Kootenay River White Sturgeon. Studies in British Columbia, 2001

Transcription

1 Kootenay River White Sturgeon Studies in British Columbia, 2001 Matthew D. Neufeld and Colin R. Spence Ministry of Water, Land and Air Protection Victoria Street Nelson, BC V1L 4K3 June 2002 This project was funded by the Bonneville Power Administration (Columbia Basin Fish and Wildlife Authority), in co-operation with the Idaho Department of Fish and Game, and the Kootenai Tribe of Idaho.

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3 Abstract Juvenile white sturgeon (Acipenser transmontanus) were sampled in the Kootenay River between the Canada U.S. border and the Creston Delta at the south end of Kootenay Lake between June 19 and September 7, Sampling efforts resulted in a total of 98 sturgeon captures. Gill nets were the primary sampling gear, resulting in net-hours of effort and capture of 97 juvenile sturgeon. Angling and cod traps were used to a lesser extent, resulting in 40 rod-hours and 10.2 trap-days of effort respectively. One juvenile sturgeon was captured through angling efforts and none were captured in cod traps. As in previous years, gill net sampling was the most effective capture method. Catch rates varied by location, time period, and depth; however, no sturgeon were captured in the East Channel or Corn Creek Slough. Sturgeon catch rates were low on the Creston Delta but increased as sampling progressed upstream towards the Canada/U.S. border. Catch rates increased steadily from June 19 through to the end of the study period on September 7, as in previous studies. The minimum and maximum set depths of nets that captured sturgeon were significantly deeper than the minimum and maximum depths of all net sets. Comparisons of the depth frequency distribution of sturgeon capture and all sets also showed significant differences; juvenile sturgeon were captured more frequently in deeper habitats. Sturgeon fork lengths ranged from 190 to 705 mm (mean 298 mm) while weights ranged from 45 to 2230 g (mean 195g). The relative weight (W r ) of juveniles ranged from 64 to 166% (mean 83%). Temperature recorders were deployed in five locations in the study area to examine trends related to catch rate and temperature, and to identify the suitability of backchannel habitats for juvenile sturgeon rearing. Although no relationship between catch rate and temperature was identified, the temperatures recorded in all the backchannel habitats were suitable, and in some cases very favourable, for juvenile sturgeon rearing. Kootenay River White Sturgeon Studies 2001 i

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5 Table of Contents Abstract...i Table of Contents...iii List of Tables... v List of Figures...vi List of Appendices...vii 1.0 Introduction Study Area Methods Sampling Stratification Spatial Stratification Temporal Stratification Depth Stratification Fish Capture Gill Nets Cod Traps Angling Capture Data Sonic Tagging Temperature Recorders Results Fish Capture Gill Nets By-Catch Sturgeon Capture Locations Sturgeon Capture Dates Sturgeon Capture Depth Gill Net Selectivity Crawford Bay Sampling Cod Traps Angling Life History Recapture Information Sonic Tagging Temperature Recorders...26 Kootenay River White Sturgeon Studies 2001 iii

6 5.0 Discussion Gear Efficiency Life History Movements Water Temperature Recommendations Acknowledgements Literature Cited Appendices Kootenay River White Sturgeon Studies iv

7 List of Tables Table 1. Summary of catch and catch-rate (CPUE=number juveniles caught/net-hour) of white sturgeon captured, by sample location, in Kootenay River and Lake Table 2. Summary of catch and catch-rate (CPUE=no. juveniles caught/net hour) of white sturgeon captured, by time period, in Kootenay River and Lake Table 3. Gill netting effort (net-hours) by time strata and location Table 4. Summary of catch and catch-rate (CPUE= no. juveniles caught/net hour) of juvenile white sturgeon captured, stratified by set depth, in Kootenay River and Lake Table 5. Summary of minimum and maximum set depths of sets that captured sturgeon and all sets. Includes comparisons for all sets, and for sets excluding R-2 and S Table 6. Summary of catch and catch-rate (CPUE= no. juveniles caught/net hour) of juvenile white sturgeon captured, stratified by mesh size, in Kootenay River and Lake Table 7. Summary of the number of sets that captured sturgeon and all sets, stratified by mesh size Table 8. Summary of data from sturgeon captured by angling Table 9. Growth rates for juvenile sturgeon recaptured in Table 10. Summary of life history information from the three radio tagged juvenile sturgeon Table 11. Location and depth, as well as deploy and recovery dates of temperature recorders Kootenay River White Sturgeon Studies v

8 List of Figures Figure 1. Location of juvenile white sturgeon studies on the Kootenay River and Kootenay Lake Figure 2. Kootenay Lake and the Kootenay River near Creston, B.C., showing river kilometer markers as well as stratification boundaries and identification symbols... 5 Figure 3. Juvenile sturgeon equipped with an external mount sonic tag on the Kootenay River delta, August 16, Figure 4. Juvenile sturgeon capture locations in Time Strata 1 (a; June 17 - July 14), 2 (b; July 15 - August 10), and 3 (c; August 11 September 8), as well as the location of all net sets (d) Figure 5. Location of gill net sets which captured sturgeon Figure 6. Proportion of net sets at different minimum set depths for all sets vs. sets that captured sturgeon (a), and all sets vs. sets that captured sturgeon, excluding sets from R-2 (East Channel) and S-1 (Corn Creek Slough) (b) Figure 7. Proportion of net sets at different maximum set depths for all sets vs. sets that captured sturgeon (a), and all sets vs. sets that captured sturgeon, excluding sets from R-2 (East Channel) and S-1 (Corn Creek Slough) (b) Figure 8. Cod trap set locations Figure 9. Length frequency histogram for juvenile sturgeon captured in Figure 10. Tracking locations of a juvenile sturgeon, sonic tag code 8-2-8, on the Kootenay River Figure 11. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-2, on the Kootenay River Figure 12. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-7, on the Kootenay River Figure 13. Location of temperature recorders deployed in Figure 14. Water temperatures for the Kootenay River and nearby slough habitats, July 24 through September 24, Figure 15. Water temperatures for Kootenay Lake at the Creston Delta, July 26 through September 24, Kootenay River White Sturgeon Studies vi

9 List of Appendices Appendix A. Summary of gill net set data, Appendix B. Capture information from juvenile sturgeon captured in Appendix C. Summary of sturgeon recapture and life history information Appendix D. Summary of adult sturgeon capture data Appendix E. Summary of incidental gill net catch, Appendix F. Cod trap set records, Appendix G. Cod trap catch records, Appendix H. Gill net set data from sampling in Crawford Bay, Appendix I. Gill net catch records from net sampling in Crawford Bay, Appendix J. Locations of juvenile sturgeon equipped with sonic tags in the summer of Kootenay River White Sturgeon Studies vii

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11 1.0 Introduction White sturgeon (Acipenser transmontanus) occur along the Pacific coast of North America from central California to the Aleutian Islands. In south-eastern British Columbia, the range of this species extends into Kootenay Lake and the Kootenay River (spelled Kootenai in the U.S.), located in the upper Columbia River basin. The Kootenay population is distinct from other Columbia River sturgeon (Anders et al. 2000), having been isolated by Bonnington Falls since the last glaciation (Northcote 1973). The range of this population is now further restricted by several dams, which have also altered river and lake environments. The Kootenay population is now distributed from Kootenai Falls, Montana, downstream through Kootenay Lake to Corra Linn Dam on the lower West Arm of Kootenay Lake, B.C. (Figure 1). The Kootenay River white sturgeon population began to experience recruitment failure during the mid-1960 s (Partridge 1983). Libby Dam, located on the Kootenai River system upstream of Kootenai Falls in Montana, began operations in 1972 and has been linked to recent, more extensive problems with recruitment (U.S. Fish and Wildlife Service 1999). The population has now been listed under the U.S. Endangered Species Act, as well as by B.C. s Conservation Data Center (Red Listed critically imperilled). A Recovery Plan has recently been implemented, providing direction for ongoing studies, modifications to Libby Dam operations and conservation aquaculture operations (U.S. Fish and Wildlife Service 1999). Concern for Kootenay white sturgeon has prompted initiation of detailed studies in both Idaho and British Columbia. Co-operative investigations by the Idaho Department of Fish and Game and the B.C. Ministry of Water, Land, and Air Protection (MWLAP) began in 1994 with funding from the Bonneville Power Administration (Columbia Basin Fish and Wildlife Authority). Juvenile white sturgeon sampling has been completed annually since 1998 in the Kootenay River between the Canada U.S. border and the Creston Delta at the south end of Kootenay Lake. Although adult sturgeon in Kootenay system have been studied extensively (e.g. RL&L 1999, Paragamian et al. 1999), the life history of juvenile sturgeon is less well understood. Recent studies on the Kootenay River (Paragamian et al. 1999, Vandenbos and Spence 2001, Young and Scarnecchia 1999) have identified gill nets and ultrasonic telemetry as particularly useful in describing behaviour and habitat use patterns. Also, on the Columbia River, gill nets are now frequently used in place of bottom trawls to sample juvenile sturgeon (Kerr et al. 2001). Kootenay River White Sturgeon Studies

12 Figure 1. Location of juvenile white sturgeon studies on the Kootenay River and Kootenay Lake. Kootenay River White Sturgeon Studies

13 Studies completed in 2001 were a continuation of the aforementioned projects, and were aimed at assessing progress in the recovery of Kootenay white sturgeon within B.C. Specifically, our objectives were to: describe trends related to growth, distribution, survival and abundance of juvenile white sturgeon; determine large scale habitat preferences of wild and hatchery produced juveniles; determine the age distribution of wild and hatchery produced juveniles; experiment with small mesh gill nets to determine if larval sturgeon released in 2000 had survived; further test the capture efficiency of cod traps for juvenile sturgeon sampling; and determine if the temperature regime in various slough habitats along the lower Kootenay River were suitable for juvenile sturgeon rearing. 2.0 Study Area The Canadian portion of the Kootenay white sturgeon range is located in south-eastern British Columbia, immediately north of the state of Idaho (Figure 1). The Kootenay River enters Kootenay Lake at its southern tip. The lake is also fed by the Lardeau and Duncan rivers at the north end, and numerous other much smaller tributaries. The outlet of Kootenay Lake flows from the lake s mid-point for approximately 70 km in a westerly direction, eventually descending over a series of dams and entering the Columbia River near Castlegar. These dams, as well as a dam on Lardeau/Duncan system, currently restrict distribution of white sturgeon in Kootenay system within B.C.. A more detailed description of Kootenay Lake can be found in Daley et al. (1981). The present study was conducted in a small portion of the present range of Kootenay white sturgeon, and included 50 km of Kootenay River from the Canada - U.S. border, downstream to, and including the entrance to Kootenay Lake (Figure 2). The area where the river enters Kootenay Lake is referred to as the Creston Delta. 3.0 Methods 3.1 Sampling Stratification The Kootenay River between the Canada U.S. border and the Creston Delta were divided into spatial, temporal, and depth strata for sampling purposes. We attempted to distribute fishing effort uniformly between the various strata, to ensure each was afforded sufficient attention that trends might be identified Spatial Stratification The sampling area was divided into nine spatial strata (Figure 2). The Kootenay River (river km ) was divided into six strata, each of which was approximately 10 km in length (R-1 to R-6). The Creston Delta at the south end of Kootenay Lake was Kootenay River White Sturgeon Studies

14 divided into two strata (DW and DE). Also, the Corn Creek slough near the Creston boat launch (river km 150), which included a network of channels that ran west of the Kootenay River along the valley bottom, were grouped into one stratum (S-1) Temporal Stratification The sampling period (June 17 September 8) was divided into three separate time periods of approximately four weeks in length. The three strata were defined as June 17 - July 14, July 15 - August 10, and August 11 September Depth Stratification Depth of captures in the Kootenay River and Creston Delta were divided into two strata. Capture depths in the river and delta were stratified by maximum set depths of <15m in the shallow strata and minimum set depths of >15m in the deep strata. The depth of stratum division was based on an examination of habitat availability and catch records from previous years, where we determined that most of the deeper pool habitats were at least 15 m in depth, where glides were typically less (Vandenbos and Spence 2001). Due to differences in habitat types, the East Channel of the Kootenay River (R-2) and Corn Creek slough were not stratified by depth. The maximum depths in Corn Creek Slough (river km 150) and the East Channel do not exceed 15m, and therefore sets in these areas were all grouped into the shallow depth stratum. 3.2 Fish Capture Juvenile sampling was conducted from a 7.0 m boat. Locations were determined by GPS (Trimble Geoexplorer II). Set and pull times were recorded for each set. Maximum and minimum set depths were recorded for all net sets and set depth was recorded for cod trap sets using a Lowrance (model LMS-350a) depth sounder. Set areas were occasionally limited by bottom conditions; nets were not set in areas with high concentrations of woody debris because of potential problems with lost or damaged gear Gill Nets Juvenile white sturgeon were captured using multi-strand nylon gill nets of 45 m long by 1.8 m high. Nets consisted primarily of 5cm stretch measure mesh, which has proven the most effective size for capturing juvenile young-of-the-year (YOY) white sturgeon in previous work on the Columbia River (Burner et al. draft 1999) and is also the size of mesh that has been used on the Kootenay River during previous years of juvenile sampling (Vandenbos and Spence 2001). Smaller mesh nets (2.5 cm stretch measure) were used on a trial basis in approximately one quarter of net sets to identify smaller white sturgeon resulting from a larval sturgeon release into the Kootenay River in the summer of The target length of sets was intended to be 1 hour in duration; however, some sets were as long as 1.75 hours due to the time involved in examining captured juvenile sturgeon. Kootenay River White Sturgeon Studies

15 E-D W-D R-2 R-1 R-3 R-4 S-1 R-3 Stratum ID Stratum Boundary R-5 R-6 Figure 2. Kootenay Lake and the Kootenay River near Creston, B.C., showing river kilometer markers as well as stratification boundaries and identification symbols. Kootenay River White Sturgeon Studies

16 3.2.2 Cod Traps Cod traps were used in a small number of sets on a trial basis. The traps were based on a design used by the marine commercial fishing industry to catch black cod (Anaplopoma fimbria) on the Pacific coast and are described more fully by Spence (1999). All traps were baited with kokanee (Oncorhynchus nerka) spawner carcasses. Cod traps have been used in previous years to capture juvenile sturgeon with limited success (e.g. Spence 2000). However, with the expectation of a much larger juvenile sturgeon population in 2001 than in previous years, we again tested the utility of cod traps Angling Angling was undertaken on a casual basis, between sets, while gill net sampling. Size 6 and 8 hooks were used on a still-fished bottom rig, lighter in weight but otherwise similar to that commonly used for adult sturgeon. Bait used included small pieces of kokanee spawner carcasses and earthworms. A formal record of angling hours was not maintained. However an estimate of angling effort and catch was developed based on consultation with the field crew Capture Data All captured white sturgeon were brought into the boat for sampling. Smaller juveniles were placed in a plastic container filled with water. Larger juveniles and all adults were placed in a waterproof stretcher, with enough water to allow for respiration. Fresh water was frequently added to the stretcher during the processing period. After processing, sturgeon were returned to the water and released once normal respiration, orientation and swimming behaviour were established. All white sturgeon were first examined for previous marks. Previous marks included Passive Integrated Transponder (PIT) tags (placed either on the right side just ventral to the dorsal fin, or near the head), scute removal (left and/or right side, counted from the anterior end), and/or evidence of previous fin clips on either the right or left pectoral fin. Recaptured sturgeon with the second scute removed on the left side (2L) were previously marked on the Kootenay system while sampling, while hatchery produced fish had scutes removed on both sides indicating the year of hatch (e.g., 9L 5R = 1995 brood). All sturgeon were measured for fork length (FL) and total length (TL) to the nearest millimetre. Weight was determined for all fish using a spring scale with the appropriate capacity. Newly captured adults were marked with the application of a PIT tag on the right side below the dorsal fin, and with removal of the 2L scute. Hatchery produced juveniles that had a non-responsive or lost PIT tag were marked with the application of a new PIT tag on the right side. One hatchery juvenile with a non responsive or lost PIT tag was released before it was re-tagged. All incidental catches were identified by species, measured for FL (mm), returned to water and released when or if normal swimming behaviour was observed. Kootenay River White Sturgeon Studies

17 3.3 Sonic Tagging Three juvenile sturgeon were fitted with externally attached sonic transmitters (Sonotronics Model IT95-2) which were 14 mm wide by 45 mm long and weighed 5 g in water. Sonic tags were equipped with holes at each end to allow wire to be passed through for attachment purposes. Fine, plastic coated wire was threaded through the holes in the radio tag and a neoprene backing pad. In the case of two sturgeon, two sterilized spinal needles were then passed through the dorsal musculature within five dorsal scutes of the head. One sturgeon was large enough to facilitate the use of a drill to create two holes through two of the dorsal scutes. The wire from each end of the radio tag was then inserted through the spinal needles as a means to pass it through the dorsal musculature. The needles were then removed. For the fish in which the dorsal scutes were drilled, the wire was inserted directly through the freshly drilled openings. The two ends of the wire were then passed through a neoprene pad and a plastic backing plate. The two ends of the wire were drawn tight around the back of the backing plate and secured using wire crimps (Figure 3). Sonic tags, wire, backing plates, drill bit and spinal needles were sterilized in Germiphene prior to attachment. Figure 3. Juvenile sturgeon equipped with an external mount sonic tag on the Kootenay River delta, August 16, Kootenay River White Sturgeon Studies

18 3.4 Temperature Recorders Five TidBit TM temperature recorders were deployed in the study area. One recorder was deployed on the Creston Delta on July 26 and in the Kootenay River on July 24. The remaining three recorders were deployed on July 24 in slough or back channel habitats in Leach Lake, Six Mile Slough and Corn Creek Slough. Temperature recorders were attached to a concrete block and placed on the bottom substrate at each sample location. Temperature recorders were calibrated to record temperatures every two hours. Data from all five temperature recorders were recovered on September 24. Kootenay River White Sturgeon Studies

19 4.0 Results 4.1 Fish Capture Gill Nets In 2001, gill nets were set 340 times between June 19 and September 7. Two of these sets became badly tangled on the bottom substrate and were not used in our calculations. In previous years high river discharge and extreme wave conditions had occasionally limited set locations (Vandenbos and Spence 2001). Set locations were not limited by river and lake conditions in 2001 because of favourable weather and low river levels. The 338 sets that fished effectively accounted for a total effort of net-hours and a catch of 96 juvenile sturgeon (Appendices A and B). One juvenile sturgeon was captured twice in 2001, accounting for a total of 97 net captures of young sturgeon By-Catch A total of 355 fish of species other than sturgeon were captured incidentally during this study, for a by-catch of fish per net-hour (Appendix E). Species captured included longnose sucker (Catostomus catostomus), largescale sucker (Catostomus macrocheilus), peamouth (Mylocheilus caurinus), northern pikeminnow (Ptychocheilus oregonensis), kokanee (Oncorhynchus nerka), mountain whitefish (Prosopium williamsoni), pumpkinseed (Lepomis gibbosus), yellow perch (Perca flavescens), black catfish (Ameiurus melas), and redside shiner (Richarsonius balteatus). Peamouth accounted for the highest number of captures (n=113), although whitefish and northern pikeminnow were also captured frequently (n= 92 and 53, respectively) Sturgeon Capture Locations Sampling was performed in all nine spatial strata (Table 1). No sturgeon were captured in the Kootenay River East Channel (R-2), or the Corn Creek Slough (S-1). Catch rates were low on the Creston Delta and in the lowest ten kilometres of Kootenay River (DE, DW, and R-1). Above river kilometre (rkm)130, catch rates increased as the river kilometre increased with the highest catch rates near the Canada/US border (R-7). More effort was expended in R-6 because catch rates were highest in that stratum, and therefore life history information could be gathered with greater efficiency. Because it was unclear if S-1 represented suitable juvenile habitat, less effort was expended in this strata. While sets were placed in all areas of the river, sets that captured fish were generally set in the deep areas associated river bends (Figure 4). Few fish were captured on the shallow, flat bottom glides between river bends Sturgeon Capture Dates Sampling effort was distributed over all three time strata (Table 2). A minimum of 12 sets were completed in spatial strata during each time period. Catch rates were higher in late August and early September than in June or July. The spatial distribution of sturgeon captures differed by time strata. However, the expenditure of effort over each time strata was relatively similar by location (Table 3). Therefore, time period differences in the location of captures were not a result of changes Kootenay River White Sturgeon Studies

20 in effort expenditure. Sturgeon captures were limited to the area between river kilometer 160 and 170 (R-6) in time stratum 1 (June17-July 14; Figure 8a). In time stratum 2 (July 15-August 10), juvenile sturgeon were captured in an area between river kilometer 140 and 170 (R-4 to R-6), as well as one juvenile capture between river kilometer 120 and 130 (R-1; Figure 8b). In time stratum 3 (August 11-September 8) juvenile sturgeon were captured between river kilometer (R3 to R-6), and in both spatial stratum on the Creston Delta (DE and DW; Figure 5). No juvenile sturgeon were captured in Corn Creek Slough (S-1), between river kilometer (R-1) or in the East Channel (R-2) during time stratum 3. Table 1. Summary of catch and catch-rate (CPUE=number juveniles caught/net-hour) of white sturgeon captured, by sample location, in Kootenay River and Lake. Spatial Sample Net White sturgeon Stratum Location Hours Catch CPUE (DE) East Delta, Kootenay Lake (DW) West Delta, Kootenay Lake (R-1) Kootenay River km (R-2) Kootenay River, East Channel (R-3) Kootenay River km (R-4) Kootenay River km (R-5) Kootenay River km (R-6) Kootenay River km (S-1) Back Channel and Slough Habitat (Rkm 150) Total Table 2. Summary of catch and catch-rate (CPUE=no. juveniles caught/net hour) of white sturgeon captured, by time period, in Kootenay River and Lake. Time Date Net White sturgeon Strata Hours Catch CPUE 1 June 17 - July July 15 - August August 11 - September to 3 June 17 - September Table 3. Gill netting effort (net-hours) by time strata and location Time DE DW S-1 R-1 R-2 R-3 R-4 R-5 R-6 Strata Kootenay River White Sturgeon Studies

21 Figure 4. Location of gill net sets in which white sturgeon were captured. Kootenay River White Sturgeon Studies

22 Figure 5. Juvenile sturgeon capture locations in time stratum 1 (a; June 17 - July 14), stratum 2 (b; July 15 - August 10), and stratum 3 (c; August 11 September 8), as well as the location of all net sets (d). Kootenay River White Sturgeon Studies

23 Sturgeon Capture Depth We compared the depths of gill net sets that captured young sturgeon to those that did not. During the analysis, we noted that it was unclear if Corn Creek Slough (S-1) and the East Channel of the Kootenay River (R-2) represented suitable juvenile sturgeon rearing habitat, as no juvenile sturgeon were captured in these areas and all sets in these two areas were less than 15 m. Although studies on juvenile sturgeon in the Fraser River (Lane and Roseneau, 1993) indicated that backchannel areas were consistently used as juvenile rearing habitat, backchannel areas with unidirectional flow and depths of less than 5 m were rarely used. These two areas (R-2 and S-1) both have unidirectional flow and only one small area in the East Channel (R-2) that exceeds 5 m in depth. Because of this uncertainty, comparisons of set depths were completed with and without the sets from these strata. We compared catch rates in the two depth strata based on all sets, higher values occurred in sets 15 m or greater in depth. Net sets that were greater than 15 m in depth accounted for 84% of the catch and only 42% of the effort (Table 4). When we compared sets, excluding sets from R-2 and S-1, catch rates in sets greater than 15 m were still much higher, accounting for 84% of the catch and only 49% of the effort (Table 4). Table 4. Summary of catch and catch-rate (CPUE= no. juveniles caught/net hour) of juvenile white sturgeon captured, stratified by set depth, in Kootenay River and Lake. All Sets Sets excluding S-1 and R-2 Set Depth Sturgeon Captures Effort CPUE Effort CPUE %(n) %(hr) n/hr %(hr) n/hr Deep (>15 m) 84 (81) 42 (164.2) (164.2) Shallow (<15 m) 16 (16) 58 (223.7) (170.7) Total 100 (97) 100 (387.9) (334.9) We also compared mean minimum and maximum set depths for all sets, including sets from R-2 and S-1. The mean minimum set depth of nets that captured sturgeon was 15.7 m - significantly deeper than the mean minimum set depth of all sets at 10.7 m (Mann- Whitney U=4846.0, P < 0.000; Table 5). The mean maximum set depth of nets that captured sturgeon was again significantly deeper than the mean maximum set depth of all sets (Mann-Whitney U=5279.5, P < 0.000; Table 5). Comparisons of mean set depth, excluding sets from R-2 and S-1, yielded similar results. Mean minimum and maximum set depths for sets that captured sturgeon were again significantly deeper than the means for all sets (Mann-Whitney P < 0.000; Table 5). Kootenay River White Sturgeon Studies

24 Table 5. Summary of all gillnet sets and minimum and maximum depths of sets that captured sturgeon. Comparisons for all sets, and for sets excluding R-2 and S-1, are included. Set Minimum Set Depth Maximum Set Depth Depth (m) Capture sets All sets Capture sets All sets All Sets Minimum Maximum Mean Mann-Whitney U = P-Value < U = P-Value < Sets excluding R-2 and S-1 Minimum Maximum Mean Mann-Whitney U = P-Value < U = P-Value < When comparing sets from all spatial strata, there was a significant difference in the minimum depth distribution of sets that captured sturgeon and all net sets (Kolmogorov- Smirnov, ks=0.38 P<0.000). Minimum set depth comparisons (Figure 6) illustrate that, compared to all net sets, those that captured sturgeon were proportionally lower in depths under 15 m, and proportionally higher in depths over 15 m. There was also a significant difference in the maximum depth distribution between sets that captured sturgeon and all net sets (Kolmogorov-Smirnov, ks=0.34 P<0.000). Similarly, maximum set depth comparisons (Figure 7) showed that, compared to all sets, sturgeon captures were proportionally lower at depths of 0-11 m, relatively equal at m, and higher at depths greater than 19 m. The higher proportion of sturgeon captures at minimum depths of greater than 15 m and maximum depths of greater than 19 m, suggests that habitat use is highest in river depths of 15 m and deeper. Comparisons of set depth, excluding sets from spatial strata S-1 and R-2 yielded similar results. A significant difference occurred in the minimum depth distribution between sets that captured sturgeon and all net sets (Kolmogorov-Smirnov, ks=0.29 P=0.001). Excluding sets from R-2 and S-1 affected the frequency of sets in the shallowest habitat (0-5 m), but did not change the overall shape of the frequency distribution (Figures 9a and b). There was also a significant difference in the maximum depth distribution between sets that captured sturgeon and all net sets (Kolmogorov-Smirnov, ks=0.26 P=0.004). Again, excluding sets from R-2 and S-1 affected the frequency of sets in the shallower habitat (0-9 m), but did not change the overall shape of the frequency distribution (Figure 7 a, b). The minimum set depth frequency distributions exhibit a low relative frequency of minimum set depths from 7-15 m (Figure 6). The irregular shape of the minimum set depth frequency distribution is the result of field constraints resulting from the depth stratification scheme. Few sets were placed at minimum depths from 7-15 m in order to prevent the maximum depth of these shallow sets exceeding 15 m, the stratification boundary for set depth. Kootenay River White Sturgeon Studies

25 Proportion of nets a Sturgeon Capture Sets All Sets 0.05 Proportion of nets Minimum depth (m) of nets b Sturgeon Capture Sets All Sets Minimum depth (m) of nets Figure 6. Proportion of net sets at different minimum depths for all sets vs. those that captured sturgeon (a), and all sets vs. those that captured sturgeon, excluding sets from R-2 (East Channel) and S-1 (Corn Creek Slough) (b). Kootenay River White Sturgeon Studies

26 Proportion of nets a Sturgeon Capture Sets All Sets Proportion of sets Maximum depth (m) of nets b Sturgeon Capture Sets All Sets Maximum depth (m) of sets Figure 7. Proportion of net sets at different maximum set depths for all sets vs. those that captured sturgeon (a), and all sets vs. those that captured sturgeon, excluding sets from R-2 (East Channel) and S-1 (Corn Creek Slough) (b). Kootenay River White Sturgeon Studies

27 Gill Net Selectivity Larger mesh size gill nets captured juvenile sturgeon more efficiently than the small mesh size in The CPUE for sets of 5 cm stretch mesh size was more than two times as high as sets with 2.5 cm stretch mesh size (Table 6). Table 6. Summary of catch and catch-rate (CPUE= no. juveniles caught/net hour) of juvenile white sturgeon captured, stratified by mesh size, in Kootenay River and Lake. Mesh Size Sturgeon Captures Effort CPUE (cm) %(n) %(hr) n/hr (13) 24 (92.6) (84) 76 (295.3) Total 100 (97) 100 (387.9) To further investigate gill net selectivity, a statistical comparison of mesh size capture efficiencies was completed when sets of 2.5 and 5 cm mesh were stratified by sets that captured sturgeon and all sets (Table 7). There was no significant difference in the frequency of these sets that captured sturgeon (Yates continuity correction, chi-square χ 2 = 0.412, P = 0.521). For the investigation of mesh size capture efficiency, a post hoc power analysis was performed to investigate if there was no effect (no capture efficiency difference) or whether the analysis had a low probability of detecting an effect if one was present (Peterman 1990). The power of the effect size observed in the sample and the detectable effect size was estimated with G*Power software (Erdfelder et al. 1996; Buchner et al. 1997). The detectable effect size was estimated when alpha and beta were set at 0.05 and 0.20, respectively and with the observed sample size and variance (Peterman 1990). In the comparison of mesh size capture efficiencies, the detectable effect size (w = 0.28) was much higher than the observed effect size (w = 0.04), and thus power was very low (power = 0.07). The low power of this test indicates that, if there was a difference in capture efficiencies, there was a low probability of detecting it. Table 7. Summary of the number of sets that captured sturgeon and all sets, stratified by mesh size. Mesh Size Sturgeon Capture Sets All Sets Total (cm) n (%) n (%) n (%) (18) 81(23) 91(23) 5 43(82) 257(77) 300(77) Total 53(14) 338(86) 391(100) Chi-Square P Value Kootenay River White Sturgeon Studies

28 Crawford Bay Sampling Independent from our Kootenay River studies, one day of gill net sampling for juvenile sturgeon was spent on the Crawford Creek delta in Kootenay Lake. Despite some sampling effort in previous years, no juvenile sturgeon have ever been captured in Crawford Bay (RL&L 1998). In 2001, a total of 12 net sets resulted in 15.0 net-hours of effort on September 4 (Appendix H). Minimum set depths ranged from 3 to 17.3 m with a mean depth of 8.5 m. Maximum set depths ranged from 17.9 to 23.3 m (mean 21.7 m). Again in 2001, no juvenile sturgeon were captured at this location. By-catch included yellow perch, northern pikeminnow, and mountain whitefish, for a total of 12 fish (Appendix I) Cod Traps Cod traps were set in ten locations for a total of 10.2 trap-days of effort (Figure 8; Appendix F). Sampling effort was concentrated between river kilometre 145 and 170. Trap depths averaged 21.9 m (ranged m). Two of the ten sets were completed using a cod trap that had been modified with a solid piece of smooth fabric sewn into the lead. It was hoped this modification would improve the capture efficiency of these traps by allowing easier passage through the trap lead for juvenile sturgeon. No sturgeon were captured in any trap sets. By-catch was low and included twelve fish captured in the eight un-modified trap sets; no fish captured in the two modified cod trap sets (Appendix G) Angling An estimated 40 rod-hours were expended on the Kootenay River. Angling locations were not recorded, but were concentrated between river kilometre 150 and 170. Catches of species other than sturgeon were high and consisted primarily of peamouth and northern pikeminnow. These two species accounted for catches in the range of 5-7 fish/rod hour. One juvenile and one adult sturgeon were captured through angling efforts (Table 8). Both sturgeon were angled using small pieces of kokanee spawner carcass. Table 8. Summary of data from sturgeon captured by angling. Length (mm) Weight Missing Scutes New Date Fork Total (g) L# R# Pit Tag # Pit Tag# 7-Aug F7D3E Sep D53360B Kootenay River White Sturgeon Studies

29 Figure 8. Cod trap set locations. Kootenay River White Sturgeon Studies

30 4.1.4 Life History The length of juvenile white sturgeon captured in 2001 in the Kootenay River and on the Creston Delta ranged from 190 to 705 mm FL (mean 298 mm; Figure 9, Appendix B). The majority of captures (95%) in 2001 were hatchery fish from the 1999 brood year. Juvenile white sturgeon captures from this year class ranged in length from 190 to 390 mm FL (mean 283 mm). The large number of captured juveniles from the 1999 brood year is apparent in the length frequency histogram as a large proportion of fish between 200 and 400 mm in length (Figure 9). The weight of juvenile white sturgeon captured in 2001 ranged from 45 to 2230 g with a mean weight of 195g (Appendix B). The weight of juvenile white sturgeon from the 1999 brood year ranged from 45 to 315 g (mean 134 g). Juvenile sturgeon captured in 2001 ranged in age (based on IDFG database) from 2 to 11 years (mean 2.3 years) Relative Frequency (%) Fork Length (mm) Figure 9. Length frequency histogram for juvenile sturgeon captured in Condition factor is recognized as an indicator of forage, feeding and health problems for wild fish and hatchery fish adapting to the natural environment (Ricker 1975; Ireland et al. draft 2001). The relative weight index (W r ) has become the primary method of comparing the condition of white sturgeon populations through most of their range (Beamesderfer, 1993; Ireland et al. in prep. 2001). In the contrast with traditional approaches to condition factor, the relative weight index facilitates comparisons among different populations and between individuals of different lengths (Beamesderfer 1993). The index is expressed as a percent where 100% represents a sturgeon population in better than average condition. The relative weight index (W r ) was calculated using the following formula (Beamesderfer 1993): β Wr = ( W / αl ) *100 Kootenay River White Sturgeon Studies

31 where W is the fish weight, α is a regression line intercept for the Kootenai River white sturgeon population (7.13E-07), L is the total fish length and β is a regression line slope for the Kootenai River white sturgeon population (3.394; from Beamesderfer 1993). The index for all juvenile sturgeon captured in 2001 ranged from 64 to 166% (mean 82.2%). The relative weight of sturgeon released in the fall of 2000 and recaptured in 2001 ranged from 68 to 167% (mean 90.4%). Of the 32 hatchery recaptures from stocking in the fall of 2000, 27 (84%) showed a decrease in relative weight between release and recapture. The mean change in relative weight for this group was -12%, with a range of -38 to 66%. The relative weight of sturgeon released in the spring of 2001 ranged from 64 to 91% (mean 78.5%). Of the 52 hatchery recaptures, stocked in the spring of 2001, 50 (96%) showed a decrease in relative weight between release and recapture. The mean change in relative weight for this group was -17%, with a range of to 3.5%. All other juveniles captured in 2001 (n=5) ranged in relative weight from 76 to 83% (mean 79.7%). Previous weight data was only available for four of these fish. Three of these four fish showed an increase in relative weight with only one fish decreasing (range -2.5 to 6.4%). 4.2 Recapture Information All juvenile sturgeon captured in 2001 were hatchery release recaptures or recaptures of wild fish marked on previous years. One of the two adult sturgeon captured in 2001 was a recapture. Five (5%) of the 97 juvenile sturgeon captured in 2001 had either lost their PIT tag or had a PIT tag that was non-functional or not recognized by the reader unit; however, it was not possible to differentiate between these cases. Fish with missing or non-functioning PIT tags were identified by the presence of scute marks. Based on observations of fish size and scute marks, these fish were likely hatchery releases from the 1999 brood year. However, we also found occasional inconsistencies in scute marking patterns (e.g. L10 scute missing instead of L9) that precluded definite identification of the origin of some fish (Appendix B). Previous catch information was summarized by matching PIT tag numbers to those recorded in the IDFG database. Unfortunately, for four records, there was no match found in this database. In addition, the weight of one fish was not recorded on the previous capture date, and therefore, comparisons of growth were completed without the inclusion of this record. Juveniles were at large for 31 to 2192 days between captures (mean 242 days; Appendix C). All sturgeon recaptured in 2001 had moved downstream, with a maximum movement of 124 km over a period of 2192 days. Of the 84 hatchery fish recaptured from the 1999 brood stock year, 10 were stocked at river kilometer (Copeland Bridge and 74 were stocked at the Canada/US border (river kilometer 170). Of the ten recaptures originally stocked at the Copeland Bridge, 10% were from the fall 2000 release and 90% were from the spring 2001 release. In contrast, of the 74 recaptures originally stocked at the Canada/US border, 42% were from the fall 2000 release and 58% were from the spring 2001 release. Kootenay River White Sturgeon Studies

32 Mean growth rates for all juveniles, measured as TL, FL and mass, were higher than fish released in fall, 2000, but lower than fish released in spring, 2001 (Table 9). Only 9 (9%) fish lost weight, eight of which were hatchery fish stocked in the spring of 2001, and recaptured later that year. One fish that lost weight was a fish of unknown year class previously captured in summer, Table 9. Growth rates for juvenile sturgeon recaptured in FL (cm/yr) TL (cm/yr) Weight (g/yr) Release Group Minimum (cm/yr) Maximum (cm/yr) Mean (cm/yr) All Juveniles Fall Spring Release Group Minimum (cm/yr) Maximum (cm/yr) Mean (cm/yr) All Juveniles Fall Spring Release Group Minimum (g/yr) Maximum (g/yr) Mean (g/yr) All Juveniles Fall Spring Sonic Tagging A total of 3 juvenile sturgeon were sonic tagged on the Creston Delta in August, 2001 (Table 10). Subsequently, 7 days of sonic tracking were completed as part of other field work on the Kootenay River. All 3 fish were located in this period; however, August was the last time all the fish were located in one sampling day. Sonic contacts were restricted to the Creston Delta and the lowest 2 kilometers of the Kootenay River (Figures 10, 11 and 12). Since August 2001, all 3 tagged fish have not been accounted for at some point. It is probable that these fish had moved into deep water in Kootenay Lake, but poor weather conditions (high wind and waves) and time restrictions made tracking these fish impossible. Tracking will continue until the summer of 2002, as the battery life of tags is anticipated to expire in August As such, information on habitat use in spring has not yet been collected. Table 10. Summary of life history information from the three sonic tagged juvenile sturgeon. Length (mm) Scutes Date Fork Total L# R# PIT Tag # Comments 15-Aug E6D181C Sonic tagged with tag # 828 / Frequency 72 khz. 15-Aug F6C7F1B 16-Aug F7D424B72 Dorsal fin split / Sonic tagged with tag # 832 / Frequency 74 khz. Sonic tagged with tag # 837 / Frequency 76 khz / External scute drill method. Kootenay River White Sturgeon Studies

33 Figure 10. Tracking locations of a juvenile sturgeon, sonic tag code 8-2-8, on the Kootenay River. Kootenay River White Sturgeon Studies

34 Figure 11. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-2, on the Kootenay River. Kootenay River White Sturgeon Studies

35 Figure 12. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-7, on the Kootenay River. Kootenay River White Sturgeon Studies

36 4.4 Temperature Recorders Five temperature recorders were deployed in the study area; 4 recorders were deployed in the Kootenay River and surrounding backchannel and slough habitats, and 1 was deployed on the Creston Delta (Table 11, Figure 13). Water temperatures in the Kootenay River and surrounding back channel habitats followed a similar regime throughout the study period (Figure 14). Near the end of July, the Corn Creek slough provided the coolest temperatures, while Leach Lake provided the warmest. In the last few weeks of August, and in most of September, the temperatures recorded in all four locations were very similar, with less than a degree separating temperatures at all locations. The maximum temperature in any of the four locations was recorded at 21.9 C in Leach Lake on August 19. The minimum temperature in any of the four locations was recorded at 15.6 C in Six Mile Slough on September 11. The temperatures recorded in all four Kootenay River locations were suitable for sturgeon rearing. Table 11. Location and depth, as well as deploy and recovery dates of temperature recorders. Location Depth Date Date (m) Deployed Recovered Corn Creek Slough 5 24-Jul Sep-01 Kootenay River Jul Sep-01 Leach Lake Channel into Pond # Jul Sep-01 Six Mile Slough Pond # Jul Sep-01 Creston Delta Jul Sep-01 The three back channel habitats which were measured for temperature showed significant morphological differences. The Corn Creek Slough and the Kootenay River are connected by an open channel. Flow in the Corn Creek Slough is unidirectional, driven by the inflow from Corn Creek and other small tributaries. Leach Lake and Six Mile Slough are enclosed by dikes, and showed no signs of any current. While parts of Leach Lake have a small amount of inflow from Summit Creek and other tributaries, Six Mile Slough has no discernable inflow. Temperatures in Kootenay Lake on the Creston Delta were extremely variable, ranging from a minimum of 8.4 C on August 5 to a maximum of 20.4 C only 11 days later (Figure 15). Beginning August 5, temperatures rose from 8.4 C to 18.8 C over a period of 5 days. Extreme fluctuations in temperature similar to this event occurred on at least four separate occasions in the two months that temperatures were recorded on the delta. Such fluctuations in temperature were likely the result of storm events which forced cold hypolimnetic water into the epilimnion. Kootenay River White Sturgeon Studies

37 Figure 13. Location of temperature recorders deployed in Kootenay River White Sturgeon Studies

38 Kootenay River and Sloughs Six Mile Slough Leach Lake Corn Creek Slough Kootenay River Temperature (C) Jul 28-Jul 07-Aug 17-Aug 27-Aug 06-Sep 16-Sep 26-Sep 06-Oct Date Figure 14. Water temperatures for the Kootenay River and nearby slough habitats, July 24 through September 24, Creston Delta Temperature (C) Jul 28-Jul 07-Aug 17-Aug 27-Aug 06-Sep 16-Sep 26-Sep 06-Oct Figure 15. Water temperatures for Kootenay Lake at the Creston Delta, July 26 through September 24, Date Kootenay River White Sturgeon Studies

39 5.0 Discussion 5.1 Gear Efficiency In 2001, we again tested the utility of cod traps for capturing juvenile sturgeon. Despite a larger number of juvenile sturgeon in the study area than previous years, none were captured in these traps. By-catch was also low in comparison to gill nets. Based on the data from the previous sampling program (Vandenbos and Spence 2001) and the limited amount of work completed in 2001, it is apparent cod traps are not a suitable method for sampling juvenile sturgeon. Although angling was only pursued on a casual basis and not as the primary means of sampling, enough data was collected for a preliminary evaluation of its value as a capture method for juvenile sturgeon. Only one juvenile sturgeon was captured in an estimated 40 rod hours, suggesting angling was not particularly effective. In some cases, juvenile sturgeon may have been precluded by other more aggressive species present in large numbers and attempting to feed on the bait. Fishing with other baits and in habitats with high concentrations of sturgeon and lower concentrations of non-target species may address this problem. Angling may therefore prove to be more efficient in the future as knowledge of juvenile habitat use improves and as the number of juvenile sturgeon in the study area increases. On the Fraser River, recreational anglers targeting adult sturgeon frequently catch juveniles (L. Hildebrand, pers comm.). As in the past, gill nets proved to be the most effective method of capturing juvenile sturgeon. A comparison of mesh size capture efficiencies showed that 5 cm mesh captured fish more effectively than 2.5 cm mesh. Since the majority (95%) of sturgeon captured in 2001 were 2 year old hatchery fish, the difference in capture efficiency is primarily of comparison of the efficiency of these mesh sizes at capturing fish of that size. Size selectivity of gill nets by mesh size is widely recognized (McCombie and Berst 1969, Hamley 1975 and references therein, Hilborn and Walters 1992) and previous sampling programs for juvenile sturgeon studies on the Fraser River have fished multiple mesh sizes to allow for the capture of all juvenile age classes (Lane and Roseneau, 1993). Also, two inch mesh is used to capture YOY sturgeon on the Columbia River because it is more selective for fish <35 cm than other mesh sizes (Burner et al. 2000). The mesh sizes used in 2001 were effective at capturing most of the age classes of juvenile sturgeon known to be present in the study area. However, few fish larger than age 2 were captured (n=5, 5% of 2001 sample). It is unclear to what degree this is a function of relatively few age 2+ fish, gill net selectivity, or a combination of these factors. Given that different mesh sizes result in size selectivity and that the age structure of the juvenile population will continue to expand with further hatchery releases, larger mesh sizes similar to mesh sizes used on the Fraser River (Lane and Roseneau, 1993) could be used to ensure the entire spectrum of young sturgeon in the population are represented in the catch. 5.2 Distribution of Catch Gill net catch rates were highest in the 10 kilometres of river nearest the Canada/US Kootenay River White Sturgeon Studies