Peary caribou and barren-ground caribou COSEWIC assessment and status report: chapter 9
Population Sizes and Trends
Documenting population trends within narrow limits of confidence is difficult because of the irregularity of surveys and the inconsistency of survey coverage and methods. Surveys are expensive because of the vast area involved. Weather conditions can prevent completion of a planned survey. The caribou make it more difficult by moving unpredictably among islands within their ranges, so that investigators have to cover all major islands to be sure they have not missed sizable proportions of the herds. All populations have never been surveyed in 1 year. Only 3 times have most of the western Queen Elizabeth Islands been covered in 1 survey period: 1961, 1972-1974 and 1997. Various authors have used different assumptions in extrapolating to islands not covered in 1 survey to compare with populations estimated in another. Also, some authors included calves while others did not, making it difficult to compare surveys. Finally, aerial surveys of low and clumped caribou densities may have unrealistically wide or narrow confidence intervals, depending on what proportion of the clumps were captured in the transects. The confidence intervals given in the text are ± Standard Error unless otherwise noted. The graphs in this section do not show confidence intervals (which in many cases were not available) and it should not be assumed that each point is significantly different from its neighbours. Cases in which the validity of the trends or of the underlying estimates is in question, are discussed individually.
In 1961 Tener (1963) completed the only survey of the Queen Elizabeth Islands, estimating 25 802 caribou. Therefore, allowing for Peary caribou on Somerset Island and Boothia Peninsula, the total must have exceeded 30 000 Peary caribou. By adding all of the first counts for all populations (which occurred in different years as much as 2 decades apart) a maximum of nearly 50 000 Peary caribou is obtained (Appendix 1). Currently there are about 7000 Peary caribou (Table 10).
Queen Elizabeth Islands
For the western Queen Elizabeth Islands, the population (total caribou, including calves) from Tener’s (1963) 1961 estimate of 24 320 declined to 5244 in 1973 and 2674 in 1974 (Miller et al., 1977a). In 1987 there were about 2100 total caribou and in 1997, 1100 total caribou (Miller and Gunn 2003b). This seemingly constant decline masks quite different trends in the Melville Island complex and the Bathurst Island complex.
Population estimates in the Melville Island complex are complicated because some segments of the local population seasonally migrate between Melville Island and Prince Patrick Island; in addition, there are irregular movements among these and other islands in this complex. Since Tener’s 1961 survey (Tener 1963), the population has declined. It may have had a recovery during 1987-1996 which is not demonstrated in population aerial surveys due the long gaps between surveys, but can be inferred from the estimated 371 carcasses found in 1997 after a die-off the previous winter (Miller 1998, Gunn and Dragon 2002, Miller and Gunn 2003a). Based on aerial population surveys summarized by Gunn and Dragon (2002), however, the Melville Island local population showed an overall steady decline of 7.4% per year between 1961 and 1997 (Figure 8). The smaller local population of the Prince Patrick Island group (including the smaller "satellite" islands of Eglinton, Emerald, Mackenzie King and Brock islands) declined at a rate of 10.7% per year during that time (Figure 8). Surveys in the 1970s and 1980s did not include all of the islands and so resulted in estimates below the trend line. Die-offs resulting from adverse snow conditions in both Melville and Prince Patrick local populations, although not revealed in the long term population trend data from major surveys, have been inferred from carcass counts in 1974, 1995, 1996 and 1997, (Miller and Gunn 2003a). The timing was concurrent with die-offs in the Bathurst Island complex (see below). The last survey of the Melville Island complex, in 1997, found 871±103 for 1+ year old caribou, although only 2 calves were seen and none on the main islands (Gunn and Dragon 2002). Population estimates and trends are given in Appendix 1, Table 5.
The caribou in the Bathurst Island complex have been the most studied. The population declined between 1961 and 1973, crashed during 1973-1974, increased at about 13% per year for the next 2 decades (but more sharply during 1988–1994 as noted previously), and then crashed again during 1995-1997. The last published survey of the Bathurst Island complex, in 1997, resulted in an estimate of 78±26 for 1+ year old caribou, which were mostly breeding age cows, suggesting a high potential for recovery (Gunn and Dragon 2002). Severe winter weather characterized by deep snow with icing events caused the crashes; other possible causes such as hunting, predation, competition with muskoxen or forage depletion have been ruled out (F.F. Slaney & Co. Ltd. 1975a, Miller et al. 1977a, Ferguson 1987, Miller 1991, Gunn and Dragon 2002, Miller and Gunn 2003b).
In two surveys in May 2001, Ferguson (Nunavut Wildlife Service, pers.comm., November 19, 2002) estimated populations of 240 (95% CI=150-283) and 289 (95% CI=166-503) by distance sampling for 1+ year old caribou on Bathurst Island (21% and 41% of occupied watersheds were surveyed in these 2 surveys). The higher of these is shown in Figure 9 and used in the calculations; however, this estimate is not strictly comparable to the previous estimates because of the different methods used. Population estimates and trends are given in Appendix 1, Table 5.
The most complete survey of the eastern Queen Elizabeth Islands complex was carried out in 1961, when Tener (1963) estimated 1482. Although his estimates were conservative, some Inuit in Grise Fiord and Resolute Bay doubt that the population could have been that high (Ferguson et al. 2001). Riewe (1973) estimated about 145 caribou on southern Ellesmere Island. In 1989, about 90 caribou were estimated on southern Ellesmere Island (Case and Ellsworth 1991). Gauthier (1996) counted 63 caribou on central Ellesmere and Axel Heiberg islands in 1995 in unsystematic surveys. Ferguson et al. (2001) reported no evidence of caribou die-offs on southern Ellesmere Island where local Inuit travel extensively in late winter and spring; however, local Inuit suspect that an apparent decline and unusual distributions during the 1970s were caused by seismic activity over extensive areas, especially in important caribou habitats. Since the mid-1990s, caribou have been found in several areas on southern Ellesmere and northern Devon islands where they had not been seen since the 1960s (Ferguson et al. 2001). Caribou have been in good physical condition in recent years, including bulls in late winter. They observed that even some young females were pregnant in late winter. In 2 of 3 recent summers, a geoscientist noticed several caribou on Ellef Ringnes Island (Tener 1963, saw 21 there in 1961 and estimated a population of 114). Although the current population of the complex cannot be reliably estimated, the Peary Caribou Recovery Team estimated around 1480 caribou, based on published and unpublished information (Peary Caribou Recovery Team 2001). Population estimates and trends are given in Appendix 1, Table 5.
Banks Island–northwestern Victoria Island
The population on Banks and northwestern Victoria Island declined in the early 1950s and early 1960s (Elias 1993, Gunn 1993). The Banks Island local population subsequently increased to an estimated 12 098 in 1972 (Urquhart 1973), and was relatively stable to 1982 when Latour (1985) estimated the total number of caribou at 11 034 (9015 1+year old caribou) (P. Latour’s data reworked by J. Nagy, Northwest Territories Wildlife Service, pers. comm. February 2, 2004). Caribou numbers on Banks Island then declined between 1982 and 1992 to an estimated 1018 1+year old caribou, 757–1279 95% Confidence Interval (Nagy et al. 1996, Larter and Nagy 2000a, J. Nagy, Northwest Territories Wildlife Service, pers. comm. February 2, 2004). The decline appeared to continue during the 1990s based on lower estimates in 1994 and 1998, but there were technical problems including poor weather with the 2 surveys. If real, the rate of decline from 1982 to 1998 was about 17% per year (l=0.83) (Figure 10). The survey in 2001 had excellent conditions and returned an estimate of 1196 1+year old caribou (1137–1254 95% CI) suggesting that the caribou numbers were stable to slowly increasing during the 1990s (J. Nagy, Northwest Territories Wildlife Service, pers. comm. February 2, 2004) (data in Appendix 1, Table 7).
Trends for the northwestern Victoria Island local population are given in Appendix 1, Table 7, but not illustrated because of their uncertainty. The low point for the northwestern Victoria Island caribou population was in the early 1960s, coincident with both a freezing rain event and with the introduction of snow machines (Elias 1993) and again in the early 1990s (Gunn 1993). Die-offs occurred in the 1950s, 1977-1978, and 1980s.The decline in Peary caribou of northwestern Victoria Island lagged behind the decline on Banks Island (Elias 1993).
The 1980 estimate of 4512±988 included calves. In 1987 Gunn’s (1993) estimate was for 3500 total caribou; confidence limits could not be calculated, but since the estimate was within the confidence interval of the 1980 estimate there was no evidence for a decline. They then declined to an estimated 114 adult caribou in 1993 (Gunn 1993) and in 1994 just 6 caribou were seen (Nishi and Buckland 2000). A weather-related die-off probably occurred in 1993-1994: no carcasses were reported, but it was an exceptionally heavy winter. The population then apparently increased to 508±75 for 1+ year old caribou (633±81 for all caribou) in 1998 (Inuvialuit Game Council 2002b) and 1272±384 1+ year olds, or 1628±501 for all caribou (J. Nagy, Northwest Territories Wildlife Service, pers. comm. January 6, 2003) in 2001.
An increase from 114 in 1993 to either 633 in 1998 or 1628 in 2001 would require a rate of about 40% per year (l=1.41 and 1.39, respectively), higher than the maximum reproductive potential of caribou discussed above. One explanation is immigration from Banks Island. However, a more likely explanation is that some, perhaps a large proportion, of the northwestern Victoria Island caribou counted in 1998 and 2001 were from the Dolphin and Union herd.
Most of the caribou counted on northwest Victoria in July 2001 were east of Richard Collinson Inlet which is adjacent to ranges used by Dolphin and Union caribou in 1987 and 1996-98 based on satellite telemetry (Gunn and Fournier 2000). To answer the question of whether the 2001 estimate included caribou from the Dolphin and Union herd, John Nagy followed up his 2001 survey results by fitting satellite collars to 10 cows east of Richard Collinson Inlet in August 2003. The 10 collared cows reached the south coast of Victoria Island by early November 2003 and 9 cows crossed to the mainland (1 had died). Those movements strongly suggest that the caribou counted on northwest Victoria Island in 2001 included an unknown number of Dolphin and Union caribou. The Minto Inlet herd still exists as tracks were seen north of Minto Inlet in December 2003 but the extent of recovery of the Minto Inlet caribou is currently uncertain (J. Nagy, Government of the Northwest Territories, pers. com. 25 January 2004; A. Gunn, Government of the Northwest Territories, pers. com. February 20, 2004).
Hunters from Holman, on western Victoria Island, hunt caribou of the Minto Inlet herd (i.e., northwestern Victoria Island) in winter, but the difficulties of distinguishing the Minto Inlet harvest records from the Dolphin and Union harvest records has prevented a detailed analysis of the effects of hunting. More work is needed to provide a basis to distinguish harvest records for the 2 populations on Victoria Island, as well as their respective ranges, particularly calving areas (Nishi and Buckland 2000).
In view of the improbability that the northwestern Victoria Island local population having increased at 40% per year after 1993 and the certainty that at least some of the caribou counted were from the Dolphin and Union herd, the estimates require adjustment. For the purpose of trend and current status calculations, the report writer arbitrarily divided the 2001 estimate by half in Table 7 and Table 10.
Dolphin and Union
Anderson (1922), a mammalogist who studied wildlife in the Coronation Gulf area from 1908 to 1916, estimated that 100 000 to 200 000 caribou migrated across Dolphin and Union Strait. Manning (1960) accepted the more conservative value, based in part on the projected density for the population in the land area of Victoria Island compared to other barren-ground caribou densities. The Dolphin and Union caribou stopped migrating across Dolphin and Union Strait after 1924. However, morphologically similar caribou with a distinct genotype now occupy the island and most now migrate across Dolphin and Union Strait somewhat as before. They may be a relict population currently on the rebound, or they may be the native, resident caribou, or, less likely, a mixture of these 2 plus barren-ground caribou from the mainland.
The first recent estimate was 1000 caribou in 1949, with the summer distribution shown around Prince Albert Sound (Banfield 1950). In 1980, 7936±1100 caribou were estimated on Victoria Island (Jackimchuk and Carruthers 1980), but 4512±988 were Peary caribou on northwestern Victoria Island, leaving 3424±522 Dolphin and Union caribou on the remainder of the island. This estimate, however, is problematic, as discussed below. Later surveyors found 14 529±1016 caribou in 1994 and 27 786±3366 in 1997 (Gunn and Nishi 1998).
Figure 11 shows the population data with a fitted trend line for 1980 to 1997, an annual increase of about 13% (the trend line and rate estimate split the difference between the 1994 estimate, which is too low for the exponential growth model, and the 1997 estimate, which is too high). However, if the annual rates of increase from 1980 to 1994 and from 1994 to 1997 are calculated separately, the former would have been 11% and the latter, 24% (from 14 529 to 27 786, 3 reproductive years, l=1.24).
Despite the apparent precision of the estimates, these values are problematic. First, the 1980 survey had a low coverage of the island, so that if 1 or more sizeable groups of caribou were missed, the population would have been under-estimated. Second, annual harvests for Cambridge Bay were 2351±59 in 1983 (Jingfors 1986) and 1445±38 in 1994 (Kitikmeot Hunters' and Trappers' Association 1996), and for all communities in the late 1980s to early 1990s, 2000 to 3000 (Gunn and Nishi 1998). A population of only ~3200 caribou could not have supported such a high harvest rate. Therefore, either the 1980 survey underestimated caribou numbers, or the subsequent increase was due partly to immigration. If so, then both the rates of increase for 1980 to 1994 and 1980 to 1997 would have been less than the 11% and 13% per year, respectively, that were mentioned above.
Elias (1993) reported Aboriginal traditional knowledge that both hunting and weather were factors in the decline in the early 1900s: One elder remembered hunting caribou with bows and arrows from kayaks after herding them into the water. Only after the widespread availability of rifles, and after the 1960s, snow machines, did hunting affect the populations. Several elders reported wastage of meat after high-powered rifles were available and caribou were killed only for their skins. In times of freezing rains in the fall (several elders recalled such an event in the 1960s), the elders thought that the caribou moved away and should have had no trouble finding ice-free vegetation because Victoria Island is so large.
Prince of Wales–Somerset Island
Despite scanty population data, a serious, recent decline is obvious. Aboriginal traditional knowledge shows that Peary caribou on Prince of Wales and Somerset islands declined during the 1930s and were scarce in the mid-1940s (Ferguson et al. 2001). The population started to increase in the late 1950s, and was stable through the 1970s. Estimates of adult caribou for 1974 and 1975 were 4540 and 3607, respectively (Fischer and Duncan 1976). Accounting for the percentage of calves they counted in spot-checks on Prince of Wales and Somerset islands, there were 5516 and 4383 total caribou in 1974 and 1975, respectively. In 1980 Gunn and Decker (1984, cited in Gunn and Dragon 1998) estimated 5100 1+ year old caribou (6043 total caribou) on these islands. In 1995 Gunn and Dragon (1998), in response to Inuit concerns about difficulty in finding caribou during winter hunting trips, surveyed the same area covered in 1980, using the same survey methods. The observers, who included an experienced Inuit hunter, counted 7 caribou on Prince of Wales and Somerset islands, too few for a meaningful population estimate. (60±20 is used herein as the estimate for graphing and tabulation purposes as suggested by F. Miller, Canadian Wildlife Service, pers. comm. Dec. 21, 2002). A constant decline from 6043 to 60 adult caribou would be 26% per year (l= 0.73529). Figure 12 gives the estimates, along with a 26% population decrease curve (from 6043 to 60) for 1980-1995. It may be misleading, however, to display the population decrease curve with the estimated population trend, because the decline may have been sudden, rather than gradual.
In the late 1970s and early 1980s, annual harvests were 150-250 caribou during the time when Resolute hunters voluntarily stopped hunting on Bathurst Island after the 1973–1974 die-off and hunters instead travelled to Prince of Wales and Somerset (Gunn and Decker 1984). Harvests then declined in the late 1980s to annual harvests of 85 to 170 caribou on Prince of Wales and Somerset islands islands (Donaldson 1988 and A. Idlout pers. comm. cited in Ferguson et al. 2001). An uncertain factor, however, is the amount of harvest on the Boothia Peninsula, where some Prince of Wales-Somerset caribou winter, by hunters from Taloyoak.
The decline of the Prince of Wales-Somerset population of Peary caribou coincided with increases in the populations of Peary caribou on Boothia Peninsula to the south, the Bathurst Island complex to the north, and the Dolphin and Union herd of barren-ground caribou to the west. It is possible that, instead of decreasing because of internal mechanisms, large numbers of them emigrated. If so, Boothia is the most likely destination, although Gunn and Dragon (1998) found little evidence of immigration during their survey of Boothia in 1995. On the other hand, Inuit hunters from Taloyoak prefer Peary caribou (which they call “kingailik tuktu” meaning “Prince of Wales Island caribou”) because the meat is more flavourful and tender (F. Miller, Canadian Wildlife Service, Dec. 21, 2000). The high harvest rates of about 22% per year during the late 1980s from a population of only about 4800 caribou (1985 estimate) suggests such an influx (i.e., the population was being augmented by immigrants from the north). Fisher and Duncan (1976) also thought that caribou from Prince of Wales–Somerset complex migrated to the Boothia Peninsula between 1974 and 1975 because of declining numbers in the former concurrent with increasing numbers in the latter.
Some Inuit from Resolute Bay believed the decline to have been caused by effects of high caribou densities on their forage (Ferguson et al. 2001) and at least one thought, without having seen any physical evidence, that some may have emigrated to the Bathurst Island complex (D. Kaomayok of Resolute Bay, cited in Gunn and Dragon 1998). They saw no evidence of unusually severe snow conditions and believed that Peary caribou persisted on Somerset despite Gunn and Dragon’s low count in 1995. That count was, however, consistent with an unsystematic survey flown under ideal conditions in May 1996 when Miller (1997a) found only 2 caribou and almost no tracks. Moreover, other Inuit from the same village did not mention competition or forage depletion and felt that the causes might have been wolf predation or disease (F.L. Miller, Canadian Wildlife Service, May 21, 2003, recalling a meeting at Grise Fiord in October 1997 at which several Inuit from Resolute Bay were present).
Gunn and Dragon (1998) reviewed the possible causes of the decline, including inaccurate surveys, emigration and factors affecting deaths and/or births rates such as hunting, predation, winter weather, diseases, and parasites and competition with the muskox population, which was increasing. They had only scanty data on calf production and survival, which, however, did not point to depression from winter severity; nor was there any evidence of a die-off (Inuit hunters from Resolute reported some carcasses in the winter of 1992 but the carcasses were not in poor condition). Although there were no data on wolf populations in the area, Resolute Bay hunters reported increased wolf numbers on Prince of Wales Island during the 1990s and suggested that the 5-fold increase in muskoxen would support a high wolf population. There was no evidence that drier summer weather had reduced plant growth, which is moisture limited, sufficiently to affect the fat reserves needed to survive the winter (Gunn and Dragon 2002). Although they could not attribute all of the decline to any of these, they concluded that (a) harvest could have been a factor in the early 1980s when hunters were taking 150 to 250 caribou per year, and (b) predation or winter malnourishment (perhaps in competition with muskoxen, or associated with climate change) may have hastened the decline. In any case, the numbers are now so low that recovery will be slow and uncertain (Gunn and Dragon 1998).
Caribou on the Boothia Peninsula were numerous before the 1930s to 1940s, when the migration through the Boothia Isthmus dwindled, then stopped (Gunn 1998a). Inuit hunters said that caribou were scarce in the 1950s and a Canadian Wildlife Service unsystematic survey found no animals in 1958; however, in 1974 and 1975, Fisher and Duncan (1976) estimated 428 and 1443 adult caribou, respectively on Boothia Peninsula. Accounting for the percentage of calves they saw in spot-checks, the estimates of total caribou for 1974 and 1975 were 556 and 1890, respectively. In those surveys, barren-ground and Peary caribou were not distinguished, but the population was assumed to be mostly Peary caribou (Gunn 1998a).
The Boothia Peninsula estimates apparently increased from 4831± 543 1+ year old to 6658±1728 total caribou during 1984-1995 (Gunn and Dragon 1998, Gunn et al. 2000b), but the wide standard errors belie their statistical significance. Also, the 1985 survey was at the beginning of calving and the few calves seen were not counted, but the 1995 survey was after calving and calves were included, further complicating the comparison (A. Gunn, Government of the Northwest Territories, pers. comm., November 22, 2002). Gunn and Dragon (1998) noted that observers on the 1995 survey did not differentiate between Peary and barren-ground caribou, although both were observed. Barren-ground caribou have apparently been increasing on Boothia (Gunn 1998a) and Peary caribou decreasing (F. Miller, Canadian Wildlife Service, pers. comm. Dec. 21, 2002). The preference for kingailik caribou by Inuit from Taloyoak as noted in the previous section is a possible mechanism for such a shift in caribou subspecies predominance, along with others such as climate change-induced vegetation changes. If only half were Peary caribou in 1995, as estimated by F. Miller (Canadian Wildlife Service, pers. comm. Dec. 21, 2002), then that estimate would fall to 3329, a constant annual decline rate of 3.7% per year from 1985 to 1995 (Figure 13). These estimates, although the best available, are quite unsatisfactory.
King William Island and nearby smaller islands once supported large numbers of caribou that were presumed to be migrants from the mainland, but migrations apparently ceased in the 1930s (Miller 1991). Few caribou have been seen in recent surveys. However, Inuit from Gjoa Haven recognize 2 types of caribou on King William Island: mainland caribou (i.e., barren-ground caribou) and Peary-type caribou that they believe cross over from Victoria Island (i.e., Dolphin and Union caribou); they say that mainland caribou have only been crossing from Queen Maud Gulf within the last few years and are increasing in number annually (Dave White, Government of Nunavut, pers. comm. February 6, 2004).
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