Kootenay River White Sturgeon Studies in British Columbia, 2001 Matthew D. Neufeld and Colin R. Spence Ministry of Water, Land and Air Protection 401 – 333 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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Kootenay River White Sturgeon
Studies in British Columbia, 2001
Matthew D. Neufeld
and
Colin R. Spence
Ministry of Water, Land and Air Protection 401 – 333 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.
Kootenay River White Sturgeon Studies – 2001 i
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, 2001. Sampling efforts resulted in a total of 98 sturgeon captures. Gill nets were the primary sampling gear, resulting in 387.9 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 (Wr) 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 ii
Kootenay River White Sturgeon Studies – 2001 iii
Table of Contents
Abstract ........................................................................................................................................... i
Table of Contents..........................................................................................................................iii
List of Tables .................................................................................................................................. v
List of Figures ............................................................................................................................... vi
List of Appendices........................................................................................................................vii
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. .......................... 10 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. ................................. 10 Table 3. Gill netting effort (net-hours) by time strata and location .............................................. 10 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. ............ 13 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-1. ............... 14 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............ 17 Table 7. Summary of the number of sets that captured sturgeon and all sets, stratified by mesh
size................................................................................................................................. 17 Table 8. Summary of data from sturgeon captured by angling..................................................... 18 Table 9. Growth rates for juvenile sturgeon recaptured in 2001. ................................................. 22 Table 10. Summary of life history information from the three radio tagged juvenile sturgeon. .. 22 Table 11. Location and depth, as well as deploy and recovery dates of temperature recorders. .. 26
Kootenay River White Sturgeon Studies - 2001 vi
List of Figures
Figure 1. Location of juvenile white sturgeon studies on the Kootenay River and Kootenay Lake.
......................................................................................................................................... 2 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, 2001..................................................................................................... 7 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). .......................................................................................................................... 12
Figure 5. Location of gill net sets which captured sturgeon. ........................................................ 11 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)................................................................... 15
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)................................................................... 16
Figure 8. Cod trap set locations. ................................................................................................... 19 Figure 9. Length frequency histogram for juvenile sturgeon captured in 2001............................ 20 Figure 10. Tracking locations of a juvenile sturgeon, sonic tag code 8-2-8, on the Kootenay
River. ............................................................................................................................. 23 Figure 11. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-2, on the Kootenay
River. ............................................................................................................................. 24 Figure 12. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-7, on the Kootenay
River. ............................................................................................................................. 25 Figure 13. Location of temperature recorders deployed in 2001.................................................. 27 Figure 14. Water temperatures for the Kootenay River and nearby slough habitats, July 24
through September 24, 2001.......................................................................................... 28 Figure 15. Water temperatures for Kootenay Lake at the Creston Delta, July 26 through
September 24, 2001. ...................................................................................................... 28
Kootenay River White Sturgeon Studies - 2001 vii
List of Appendices Appendix A. Summary of gill net set data, 2001.......................................................................... 43 Appendix B. Capture information from juvenile sturgeon captured in 2001. ............................. 53 Appendix C. Summary of sturgeon recapture and life history information.................................. 56 Appendix D. Summary of adult sturgeon capture data................................................................. 59 Appendix E. Summary of incidental gill net catch, 2001. ............................................................ 60 Appendix F. Cod trap set records, 2001. ...................................................................................... 64 Appendix G. Cod trap catch records, 2001................................................................................... 64 Appendix H. Gill net set data from sampling in Crawford Bay, 2001. ........................................ 65 Appendix I. Gill net catch records from net sampling in Crawford Bay, 2001. ........................... 65 Appendix J. Locations of juvenile sturgeon equipped with sonic tags in the summer of 2001.... 66
Kootenay River White Sturgeon Studies - 2001 1
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 - 2001 2
Figure 1. Location of juvenile white sturgeon studies on the Kootenay River and Kootenay Lake.
Kootenay River White Sturgeon Studies - 2001 3
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.
3.1.1 Spatial Stratification The sampling area was divided into nine spatial strata (Figure 2). The Kootenay River (river km 120.5-170.0) 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 - 2001 4
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).
3.1.2 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 8.
3.1.3 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.
3.2.1 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 2000. 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 - 2001 5
R-2
R-1
R-3
R-4
R-5
R-6
S-1
W-D
E-D
Stratum BoundaryR-3 Stratum ID
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 - 2001 6
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.
3.2.3 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.
3.2.4 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 - 2001 7
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, 2001.
Kootenay River White Sturgeon Studies - 2001 8
3.4 Temperature Recorders Five TidBitTM 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 - 2001 9
4.0 Results 4.1 Fish Capture
4.1.1 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 387.9 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.
4.1.1.1 By-Catch A total of 355 fish of species other than sturgeon were captured incidentally during this study, for a by-catch of 0.915 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).
4.1.1.2 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.
4.1.1.3 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 - 2001 10
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 130-170 (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 120-130 (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 41.5 2 0.048 (DW) West Delta, Kootenay Lake 42.1 2 0.048 (R-1) Kootenay River km 120-130 44.2 1 0.023 (R-2) Kootenay River, East Channel 39.9 0 0.000 (R-3) Kootenay River km 130-140 42.5 4 0.094 (R-4) Kootenay River km 140-150 44.8 7 0.156 (R-5) Kootenay River km 150-160 47.7 27 0.566 (R-6) Kootenay River km 160-170 72.1 54 0.749 (S-1) Back Channel and Slough Habitat (Rkm 150) 13.1 0 0.000
Total 387.9 97 0.250
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 14 140.4 20 0.142 2 July 15 - August 10 131.6 34 0.258 3 August 11 - September 8 115.9 43 0.371
1 to 3 June 17 - September 8 387.9 97 0.250 Table 3. Gill netting effort (net-hours) by time strata and location
Figure 4. Location of gill net sets in which white sturgeon were captured.
Kootenay River White Sturgeon Studies - 2001 12
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 - 2001 13
4.1.1.4 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-2Set Depth Sturgeon Captures Effort CPUE Effort CPUE
%(n) %(hr) n/hr %(hr) n/hr Deep (>15 m) 84 (81) 42 (164.2) 0.493 49 (164.2) 0.493 Shallow (<15 m) 16 (16) 58 (223.7) 0.072 51 (170.7) 0.094
Total 100 (97) 100 (387.9) 0.250 100 (334.9) 0.290 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 - 2001 14
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 5.2 0.9 10.1 1.3 Maximum 25.5 26 29.2 34.4
Mean 15.7 10.7 19.6 14.5 Mann-Whitney U =4846.0 P-Value < 0.000 U =5279.5 P-Value < 0.000
Sets excluding R-2 and S-1 Minimum 5.2 1.2 10.1 1.3 Maximum 25.5 26 29.2 34
Mean 15.7 12.1 19.6 16.2 Mann-Whitney U =4846.0 P-Value < 0.000 U =5279.5 P-Value < 0.000
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 11-19 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 - 2001 15
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).
4.1.1.5 Gill Net Selectivity Larger mesh size gill nets captured juvenile sturgeon more efficiently than the small mesh size in 2001. 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.
Total 100 (97) 100 (387.9) 0.250 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 χ2 = 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 (%) 2.5 10(18) 81(23) 91(23) 5 43(82) 257(77) 300(77)
Total 53(14) 338(86) 391(100) Chi-Square
P Value 0.521
Kootenay River White Sturgeon Studies - 2001 18
4.1.1.6 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).
4.1.2 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 17.2- 26.0 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).
4.1.3 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#
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).
0
5
10
15
20
25
30
35
40
45
50
151 -
200
201 -
250
251 -
300
301 -
350
351 -
400
401 -
450
451 -
500
501 -
550
551 -
600
601 -
650
651 -
700
701 -
750
Fork Length (mm)
Rel
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e Fr
eque
ncy
(%)
Figure 9. Length frequency histogram for juvenile sturgeon captured in 2001. 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 (Wr) 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 (Wr) was calculated using the following formula (Beamesderfer 1993):
100*)/( βαLWWr =
Kootenay River White Sturgeon Studies - 2001 21
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 -70.2 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 199.5 (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 - 2001 22
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, 2000. Table 9. Growth rates for juvenile sturgeon recaptured in 2001.
Release Group Minimum (cm/yr) Maximum (cm/yr) Mean (cm/yr) All Juveniles 1.4 22.4 9.2
Fall 2000 1.9 9.8 5.2 FL (cm/yr)
Spring 2001 6.6 22.4 12 Release Group Minimum (cm/yr) Maximum (cm/yr) Mean (cm/yr)
All Juveniles 0.11 27.1 9.7 Fall 2000 2.1 10.7 5.8
TL (cm/yr)
Spring 2001 6.6 27.1 12.4 Release Group Minimum (g/yr) Maximum (g/yr) Mean (g/yr)
All Juveniles -68.7 263.6 63.8 Fall 2000 11.5 168.7 45.1
Weight (g/yr)
Spring 2001 -68.7 146.8 69.3 4.3 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 2002. 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)Date Fork Total L# R# PIT Tag # Comments
15-Aug-01 440 513 9 5 504E6D181C Sonic tagged with tag # 828 / Frequency 72 kHz.
15-Aug-01 520 600 9 6 504F6C7F1BDorsal fin split / Sonic tagged with tag # 832 / Frequency 74 kHz.
16-Aug-01 705 805 9 3 7F7D424B72 Sonic tagged with tag # 837 / Frequency 76 kHz / External scute drill method.
Scutes
Kootenay River White Sturgeon Studies - 2001 23
Figure 10. Tracking locations of a juvenile sturgeon, sonic tag code 8-2-8, on the Kootenay
River.
Kootenay River White Sturgeon Studies - 2001 24
Figure 11. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-2, on the Kootenay
River.
Kootenay River White Sturgeon Studies - 2001 25
Figure 12. Tracking locations of a juvenile sturgeon, sonic tag code 8-3-7, on the Kootenay
River.
Kootenay River White Sturgeon Studies - 2001 26
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-01 24-Sep-01 Kootenay River 12 24-Jul-01 24-Sep-01 Leach Lake – Channel into Pond #1 1.5 24-Jul-01 24-Sep-01 Six Mile Slough – Pond #2 3.3 24-Jul-01 24-Sep-01 Creston Delta 15 26-Jul-01 24-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 - 2001 27
Figure 13. Location of temperature recorders deployed in 2001.
Kootenay River White Sturgeon Studies - 2001 28
Figure 14. Water temperatures for the Kootenay River and nearby slough habitats, July 24 through September 24, 2001.
Figure 15. Water temperatures for Kootenay Lake at the Creston Delta, July 26 through September 24, 2001.
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 - 2001 30
border (river kilometer 160-170) and generally declined as we moved downstream towards Kootenay Lake. This trend is likely the result of downstream dispersion from hatchery stocking locations at and above the border (river kilometer 170 and 199.5+). Catch rates also increased from the first sampling period in June and early July (CPUE 0.142) through to the last sampling period in late August and early September (CPUE 0.371). This increase may be a function of increased fish movement in later summer, additional fish moving into the study area later in the year from upstream locations (immigration), or the location of fish in more of the sample area (better distribution), however identification of the cause of temporal differences in catch rate was not possible. This trend of increased catch rates in late summer was also noted in 2000, while catch rates in 1999 were variable throughout the summer with no clear pattern (Vandenbos and Spence 2001). No sturgeon were captured in the two backchannel areas sampled on the Kootenay River (Corn Creek Slough (S-1) and the East Channel of the Kootenay River (R-2)). 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 meters 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 meters in depth, and therefore, it is possible that these areas do not represent suitable juvenile habitat. Data on capture depth from 2001 indicated that juvenile sturgeon in the Kootenay River primarily used habitat greater than 5 and less than 31 m in depth, as all captures were concentrated in this range despite effort in shallower and deeper habitats. Captures were most common in deeper habitats within the river (mean set depth of captures; minimum 15.7 m, maximum 19.6 m). Also, the sampling methodology stratified net sets by depths of greater and less than 15 m, of which the sets greater than 15 m captured proportionally more sturgeon than sets less than that depth. This use of deep lake and river habitats has also been documented in previous studies on white sturgeon in this area (Young and Scarnecchia 1999, 2000; Vandenbos and Spence 2001) and on the Columbia River (Beamesderfer et al. 1989, DeVore et al. 1993, Kerr et al. 2001). 5.2 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 FL=298 mm; Appendix B). Juveniles captured in 1999 and 2000 were larger than those captured in 2001, with a minimum and maximum FL of 260 and 885 mm, and 455 and 1020 mm in 1999 and 2000 respectively (Vandenbos and Spence 2001). The smaller size of fish in 2001 is an artefact of the presence of younger fish from a recent 1999 brood year hatchery release at the upper end of the study area. In fact, the majority of captures (95%) in 2001 were hatchery fish from the 1999 brood year. Juvenile white sturgeon captures from this year class were relatively small and ranged in length from 190 to 390 mm FL (mean =283 mm).
Kootenay River White Sturgeon Studies - 2001 31
The mean total and fork length growth rate for all juvenile sturgeon captured in 2001 was similar at 9.7 and 9.2 cm/yr respectively, although significant variation occurred around these means. Present study results show higher growth rates than longer term baseline data on hatchery fish growth rates in the Kootenay River (mean 6.4cm/yr; Ireland et al. draft 2001). This difference in growth rate is probably the result of high numbers of age two fish (95% of total sample) in our sample, since greater length growth generally occurs among these smaller juvenile fish (Ireland et al. draft 2001). The mean weight growth for all juvenile sturgeon captured in 2001 was much lower than baseline data on hatchery fish growth rates in the Kootenay River (Ireland et al. draft 2001). The difference in weight growth rate may again be the result of high numbers of age two fish (95% of total sample) in the 2001, as little or no weight gain often occurs among fish within the first two years of release (Ireland et al. draft 2001). The mean total length growth rate of hatchery sturgeon released in the fall of 2000 was lower than the rate for fish released in the spring of 2001. Similarly, the mean weight growth for juveniles released in fall 2000 lower than the rate for fish released in spring 2001. Fish stocked in the spring and then recaptured later that summer have been in the river for the period of the year that has the highest water temperatures and food availability, both of which increase sturgeon growth. In contrast, fish that have spent a winter and spring in the river system have been in the river during the time expected to yield the lowest growth rates, as well as the productive summer season. This difference in riverine residence period probably accounts for the disparity in growth rates between these two groups. Data collected from this same cohort in future years will likely yield comparisons of fall and spring release group growth rates that are more applicable to evaluating these two stocking strategies. The mean relative weight at recapture for all juveniles captured in 2001 was 82.2% and was slightly higher than baseline data on Kootenay River hatchery juveniles (mean 78%). The mean relative weight of hatchery sturgeon released in fall 2000 (90.4%) was higher than the mean relative weight of sturgeon released in spring 2001 (78.5%). Ireland et al. (draft 2001) reported that, for juvenile hatchery released sturgeon on the Kootenay River, condition factor is inversely correlated with growth in total length. Thus, given the differences in TL growth rates observed between these two release groups, the fall release group would be expected to have a higher condition factor. The relative weight of recaptures generally decreased between release or previous capture and recapture. In 2001, 91% of juveniles recaptured showed a decrease in relative weight. Ireland et al (draft 2001) reported that 77% of hatchery fish lost weight between release and recapture. Of the hatchery sturgeon that were released in the fall of 2000 and the spring of 2001 (1999 progeny), 92% showed a decrease in relative weight, while only 25% of the hatchery fish from previous years releases (n=4) showed a loss in relative weight. The decrease in relative weight noted in 2001 for most recaptures is most likely a result of adaptation of hatchery released fish to the natural environment.
Kootenay River White Sturgeon Studies - 2001 32
5.3 Movements All recaptured juveniles were captured downstream from their previous capture or hatchery release location. However, because 95% of the fish captured in 2001 were from hatchery releases above the study area and had not been captured in the river previously, it is possible that the movement of individuals downstream was part of a dispersal of fish from stocking locations and was taking place in both an upstream and downstream direction. If this is the case, our study would only sample fish moving downstream because the study area was located entirely downstream from all stocking locations. Downstream movement of juvenile sturgeon was also observed in previous sampling programs on the Kootenay River. In 1999 and 2000, all but one juvenile sturgeon was captured downstream from its previous location or hatchery release site (Vandenbos and Spence 2001). In these years it was noted that the majority of sampling programs had taken place in Idaho, upstream of the study area. Again, this increased the probability that recaptures would have been originally captured upstream, and observed movement patterns may have been an artefact of the previous sampling programs and stocking locations. 5.4 Water Temperature Temperatures recorded in the Kootenay River and associated slough/backchannel habitats showed similar temperature regimes during the sample period. Although variation in temperature existed between the sites, all temperatures recorded were within a range favourable for juvenile sturgeon rearing. The summer of 2001 was dry and very warm, and therefore the data collected may represent a worst case scenario for maximum water temperatures in these habitats. Backchannel habitats in Leach Lake and Six Mile Slough exhibited temperatures that were up to 2ºC warmer than the river main-stem for a period of the study, while Corn Creek Slough exhibited temperatures that were less than or similar to the temperature in the Kootenay River. On the Fraser River, backchannel habitats that were regularly used by sturgeon had temperatures warmer than those in the Fraser River main-stem by up to 5ºC (Lane and Roseneau, 1993). The temperatures recorded in Leach Lake and Six Mile Slough, which are inaccessible to sturgeon due to the presence of dikes, suggest that water temperatures in these habitats are suitable for juvenile sturgeon rearing. Although initial investigations show promising results, it is still unclear if these areas are suitable for sturgeon rearing as water chemistry has yet to be investigated and the impact on sturgeon of numerous non-native species in these bodies of water is unknown . There was no obvious relationship between catch rates (CPUE) and water temperature during the study period. On the Creston Delta it was not possible to identify trends between temperature and CPUE as temperatures recorded on the Delta were extremely variable and catch rates were extremely low (n=4). The trends in CPUE and temperature on the Kootenay River also did not appear to be correlated. On the Kootenay River, catch rates increased from the first time strata through to the last (July to September), while water temperatures increased through July and early August and then decreased in late August and September. From the data available through this sampling program it appears that water temperature and catch rates are not closely related. However,
Kootenay River White Sturgeon Studies - 2001 33
continuous catch data from one location over the whole study period would be necessary to fully evaluate this relationship.
Kootenay River White Sturgeon Studies - 2001 34
Kootenay River White Sturgeon Studies - 2001 35
Recommendations
� Although a site index approach will be used to sample juveniles in 2002, the stratified sampling program aimed at maintaining an even distribution of sampling effort used in 2001 should be implemented every 4 years to track changes in habitat use as the juvenile populations grows.
� Consultation with the Idaho Department of Fish and Game, and the Kootenai
Tribe of Idaho should take place before sampling in 2002 to develop a consistent approach to sampling over the entire range of white sturgeon in the Kootenay/Kootenai River.
� 2.5, 5, and 7.5 cm stretched measure nets should be used in future sampling
projects, to avoid biases associated with mesh size selectivity and to facilitate a better understanding of net size capture efficiencies.
� Angling should continue to be used, on a casual basis, between sets to capture
sturgeon; however an accurate record of location, effort, and catch should be recorded, and various types of bait should be used on an experimental basis.
� An expanded sonic tagging program, similar to the one carried out in 2001, should
be considered in future years to identify juvenile habitat use throughout Kootenay Lake.
� Temperature data indicated a trial stocking program of surplus age 1+ juvenile
sturgeon could be carried out in one of the two impounded slough habitats along the Kootenay River to identify the utility of these areas for juvenile sturgeon rearing.
� Standard cod traps again proved ineffective at capturing sturgeon in 2001 and
should not be used as a sampling method in future years.
Kootenay River White Sturgeon Studies - 2001 36
Kootenay River White Sturgeon Studies - 2001 37
Acknowledgements Don Miller of Kootenay Wildlife Services assisted in much of the fieldwork. Beth Wright of the Ministry of Water, Land and Air Protection, Tola Cooper of the Department of Fisheries and Oceans Canada as well as Laird Siemens and the staff at the Kootenay Trout Hatchery also provided field assistance. Jay Hammond (MWLAP) and Vaughn Paragamian (IDFG) provided administrative support and technical direction. In addition, the Bonneville Power Administration (Columbia Basin Fish and Wildlife Authority) funded the project through the Idaho Department of Fish and Game and the Kootenai Tribe of Idaho.
Kootenay River White Sturgeon Studies - 2001 38
Kootenay River White Sturgeon Studies - 2001 39
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1 Identification number from the Idaho Fish and Game database..
Kootenay River White Sturgeon Studies - 2001 59
Appendix D. Summary of adult sturgeon capture data. Set Length (mm) Weight Scutes New
Date ID1 Fork Total (lb) L# R# Pit Tag # Pit Tag# Comments
05-Jul-01 84 2000+ Escaped at boat. Bloated stomach, skin air blisters, etc, but swam away. 17-Jul-01 145 1400+ Lost at the boat. No Data 07-Aug-01 Angled 1495 1690 62 - - - 7F7D3E2051 Possible left fin ray clip. Put in pit tag / Removed L2 scute 10-Aug-01 245 1615 1820 60 2 - 7F7D417F1D Brown floy tag (KT00147), Surgery Scar, L2 scute
1 For set information see appendix A.
Kootenay River White Sturgeon Studies - 2001 60
Appendix E. Summary of incidental gill net catch, 2001. Capture Set ID Length Capture Set ID Length