Northern Mountain Caribou Population Dynamics Peace River Region

Transcription

1 Peace River Region Sara Duncan University of Victoria May 2009

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3 Executive Summary Executive Summary Past and current population sizes and demographics for six caribou herds in British Columbia s Peace River region (Frog, Gataga, Rabbit, Muskwa, Pink Mountain, and Liard Plateau) were compiled for this report. Information on the size and demographic trends of these herds will help to inform herd-specific management used in conjunction with the broader regional planning of the federal Northern Mountain Caribou Plan in draft for release in This report provides a synthesis of population count data from unpublished government records, consultant reports, published literature, and harvest statistics from 1976 to 2007 for each herd separately. The literature on caribou mortality and recruitment is also discussed with respect to the northern mountain herds in the Peace Region, including a summary of the wolf removal experiments in northern BC. The Frog and Liard Plateau herd appear to be small but stable (approximately 150 members), with low and moderate confidence in those ratings, respectively. The Muskwa, Gataga, and Rabbit herds all appear to have increased in size over the past few decades. The Gataga herd population appears to be stable at approximately 250 animals (± 75), while the Muskwa and Rabbit herds appear to be continuing to increase (>700 and >1100 animals, respectively). All of the herds considered in this report could benefit from further counts, but where research budgets are limited, the most efficient use of funding would be achieved by focusing on the Frog, Pink Mountain, and Liard Plateau herds. There is no demographic information available for the Frog herd, only population estimates, and this information is needed before the status of this herd can be determined with any confidence. Population counts for the Pink Mountain herd have been most consistent; however, it was the only herd for which evidence of a decreasing population was observed, and more monitoring is required to determine whether this is a longterm trend, or a short-term population fluctuation. The Liard Plateau herd is known to be small, but relatively stable. Powell (2006) has suggested a moratorium on hunting of this herd based on the limited demographic information available; more data on recruitment and mortality rates would help to determine whether a harvest moratorium is indeed warranted to preserve this herd. i

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5 Table of Contents Table of Contents Executive Summary... i! Table of Contents...iii! List of Tables... v! List of Figures... vii! 1.0! Introduction... 1! 2.0! Herd Demography... 3! 2.1! Frog Herd... 5! 2.2! Gataga Herd... 6! 2.3! Rabbit Herd... 8! 2.4! Muskwa Herd... 9! 2.5! Pink Mountain Herd... 12! 2.6! Liard Plateau Herd... 15! 3.0! Harvest History and Statistics by Herd... 17! 3.1! Harvest Summary Statistic Analysis Methods... 17! 3.2! Harvest Statistic Analysis Results by Herd... 19! 3.2.1! Frog Herd...19! 3.2.2! Gataga, Rabbit, and Muskwa Herds...22! 3.2.3! Pink Mountain Herd...27! 3.2.4! Liard Plateau Herd...30! 3.3! Tooth Age of Harvested Caribou... 31! 3.4! Harvest Rates of Other Ungulates in Peace Region Caribou Herd Ranges... 41! 4.0! Wolf Removal Studies Summary... 45! 5.0! Herd Status Summary... 48! 6.0! Recommendations for Future Studies... 52! 7.0! References Cited... 55! iii

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7 List of Tables List of Tables Table 2-1 Gataga Herd Population Counts and Structure...6! Table 2-2 Gataga Herd Population Dynamics...7! Table 2-3 Rabbit Herd Population Counts and Structure...8! Table 2-4 Muskwa Herd Population Counts and Structure...10! Table 2-5 Muskwa Herd Population Dynamics...11! Table 2-6 Pink Mountain Herd Population Counts and Structure...13! Table 2-7 Pink Mountain Herd Population Dynamics...14! Table 2-8 Liard Plateau Herd Population Counts and Structure...15! Table 2-9 Liard Plateau Herd Population Dynamics...16! Table 5-1 Peace River Northern Mountain Caribou Herd Population Summary...49! v

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9 List of Figures List of Figures Figure 3-1! Total Caribou Harvest in MU 7-52 (Frog and Horseranch Herds) from 1976 to ! Figure 3-2! Total Number of Hunters and Average Hunt Success Rate for MU 7-52 (Frog and Horseranch Herds) from 1976 to ! Figure 3-3! Number of Kills Within the Frog Herd Boundary from 1976 to ! Figure 3-4! Total Caribou Harvest in MU 7-51 (Gataga, Rabbit and Muskwa Herds) from 1976 to ! Figure 3-5! Total Number of Hunters and Average Hunt Success Rate for MU 7-51 (Gataga, Rabbit and Muskwa Herds) from 1976 to ! Figure 3-6! Total Caribou Harvest in MUs 7-50 and 7-54 (Muskwa Herd) from 1976 to ! Figure 3-7! Total Number of Hunters and Average Hunt Success Rate for MU 7-50 and 7-54 (Muskwa Herd) from 1976 to ! Figure 3-8! Total Muskwa Caribou Harvest (MUs 7-50, 7-54 and 7-51) from 1976 to ! Figure 3-9! Total Number of Caribou Harvested from the Rabbit Herd in MU 7-51 from 1978 to ! Figure 3-10! Total Number of Caribou Harvested from the Gataga Herd in MU 7-51 from I978 to ! Figure 3-11! Total Caribou Harvest in MUs 7-42, 7-43, 7-57, and 7-58 (Pink Mountain Herd) from 1976 to ! Figure 3-12! Total Number of Hunters and Average Hunt Success Rate for MUs 7-42, 7-57 and 7-58 (Pink Mountain Herd) from 1976 to ! Figure 3-13! Total Caribou Harvest in MU 7-53 (Liard Plateau Herd) from 1976 to ! Figure 3-14! Total Number of Hunters and Average Hunt Success Rate for MU 7-53 (Liard Plateau Herd)...31! Figure 3-15! Frog Herd Harvest Age Distribution Over Time...32! Figure 3-16! Gataga Herd Harvest Age Distribution Over Time...33! Figure 3-17! Rabbit Herd Harvest Age Distribution Over Time...34! Figure 3-18! Muskwa Herd Harvest Age Distribution Over Time...34! Figure 3-19! Pink Mountain Herd Harvest Age Distribution Over Time...35! Figure 3-20! Liard Plateau Herd Harvest Age Distribution Over Time...36! Figure 3-21! Tooth Age Versus Harvest Regulations for the Frog Herd...37! Figure 3-22! Tooth Age Versus Harvest Regulations for the Gataga Herd...38! Figure 3-23! Tooth Age Versus Harvest Regulations for the Rabbit Herd...39! vii

10 List of Figures Northern Mountain Caribou Population Dynamics Figure 3-24! Tooth Age Versus Harvest Regulations for the Muskwa Herd... 39! Figure 3-25! Tooth Age Versus Harvest Regulations for the Pink Mountain Herd... 40! Figure 3-26! Tooth Age Versus Harvest Regulations for the Liard Plateau Herd... 41! Figure 3-27! Number of Hunters by Ungulate Species in the Frog Herd Range (MU 7-52) from ! Figure 3-28! Number of Hunters by Ungulate Species in MU 7-51 (Gataga, Rabbit, and Muskwa Herds) from ! Figure 3-29! Number of Hunters by Ungulate Species in the Muskwa Herd Range (MUs 7-50 and 7-54) from ! Figure 3-30! Number of Hunters by Ungulate Species in the Pink Mountain Herd Range (MUs 7-42, 7-57, and 7-58) from ! Figure 3-31! Number of Hunters by Ungulate Species in the Liard Plateau Herd Range (MU 7-53) from ! Figure 4-1! Wolf Harvest Versus Calves per 100 Cows for the Muskwa Herd viii

11 List of Appendices List of Appendices Appendix 1.0 Appendix 2.4 Appendix 3.4 Herd Range Map Muskwa Herd Population Count Data Harvest Figures for Large Ungulates in Peace Region Caribou Herd Ranges ix

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13 Introduction 1.0 Introduction The purpose of this project was to gather and present information on the past and current population sizes and demographics for six caribou herds (Frog, Gataga, Rabbit, Muskwa, Pink Mountain, and Liard Plateau) in the Peace River region (see herd boundary figure in Appendix 1.0). These herds fall within the COSEWIC (Committee on the Status of Endangered Wildlife in Canada) designated Northern Mountain National Ecological Management Area (NMNEA), and have been ranked with Special Concern conservation status (COSEWIC 2002). A ranking of Special Concern indicates that these herds are not currently believed to be in danger of extinction, but that they are vulnerable to changes in available habitat, predation, disease, or human-caused mortality. The Canadian Species at Risk Act (SARA) legislation requires that a management plan be created for all species designated Special Concern within three years of designation (Douglas 2002); to this end, the draft management plan for the caribou in the NMNEA is being developed for release in 2009 (Northern Mountain Caribou Management Team Newsletter 2008). Information on the size and demographic trends of these herds will help to inform herd-specific management used in conjunction with the broader regional planning of the northern mountain caribou management plan. The testimonies recorded in diaries, correspondence and official reports suggest that caribou were widespread and numerous at the time of European arrival in British Columbia, and these reports continued to describe caribou populations as abundant until 1828 (Spalding 2000). In the late 1800 s caribou began to decline (Spalding 2000); populations reached a low in the 1940 s and 1950 s, with an upswing in numbers in the 1960 s following widespread wolf removal programs from 1949 to 1962 (Bergerud 1978, Bergerud and Elliot 1986). The population trend of northern caribou since the 1970 s has been less certain; Bergerud (1978) recorded population decreases in the 1970 s compared to the 1960 s, yet many of the herds have not been regularly censused since. The most recent published estimates for the northern herds are provided in the 2002 COSEWIC report (Thomas and Gray 2002). To gain insight into the most current population size and demographics of the Peace Region herds, this report provides a synthesis of population count data from unpublished government records, consultant reports, and the published literature for each herd separately (Section 2.0). 1

14 Introduction Northern Mountain Caribou Population Dynamics The summary harvest statistics for each herd from 1976 to 2007 were also reviewed to determine whether harvest success rate might indicate relative changes in population sizes. Caribou harvests were attributed to specific herds by assuming that all caribou harvests reported in a given wildlife Management Unit (MU) (as defined by BCMOE 2008) were of individuals belonging to the caribou herd with a known herd range within that MU. Where multiple herds were found in a single MU, kill locations from the Compulsory Inspection forms (recorded with 1 kilometre precision) were used to plot each kill in ESRI s ArcGIS 9.1 ArcMap software product, and kills falling within a known herd range were attributed to that herd. Harvest data was interpreted in the context of the harvest regulations in order to determine whether changes in caribou harvest could be attributed to changes in the harvested population size, or harvest restrictions. Tooth age data reported on Compulsory Inspection forms was also analysed to determine whether harvest had resulted in obviously skewed age distributions for bulls. Finally, the number of hunters hunting other large ungulate species in the Peace caribou herd ranges, and the number of other large ungulates killed, was briefly examined for trends in other game species and large game hunters that might relate to caribou. All analysis of the information obtained from harvest data is contained in Section 3.0. In Section 4.0, the literature on the known impact of wolf predation on the recruitment rates of caribou in the northern mountain herds is discussed, which includes a summary of the wolf removal experiments conducted in the Muskwa-Kechika during the 1980 s. A summary of the findings for each herd and recommendations for further studies are also provided at the end of the report, in Sections 5.0 and

15 Herd Demography 2.0 Herd Demography Total counts provide a minimum number for a caribou herd based on the actual number of animals seen, though it is expected that some individuals will be missed. To determine whether a herd is increasing or decreasing by minimum numbers alone, several consecutive years of counts are required, and it is preferable to have an estimate of the percentage of the herd that was counted. Population structure, however, when collected in conjunction with the total count, can provide a snapshot of the herd s potential population trajectory. This population structure is usually interpreted in terms of percent of calves in the population, calf to cow ratios, bull to cow ratios, and age distribution. Caribou populations generally have low rates of increase, rarely exceeding a growth rate of 24 percent per year (MWLAP 2004), with an estimated maximum growth rate of 35 percent per year (Hayes et al. 2003). This population growth limitation is not due to low fertility; Bergerud s literature review found that the average pregnancy rate reported for all subspecies of caribou in North America was 82 percent (1980; cited in Bergerud and Elliot 1986). Wittmer et al. (2005) found an average pregnancy rate of 92 percent in the mountain ecotype caribou herds of British Columbia, which is similar to the 90 to 97 percent pregnancy rates reported by Seip and Cichowski (1996; cited in MWLAP 2004), and Gustine et al. (2006). Parturition rates are also fairly high in the caribou species; Gustine et al. (2006) observed a percent parturition rate in their collared females between 2001 and The factors most likely to affect caribou population stability are calf recruitment, or the number of calves that survive their first year, and the mortality rate of adults. Caribou calf mortality is known to be high; Gustine et al. (2006) found that nearly 40 percent of calves died in the first 2 months following birth (ranging between 20 and 60 percent), primarily due to wolf and grizzly bear predation. Wittmer et al. (2005) also found that of collared females found to be pregnant in the spring, only 11 percent had a calf survive to 9 months of age. Natural adult mortality for caribou is typically much lower than that of calves. A study of the Frog/Gataga herds (Elliot 2004) found that the annual mortality rate in collared cows was 10 percent between 2000 and 2003, which corresponds to several studies that place the average annual adult caribou mortality rate between 7 and 16 percent per year in stable or increasing populations (Bergerud 3

16 Herd Demography Northern Mountain Caribou Population Dynamics and Elliot 1998, Hayes 2003, Wittmer et al. 2005). These adult mortality rates corroborate Bergerud s calculation that for a caribou population to be stable, 9-month-old calves should make up 12 to 16 percent of the total population to offset adult mortality (Bergerud 1974, in Wittmer et al. 2005). In terms of calf:cow ratios, Bergerud and Elliot (1998) found that a depredated caribou population remained stable (rate of increase, r = 1) with 24 calves per 100 cows, while Hayes et al. (2003) found that a depredated caribou population in the Aishihik, Yukon, was stable at a recruitment rate of 26 calves per 100 cows. Yukon caribou management guidelines are more conservative, and stipulate that caribou populations should be managed to maintain a calf to cow ratio of 30 calves per 100 cows (Yukon Renewable Resources 1996). Yukon management guidelines (Yukon Renewable Resources 1996) also recommend a ratio of 30 bulls per 100 cows to maintain full pregnancy rates, similar to Bergerud s (1978) suggestion that adult sex ratios should be 1 bull for every 2 cows. The population sizes and demographic trends in each of the Frog, Gataga, Rabbit, Muskwa, Pink Mountain, and Liard Plateau herds are provided below, and discussed within the context of the recruitment and mortality figures from the literature described above. The approximate number of animals available for human harvest in a given year were also calculated where the data are available, to compare the potential number of animals that could have been harvested sustainably, with the recorded number of animals that were harvested. This calculation involved subtracting the natural adult mortality rate from the recruitment rate: the remainder was considered surplus, or available for human harvest without reducing herd populations. The recruitment rate was taken from the demographic data, but the adult mortality rate was calculated. Bergerud (1978) derived the formula y = x to approximate the observed adult mortality rate in caribou herds in BC at various recruitment rates in 8 herds in BC and Alaska. For this equation, x equals the percent of yearling calves in a herd in a given year, and y equals the percentage of adult mortality. Bergerud s formula frequently calculates a larger harvestable population than that provided by Hayes et al. s (2003) recommendation that no more than 2 percent of a caribou population should be harvested in any given year. Hayes et al. s (2003) recommendation was based on observed declines in Yukon caribou populations 4

17 Herd Demography harvested at rates higher than 2 percent. Of the herds in the Peace River region with occasional or sustained harvests above the 2 percent guideline (Frog, Muskwa, Pink Mountain, and Liard), only the Pink Mountain herd appeared to be declining. The percentage of caribou which are available for harvest is obviously contingent on the recruitment rate; herds with high recruitment and increasing populations can likely sustain a higher harvest rate. Two percent is a good conservative guideline, however, as none of the Yukon herds were seen to decline at that low harvest rate, even when periods of high predation or poor winters lead to lowered recruitment or adult survival. The number of animals available for harvest based on Bergerud s (1978) formula and as 2 percent of the total population are provided for comparison where possible. Factors that affect caribou mortality and demographics such as disease, weather, changes in food supply, or human access and development are not discussed here. Data quantifying these factors, such as calf mortality due to hypothermia or changes in habitat use due to road development, are not available specifically for these herds (though see Bergerud and Elliot 1998, Hayes et al. 2003, James et al. 2000, Seip et al. 2007, and Terry et al for discussions of the relative importance of these factors for woodland caribou). 2.1 Frog Herd There are no population count data for the Frog herd. The published estimates of the herd s size are from Heard and Vagt (1998), and regional biologists cited in Thomas and Gray (2002), who guessed that the Frog herd numbered 150 animals in 1996 and 2000, respectively. The harvest data from the Frog herd seems to indicate a relatively stable, though small, population (see Section 3.2.1, below). Hayes et al. (2003) recommend that the harvest rate for caribou should be no more than 2 percent of the population in any given year: if the Frog herd population has remained near the estimated value of 150 animals, the number of animals available for harvest is 3 per year, which is less than the average harvest of 6 bulls per year from within the Frog herd boundaries (see Section 3.2.1, Figure 3-3). 5

18 Herd Demography Northern Mountain Caribou Population Dynamics It was hypothesized in Elliot s (2004) report that the Frog herd is supplemented with individuals moving east from the Spatsizi herd, and a 2009 fly-over count found approximately 600 caribou in the region northwest of the Frog herd boundary - where the caribou population was formerly believed to be sparse (Thiessen, pers. comm.). From these reports and the size of the harvest recorded, it is likely that the Frog herd may be much larger than estimated, or part of a larger population with significant transfer of individuals between herd ranges. 2.2 Gataga Herd If Bergerud s (1978) and Heard and Vagt s (1998) estimates are accurate, then the Gataga herd appears to have increased throughout the last two decades of the 20 th century (Table 2-1). Table 2-1 Gataga Herd Population Counts and Structure Date Cows Bulls Calves Unknown Adults Count (Estimate) Reference 1978 (150) Bergerud (250) Heard & Vagt 1998 Oct Unpub. data 2 Feb Unpub. data 2 Mar Unpub. data 3 1 In 1978, Bergerud counted a Johiah Lake herd and a Gataga River herd- both areas are within the currently defined Gataga herd range and the estimates for each herd (100 and 50, respectively) were aggregated 2 Data from unpublished counts completed from the air and with tracking of VHF-collared individuals 3 Incidental count from the air during a Ministry of Environment Stone s sheep survey The additional 73 individuals found during the February 2001 count suggests that the October 2000 count either missed those Gataga individuals, or that individuals from other herds move into the Gataga herd range in winter. Both possibilities are likely; caribou herds are known to mingle during calving and winter (Thomas and Gray 2002), and October counts may miss some females with calves at heel that do not move into the rutting grounds with the rest of the herd (Hatler 1986). The 2007 count, while much lower than the 2000/2001 count is also likely to have missed individuals, as the purpose of the count was to observe Stone s sheep, and not all suitable caribou habitat was searched. The calf:cow ratio is used as an indicator of recruitment rate, and the calf:cow ratio of the Gataga herd was approximately 25 calves per 100 cows around the turn of the century (Table 2-2). 6

19 Herd Demography Table 2-2 Gataga Herd Population Dynamics Date Calf:Cow Ratio Bull:Cow Ratio % Calves Oct Feb Mar The February estimate is likely more accurate than the October estimate, both due to the sighting of more animals during the count, and the likelihood that there would be calf mortality over the winter that would decrease the number of calves living to recruitment age. Recruitment can be approximated by the number of calves counted at 9 months of age, which is usually March, when the calf mortality rate declines to the adult mortality rate (Bergerud 1978). The Gataga herd was therefore likely to be stable according to Bergerud s (1974, cited in Bergerud 1978) and Bergerud and Elliot s (1998) recommendations in 2000/2001. The bull:cow ratio determined from the count in October 2000 is adequate, while the bull:cow ratio determined from the count in February 2001 is lower than recommended to maintain full pregnancy rates (Bergerud 1978, Yukon Renewable Resources 1996). The October count may have missed some cows, as stated above, and resulted in an overestimate of the bull:cow ratio; it is interesting to note that the total number of bulls counted was the same for both surveys. The harvest data for Management Unit 7-52, in which the Gataga herd resides, does appear to indicate declining harvests since the late 1990 s (Section Figure 3-4), but the records also indicate that the bulls harvested from within the Gataga herd boundary are a small portion of the caribou harvest in that MU, and that this herd is not even harvested every year (Section 3.2.2, Figure 3-10). Based on the recommended harvest rate of 2 percent per year, the Gataga herd, at the 2001 population size of 338 animals could have had approximately 7 animals available for harvest, and only 4 were taken. Even at the lower boundary count of 138 animals in 2007, the herd would have 3 animals available for harvest, while only 1 was taken in that year, which would suggest that this herd is being harvested sustainably. However, taken from another direction, the observed adult mortality rate in 2001 was 10 percent (Elliot 2004), and using Bergerud s (1978) formula: y = x, the Gataga herd adult mortality rate in 2007 was estimated at 10 percent. Given calf recruitments of 17 percent in 2001 and 9 percent 7

20 Herd Demography Northern Mountain Caribou Population Dynamics in 2007, this leaves 24 caribou available for harvest in 2001 and no surplus for harvest in 2007 (10 percent adult mortality exceeds the 9 percent calf recruitment). 2.3 Rabbit Herd The count data for the Rabbit herd since 1965 suggests that this herd may have had a population decline in the 1970 s, but has since increased at a rate of approximately 7 percent per year since 1978 (Table 2-3). Table 2-3 Rabbit Herd Population Counts and Structure Date Cows Bulls Calves Unknown Adults Count (Estimate) Reference Bergerud Bergerud June (800) Unpub. data 2 (Heard & Vagt 1998) Mar Unpub. data 3 1 In 1978 Bergerud counted caribou in the Muncho Lake Herd,and Rabbit River Herd, both of which are within the currently defined Rabbit herd boundary. Counts (150 and 44, respectively) from both herds are aggregated here. 2 Data from unpublished counts completed from the air during a goat count for MU Incidental count from the air during a Ministry of Environment Stone s sheep survey Since the 2007 count was incidental, and therefore likely to have missed animals, the total of 1133 animals is only a minimum count, yet is still much higher than the 800 caribou estimated for this herd in The number of caribou counted in 1996 was low, compared to this estimate, but could reasonably have missed up to 50 percent of the population in the forest over the large Rabbit herd range (approximately 11,791 km 2 ), especially since the count was incidental during a goat count. Unfortunately, the only count from which there is good population structure data is the June 1996 count. June is not a preferable time of year to get population structure data from caribou; the caribou are widely spaced and difficult to count while the cows are still on calving ranges, while the calf mortality rate is high through the summer, so the number of calves counted (18 percent) is a likely to be an over-estimation of the recruitment in the herd. There were also a large number of unclassified adults from the June count, which makes sex ratios calculated from the few individuals that were sexed likely to be inaccurate. 8

21 Herd Demography The 2007 data suggests that calves make up 14 percent of the total population, which results in a calculated adult mortality rate of 8.4 percent, using Bergerud s (1978) formula. This translates to a 5.6 percent surplus of harvestable individuals, or approximately 66 animals. According to harvest records, there were 11 bulls harvested from the Rabbit herd in 2007 (Section 3.2.2, Figure 3-9). 2.4 Muskwa Herd The Muskwa herd has the most extensive population count and structure data of all the herds in the Peace Region, and counts obtained in 8 years between 1977 and 2007 are displayed in Table 2-4, below (for full data, see Appendix 2.4). Where only one count point was obtained in a year, the month is included in the date, and where more than one count was done in a calendar year, the highest count obtained was usually in October, and that is the count that is displayed. There were more calves recorded in June, but, as predation rates on caribou calves are very high during the summer (Gustine et al. 2006, Page 1985, MLWAP 2004, Wittmer et al 2005), June calf counts likely overestimate recruitment. In 2001/2002, no calves were recorded in October or late winter, which could indicate that cows with calves were being missed; however, the actual number of cows counted was highest in October, suggesting that most, if not all, of the calves born in the spring of 2001 may have been lost. 9

22 Herd Demography Northern Mountain Caribou Population Dynamics Table 2-4 Muskwa Herd Population Counts and Structure Total Count Date Cows Bulls Calves Unk. Adults Total Count Adjusted (estimate) 1 Reference Feb Bergerud Feb Bergerud (1250) Heard and Vagt 1998 Oct (1250) Tripp et al in Thomas & Gray 2002 Oct Tripp et al Oct Tripp et al Oct Tripp et al Jun Tripp et al Mar Unpub. data 4 1 Counts from Tripp et al. are shown adjusted for the sightability index (see Appendix 2.4). The number of collared caribou sighted varied from only 37 percent in October 2001, to 92 percent in February In 1977 and 1978 Bergerud counted the Racing River Herd and Toad River Herd, both of which are within the currently defined Muskwa herd boundary. The count from both herds was aggregated here (219 in each year from the Toad River Herd, and 60 and 75 in 1977 and 1978, respectively). 3 Counts for 2001, 2002, and 2003 were completed from helicopter with tracking of VHF and GPS-collared individuals in the late winter, calving season and rutting season, but only the data from the rutting season (October) is shown in this table, as the highest counts were obtained at this time. 4 Incidental count from the air during a Ministry of Environment Stone s sheep survey Direct comparison of counts between years is confounded by the difference between the study areas in each year; the counts from 1977 to 1996 were taken over an area of unknown size covering known rutting and wintering ranges, the counts from 2001 to 2004 were conducted over less than half of the known Muskwa range (8,900 km 2 out of the known 22,025 km 2 range), and the 2007 count, while covering a wide section of the known range, still did not cover all possible caribou habitat. Even counts within the same study area show dramatic fluctuation in the number of caribou over the years; seemingly 427 caribou were lost between October 2001 and October 2002, which suggests that many of the herd were not with collared animals and were being missed in the counts, and/or there is considerable movement of caribou within the Muskwa range, or between other herd ranges, from year to year. Calf:cow ratios in Table 2-5 in italics (1979 to 1990) are from Bergerud and Elliot s 1998 report on wolf removal experiments in the Muskwa and Kechika drainages. Bergerud and Elliot (1998) looked at the relationships between recruitment and mortality of elk, Stone s 10

23 Herd Demography sheep, moose and caribou; wolf numbers and pack size; and snow depth prior to partuition. During the decade of the study in this area, Bergerud and Elliot (1998) found that high wolf densities were significantly negatively correlated with caribou calf recruitment, and had much stronger effect on calf recruitment than snow conditions. The ratios included in this table are from Table 5 in that report: number of calves per 100 females at 9 months of age. Wolves were removed from the Muskwa range in 1984, 1985, and 1987 by wildlife biologists, and by guide outfitters prior to Calf:cow ratios were high in the years up to 1987, and coincident with wolf populations re-establishing by 1990, calf:cow ratios decreased again (Bergerud and Elliot 1998). It is interesting to note that calf:cow ratios have been increasing again since 2002, while recorded wolf harvests are at historical highs (see Section 4.0 for discussion, and Table 4-1). Table 2-5 Muskwa Herd Population Dynamics Adult mortality (% calculated) 3 Highest Count or Estimate Harvestable Surplus (Mortality % calves) Harvestable Surplus (2 % of total) Date Calf:Cow Ratio 1 Bull:Cow Ratio % Calves Actual Harvest (1250) Years and calf:cow ratios in italics ( ) are from Bergerud and Elliot s (1998) report on wolf removal experiments in the Muskwa and Kechika drainages. The ratios included in this table are from Table 5 in that report: number of calves per 100 females at 9 months of age. 2 Calf:cow ratio for 2000 was calculated using the 19 calves spotted in January 2001, since it was assumed that these calves existed in October, but were missed in the counts. 3 Adult mortality is y = x from Bergerud (1978), where x is calf recruitment. By calculating the adult mortality using Bergerud s (1978) formula based on calf recruitment, and subtracting the calf recruitment for each year, the harvestable surplus as a percentage of the total population (adjusted or highest estimate) was determined. Using only the 2 percent recommendation, harvest was higher than sustainable in all years except 2000, and by 11

24 Herd Demography Northern Mountain Caribou Population Dynamics Bergerud s calculation, harvest was higher than sustainable in all years except 2003 and Both calculations agree that more animals were harvested than were surplus in 1977, 1978, 2001, 2002, and 2007.The harvest statistics indicate that harvest success has dropped since the early 1990 s, and the number of hunters has declined despite lengthening harvest seasons and decreased bull size restrictions (see Section 3.2.4, Figures 3-4 to 3-7). However, the bull:cow ratios for the Muskwa herd displayed in Table 2-5, above indicate that there has been an adequate sex ratio between bulls and cows for every year that data was collected; if the herd was being overharvested, one would expect the sex ratio to be skewed toward cows, or the harvested bull age distribution to be skewed toward younger animals, which it is not (see discussion in Section 3.3). In addition, the calculations of harvestable surpluses are presented with low confidence for this herd, since the total number of animals counted is likely to be lower than the number residing in the MU s encompassing the Muskwa range. 2.5 Pink Mountain Herd Bergerud s 1978 report discusses the Pink Mountain ( Pink Mountain-Prophet River ) herd in relatively high detail compared to the other Peace Region herds. He states his belief that the 1969 count likely captured 75 percent of the population, which would have placed the total population at approximately 3567 individuals. He goes on to state that the late 1960 s and early 1970 s were a historical high point for caribou populations in this area: In 1969, this herd was probably the second largest herd in British Columbia (1978, p.77). He also considers it unlikely that he missed much of the herd in 1978, and states that guide outfitters had been having trouble finding the caribou in this area even during the rut. Bergerud s conclusion was that this herd suffered from overharvest and poor recruitment during the early 1970 s. If we take Bergerud s 1978 estimate as close to the true number of the herd, then it appears that this herd increased throughout the 1980 s and 1990 s. A deficiency of the count data set is that it shows large fluctuations from year to year; in the three years from 1993 to 1995, for example, the data show a loss of 362 individuals, followed by a gain of 561 the next year (Table 2-6). 12

25 Herd Demography Table 2-6 Pink Mountain Herd Population Counts and Structure Date Cows Bulls Calves Unk. Adults Total (estimate) Reference Feb Bergerud 1978 Feb Luckhurst 1969 in Bergerud 1978 Dec Bergerud 1978 Feb (342) Bergerud 1978 count Bergerud 1978 estimate Feb Unpub. data 1 Feb Unpub. data 2 Feb Unpub. data (1300) Heard & Vagt 1998 Mar (850) Unpub. data 4 in Thomas & Gray 2002 Mar Unpub. data 5 1 Unpublished data for 1993 was collected by provincial wildlife biologists along transects from fixed wing aircraft between the Prophet River and Halfway River during a Stone s sheep and caribou survey. 2 Unpublished data for 1994 was collected by provincial wildlife biologists along transects from fixed wing aircraft between the Prophet River and Halfway River during a Stone s sheep and caribou survey, with tracking of VHF-collared individuals 3 Unpublished data for 1995 was collected by provincial wildlife biologists along transects from fixed wing aircraft with tracking of VHF-collared individuals 4 Unpublished data for 2000 was collected by provincial wildlife biologists during a caribou inventory for MUs 7-42, 7-57, and 7-58, with tracking of VHF-collared individuals 5 Incidental count from the air during a Ministry of Environment Stone s sheep survey This fluctuation is likely due to the fact that counts from 1993 and 1994 were done for Stone s sheep and caribou, simultaneously, and would not have covered lower forested elevations. As a result, this data represents at best a very conservative minimum count, and one could assume that only 50 to 75 percent of the herd was being counted in some years (as per Bergerud 1978, Tripp et al. 2006). Heard and Vagt s (1998) estimate of approximately 1300 animals in 1996 is plausible; in 1995, if only 50 to 75 percent of the herd was counted, there could have been anywhere from 1100 to 1650 animals in total. However, using the conservative estimate that only 50 percent of the herd was counted in 2000, then the herd could have suffered a decline of 58 percent between 1996 and 2000 (377 animals counted in 2000, estimated 754 animals in total). The 2007 count could also reasonably be expected to have missed more animals than previous surveys: if only 50 percent might be sighted when caribou are the animal of interest, then it is likely that an incidental count would be even less accurate. 13

26 Herd Demography Northern Mountain Caribou Population Dynamics Table 2-7 Pink Mountain Herd Population Dynamics Adult Total mortality (Highest % (% Count or Calves calculated) Estimate) Harvestable Surplus (Mortality % calves) Harvestable Surplus (2 % of total) Date Calf:Cow Ratio Bull:Cow Ratio Actual Harvest The harvestable surplus was calculated from the highest count or estimate available, first using Bergerud s (1978) adult mortality formula, displayed in Table 2-7 as Harvestable Surplus (Mortality - % calves), and as 2 percent of the total population, displayed as Harvestable Surplus (2% of total). The actual number harvested is shown in the column Actual Harvest. Based on a harvest guideline of 2 percent, the harvest rate was higher than sustainable for all years, but only higher than sustainable in 1993, 1994, and 2000 based on recruitment and calculated adult mortality. However, as with the Muskwa herd, the harvestable surplus numbers are presented with low confidence due to the aforementioned likelihood that the counts are unrepresentative of the true total. The harvest data (Section 3.2.3, Figures 3-11 and 3-12) shows that the harvest declined steadily through the 1990 s, and the number of hunters and hunter success rates dropped even as regulations were loosened (see discussion in Section 3.2.3). The calf:cow and bull:cow ratios are lower than suggested for a sustainable caribou population; in 2000, the last year for which population structure is available, both ratios are less than half what they should be to ensure a recruitment rate that offsets adult mortality and full pregnancy rates. Thus, it seems likely that the population increased from the late 1970 s to a high near 1300 in the mid-1990 s, but has declined since then. Due to the uncertainties with the accuracy of the counts, however, it is difficult to determine what the actual population size is, and whether this decline is a part of a normal fluctuation or an indication of genuine decline. 14

27 Herd Demography 2.6 Liard Plateau Herd The Liard Plateau caribou herd does not appear to have ever been a large herd, yet has remained stable, albeit small, for the last 30 years (Table 2-8). The ratios of calves and bulls to cows, as well as the total percentage of calves in the herd, are lower than recommended (except the percent calves in 2005). The reason for the low recruitment is likely to be predation by bears and wolves; Bergerud (1978) reported that this area had some of the highest wolf and grizzly bear densities he encountered during his caribou surveys, Bear sign was heavy more than we had seen anywhere in the summer 11 scats in 39 miles of walking. Also we found 11 wolf droppings (1978, p 70). In his report to Yukon Wildlife Management Branch, Powell (2006) asserts that based on these parameters and the herd size, this herd would be closed to hunting under Yukon regulations. Table 2-8 Liard Plateau Herd Population Counts and Structure Date Cows Imm. Bulls Bulls Calves Unk. Adults Total (estimate) Reference Feb Bergerud (125) Bergerud 1978 Bergerud Bergerud 1978 Feb Bergerud (150) Heard & Vagt (150) in Thomas & Gray 2002 Feb 2002 (<200) J. Adamczewski, in Powell Oct Powell BC Hydro count from a helicopter survey, reported in Bergerud Yukon Department of Environment, Liard Regional Biologist Jan Adamczewski s count during caribou collaring 3 Yukon Department of Environment classification count by helicopter It is difficult to decide what the trajectory of this herd is; the recruitment is lower than suggested, and the bull:cow ratio is low(table 2-9). The calculated harvestable surplus was less than the actual harvest based on calculated adult mortality and recruitment in 1977 and 1978, and based on the harvest guideline of 2 percent of the total population, this herd was overharvested in 1978, 2000, and The harvest in this region is mostly by Non-Resident hunters flown in by guide outfitters, and the success rate and number of hunters is highly variable from year to year; however, the age of bulls harvested from this herd are lower than 15

28 Herd Demography Northern Mountain Caribou Population Dynamics any other herd, at an average of 5 years of age (Section 3.3, Figure 3-20) suggesting that this herd is being harvested at or near its maximum capacity. Table 2-9 Liard Plateau Herd Population Dynamics Adult Harvestable Mortality Surplus % (% (Mortality Calves calculated) Total % calves) Harvestable Surplus (2 % of Total) Date Calf:Cow Ratio Bull:Cow Ratio Actual Harvest 16

29 Harvest History and Statistics 3.0 Harvest History and Statistics by Herd The harvest history of caribou herds can be used to make inferences about population trends. A decline in harvested numbers may indicate a declining population, but there are external factors that can influence harvest rates such as increased harvest restrictions, lower numbers of hunters, or hunters switching game preferences. A more appropriate indication of game abundance may be hunter success rates; Bergerud, Jakimchuk, and Carruthers (1984) used hunter success rates to indicate whether a herd was being over-harvested: when success rates drop, it may be an indication of a declining population of caribou. In Bergerud s (1978) discussion of caribou population trends in BC, he states that hunting regulations became more strict in 1974; however, when discussing the plummeting numbers of caribou harvested in BC in 1973 and 1974, from more than 1200 to approximately 500 animals, he states that the decline in the harvest cannot be explained by increased hunting restrictions alone (p. 96), and suggests that the decline is in part due to lower numbers of caribou, as well. Bergerud goes on to recommend hunting closures for several management units (MUs), including 7-51, which contains the Gataga and Rabbit herds; 7-52, which contains the Frog herd (as well as the Horseranch herd); and 7-53, which contains the Liard Plateau herd. Closures for these MUs were not enacted, but the harvest regulations that were put in place for each MU are described in the herd summaries, below. 3.1 Harvest Summary Statistic Analysis Methods In order to determine whether harvest of caribou in the Peace Region provides an indication of population trends, harvest statistics for big game collected by the Ministry of Environment between 1976 and 2006 were used to determine total harvested caribou (taken by resident hunters and non-resident hunters) and average caribou hunter success rate (number of kills/number of hunters) for each year. The number of caribou harvested by residents and nonresidents in 2007 was also included, though total hunter numbers and hunter hours are not yet available for that year. The following assumptions were made regarding the assignment of harvested caribou to specific herds: the Liard herd range is contained entirely within MU 7-53, thus all animals 17

30 Harvest History and Statistics Northern Mountain Caribou Population Dynamics harvested within 7-53 were assumed to belong to the Liard herd; all animals taken within MUs 7-42, 7-57, and 7-58 were assumed to be from the Pink Mountain herd; and all animals harvested in MUs 7-50 and 7-54 were assumed to be from the Muskwa herd. The Frog and Horseranch herd ranges are both within MU 7-52; MU 7-51 contains portions of the Muskwa herd range, and all of the Gataga and Rabbit herd ranges. In order to get a more accurate description of the relative number of caribou from each herd being harvested in the latter two MUs, the approximate harvest locations recorded on Compulsory Inspection forms from 1978 to 2007 were plotted in ESRI s ArGIS 9.1 ArcMap software, and the kill numbers separated and summarized by location within defined herd ranges (British Columbia Peace Region Draft Caribou Herd Boundaries Map, August 2008). MUs 7-57 and 7-58 were split from MU 7-43 in 1990, so Compulsory Inspection form kill locations recorded in MU 7-43 prior to 1990 within the Pink Mountain herd range were attributed to the Pink Mountain herd as well. A number of UTM coordinates recorded by hunters on the CI forms were found to be inaccurate, positioning the kill location at great distances from the kill site description. Where there was a discrepancy between kill site description (e.g. South Gataga Lakes) and the UTM coordinates provided, the point location was manually re-positioned near the written location, as it was more likely that the hunter knew the name of his location and made an error in recording the geographic coordinate, than that he committed the opposite error. During analysis of the harvest statistics, a marked decrease in the number of caribou harvested from the Pink Mountain, Gataga, Rabbit, and Muskwa herd ranges became apparent. This decline was always associated with a decrease in hunters, and occasionally with declining success rates. Thus, to determine whether the declining numbers of caribou hunters could have been due to external factors rather than declining herd populations two external factors were reviewed. The first factor was harvest regulations; regulations in place between 1976 and 2006 were reviewed. In general, changes in the regulations were made in most MUs in 1986, to restrict harvest to bulls with at least 5-points on their antlers, and then again in 1996, when part of the season was again opened to all bulls. It was also recognized that the harvest regulations were likely driven by changes in caribou populations - with greater restrictions and shortened seasons when populations are believed to be declining, and a relaxation of restrictions when 18

31 Harvest History and Statistics herds are believed to be robust. Implicit in the discussion of harvest pressure on these herds is the assumption that the recorded harvest is representative of the actual harvest; that is, that poaching is not a significant contribution to caribou mortality through human harvest. The number of hunters pursuing other ungulates in the same MUs was also compared to the number of caribou hunters to determine whether there were patterns in the harvest rates that would suggest caribou harvest pressure is correlated to harvest rates of other species (the average Resident hunter in B.C. takes out two big game species licenses per season (Sun et al. 2004)), or whether changes in harvest rates reflected known changes in ungulate abundances (e.g. moose and elk, approximated by harvest numbers). This analysis consisted of plotting the total number of big game (moose, elk, white-tailed deer, mule deer, mountain goat and sheep) hunters each year against the number of caribou hunters, and plotting the number of each species harvested over time. 3.2 Harvest Statistic Analysis Results by Herd Frog Herd The number of caribou harvested in MU 7-52, which encompasses the Frog herd range, was at a considerable low from approximately 1978 to 1985 in comparison to other years (Figure 3-1). This decline in caribou harvested corresponds to increased harvest restrictions during this time; hunting season for caribou was restricted to bulls only (from both sexes prior to 1978) and only 3 to 4 weeks in late August to early September (down from 12 to 14 week seasons prior to 1978). In 1986, the season was lengthened to five weeks (from August 23 to September 30) but restricted to 5-point bulls only, which resulted in an increase in the number of caribou harvested again. Evidently, restrictions on the size of the bulls harvested did not decrease the number of bulls available for harvest; it is possible that the population had grown during the period the hunting season was shortened, allowing for a greater harvest when the season was lengthened again. Alternatively, the increase in harvest rate and number of hunters could be due to an increase in available access at that time, which has been maintained to the present. The season was lengthened again in 1996, when a two-week period was opened for all bulls following the four-week 5-point bull season (in 1998, the all bull season was switched to the 19