Wendy Calvert

Genetic structure of the world’s polar bear populations

We studied genetic structure in polar bear (Ursus maritimus) populations by typing a sample of 473 individuals spanning the species distribution at 16 highly variable microsatellite loci. No genetic discontinuities were found that would be consistent with evolutionarily significant periods of isolation between groups. Direct comparison of movement data and genetic data from the Canadian Arctic revealed a highly significant correlation. Genetic data generally supported existing population (management unit) designations, although there were two cases where genetic data failed to differentiate between pairs of populations previously resolved by movement data. A sharp contrast was found between the minimal genetic structure observed among populations surrounding the polar basin and the presence of several marked genetic discontinuities in the Canadian Arctic. The discontinuities in the Canadian Arctic caused the appearance of four genetic clusters of polar bear populations. These clusters vary in total estimated population size from 100 to over 10 000, and the smallest may merit a relatively conservative management strategy in consideration of its apparent isolation. We suggest that the observed pattern of genetic discontinuities has developed in response to differences in the seasonal distribution and pattern of sea ice habitat and the effects of these differences on the distribution and abundance of seals.

Habitat preferences of polar bears in the western Canadian Arctic in late winter and spring

Between late March and May, from 1971 through 1979, we surveyed 74,332 km 2 of sea-ice habitatin the eastern Beaufort Sea and Amundsen Gulf in the western Canadian Arctic. We defined seven sea-ice habitat types and recorded sightings of polar bears and their tracks in each to determine their habitat preferences. 791 bears (including cubs) and 6454 sets of tracks were recorded. 42.3%, 39.7%, and 15.6% of the bears were seen on floe-edge, moving ice, and drifted fast-ice habitats, respectively. Significant differences in habitat preferences were shown by bears of different sexes and age classes. Adult females accompanied by cubs of the year were the only group that showed a strong preference for fast ice with drifts, probably because they could feed adequately there while avoiding adult males that might prey upon their cubs. The highest densities of seals are found in floe-edge and moving ice habitats and this likely explains the predominance of bears there. Lone adult females and females with two-year-old cubs, adult males, and subadult males were found two and one-half to four times more frequently than predicted in floe-edge habitat. Since there are no data to suggest seals are more abundant along the floe edge than in moving ice habitat, the preference of these groups of adult polar bears for the floe edge in spring may be related to reproductive behavior.

Notes on winter feeding of crabeater and leopard seals near the Antarctic peninsula

SummaryStomach contents of crabeater (Lobodon carcinophagus) and leopard (Hydrurga leptonyx) seals collected in the pack ice west of the antarctic Peninsula in August–September 1985 were analyzed. Food remains were found in 7 of 56 crabeater seals and 5 of 29 leopard seals. The primary foods were krill (Euphausia superba) which occurred in all 12 stomachs, and fish (Pleuragramma antarcticum) which occurred in 3. Eleven of the seals with food in their stomachs were collected in the southern portion of Bismark Strait. The incidence of feeding seemed highest in pregnant females. These results, and comparisons with previous collections, suggest that krill were not abundant or widely distributed in the area at the time the seals were collected. The sizes of krill eaten by crabeater and leopard seals were very similar, and were significantly larger than krill found in 2 samples taken by midwater trawls in nearby open water.

Male-biased harvesting of polar bears in western Hudson Bay

We examined the number, sex, and age composition of polar bears (Ursus maritimus) killed by harvest, destroyed as problem bears, relocated to zoos, and killed during handling from western Hudson Bay between 1966 and 1992. Harvest and removal of problem bears were biased towards males (66.7-70.1%) with most bears (71.7%) taken under a managed quota, but destruction of problem bears (13.6% ) was also an important component of removal. An average of 42 bears per year were removed from the population with a mean age of 5.3 years for females and 6.1 years for males. Females were most vulnerable to harvest at 1-4 years of age and males at 2-4 years. Number of bears removed each year averaged 6% of the population and adult females removed represented 1% of the population. The harvest appeared sustainable due to the male bias and young age of harvested bears. Male-biased harvest was the most likely explanation for the preponderance of females in the population.

Interactions between Polar Bears and Overwintering Walruses in the Central Canadian High Arctic

There are few records of predation by polar bears (Ursus maritimus) on walruses (Odobenus rosmarus), although their distributions overlap extensively. During the late winter and early spring from 1981 through 1989, we recorded interactions between polar bears and walruses in the central Canadian High Arctic, where walrus movements are severely restricted in the winter by limited areas of open water for breathing and haulout holes. Predatory behaviour of bears and anti-predator behaviour of walruses were observed. We found evidence that polar bears made wounding but non-fatal attacks on 3 walruses, killed 3 walruses, and probably killed 4 others. One walrus was frozen out of its breathing hole and vulnerable to predation. Although the vulnerability of walruses to polar bear predation would vary with habitats and seasons, it is clear that polar bears are important predators of walruses in the central Canadian High Arctic in late winter-early spring. Int. Conf. Bear Res. and Manage: 8:351-356 Walrus and polar bear distributions overlap in a variety of habitats and seasons including the floe edge or drifting pack ice throughout the year in some areas, terrestrial haulouts where all the ice has melted in the summer, and polynyas of variable sizes during the winter. The vulnerability of walruses to predation by polar bears may vary significantly among these shared habitats, but there are few confirmed reports of predation (Perry 1966, Kiliaan and Stirling 1978) and little quantitative information about the nature and magnitude of the predation. Most of the observations of interactions between polar bears and walruses have been made at terrestrial or iceedge haulouts or in pack ice. Polar bears are powerful predators, capable of taking large prey such as bearded seals (Erignathus barbatus) (Stirling and Archibald 1977) and belugas (Delphinapterus leucas) (Lowry et al. 1987), but walruses are the largest of the polar bears possible prey, and they are able to use their tusks for defence. Loughrey (1959) felt there was little doubt polar bears prey on calves and subadults, but found factual accounts scarce. Fay (1982) stated that he knew of no confirmed records of predation by bears on walruses. He concluded that contact between polar bears and walruses occurred mainly in summer and that only younger walruses are really vulnerable to predation. Although Fay (1985) listed predation by polar bears as 1 of 3 primary causes of mortality among walrus calves (along with predation by killer whales [Orcinus orca] and crushing), he noted that Mansfield (1958) has calculated that total mortality of walrus calves is low compared to otherpinnipeds. It is hard to assess if this predation would be significant to the population. In the central Canadian High Arctic, small groups of walruses winter in polynyas, including a group of 50100 walruses at the Dundas Polynya at Cape Collins (Fig. 1) on the northeastern tip of Dundas Island (Stirling et al. 1981). Open water where walruses can breathe and feed Fig. 1. Kills or attacks by polar bears on walruses in the Penny Strait and Queens Channel area from 1981 through 1988: 1)10 Apr 1981, confirmed kill of young adult, found partially eaten, tusks <30 cm; 2) 3 Apr 1982, confirmed kill, 1 large bear pulling adult walrus (length 247 cm) from hole, 2 walruses hauled out nearby; 3) 26 Apr 1983, evidence of attack but not kill; 4)12 Apr 1984, young adult female frozen out >2 days, not killed, tusks -20 cm; 5) 19 Mar 1985, possible attack, blood around hole; 6) and 7) 30 Mar 1985, old kill of 1 adult and 1 yearling walrus, carcasses dismembered, adult female polar bear and 2-year cub feeding on them; 8) 30 Mar 1985, confirmed fresh kill of young female walrus, tusks 10 cm, 2 adult bears feeding; 9) 11 Apr 1985, possible attack, blood near hole, bear tracks windblown; 10) 21 Apr 1986, kill of young walrus, length 185 cm, tusks 3.8 cm; 11) 23 Apr 1987, adult male carcass (length >275 cm, tusks 33 cm) at tide crack, probably killed by a polar bear, scavenged by many bears. 352 BEARS-THEIR BIOLOGY AND MANAGEMENT during the winter is maintained there and at several other locations in eastern Penny Strait by strong tidal currents (Topham et al. 1983). In addition, multiyear floes that become grounded in shallow water in the late summer throughout this region will remain frozen in place through the winter. These floes are rocked by tidal currents and winds, creating a border of weaker broken ice where walruses are also able to breathe and haul out. The walruses may remain at these floes for weeks or months at a time (Stirling et al. 1981: Fig. 3). On 2 occasions, Kiliaan and Stirling (1978) found lone walruses, one an adult, the other almost 2-years-old, that had been attacked and killed by a polar bear at a haulout hole. They also reported a kill by Inuit of a walrus at a frozen-over hole, and an observation of an adult walrus that had been attacked by a polar bear but survived. From these observations, they suggested that walruses overwintering in areas with restricted breathing and haulout sites might be more vulnerable to predation, and that predation by polar bears might be more frequent than previously seemed apparent. This paper presents observations of predation by polar bears on both young and adult walruses in a polynya area during the late winter and early spring. We gratefully acknowledge the support of the Polar Continental Shelf Project, the Canadian Wildlife Service, World Wildlife Fund (Canada), and the Department of Fisheries and Oceans. We thank J.J. Burs, Fairbanks; T. Eley and K. Frost, Alaska Department of Fish and Game, Fairbanks; D. Grant, Yellowknife; and M.Taylor, Northwest Territories Department of Renewable Resources, for permission to use their unpublished observations. In the field, we had the help and good company of D. Andriashek, H. Cleator, I. Cote, D. Keith, N. Lunn, B. Sjare, and C. Spencer. S.C. Amstrup, J.J. Burs, A. Derocher, and T.G. Smith provided many helpful comments on an earlier draft of this paper. S. MacEachran drew the figure. METHODS We conducted studies of the biological importance of the Dundas Polynya to overwintering marine mammals in the late winter and early spring from 1981 through 1989. Our observations concentrated on walruses and polar bears and to a lesser extent on ringed seals (Phoca hispida) and bearded seals. We were able to observe polar bears and walruses up to 6 km away almost continually during daylight hours. Visibility was occasionally obscured by poor weather, but it was rarely <2 km. The animals appeared undisturbed by our presence in a hut at the top of a 90-m cliff overlooking the polynya. On an opportunistic basis, we recorded the hunting behaviour of polar bears, occasional interactions between polar bears and walruses, and the behaviour of walruses while hauled out and vulnerable to predation. We used a helicopter to survey Penny Strait and Queens Channel also. On each survey, we followed the same general route north from the Dundas Polynya along the western coast of Devon Island and returned via the middle of Penny Strait and Queens Channel past Hyde Parker Island, the Cheyne Islands, and the northern end of Baillie-Hamilton Island (Fig. 1). The exact route varied within and among years, depending on the distribution of walruses, changes in ice conditions, and prevailing weather conditions. Surveys were conducted 2-6 times each year at approximately 2-week intervals between mid-March and early May and covered a distance of 150-400 km. We flew between about 1000 and 2000 hrs EST, at an altitude of about 70 m and an airspeed of about 100 km/hr. The surveys were primarily to map walrus and polynya distribution and record the underwater vocalizations of walruses and seals for another study, but we also noted all polar bears, polar bear tracks (and an estimation of their freshness), and any indications of interactions between polar bears and walruses. When a walrus carcass was found, ice conditions and presence of bears were noted. When possible, measurements and photographs were taken, and a tooth was collected for age determination. RESULTS AND DISCUSSION Sightings of Polar Bears Polar bears den, hunt and feed on seals, and mate in the study area (Stirling et al. 1984), and bears of all ageand sex-classes were seen on the ice adjacent to the polynya where the walruses haul out to rest. Polar bears hunted along pressure ridges and small refrozen cracks in the area for the subnivean breathing holes and birth lairs of ringed and bearded seals. Bears also searched along the edges of the main polynya and smaller areas of open water and investigated the breathing holes used by walruses, their haulout sites, and the hauled-out walruses themselves. In most years, bears were observed every 2-4 days at Cape Collins (Table 1), but there were some periods when none were seen for several weeks. There were undoubtedly some bears present in the area that were not seen. There was no obvious trend in numbers or correlations among months or years and the number of bears recorded. The variation in numbers of bears seen among years was also independent of the number of walruses present or the POLAR BEAR AND WALRUS INTERACTIONS * Calvert and Stirling 353 Table 1. Number of days of observation at the Dundas Polynya at Cape Collins and number of polar bears seen. Year Month Days of Bears Minimum observation seen bears/day

Evironmental threats to marine mammals in the Canadian Arctic

The Arctic Ocean is the home of three major groups of mammals that depend on the sea for survival and show varying degrees of adaptation for maritime life. Most fully adapted are the whales (Cetacea), which never leave the water, and the seals and walruses (Pinnipedia) that feed entirely at sea but emerge onto land or ice for pupping and basking. Less exclusively marine are two species of the order Carnivora—Polar Bears ( Ursus maritimus ), that seldom live far from the sea because they feed almost entirely upon seals, and Arctic Foxes ( Alopex lagopus ), some of which move out onto the sea ice during the winter, mainly to scavenge on the remains of seals killed by Polar Bears.

St. Matthew Island reindeer crash revisited: Their demise was not nigh—but then, why did they die?

Twenty-nine yearling reindeer (Rangifer tarandus) were released on St. Matthew Island in the Bering Sea Wildlife Refuge in 1944: 24 females and five males. They were reported to have increased to 1350 reindeer by summer 1957 and to 6000 by summer 1963. The 6000 reindeer on St. Matthew Island in summer 1963 were then reduced by 99% to 42 by summer 1966. The evidence suggests that after growing at a high average annual rate of lamda = 1.32 for 19 years, the entire die-off occurred in winter 1963—64, making it the largest single-year crash ever recorded in any R. tarandus population. Although a supposedly meaningful decline in successful reproduction and early survival of calves was originally reported for the population between 1957 and 1963, our reevaluation indicates this is an error resulting from the wrong sample being used in the between-year comparison. The quantitative data indicate no meaningful change occurred, and the calf:cow ratio was about 60 calves:100 cows in both 1957 and 1963. Calf production and survival were high up to the crash, and in the die-off population the age distribution (72%, 1—3 years old) and the sex ratio (69 males:100 females) reflected a still fast-growing R. tarandus population. All of these parameters do not support the hypothesis that the limited abundance of the absolute food supply was at a lethal level between 1957 and 1963 or in winter 1963—64. We now know from other studies that a high density of R. tarandus is not a prerequisite for a major single-year winter die-off. Existing population dynamics data do not support lack of lichens as a major causative factor in this single-year crash. If a decline had been caused by the limitation of the absolute food supply, it would have followed a multi-year pattern—it would not have been a single-year event. There was no evidence of a sudden, massive, island-wide loss of the absolute food supply, or that its nutritional value was inadequate for sustaining the reindeer. Mean weights of reindeer by sex and age class declined between 1957 and 1963, but only to levels similar to those of mainland reindeer. The reindeer population on St. Matthew Island undoubtedly was or soon would have been seriously influenced by heavy use of the lichens and the future did not bode well for continued population growth. Although the food supply through interaction with climatic factors was proposed as the dominant population-regulating mechanism, a general acceptance that only density-dependent food-limitation was necessary to cause the crash remains strong in some quarters. We challenge this; we believe that the winter weather was the all-important factor that led to the premature, extreme, and exceptionally rapid, near total single-year loss of 99% of the reindeer on St. Matthew Island in winter 1963—64.

Rethinking the basic conservation unit and associated protocol for augmentation of an "endangered" caribou population: An opinion

Use of the subspecies as the basic unit in the conservation of endangered caribou (Rangifer tarandus) would produce a “melting pot” end-product that would mask important genotypic, phenotypic, ecological, and behavioral variations found below the level of the subspecies. Therefore, we examined options for establishing the basic conservation unit for an endangered caribou population: use of subspecies based on taxonomy, subspecies based solely on mtDNA, Evolutionarily Significant Units, and the geographic population. We reject the first three and conclude that the only feasible basic unit for biologically and ecologically sound conservation of endangered caribou in North America is the geographic population. Conservation of endangered caribou at the level of the geographic population is necessary to identify and maintain current biodiversity. As deliberations about endangered caribou conservation often involve consideration of population augmentation, we also discuss the appropriate augmentation protocol for conserving biodiversity. Management of a critically endangered caribou population by augmentation should only be initiated after adequate study and evaluation of the genotype, phenotype, ecology, and behavior for both the endangered caribou and the potential‘donor’ caribou to prevent the possible ‘contamination’ of the endangered caribou. Translocation of caribou into an endangered population will have failed, even if the restocking efforts succeed, if the donor animals functionally alter the population’s gene pool or phenotype, or alter the ecological and behavioral adaptations of individuals in the endangered population. Most importantly, a seriously flawed restocking would risk irreversibly altering those functional characteristics of caribou in an endangered population that make them distinct and possibly unique. It might even result in the loss of the endangered population, thus eliminating a uniquely evolved line from among the caribou species.