number of fish per trap per day. Zone LNC NSC PCC RSC SU Littoral Figure 8. Trap CPUE for northern pikeminnow, peamouth and redside shiner demonstrating seasonal distribution by littoral index site on the Duncan Reservoir in

31 Trap Selectivity Data indicates that traps selected for individuals ranging from mm. A length frequency histogram for each species captured is provided in Figure 9. Most of the species encountered represent the juvenile or early life stages of their life cycle within the reservoir. Adult and subadult peamouth chub, northern pikeminnow and sucker were also encountered in pelagic and littoral gillnetting surveys. Figure 9. Length frequency data from gee traps by species at littoral index site on the Duncan Reservoir in Stomach Contents Diet samples were collected for target species from gillnetting on the Duncan Reservoir in Diet information from stomach analysis was used to determine the food habits of target species 22

32 and preferences within the Duncan Reservoir. A range of fish sizes were selected to provide information on dietary requirements by age; however, the low number of data in each size class for each species, and the presence of numerous empty stomachs, means that the following discussion is largely qualitative. A total of 23 stomach content samples from bull trout (n=8), kokanee (n=11) and rainbow trout (n=4) were analyzed. Diet data demonstrated that adult and sub-adult bull trout were primarily piscivorous, foraging upon juvenile salmonids, redside shiners and peamouth (Table 14). As no juvenile salmonids were captured in minnow traps in the littoral zone, the juvenile salmonids in the stomach contents likely represent juvenile kokanee from the pelagic zone, although the sample was badly decomposed. In addition to the fish component of the diet, one individual bull trout (422 mm) had foraged upon aquatic invertebrates (chironomids). Kokanee stomach data demonstrated seasonal changes in diet from spring to summer, coinciding with the seasonal progression of zooplankton in the reservoir (Chipps and Bennett 2000; Clarke and Bennett 2004). Copepods dominated in the diet of kokanee in the spring, while cladocerans, considered the preferred macrozooplankton (Northcote and Lorz 1966, Askey and Andrusak in Andrusak et al. 2008), were predominate in stomach samples by late summer. One kokanee (278 mm) sample from winter gillnetting indicated it had foraged extensively on the freshwater opossum shrimp, Mysis relicta. Only four rainbow trout were captured in gillnetting in Diet data suggests that the rainbow trout predominately feed on terrestrial insects. Table 14. Summary of stomach contents from selected fish. Species Season Size (mm) Fish Invertebrates Zooplankton Comments BT Spring vertebrate, chironomids BT Spring mm salmonid, 1 tail remnant BT Spring mm peamouth, 180 mm unknown BT Summer redside shiners BT Summer 365 Empty BT Summer 247 Empty BT Winter 665 Empty BT Winter mm unknown fish species KO Spring 168 Empty KO Spring Abundant zooplankton (copepod) KO Spring Abundant zooplankton (copepod) KO Spring Abundant zooplankton (copepod) KO Spring 218 Empty KO Summer Daphnia spp KO Summer 158 Empty KO Summer Daphnia spp KO Summer 165 Empty KO Winter KO Winter Mysis relicta 23

33 Species Season Size (mm) Fish Invertebrates Zooplankton Comments RB Spring RB Spring RB Summer RB Winter sculpin spp. ++ dominate stomach contents + present, but < 20% of total contents 4.2 Tributary Surveys Fish Sampling Overview Five tributaries were surveyed during the last year of study, with four tributaries surveyed consistently in each of the 3 seasonal surveys. Initially, sample sites were to be randomly selected to allow estimates of overall abundance within each tributary to be calculated using hierarchical Bayesian techniques (Wyatt 200, Gelman et. al. 2004). However, as low numbers of fish were expected to be encountered within the drawdown zones of each tributary based on the low complexity of the habitat, sites during the May sampling were chosen based on good habitat so that species presence could be documented. Low velocity areas and areas with cover were therefore selected. In October and November, the higher reservoir elevation meant that most of the available habitat in Glacier Creek, Griz Creek and Little Glacier Creek could be effectively surveyed, and hence these tributaries in these seasons were sampled based on discrete reaches. This approach, sampling the entire habitat available in these tributaries via consecutive subsamples, will be continued in the future, since it allows a more direct estimate of total abundance. October and November sample sites in the upper Duncan River were chosen in the same manner as in May. Snorkelling was the primary method of observing fish and is preferred to ensure consistency. Electrofishing was used in very shallow areas within the drawdown zone, and in Griz Creek. However, snorkeling proved to be effective in Griz Creek in November when low water temperatures prohibited the use of electrofishing. The fish species observed by stream and by season in 2009 are provided in Table 15. In total, 831 fish were observed during the surveys, including 75 bull trout, 259 kokanee and 13 rainbow trout. Bull trout and rainbow were observed in all four tributaries that were surveyed throughout the year. Kokanee were observed spawning in three of the four consistently surveyed tributaries, the exception being Griz Creek. Large numbers of mountain whitefish were also observed in Glacier Creek and the upper Duncan River. 24

34 Table 15. Summary of fish observations by tributary and month, Duncan Reservoir Tributary Species* May October November Total Glacier Creek BT KO RB MW Other Griz Creek BT KO RB MW Other Little Glacier BT KO RB MW Other Howser BT 0 0 KO 0 0 RB 0 0 MW 0 0 Other 1 1 Upper Duncan BT KO RB MW Other Total *BT: bull trout; KO: kokanee; RB: rainbow trout; MW: mountain whitefish. Other: consists of sculpins, suckers, longnose dace, northern pikeminnows, redside shiners and other cyprinids or salmonids observed during the snorkel surveys that could not be identified to the species level. Glacier Creek During the May survey, approximately 1.5 km of Glacier Creek within the drawdown zone was exposed. In October and November, approximately 150 m of Glacier Creek within the drawdown was exposed. All surveys ended in the large pool under the Duncan FSR Bridge. In May and October, surveys were restricted to either the left or right bank as high discharged restricted the ability of surveyors to safely access the width of the stream. In November, the entire habitat present was sampled, as the snorkel survey consisted of contiguous sites from the reservoir to the large pool under the FSR bridge, and lower flows allowed surveyors to safely access the width of the stream. 25

35 One bull trout (130 mm) was observed in May. In October, 11 bull trout ( mm), 1 rainbow trout (90 mm) and 32 kokanee were observed. Ten bull trout ( mm) were observed in November. Of note, over 200 juvenile mountain whitefish were observed in October and 40 mature mountain whitefish were observed in November. Most whitefish were observed just above the confluence of the tributary with the reservoir, which may represent spawning activity. Griz Creek Electrofishing was used to capture fish during the May and October surveys. Snorkel surveys were used in November as water temperatures were below 5 C. Both October and November surveys sampled a contiguous stretch of stream from the reservoir level to a 1m logjam/waterfall ~ 80 m upstream of the high water mark. No fish were observed during the May surveys. Three bull trout ( mm) and one rainbow trout (150 mm) were observed in October. Three bull trout were observed in November ( mm). No kokanee were observed on any of the surveys. During the November survey, the remainder of Griz Creek up to the Duncan FSR was surveyed by inspecting larger pools to determine the extent of fish distribution in this tributary. Three more bull trout were observed, indicating that the stream is accessible to fish at least as far as the culvert crossing under the Duncan FSR, a distance of ~ 750 m from the high water mark of the reservoir. Little Glacier Creek Electrofishing and snorkeling were used during the May surveys. Electrofishing was used as the only method in the lower drawdown zone in May, as limited water depths made snorkeling impractical. Only snorkel surveys were used in October and November. The October and November surveys sampled a contiguous stretch of stream from the reservoir level to ~ 80 m upstream of the high water mark. Little Glacier Creek provides habitat for all three species of interest. Seven bull trout ( mm), three rainbow trout ( mm) and two unidentified salmonids (25 70 mm) were observed in May. Except for one small (25 mm) unidentified salmonid, all observations were upstream of the high water mark of the reservoir. During the October survey, 5 bull trout, 1 rainbow trout and 224 kokanee were observed. Bull trout and rainbow trout, with one exception, were observed above the high water mark of the reservoir. Kokanee were found throughout the surveyed area. In November, 18 bull trout and 2 rainbow trout were observed. All fish in November were observed above the high water mark of the reservoir. 26

36 Howser Creek Snorkel surveys in Howser Creek were unable to be conducted in During the May surveys, visibility was extremely poor (<1 m) due to the high turbidity (90 NTU). High discharge also prevented safe access to much of the stream. Minnow trapping was conducted at three sites. The only species captured were sculpins. In October and November, the entire drawdown zone was inundated into the canyon located at the full pool elevation of the reservoir. Safety concerns and the lack of stream habitat precluded snorkel surveys or minnow trapping during these periods. Upper Duncan River May surveys were hampered by poor visibility; particularly lower in the drawdown zone due to the resuspension of sediment as the upper Duncan River eroded unstable banks. The activity of the surveyors also led to an increase in turbidity by disturbing bottom sediments. In May and October, sample sites were all located on the left bank area, as it was considered unsafe to cross the river. In November, the lower discharge allowed access to the right bank. All three species of interest were observed in the upper Duncan River. In May, 11 bull trout ( mm) were observed. In October, 1 bull trout (200 mm), 2 rainbow trout (120 mm) and 3 kokanee ( mm) were observed. In November, 5 bull trout ( mm) and three rainbow trout ( mm) were observed Bull Trout Bull trout were observed in all four tributaries surveyed (Table 16). With the exception of one 650 mm bull trout observed in the upper Duncan River in May, and three mm bull trout observed in Glacier Creek in October, all bull trout were less than 250 mm, and therefore likely represent juveniles. A length-frequency graph of all bull trout observed in the tributaries by season is provided in Figure 10. The low numbers observed, as well as the less precise nature associated with visually estimating lengths make it difficult to assign any ages to the various size ranges. No bull trout with spawning colours were observed during surveys in October. Bull trout were mostly observed above the high water mark in Glacier Creek, Griz Creek and Little Glacier Creek. The high water mark was not clearly distinguished in the upper Duncan River. Table 16. Bull trout observations by tributary and month, Duncan Reservoir, Tributary May October November Total Glacier Creek Griz Creek Little Glacier Upper Duncan Total

37 Figure 10. Length frequency histogram of bull trout observed by season in tributaries to the Duncan Reservoir, Rainbow Trout A total of 13 rainbow trout ranging in length from mm were observed (Table 17). At least one rainbow trout was observed in each of the four regularly surveyed tributaries over the course of the year. Table 17. Rainbow trout observations by tributary and season, Tributary May October November Total Glacier Creek Griz Creek Little Glacier Upper Duncan Total Kokanee Kokanee were present in Glacier Creek, Little Glacier Creek and the upper Duncan River in October. A total of 259 kokanee were observed, of which the majority (224) were found in Little Glacier Creek, 32 were observed in Glacier Creek and 3 were observed in the upper Duncan River. Kokanee were estimated to range in size from mm. 28

38 4.3 Water Sampling Lake Sampling Physicochemical Temperature Duncan Reservoir is a monomictic lake, with isothermal temperatures from late fall to early spring and stratification during the summer months (Wetzel 2001). The 2009 sampling demonstrated an early stratification of the reservoir in June with a thermocline forming near m in depth and maximum surface temperatures ranging from 17.1 to 19 C (Figure 11). By September, the thermocline was established near 20 m, with the surface temperature ranging from 18.5 to 21.1 C. The lack of a distinct thermocline suggests that the lake was beginning to de-stratify, although moderately windy conditions may also contribute to mixing. In November, the isothermal temperature profile (6-8 C), indicated that fall turnover had occurred throughout the reservoir. Table. Seasonal mean (± standard deviation), maximum, and minimum temperatures taken at 0-60 m depths, Duncan Reservoir, Season Site Mean ±SD Max Min June P June P June P September P September P September P November P November P November P Oxygen In 2009, oxygen concentrations at most depths were near saturation with respect to temperature and pressure, and there were no discernible zones of reduction indicating O 2 deficits nor was there oxygen super-saturation. In June, dissolved oxygen (DO) demonstrated an orthograde profile with O 2 concentrations showing a uniform depth distribution with little variation both among stations. In September, a similar profile was observed at P2. Data from P3 and P4 is not shown as difficulties were encountered with the DO probe at these stations, which may have been due to sediment buildup on the probe. By November, dissolved oxygen demonstrated a uniform distribution at station P2 and P3, while station P4 indicated increasing concentration with depth (Figure 12). 29

39 Figure 11. Temperature profile by station and season for Duncan Reservoir, Figure 12. Oxygen profile by station and season for Duncan Reservoir, Secchi Depth and Light Secchi depths, which evaluate the transparency of water to light and can therefore serve as a general indicator of productivity, varied seasonally and by station within the Duncan Reservoir (Figure 13). In June, measurements indicated a moderate gradient from north (Site 3) to south (Site 1) in increasing transparency, from 1.5 m to 3.3 m. Similarly, in September, measurements indicated the same gradient from north (Site 3) to south (Site 1) in increasing transparency, from 4.8 m to 6.3 m. November demonstrated a typical seasonal pattern of increasing Secchi depths with measurements that ranged from 9.0 m at the north (Site 3) to 11.0 m in the south (Site 1) and the north-south gradient was maintained. The increase in Secchi depth from June to November is consistent with the reduction in suspended sediment over the same time period. 30

40 Figure 13. Secchi depths (m) by station and season for Duncan Reservoir, Light profiles, which measure photosynthetically active radiation (PAR), were conducted in September and November sampling, indicated that light compensation depths (1% of surface intensity) followed a similar pattern as Secchi measurements. In September, light profiles indicated a gradient from north (Site 3) to south (Site 1) in increasing transparency, with compensation depths of 14 m to 17 m, respectively. A similar gradient was observed in November. Compensation depths increased substantially in the lower basin, to 32 m in the November sampling (Figure 14). Compensation depths at the upper two stations (P3 and P4) could not be calculated as the surface light level was too low. Compensation depth defines the maximum depth at which photosynthesis occurs (euphotic depth) in the reservoir during the growing season. Figure 14. Light profile measuring PAR (µmol m -2 s -1 ) by station and season for Duncan Reservoir in The horizontal lines indicate the 1% extinction lines. 31

41 Turbidity, TSS and Conductivity Total suspended solids (TSS), a measure of the sediment load, decreased from June to November and indicated a gradient from the north end of the reservoir to the south (Figure 15). High TSS in June is due to the resuspension of sediment as discharge in the tributaries increases and the reservoir fills. This is most pronounced at the north end of the reservoir where the upper Duncan River enters. Turbidity, a measure of suspended particles, indicated the same seasonal pattern, although no results are available from June (Figure 16). Figure 15. Total suspended solids (TSS) at pelagic stations by season on the Duncan Reservoir in Figure 16. Turbidity (NTU) at pelagic stations by season on the Duncan Reservoir,

42 Conductivity, a measure of the resistance of a solution to electrical flow, is predominantly due to the specific geology of the major tributaries (upper Duncan River and Howser and Glacier Creeks) that flow into Duncan Reservoir. Average conductivity in late spring was 107 µs/cm, by late summer was 78 µs/cm and by winter was 92 µs/cm (Figure 17). Figure 17. Conductivity (µs/cm) at pelagic stations by season on the Duncan Reservoir, Phosphorus Phosphorus is considered to be a key element in many biological processes and its abundance commonly limits biologic productivity (Wetzel 2001). The majority of the phosphorus inputs into the reservoir come from the upper Duncan River (Perrin and Korman 1997). Epilimnetic total phosphorus (TP), which is composed of mainly organic particulate phosphorus, indicates that Duncan Reservoir is in an ultra-oligotrophic to oligotrophic state of productivity (Wetzel 2001). In 2009, the annual average TP remained below 10 μg/l (Table 18), with all stations except the upper station (P4) recording less than 6 μg/l in June. TP levels at P4 in June were 18 μg/l, and were likely associated with inputs from the upper Duncan River (Figure 18). Epilimnetic total dissolved phosphorus (TDP) remained slightly above detection levels (>1 μg/l) on the Duncan Reservoir in Seasonal changes were observed, with the highest concentration of TDP in late summer (Figure 19). 33

43 Figure 18. Total phosphorus (TP) at pelagic stations by season on the Duncan Reservoir in Figure 19. Total dissolved phosphorus (TDP) at pelagic stations by season on the Duncan Reservoir in Nitrogen Epilimnetic total nitrogen (TN), taken from composite samples, were often below detection levels (200 μg/l) for many of the sites and throughout seasonal sampling in 2009 (Figure 20). Only in late spring, were TN concentrations above detection levels, with an average of 283 μg/l for all stations combined. However, the majority of total nitrogen is present as dissolved inorganic nitrogen (DIN), which consists of nitrate, nitrite, and ammonia, and this can be used as a surrogate for TN. DIN demonstrated strong seasonal patterns on the Duncan Reservoir in 2009 (Figure 21). A general pattern of declining DIN concentrations from spring to summer and a subsequent increase from summer to winter was evident. Late spring concentrations averaged 300 μg/l, with late summer and winter concentrations averaging 60 μg/l and 137 μg/l, 34

44 respectively (Table 18). The low summer levels may have been due to the biological utilization of nitrogen through the growing season. Figure 20. Total nitrogen (TN) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line. Figure 21. Dissolved inorganic nitrogen (DIN) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line. Alkalinity and ph Alkalinity and ph are measures of the buffering capacity and acidity, respectively, of natural waters often associated with limnological processes. Alkalinity, which differs from an alkaline ph, is the buffering capacity of lake water to resist ph changes and involves the inorganic carbon components in most fresh waters (Wetzel 2001). In 2009, ph indicated slightly alkaline conditions, ranging from for all stations sampled on Duncan Reservoir (Table 18). Total alkalinity (CaCO 3 ) demonstrated a general decline from spring to summer and a slight increase 35

45 from summer to fall (Figure 22). Late spring alkalinity concentrations ranged from 45 to 58 mg/l (as CaCO 3 ), while late summer and winter showed little variation between sites at 35 and 40 mg/l (as CaCO 3 ), respectively (Table 18). Figure 22. Total alkalinity (mg/l CaCO 3 ) at pelagic stations by season on the Duncan Reservoir in N:P (NO 3 -N:TDP) ratio The N:P (NO 3 -N:TDP) ratio (weight to weight) was used to assess possible N or P limitation of phytoplankton populations in Duncan Reservoir in The average annual N:P ratio was 84.5, indicating that phosphorus was likely the main limiting nutrient in the reservoir in Seasonally, the highest ratios occurred in June and were lowest in September before recovering in November (Table 18). Moreover, the seasonal progression during the growing season from the spring to summer demonstrates the rapid use of nitrogen, with N:P ratios suggestive of slight nitrogen limitation by late summer. Chlorophyll a Chlorophyll a (Chl a), a photosynthetic pigment, is a primary characteristic of all algae. Concentrations of this pigment are often associated with a waterbody s algal biomass and are representative of its overall productivity. Chl a samples were obtained in late spring and late summer for each of the stations on the Duncan Reservoir in There was a decline in Chl a from spring to summer, coinciding with a decline in the spring phytoplankton bloom beginning in June (Figure 23). Seasonally, Chl a ranged from 0.9 to 1.2 μg/l in the late spring and from 0.5 to 0.56 μg/l in the late summer (Table 18). 36

46 Figure 23. Chlorophyll a (μg/l) at pelagic stations by season on the Duncan Reservoir, Detection limit is marked on plot with the solid line. Table 18. Mean concentrations or measured values by season and year for chemical parameters on the Duncan Reservoir, Parameter Units June September November Average Year ph ph Conductivity µs/cm Total Dissolved Solids mg/l Total Suspended Solids mg/l <1 2 Dissolved Silicon (Si) mg/l n/a Total Alkalinity mg /L CaCO Total Phosphorus μg/l Total Dissolved Phosphorus μg/l Ortho Phosphorus μg/l Ammonia Nitrogen μg/l Nitrate μg/l Dissolved Inorganic Nitrogen μg/l Nitrite and Nitrate μg/l Chlorophyll a μg/l na 0.8 Total Particulate Phosphorus μg/l N:P (NO 3 N:TDP) weight: weight

47 Zooplankton A total of six species of zooplankton were identified in samples collected in late spring and late summer from the Duncan Reservoir in 2009 (Table 19). Two calanoid copepod species Leptodiaptomus ashlandi and Epischura nevadensis were present in samples from both sampling seasons, as well as one cyclopoid copepod species, Diacyclops bicuspidatus thomasi. Rare species were counted and measured as Other Copepods as appropriate. Two species of Cladocera were identified in both seasons: Diaphanosoma brachiurum and Bosmina longirostris. Another cladoceran, Daphnia rosea, was only recorded in the summer samples. Other species were observed sporadically and recorded as Other Cladocerans. Table 19. Zooplankton species present during seasonal sample periods in the Duncan Reservoir, Cladocera Spring Summer Bosmina longirostris + + Daphnia rosea + Diaphanosoma brachiurum + + Copepoda Diacyclops bicuspidatus thomasi + + Epischura nevadensis + + Leptodiaptomus ashlandi + + Seasonal average zooplankton densities were highest in June compared to September (Figure 24). Late spring average zooplankton density was 22.5 individuals/l compared to late summer densities of 9.4 individuals/l. Seasonal average zooplankton biomass was highest in June compared to September (Figure 25). Late spring average zooplankton biomass was 62.8 μg/l compared to late summer biomass of 39.9 μg/l. The zooplankton community was primarily composed of copepods in late spring, accounting for more than 99% of the zooplankton density and biomass. Similarly, by late summer, the zooplankton community was again numerically dominated by copepods, accounting for 84% of the zooplankton density. Although copepods were numerically superior in late summer, cladocerans accounted for more than 58% of the overall biomass. The majority of this biomass is due to the presence of larger Daphnia species. 38

48 Figure 24. Zooplankton density by season and station in the Duncan Reservoir, Figure 25. Zooplankton biomass by season and station in the Duncan Reservoir, Tributary Sampling Tributaries were sampled on May 14, September 14 and November 25, Except for Griz Creek, the tributaries are all glacially-fed, and hence the September samples reflect the contribution from glacial melt. This is reflected in the higher total suspended solids and turbidity values obtained in September, compared to May and November (Figure 26). Of note, an extremely large mass wasting event occurred in the Howser Creek watershed (in Moran Creek). This resulted in higher than normal turbidity in Howser Creek from spring until October. A large 39

49 amount of material was deposited into Howser Creek, and it is likely that much of the smaller material (sands, gravels) will be transported into the reservoir in subsequent freshets. Stream chemistry data is provided in Appendix 2. As expected, most of the TP contributed by the tributary streams was associated with suspended sediments (Figure 27). Sediment load in the tributaries was highest during the September sampling, due to the increased contribution of glacial inputs at this time. Total nitrogen in tributaries was only detected in the upper Duncan River and Howser Creek in May samples, and hence dissolved inorganic nitrogen DIN)was used as a surrogate for this parameter. DIN was highest in May, decreased in September and increased again in November (Figure 28), which likely reflects the biological utilization of nitrogen during the growing season. Figure 26. Turbidity in Duncan Reservoir tributaries by season, Figure 27. Total phosphorus in Duncan Reservoir tributaries by season in Detection limit is marked on plot with the solid line (note a higher detection limit (20μg/L) was used in May. 40

50 Figure 28. Dissolved inorganic nitrogen in Duncan Reservoir tributaries by season in Water Temperature Temperature data for five tributaries are displayed in Figure 29. All the tributaries displayed a similar temperature profile. The maximum mean daily temperature of 12 C during the summer in Griz Creek, Little Glacier Creek and Howser Creek was slightly higher than the maximum mean daily temperature of 10 C in Glacier Creek and the upper Duncan River. Figure 29. Mean daily temperature in tributaries to the Duncan Reservoir (May Nov 2009). 41