Kluane National Park and Reserve Hydroacoustic Survey Report

Transcription

1 Kluane National Park and Reserve Hydroacoustic Survey Report Report to Parks Canada, Yukon Field Unit Prepared by: Peter Hall 1, Steven MacLellan 2, and Jeremy Hume 2 March Gitksan Watershed Authorities PO Box 229 Hazelton, BC V0J 1Y0 2 Department of Fisheries and Oceans Cultus Lake Salmon Research Laboratory 4222 Columbia Valley Highway Cultus Lake, BC V2R 5B6

2 TABLE OF CONTENTS TABLE OF CONTENTS...ii LIST OF TABLES...iii LIST OF FIGURES...iii INTRODUCTION...1 METHODS...1 RESULTS...2 Trawl Catch...2 Gillnet Catch...2 Fish Size Distribution...2 Fish Ageing...2 Temperature Profiles...2 Hydroacoustic Fish Estimates...3 DISCUSSION...4 REFERENCES...7 ACKNOWLEDGEMENTS...7 ii

3 LIST OF TABLES Table 1. Trawl catch summary...8 Table 2. Gillnet catch summary...8 Table 3. Pygmy whitefish size distribution...8 Table 4. Slimy sculpin size distribution...9 Table 5. Kokanee size distribution...9 Table 6. Kathleen Lake hydroacoustic fish population estimates...9 Table 7. Louise Lake hydroacoustic fish population estimates...9 Table 8. Sockeye Lake hydroacoustic fish population estimates...10 LIST OF FIGURES Figure 1. Satellite image of Kathleen, Louise and Sockeye Lakes...11 Figure 2. Kathleen Lake hydroacoustic transects...12 Figure 3. Louise Lake hydroacoustic transects...13 Figure 4. Sockeye Lake hydroacoustic transects...14 Figure 5. Kathleen Lake transect #2 echogram...15 Figure 6. Kathleen Lake transect #7 echogram...15 Figure 7. Louise Lake transect #3 echogram...16 Figure 8. Louise Lake transect #6 echogram...16 Figure 9. Sockeye Lake daytime transect #4 echogram...17 Figure 10. Sockeye Lake nighttime transect #4 echogram...17 Figure 11. Floating gillnet set in southeast section of Kathleen Lake...18 Figure 12. Kathleen Lake pygmy whitefish length frequency histogram...19 Figure 13. Louise Lake pygmy whitefish length frequency histogram...19 Figure 14. Sockeye Lake pygmy whitefish length frequency histogram...20 Figure 15. Kokanee juvenile (79mm) scale sample...20 Figure 16. Kokanee juvenile (79mm) scale sample...21 Figure 17. Kokanee juvenile (78mm) scale sample...21 Figure 18. Temperature (C) profiles for Kathleen, Louise and Sockeye Lakes...22 Figure 19. Average target strength and fish density profiles of Sockeye Lake...22 Figure 20. Average target strength and fish density profiles of Louise Lake...23 Figure 21. Average target strength and fish density profiles of Kathleen Lake...23 iii

4 INTRODUCTION The Gitksan Watershed Authorities were contracted by Parks Canada to provide juvenile kokanee hydroacoustic estimates of three lakes within Kluane National Park and Reserve. Jeremy Hume and Steven MacLellan with the DFO s Cultus Lake Salmon Research Laboratory agreed to assist with the survey design and hydroacoustic analysis. The three lakes to be surveyed were: Kathleen, Louise and Sockeye Lakes (Figure 1). METHODS Hydroacoustic data was collected using a Biosonics DT-X split beam echosounder with a 200kHz transducer producing a 6 o beam. Several hydroacoustic transects were determined for each lake in order to get representative samples from each basin area of the surveyed lake (Figures 2-4). All hydroacoustic data (example echograms are shown in Figures 5-10) were collected at night except for transect 4 on Sockeye Lake which was also sampled during the day for comparison to data collected during the night (Figure 9 & 10). Each transect was analyzed in separate 2 meter depth layers. Average target densities were calculated for each layer by three separate methods. Briefly, the echo integration calculation method takes the average sound energy return from each layer and divides it by the average target strength to get target densities for each layer. The single target calculation method looks at the wave form of the sound energy that returns (the echo), and selects only those echoes that have specific wave form characteristics that are typical of echoes reflected from single fish, classifying these echoes as single targets. The total number of single targets in a layer is then divided by the sum of the volumes sampled by all pings, within the layer, to determine a layer density. The tracked target calculation method groups single targets together into individual target (fish) tracks which are divided by a smaller sampled wedge volume, roughly the cross sectional dimensions of the sound beam times the length of the transect, to generate density for each layer. Volumes for each depth layer and representative transect area in the lake were calculated by digitizing bathymetric maps provided by Parks Canada using OziExplorer computer software. Once the densities are determined for each layer they are multiplied by the layer volume of the lake area represented by that transect to produce a transect layer population estimate. Layer population estimates are then summed to produce transect estimates which are in turn summed to produce the total fish estimate for the entire lake or lake section. Confidence intervals reflect the variance between transects across the entire lake. The fish estimates were divided into small fish and large fish based on the distribution of target strengths from each transect and each layer. Small fish were classified as fish with target strengths from 64 to 46 db. For salmoniform fish, this target strength is approximately equivalent to fish <90 mm, based on Love s (1977) equation. Limnetic fish were sampled using two different methodologies on all three lakes. The primary catch method was with a 2 x 2-m midwater trawl. The trawl is fishable to approximately 35 m depth. The second method was with two 12 m floating Swedish gillnets which had variable mesh size panels of ½, 5/7, ¾ and 1 stretched mesh (Figure 11). All fish were preserved in 10% formalin to obtain size and age information and no measurements were taken until the samples had been preserved for at least 30 days to ensure length and weight stabilization. 1

5 RESULTS Trawl Catch No kokanee were captured by the mid-trawl in any of the lakes in over 4.5 hrs of trawling. Two other species of fish were caught in the trawl: pygmy whitefish (Prosopium coulteri) and slimy sculpin (Cottus cognatus). Most of the targets observed on transects of Kathleen and Louise Lakes were found below the maximum fishable depth of the trawl; consequently, the trawl was set at the maximum depth for most tows on these lakes. Fishing effort in Kathleen Lake, in particular, was focused on shallower areas in the east end of the lake where targets were observed above 50 m. There were a total of 169 pygmy whitefish and 3 slimy sculpin caught in 4 separate tows in Kathleen Lake (Table 1). Seven tows in both Louise and Sockeye Lakes produced 38 and 35 pygmy whitefish respectively (as well as 2 and 7 slimy sculpin respectively). Gillnet Catch Gillnets were fished for 24 net-hrs on each lake. The only fish caught in the gillnets were 3 kokanee from two gillnets set in Sockeye Lake (Table 2). The gillnet set in the west end of the lake caught 1 kokanee and the net in the east end of the lake caught 2. Fish Size Distribution The minimum and maximum lengths of the pygmy whitefish caught in the three lakes were fairly similar with a minimum length ranging from 34 mm in Louise Lake to 43 mm in Sockeye Lake and a maximum length ranging from 86 mm in Sockeye Lake to 91 mm in Louise Lake (Table 3). The average length of pygmy whitefish from Kathleen Lake, however, was much smaller than the other two lakes. Length frequency distributions of whitefish from Louise and Sockeye Lakes show a bimodal pattern that is not present in the Kathleen Lake whitefish catch (Figures 12-14). Target strength data from Kathleen shows an increasing frequency of larger fish (>-50 db or >~55 mm) beyond 50 m depth, suggesting the larger size classes of whitefish were residing beyond the reach of our trawl in this lake. Sizes for slimy sculpins ranged from a minimum of 20 mm from Sockeye Lake to 69 mm from Louise Lake (Table 4). The 3 kokanee captured in Sockeye Lake were very similar in size with two being 79 mm in length and the other being 78 mm in length (Table 5). Fish Ageing Scales from the 3 kokanee samples were analyzed for age and they were all aged as young-of-theyear, or age 0 kokanee fry (Figures 15-17). Temperature Profiles No thermocline was detected in any of the 3 surveyed lakes (Figure 18). All three lakes were isothermal to 30 meters depth at approximately 8 o C. Thirty meters of depth only reached the bottom in Sockeye Lake. Kathleen and Louise Lake are significantly deeper. 2

6 Hydroacoustic Fish Estimates High densities of fish observed in several surveyed transects of Kathleen Lake make echo integration the only appropriate method of calculating fish populations for this lake (Table 6). Lower observed densities in Louise and Sockeye Lakes allow for single target and tracked target estimates in addition to the echo integration estimate (Tables 7 & 8). Kathleen Lake had the largest fish population estimate and Sockeye had the smallest estimate which corresponds directly with the size of the lakes. Densities were highest in Kathleen Lake and lowest in Sockeye Lake. Kathleen Lake fish population was approximately 14% large sized fish (<90 mm) while Louise Lake was approximately 7.5% large sized fish and Sockeye Lake was approximately 16.5% large sized fish based on target strengths. Sockeye Lake showed increasing target strength with depth except for the 6m depth layer which contained a few large fish that skewed the mean target strength higher than in other layers (Figure 19). Fish densities in Sockeye Lake increased with depth similar to the target strength distribution (Figure 19). Louise Lake showed increasing target strength for the first 20m then remained fairly consistent after that depth (Figure 20). Similar to Sockeye Lake, fish densities increased with depth in Louise Lake (Figure 20). Kathleen Lake showed a high degree of variability in mean target strengths in the first 30m, again, the result of very low fish numbers (some of which were large fish), but then gradually increased to a peak at about 70m and then declined (Figure 21). Fish densities in Kathleen Lake had a distinct band of high density levels in the 50 to 80m depth range where target strengths were also the greatest (Figure 21). Single target and echo integration estimates were quite similar within each lake but tracked target estimates tended to be larger than the other calculation methods in both Sockeye and Louise Lakes. This is consistent with findings from other surveyed lakes. 3

7 DISCUSSION Data from the acoustic transects of all three lakes show an abundance of fish targets with target strengths in the range we would expect for kokanee juveniles (small sized fish), however, since no kokanee were captured in the trawl in any lake, we are not be able to develop any kokanee population estimates. Typically when species other than sockeye or kokanee are caught in the trawl and they are similar in size to the fish of interest (kokanee in this case) we apportion the catch based on the ratio of the number of fish caught of each species. Since no kokanee were caught in the trawl we must attribute 100% of the small sized fish targets to pygmy whitefish which are known to be present in the Alsek watershed (Scott & Crossman 1973). Perhaps a small percentage could be apportioned to slimy sculpins but since most of the sculpins that we caught, were very small, have no air bladder and are a benthic species, we expect that their proportion of the fish population estimate would be extremely small. Gillnet catches are not used quantitatively but rather to address size bias with the trawl since the 2x2m trawl begins to decline in capture efficiency as fish sizes increase from 50mm in length (Paul Rankin, DFO, Pacific Biological Station, Nanaimo B.C.). Despite this bias, pygmy whitefish up to 91 mm in length were caught in the trawl. The gillnet catch of kokanee did, however, prove that kokanee were present in Sockeye Lake. The whitefish and sculpin catches in the trawl confirm that the trawl was working properly and was effective at catching fish in the size range we would expect for juvenile kokanee. The 3 kokanee that were caught in the gillnets in Sockeye Lake were well within the size range vulnerable to the trawl although there is a significant bias against catching fish in the 75 mm plus size range. These kokanee sizes also overlapped the size range of the pygmy whitefish that were caught in Sockeye Lake, especially the second mode of the size distribution of pygmy whitefish in Sockeye and Louise Lake. This clear size overlap makes it impossible to distinguish kokanee from pygmy whitefish using target strength data. Fish that were classified in the larger size category were much less vulnerable to capture with the trawl and none were captured, so we can not attribute any species to that size classification. Some of the larger pygmy whitefish that were caught in the trawl had well developed eggs present when they were dissected suggesting that were mature. Rankin s (1999) survey of several lakes in North- Central British Columbia suggests that the maximum size pygmy whitefish attain in those lakes is approximately 130 to 180 mm. Some proportion of the large size fish estimate in each lake is therefore likely to be pygmy whitefish of potentially larger sizes classes that were not caught in the trawl. Densities of fish targets were very low to zero down to depths of 50 m in Kathleen and Louise Lakes. In Kathleen Lake in particular, hydroacoustics indicate a dense fish layer existed well below the 35 m depth capability of our trawl (Figure 5.). The species composition of the deep fish layer, which makes up the majority of the lake's fish biomass is unknown, but the observed target strengths are similar to what we have seen in other sockeye and kokanee populations. While we can not discount the possibility of kokanee in the deep layer it seems unlikely for several reasons. Typically we find that fish collected above or below a layer of high density will comprise the same fish as is in the layer although the species proportions may be different. As well this type of vertical distribution has not been observed in sockeye or kokanee rearing lakes in British Columbia. 4

8 Normally, sockeye/kokanee at such deep depths (50-80 m) would only be seen during the day, in central and southern B.C. lakes. At dusk they typically come to the surface to feed and then spend the night around the thermocline in summer or throughout the entire upper water column in the fall when the lake is less thermally structured. On rare occasions, we have seen night-time distributions approaching these depths, but there has always been a shallower component to the fish layer which we could reach with our trawl. We ve experienced these distributions on deep lakes such a Quesnel Lake when surveyed late in the year, after the thermal structure has broken down, and on Anderson Lake, which supports a large population of lake spawning kokanee. The lack of any thermocline in the first 30 m in any of the 3 lakes perhaps made the potential of capturing kokanee more difficult because without the thermocline, kokanee and sockeye do not congregate at specific layers. Temperature data collected by Jody Mackenzie-Grieve and Lloyd Freese in late July of 2005 found a thermocline in Kathleen Lake between 30 and 40 m of depth. It is unknown if that thermocline remained by the time of the hydroacoustic survey in early October since our temperature probe was only 30m long. We were able to trawl near the bottom of Sockeye Lake and did not have difficulty fishing the areas where the highest target densities were observed. Despite the fact that the trawl was effective in reaching all the depths and locations where high densities of fish targets were observed and successfully captured other fish species, the trawl failed to catch any kokanee. The hydroacoustic survey and mid-water trawl is potentially less effective at quantifying or capturing fish in the first few meters of the lake. The beam volume of the transducer is quite small in the first few meters because of its approximately cone shaped beam which results in a much smaller sample volume compared with the deeper depths. In addition, boat avoidance behaviors by kokanee make sounding and possibly catching the fish in the trawl more difficult in the upper few depth layers. The catch of kokanee in the floating gillnets in Sockeye Lake show that kokanee were present in the top few meters of the lake or are residing in the more littoral areas of the lake. High densities of sockeye and kokanee juveniles are known to inhabit the upper depth layers of lakes with high turbidity which confines food availability to the surface. The Secchi disk reading in Sockeye Lake was 13 m and the other two lakes were significantly deeper. This suggests that high turbidity that confines kokanee juveniles to the surface layers was unlikely for these lakes. In conclusion we feel that the results of our survey strongly suggest that the kokanee population in the 3 lakes is very small. These results agree with the kokanee spawner numbers observed by Parks Canada personnel in recent years. Estimates of kokanee stream spawners in 2004 were <100 spawners. Assuming a 50% sex ratio, an fecundity of 800 eggs/female (mean of 21 kokanee populations, McGurk 2000), an egg to fry survival of 15% and to fall fry of 50% (JMB Hume, data on file) this would result in a total of only 3000 fall fry in the three lakes or 0.75 kokanee/ha of lake area for all three lakes. Densities this low are virtually undetectable by all sampling techniques except for the occasional chance encounter. While it is possible that the kokanee of these lakes are in the deeper layers inaccessible to our sampling gear, it seems highly unlikely, as this has never before been observed in any kokanee or sockeye population. Thus our results strongly suggest that there is no large undocumented kokanee population spawning in some unknown locale associated with the 3 lakes since there was little evidence of the progeny of this hypothetical population. Our results are consistent with what we would expect if the total spawning population size of kokanee for the 3 lakes was in the spawner range. 5

9 RECOMMENDATIONS There is a large biomass of fish (especially in Kathleen) beyond the reach of our trawl gear, residing at 50-80m and beyond. As kokanee are not know to occupy this area of the water column in other lakes it appears unlikely that they will be kokanee. However, before we can definitely discount the possibility that they are kokanee, the species composition needs to be determined in these deeper depths. We suggest the following to address this problem: 1. Set gillnets in the deep fish layer. On transects 9-11, there appears to be some heavy concentrations of fish against the bottom (~70m) on the up slopes adjacent to the shallows that might present an opportunity for bottom set gillnets. Appropriate mesh sizes for adult and juvenile kokanee and whitefish would be needed. 2. This survey took place quite late in the year and the unfavorable fish distribution we encountered might be a function of that timing. A hydroacoustic survey mid to late summer when water temperatures are warmer should find a fish layer higher in the water column and result in more representative trawl sampling, eliminating the need to sample the deeper waters. 3. One of the driving mechanisms in juvenile sockeye/kokanee vertical distribution in most lakes is the thermal structure of the lake. A series of temperature profiles taken over the growing season may help in our understanding of the vertical distribution of kokanee and whitefish. A vertical series of 10 or more temperature data loggers suspended in the deeper part of the lake taking hourly readings is likely the most cost effective way to collect quality data. 4. Another mechanism driving distribution of juvenile sockeye/kokanee is the distribution of their zooplankton prey. Zooplankton is usually most abundant in the surface euphotic zone of the lake, but in a lake with weak thermal structure they may be more widely distributed in the water column. A series of vertically stratified zooplankton samples at different times of the year along with some diet work up from sampled fish might be helpful in explaining what is going on and why these fish are residing so deep in late fall. 5. Sockeye/Kokanee typically display diurnal vertical migration behavior, living deep in the lake by day, rising to the productive shallower waters in the evening to feed, dropping just below the thermocline for the night, and rising at dawn to feed again before descending to their daytime distribution. It might be worthwhile to monitor the fish layers in Kathleen in particular with hydroacoustics, over a 24 hour period(s), with particular attention to the dawn and dusk periods to document if such migration is taking place and if it involves the entire fish layer or just some components of the fish layer. 6. With the only capture of juvenile kokanee being from gillnets which are usually set in shallower water, we should consider the possibility that, unlike typical kokanee populations in B.C. which tend to rear in the limnetic zone, many of the juvenile kokanee in this lake system may be making their living in the relatively shallow littoral areas of these lakes where our hydroacoustic system is at a disadvantage. The presence or absence of kokanee in littoral areas could be tested by a more extensive fishing program in littoral areas using traps, trap nets, and/or gillnets. 6

10 REFERENCES Love, R. H Target strength of an individual fish at any aspect. Journal of the Acoustical Society of America 62: McGurk, M.D Comparison of fecundity length latitude relationships between nonanadromous (kokanee) and anadromous sockeye salmon (Oncorhynchus nerka). Can. J. Zool. 78: Rankin, L Phylogenetic and ecological relationship between giant pygmy whitefish (Prosopium spp.) and pygmy whitefish (Prosopium coulteri) in North-Central British Columbia. Master of Science Thesis. University of Northern British Columbia, Prince George, BC. Scott, W.B. and E.J. Crossman Freshwater fishes of Canada. Bull. Fish. Res. Board Can. 184: ACKNOWLEDGEMENTS We wish to thank Lloyd Freese for providing advice and making the initial arrangements for this project. We would like to thank Tom Elliot for making the contract arrangements. We also wish to thank Rhonda Markel and Terry Skjonsberg for their assistance in the field. Special thanks are due to Rodney Harris for the long nights of field work in Kluane National Park. 7

11 Table 1. Trawl catch summary Lake Tow Location Length Average Whitefish Sculpin (Transect) (km) Depth (m) Kathleen & Total n/a Louise & & & & & & Total n/a 38 2 Sockeye Total n/a 35 7 Table 2. Gillnet catch summary Lake Gillnet UTM Soak Time (Hours) Kokanee Kathleen 1 08 V V Louise 1 08 V V Sockeye 1 08 V V Table 3. Pygmy whitefish size distribution Kathleen Louise Sockeye Length (mm) Weight (g) Length (mm) Weight (g) Length (mm) Weight (g) Min Max Average n

12 Table 4. Slimy sculpin size distribution Kathleen Louise Sockeye Length (mm) Weight (g) Length (mm) Weight (g) Length (mm) Weight (g) Min Max Average n Table 5. Kokanee size distribution Sockeye Length (mm) Weight (g) Min Max Average n 3 3 Table 6. Kathleen Lake hydroacoustic fish population estimates Estimate Lake Size Density Population Method Section Class N/ha 95% C.I. N 95% C.I. Small ,843, ,908 West Large , ,185 Integration Total 1, ,170, ,419 Small ,128, ,477 East Large , ,385 Total ,303, ,764 Table 7. Louise Lake hydroacoustic fish population estimates Estimate Size Density Population Method Class N/ha 95% C.I. N 95% C.I. Small ,394 42,782 Integration Large ,115 2,599 Total ,509 43,880 Small , Single Target Large ,990 3,348 Total ,686 36,482 Small ,560 46,839 Tracked Targets Large ,519 4,611 Total ,079 48,572 9

13 Table 8. Sockeye Lake hydroacoustic fish population estimates Estimate Size Density Population Method Class N/ha 95% C.I. N 95% C.I. Small ,925 17,511 Integration Large ,184 4,229 Total ,109 21,250 Small ,450 10,607 Single Target Large ,865 4,285 Total ,315 14,714 Small ,863 13,578 Tracked Targets Large ,327 5,117 Total ,190 18,518 10

14 Kathleen Lake Sockeye Lake Louise Lake Figure 1. Satellite image of Kathleen, Louise and Sockeye Lakes 11

15 Gillnet 2 Trawls 1-3 Trawl 4 Gillnet 1 Figure 2. Kathleen Lake hydroacoustic transects 12

16 Gillnet 1 Trawl s 2-7 Trawl 1 Gillnet 2 Figure 3. Louise Lake hydroacoustic transects 13

17 Gillnet 2 Trawl s 1-7 Gillnet 1 Figure 4. Sockeye Lake hydroacoustic transects 14

18 Figure 5. Kathleen Lake transect #2 echogram Figure 6. Kathleen Lake transect #7 echogram 15

19 Figure 7. Louise Lake transect #3 echogram Figure 8. Louise Lake transect #6 echogram 16

20 Figure 9. Sockeye Lake daytime transect #4 echogram Figure 10. Sockeye Lake nighttime transect #4 echogram 17

21 Figure 11. Floating gillnet set in southeast section of Kathleen Lake 18

22 Frequency Kathleen Lake Fork Length (mm) Figure 12. Kathleen Lake pygmy whitefish length frequency histogram Frequency Louise Lake Fork Length (mm) Figure 13. Louise Lake pygmy whitefish length frequency histogram 19

23 Frequency Sockeye Lake Fork Length (mm) Figure 14. Sockeye Lake pygmy whitefish length frequency histogram Figure 15. Kokanee juvenile (79mm) scale sample 20

24 Figure 16. Kokanee juvenile (79mm) scale sample Figure 17. Kokanee juvenile (78mm) scale sample 21

25 0 Kathleen Lake 0 Louise Lake 0 Sockeye Lake Depth (m) Depth (m) Depth (m) Temperature (C) Temperature (C) Temperature (C) Figure 18. Temperature (C) profiles for Kathleen, Louise and Sockeye Lakes All Transects Transect Max Depth (m) Max Depth (m) Average Target Strength (db) Density of fish (fish/m3) Figure 19. Average target strength and fish density profiles of Sockeye Lake 22

26 All Transects Transect Max Depth (m) Max Depth (m) Average Target Strength (db) Density of fish (fish/m3) Figure 20. Average target strength and fish density profiles of Louise Lake All Transects Transect Max Depth (m) Max Depth (m) Average Target Strength (db) Density of fish (fish/m3) Figure 21. Average target strength and fish density profiles of Kathleen Lake 23