Spring Composition of the Ahiak and Beverly Herds, March 2008

Transcription

1 Spring Composition of the Ahiak and Beverly Herds, March 2008 D. Johnson and J. Williams Environment and Natural Resources Government of the Northwest Territories 2013 Manuscript Report No. 232 The contents of this paper are the sole responsibility of the authors

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3 ii ABSTRACT From March 2008, we conducted a fixed wing transect survey to map the late winter distribution and relative densities of caribou from the Ahiak and Beverly herds. Most of the caribou were observed above treeline north and northeast of Whitefish Lake, NWT. Below treeline, caribou were dispersed at low to medium densities from the NWT-SK border west and east to Thekulthili and Scott Lakes. Two isolated, high density pockets of caribou were observed southeast of Lutselk e in the Gagnon Lake area and in the Eileen Lake area at the edge of treeline. From March 2008, we classified 11,163 caribou from 296 groups. We observed 0.47 wolves per hour flown during the composition survey. The sex ratio of caribou was 36.7 bulls:100 cows, while the calf-cow ratio was 48.2 calves:100 cows (SE=1.7) and was higher than the mean for Beverly spring composition counts conducted in (mean=39 calves:100 cows) (Williams 1995). The calf:cow ratio increased as we moved south and was 35.1 and 69.9 calves:100 cows above and below treeline, respectively. The March 2008 composition survey results indicated that over-winter calf survival for the Ahiak and Beverly herds was high; however, there is evidence to suggest that pregnancy rates and subsequent calf production were low, and that calf recruitment in March 2009 will be greatly reduced.

4 iii TABLE OF CONTENTS ABSTRACT... ii LIST OF FIGURES... iv LIST OF TABLES... v INTRODUCTION... 1 METHODS... 3 Systematic Transect Survey... 3 Composition Survey... 4 RESULTS... 7 Systematic Transect Survey... 7 Composition Survey DISCUSSION LITERATURE CITED APPENDIX I: Observations from spring composition surveys conducted on the range of the Ahiak and Beverly caribou herds, March

5 iv LIST OF FIGURES Figure 1: Flight lines flown during the fixed wing transect survey, March Figure 2: Distribution of adult caribou observed on transect, March Figure 3: Distribution of adult caribou observed off transect, March Figure 4: Distribution of adult caribou observed on/off transect, March Figure 5: Distribution of adult caribou observed on/off transect during the systematic transect survey (17-20 March 2008) and the location of collared cows on 18 March Figure 6: Wolves (brown) and wolverine (grey) observed during the fixed wing transect survey, March Figure 7: Flight lines during the composition survey, March Figure 8: Flight lines and groups classified during the composition survey, March Figure 9: Groups classified during the composition survey conducted March 2008 overlaid on the distribution of adult caribou observed on/off transect during the fixed wing transect survey conducted March Figure 10: Groups classified during the composition survey conducted March 2008 in relation to the location of GPS (blue) and satellite (pink) collared cows on 25 March Figure 11: Other wildlife observed during the composition survey conducted March Species include muskox (yellow), moose (black), wolverine (brown) and wolf (grey)

6 v LIST OF TABLES Table 1: Daily summary of caribou classified during the composition survey, March

7 1 INTRODUCTION Over-winter calf survival is a secondary measure used by wildlife managers to monitor the health and abundance of barren-ground caribou herds in the NWT. The proportion of young provides a useful measure of the percent of young animals that survive to reach breeding age (annual recruitment) assuming that female mortality is small relative to calf mortality (McCullough 1994). In these situations, calf survival rates can be used as an index of recruitment and can be highly correlated with changes in population trend (Krebs et al. 1986). However, calf survival rates alone do not provide enough information upon which to predict changes in population trend. Independent assessments of population size are still required to validate demographic changes inferred by changes in calf survival rates (Caughley 1974). In late winter, prime and older bulls are often distributed and segregated from cows and younger caribou. We therefore calculate the percentage of calves and annual recruitment by measuring the ratio of calves to cows and adjusting the ratio by an assumed average sex ratio. Calf composition counts were last conducted on the Beverly herd of barren-ground caribou in 1995, but were conducted annually from (Williams 1995). As a result, we initiated a late winter composition of the Beverly and Ahiak herds in March 2008, with the objective to determine over-winter calf survival. Recent collaring programs that were implemented to target the Beverly herd in March 2006 and July 2007 indicate that there has been considerable overlap between the Ahiak and Beverly herds during most times of the year except the calving and early post-calving periods (GNWT unpublished data). Calving ground distribution surveys on the Beverly calving grounds in 2002 and 2007 suggest a significant and rapid decline from 1994 (Johnson et al. In prep. a). Distribution surveys of the Ahiak calving ground in 2006, 2007, and 2008 indicate that the Ahiak herd is much larger in size than the Beverly herd (Johnson et al. In prep. b). It was our

8 2 assumption that the results of this composition survey would be applicable to both the Ahiak and Beverly herds.

9 3 METHODS Systematic Transect Survey We used an aerial systematic transect survey to delineate the distribution and relative density of caribou on late winter range at 20 km spacing. The location of collared cows in late winter was used to define the survey area (GNWT unpublished data). A Cessna 185 aircraft on skis was used to conduct the systematic transect survey in March Survey altitude was 120 m above ground level (agl), survey speed was approximately 160 km/hr, and the total strip transect width was 0.8 km (0.4 km strip width for each observer). The survey was based out of Fort Smith and a camp at the Hoarfrost River, NWT (62 o N, 109 o W). Electrical tape was placed on the window to mark the outer boundary of the transect strip width on each side of the aircraft. The methodology outlined by Norton-Griffins (1978) was used to define a 0.4 km strip width on each side of the plane at an altitude of 120 m agl. Observers calibrated the outer boundary of their strip markers, while the plane flew at survey altitude on an axis perpendicular to markers that defined the distance of the strip width (0.4 km) on the ground. The survey crew 1 consisted of the pilot, an observer seated in the back left seat, and an observer/recorder seated in the right front seat of the aircraft. Observers estimated the numbers of caribou seen both on and off transect and wherever possible also classified caribou observed. We estimated the size of larger groups by estimating blocks of caribou by the tens, 50s and 100s. Caribou were classified as cows, yearling calves, and bulls, based on body size and presence of antlers. Observers called their observations to the navigator who recorded them as 1 Pilot: Brent Macdonald (Northwestern Air Lease); Left observer: Judy Williams; and Right observer/recorder: Deb Johnson.

10 4 well as a waypoint number along with the transect segment label. At the end of each day the waypoint files were downloaded to the laptop computer. The files were then imported into a Microsoft Excel spreadsheet and the waypoint coordinate data (number, latitude and longitude coordinates, date and time) were appended to the observation data. We used the GPS to create a track file so that transects flown could be accurately recorded (location recorded every ten seconds). The track files were downloaded to the laptop computer at the end of each flight. A landscape-level 20 km survey grid was applied to the survey area where transects corresponded to the east-west grid lines. Observations were compiled for each 20 km transect segment to map the distribution of relative caribou densities seen during the systematic transect survey. We used the following classes to map the relative density of caribou observed on transect: low density (<1.0 caribou/km 2 ); medium density ( caribou/km 2 ); and high density ( 10.0 caribou/km 2 ). We also summarized the number of caribou observed off transect by each 20 km transect segment using the following classes: none (no caribou observed); low (<16 caribou); medium ( caribou); and high (>160 caribou). Finally, we mapped the distribution of caribou observed both on and off transect by combining the relative density of caribou on transect and the number of caribou seen off transect. We also noted wolf sightings and expressed them as a sighting rate of wolves/1,000 hours flown. Composition Survey We used the results of the fixed wing systematic transect survey as well as the location of collared caribou to locate and classify caribou. More effort was allocated to where the highest densities of animals were observed, however, effort was also allocated to sample across the entire distribution of caribou observed on the fixed wing transect survey. We also sampled in the vicinity of all the collared cows even if we did not see any caribou in that transect segment

11 5 during the fixed wing transect survey. A Bell 206B helicopter was used to conduct the composition survey. The survey was based out of a camp at the Hoarfrost River, NWT and an established camp at Alcantara Lake, NWT (60 o N, 108 o W). The survey crew 2 consisted of the pilot, a navigator and a data recorder. We classified small groups (<40 caribou) and/or widely dispersed groups from the air and for larger and/or aggregated groups we landed and walked to within m of caribou and viewed them through a 45X power spotting scope. We classified caribou as we encountered them and assigned a GPS waypoint to each discrete caribou group. were classified based on the presence of a darkened vulval patch. Absence of a vulval patch and presence of a penis were distinguishing characteristics for bulls. We classified prime bulls as being large-bodied with no antlers. Young bulls had smaller bodies and still had antlers. Calves were small-bodied with relatively short faces. We did not consistently classify yearlings as we suspect that classification errors between 22 and 34 months are likely. Wherever possible, we recorded cows with no antlers (probably genetically bald). We also noted wolf sightings and expressed them as a sighting rate of wolves/1,000 hours flown. The calf:cow ratio was estimated as the total number of calves divided by the total number of adult cow and yearling females for each group classified. We calculated the mean calf:cow ratio (and variance) using Cochran s (1977) jackknife method in an Excel spreadsheet. The calculation of percent calves in the population was based on three different adult sex ratios of 60 males:100 cows, 50 bulls:100 cows, and 43 bulls:100 cows, as there was no current information on sex ratios for either the Beverly or Ahiak herds, and sex ratios observed from 2 Pilot: Paul Rosset (Great Slave Helicopters Ltd.); Recorder: Judy Williams; Navigator: Deb Johnson.

12 6 spring composition surveys tend to under-represent the bull:cow ratio as male groups are usually segregated from cows during this time of the year. Recruitment was considered to be the percent increase in herd size from reproduction (% of calves/% of 1+ year old caribou).

13 7 RESULTS Systematic Transect Survey From March 2008, we flew 20 hours on survey and eight hours off survey (Figure 1). Weather conditions were ideal with clear skies and calm winds, but cold temperatures. We encountered the odd period of light snow along the southern transects, but we were still able to see shadows and therefore, these areas were not re-flown. Figure 1: Flight lines flown during the fixed wing transect survey, March We counted a total of 351 adult caribou on transect and 739 adult caribou off transect during the fixed wing survey. During the ferry flights to and from the survey area we observed an additional 1,697 adult caribou. Most caribou were observed above treeline north and northeast of Whitefish Lake (Figure 2 to Figure 4). Another two high density pockets of caribou

14 8 were observed near Eileen Lake on the edge of treeline and southeast of Lutselk e in the Gagnon Lake area. Below treeline, caribou were observed at low to medium density and were located just north of the NWT-SK border, roughly bounded to the west and east by Thekulthili Lake and Scott Lakes. Figure 2: Distribution of adult caribou observed on transect, March Clear boxes indicate no caribou; green are low densities (<1.0 caribou/km 2 ); yellow are medium densities ( caribou/km 2 ); and red are high ( caribou/km 2 ).

15 Figure 3: Distribution of adult caribou observed off transect, March Group sizes indicated in this figure are as follows: clear (none); green are small groups (<16 caribou); yellow are medium ( caribou); and red are large groups (>160 caribou). 9

16 10 Figure 4: Distribution of adult caribou observed on/off transect, March Distribution is categorized as none, low, medium or high. The distribution of caribou observed during the fixed wing transect survey was similar to the distribution of GPS and satellite-collared cows during this same period (Figure 5). However, the entire distribution of caribou observed below treeline at low to medium densities was not fully represented by the collared cows. Additionally, there were no collared cows in the Eileen Lake area where caribou were observed on transect at high densities.

17 11 Figure 5: Distribution of adult caribou observed on/off transect during the systematic transect survey (17-20 March 2008) and the location of collared cows on 18 March GPS locations are represented by blue circles; satellite collars by pink circles. During the fixed wing transect survey, we counted a total of 18 wolves and 4 wolverine during 20 hours of survey flying, giving a sighting index of 900 wolves/1,000 hours flown. All wolves and wolverine were seen above treeline (Figure 6).

18 12 Figure 6: Wolves (brown) and wolverine (grey) observed during the fixed wing transect survey, March Composition Survey We flew a total of 33.9 hours during the composition survey from March 2008 (Figure 7 and Figure 8). Two days of the composition survey were conducted above treeline, while two days were spent classifying caribou below treeline based on the results of the fixed wing transect survey (Figure 9). We also classified caribou around the location of each GPS and satellite collared caribou (Figure 10).

19 13 Figure 7: Flight lines during the composition survey, March 2008.

20 Figure 8: Flight lines and groups classified during the composition survey, March

21 Figure 9: Groups classified during the composition survey conducted March 2008 overlaid on the distribution of adult caribou observed on/off transect during the fixed wing transect survey conducted March

22 16 Figure 10: Groups classified during the composition survey conducted March 2008 in relation to the location of GPS (blue) and satellite (pink) collared cows on 25 March Classifications of 11,163 caribou were made from 296 groups between March 2008 (Figure 8) (Appendix I). We observed a total of 5, year old cows (225 bald cows), 2, year old bulls, 187 yearlings and 2,879 calves (Table 1). We assumed a 50% sex ratio for yearlings and adjusted the number of 1+ year old cows and 1+ year old bulls to 6,058 and 2,226, respectively. The observed sex ratio was 36.7 bulls:100 cows. The calf:1+ year old cow ratio was 48.2 calves:100 cows (SE=1.7). Assuming a sex ratio of 60 bulls:100 cows, 50 bulls:100 cows, and 43 bulls:100 cows, the proportion of calves in the population was estimated at 23.0, 24.0 and 25.0, respectively, and the recruitment rate was 29.9, 31.6 and 33.3, respectively.

23 17 Table 1: Daily summary of caribou classified during the composition survey, March Date With Antlers Without Antlers Calves Young Yearlings 1+Yr Prime Caribou Caribou 24-Mar-08 1, , ,809 2, Mar-08 2, ,542 1, ,515 4, Mar-08 1, , ,896 2, Mar ,064 1,656 s 5, ,964 2,879 1, , ,284 11,163 During the composition survey, we saw a total of 51 muskoxen, 2 moose, 16 wolves and 6 wolverine during 33.9 survey hours giving a sighting index of 472 wolves/1,000 hours flown. All of the wolverine and all but one wolf were observed above treeline (Figure 11). The lone wolf observed below treeline was near Manchester Lake, NWT.

24 Figure 11: Other wildlife observed during the composition survey conducted March Species include muskox (yellow), moose (black), wolverine (brown) and wolf (grey). 18

25 19 DISCUSSION There was little movement of caribou observed below treeline between the fixed wing transect survey and the subsequent composition survey. However, above treeline, caribou appeared to move in a northeast direction between the two surveys. Caribou observed in the Eileen Lake area during the fixed wing transect survey were located between Eileen and Lynx Lakes, NWT during the composition survey. Similarly, during the composition survey we had to cover an area east of that flown during the fixed wing transect survey to account for the eastward movement of animals. Caribou above treeline exhibited higher winter movement rates than those below treeline; this may be related to a scarce amount of winter forage available above treeline (GNWT unpublished data). Although we observed some movement of caribou during the fixed wing transect survey and the composition survey, we did not observe any large aggregations numbering in the thousands of caribou or the northward migration of groups towards calving grounds. In general, the locations of collared cows were representative of the major densities of caribou observed during the transect surveys, but not of the entire distribution of caribou observed at lower densities. The calf:cow ratio increased as we classified groups further south. The calf:cow ratio above treeline was 35.1 calves:100 cows (SE=1.6), while below treeline the calf:cow ratio was 69.9 calves:100 cows (SE=2.4). Similarly, nursery groups that consisted of more calves than cows were seen below treeline. This may represent the segregation of breeding versus non-breeding cows, with breeding cows seen further north., both young and mature, were seen within all the groups classified above and below treeline. We observed more exclusive bull groups below treeline at the southern extent of the caribou distribution. The bull:cow ratio above and below treeline was 35.3 bulls:100 cows and 36.5 bulls:100 cows, respectively. The similar sex ratio values obtained both above and

26 20 below treeline may suggest that the bull component was under-represented and that the proportion of the calves in the population did not need to be adjusted to account for the undercounting of bulls. The unadjusted proportion of calves in the population was 26% and represented a maximum recruitment rate of 35%. The calf:cow ratio obtained in late March 2008 for caribou distributed east of Great Slave Lake from the NWT-Saskatchewan border to above treeline was higher than the average for Beverly spring composition counts conducted (mean = 39 calves:100 cows) (Williams 1995). We do not think that cow mortality was significantly greater than calf mortality; except for Lutselk e in the NWT, there was little harvest on the herd this past fall and winter. Data from a collaring program conducted in April 2008 across the late winter distribution of the Ahiak and Beverly herds indicated that cow pregnancy rates were less than 50% (GNWT unpublished data). in the late summer-fall 2007 may have extended their lactation period due to low calf fat reserves, which would have reduced subsequent pregnancy rates due to lactational infertility, but also resulted in higher over-winter calf survival. Therefore, the high calf survival rates observed in March 2008 and apparent low pregnancy rates of cows suggest that calf survival in March 2009 will be much lower than that observed in March 2008, assuming that cow mortality is not significantly higher than calf mortality during this period.

27 21 LITERATURE CITED Caughley, G Interpretation of age ratios. J. Wildlife Management 38(3): Cochran, W. G Sampling techniques, 3 rd Edition. J. Wiley and Sons Ltd., New York. 413pp. Government of the Northwest Territories Caribou forever our heritage, our responsibility: a barren-ground caribou management strategy for the Northwest Territories Environment and Natural Resources, GNWT. 38pp. Johnson. D., A. Gunn, J. Nagy and J. Williams. In prep (a). Beverly herd of barren-ground caribou calving ground survey, June Environment and Natural Resources, Government of the Northwest Territories. Johnson, D., J. Nagy and J. Williams. In prep (b). Calving ground surveys of the Ahiak herd of barren-ground caribou, June Environment and Natural Resources, Government of the Northwest Territories. Krebs. C. J., B.S. Gilbert, S. Boutin, A.R.E. Sinclair and J.N.M. Smith Population biology of snowshoe hares: I. Demography of food-supplement populations in the southern Yukon, Journal of Animal Ecology 55: McCullough, D. R What do herd composition counts tell us? Wildlife Society Bulletin 22: Norton-Griffiths, M Counting animals: Serengeti Ecological Monitoring Program Handbook No. 1. African Wildlife Leadership Foundation, Nairobi, Kenya. 110pp. Williams, M Summary of spring classification surveys of the Beverly caribou herd Department of Renewable Resources, Inuvik, NWT. Unpublished report. 44pp.

28 22 APPENDIX I: Observations from spring composition surveys conducted on the range of the Ahiak and Beverly caribou herds, March Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar

29 23 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar

30 24 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

31 25 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

32 26 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

33 27 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

34 28 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar

35 29 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

36 30 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

37 31 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose

38 32 Lat Long Date Wpt W/Antlers W/O Antlers Calves Young Prime Yearlings Mar Mar Mar Mar Mar Mar Count Muskox Wolves Wolverine Moose 5, ,964 2,879 1, , ,