U.S. Geological Survey Reports on Polar Bear Population Status in the U.S. and Canada
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Polar Bear Population Status in Southern Hudson Bay, Canada
--Nichole Hoskin 16:09, 20 August 2008 (EST)
“The Southern Hudson Bay (SH) population of polar bears (Ursus maritimus) resides in a seasonal sea ice environment and is the most southerly population in the species’ range. Therefore, SH polar bears may be among the first to show negative effects associated with climate warming and consequent loss of sea ice. Polar bears in the neighboring Western Hudson Bay (WH) population have declined significantly in body condition since the mid-1980s, and a recent study indicated that the size of the WH population declined by about 22% between 1987 and 2004. Similarly, SH bears have shown a significant decline in body condition since the mid-1980s, and an assessment of the current status of the SH population was therefore needed. We applied open population capture-recapture models to data collected from 1984-86 and 1999-2005 to estimate population size and survival. The size of the SH population appears to be unchanged from the mid-1980s (1984-1986: 641, 95% CI = 401, 881) vs. 2003-2005: 681 (95% CI = 401, 961).”[1]
“This, combined with the evidence of significant declines in body condition for all age and sex classes, which were greatest for pregnant females and subadults, suggests this population may be under increased stress at this time. However, we did not find any clear association between survival and cub-of-the-year body condition, average body condition for the age class, or extent of ice cover in our data. This lack of association could be real or attributable to the coarse scale of our average body condition measure, or to limited sample size and few years of intensive sampling. That the WH population appears to be in decline, but the SH population does not, might be explained by changes to sea ice patterns which to date have been greater in the western half of Hudson Bay (breakup 10 days earlier per decade) than in the eastern and southern portions of Hudson Bay (breakup 5-8 days earlier per decade).”[2]
“Sea ice characteristics and dynamics differ among broad regions of the Arctic, resulting in regional differences in polar bear ecology. In their forecast of future status of polar bears worldwide, Amstrup et al. recognized four ecoregions based upon differences in historic and projected sea ice conditions. Predicted impacts of climatic warming may occur first for populations near the southern edge of the range in James Bay and Hudson Bay.”[3]
“In particular, earlier break-up of sea ice likely reduces opportunities for polar bears to feed and acquire stored reserves needed to sustain them during prolonged fasting during the ice-free season — a major ecological stressor for bears inhabiting Hudson Bay.”[4]
“In contrast to populations of polar bears at higher latitudes in the Archipelago Ecoregion of the Canadian Arctic and the two ecoregions of the Polar Basin, in the Hudson Bay system as well as in Davis Strait and Baffin Bay, the bears are forced ashore every summer because the ice melts completely each year.”[5]
“Because currents flow counter-clockwise in Hudson Bay and prevailing winds are often north-westerly, remnant ice usually occurs latest in the year off the Ontario coast. The entire Bay is generally completely free of ice from mid-August or earlier to late October or later, and the Hudson Bay coast of Ontario is ice-free from mid-August until early December in most years. As a result, bears spend 4-5 months ashore until freeze-up in mid-November to early December.”[6]
“During the period ashore bears generally fast, surviving on adipose stores (Watts and Hansen 1987, Ramsay and Stirling 1988). However, when on land, polar bears in Hudson Bay and James Bay have been documented to feed on marine algae, terrestrial vegetation such as grasses, sedges, mosses, lichen, and berries of arctic blueberry (Vaccinium uliginosum) and crowberry (Empetrum nigrum), and flightless snow geese (Anser caerulescens) and other vertebrates. They may also feed opportunistically on such items as eggs of Canada geese (Branta canadensis), and have been recorded attempting to prey on caribou (Rangifer tarandus). Along the Ontario coast in late summer and fall, polar bears have been observed to scavenge carcasses of beluga whale (Delphinapterus leucas), and to capture live ringed seals (Phoca hispida) and bearded seals (Erignathus barbatus) apparently stranded at low tide, and walrus (Odobenus rosmarus) on an off-shore haul-out. Nevertheless, the significance to a bear’s yearly energy budget of these sources obtained opportunistically during the ice-free season is not well understood, but is likely to not be significant at the population level. The most important feeding period for bears in Hudson Bay is on the sea ice from early April to July when the major prey is ringed seals.”[7]
“Nevertheless, the significance to a bear’s yearly energy budget of these sources obtained opportunistically during the ice-free season is not well understood, but is likely to not be significant at the population level. The most important feeding period for bears in Hudson Bay is on the sea ice from early April to July when the major prey is ringed seals.”[8]
“The size of the SH population was estimated to be 763 ± 323 animals based on a capture-recapture study conducted from 1984-86.”[9]
“The neighbouring WH population showed a significant decline in body condition and natality from 1981-1997. A recent study estimated that the size of the WH population declined from 1194 (95% CI = 1020-1368) bears in 1987 to 935 (95% CI = 794-1076) in 2004. Demographic declines in western Hudson Bay were apparently associated with a 2-3°C rise in spring air temperatures over the past 50 years, which have caused the sea ice to break up in the spring about 3 weeks earlier than it did 30 years ago.”[10]
“Model averaged estimates of abundance, including model selection uncertainty, were similar between the periods 1984-1986 and 2003-2005 (Figure 7). The average number of bears estimated during 1984–1986 was 641 individuals (95% CI = 401, 881). The average number of bears estimated during 2003–2005 was 681 individuals (95% CI = 401, 961).”[11]
“Abundance in the Southern Hudson Bay population was unchanged between two intensive capture-recapture periods, which were separated by almost 20 years (1984–86 vs. 2003–05). This was so despite the evidence for a decline of 22% in abundance for the neighbouring Western Hudson Bay population over roughly the same period.”[12]
Polar Bear Population Status in the Northern Beaufort Sea
--Nichole Hoskin 16:52, 20 August 2008 (EST)
“The Northern Beaufort (NB) Sea polar bear (Ursus maritimus) population is situated on the perimeter of the polar basin in a region where sea ice converges on shorelines throughout most of the year. In this study, we present data on the status of this population, based on our research between 1971 and 2006. We applied open population capture-recapture models to data collected from 1971-2006 to assess the relationship between polar bear survival and sex, age, time period, and a number of environmental covariates.”[13]
“The model-averaged estimate of population size from 2004 to 2006 = 980 (± 155, 95% CI) and was not significantly different from estimates for the periods of 1972 to 1975 and 1985 to 1987 of 745 (± 246, 95% CI) and 867 (± 141, 95% CI), respectively. These abundance estimates apply primarily to that segment of the NB population residing west and south of Banks Island to the mainland coast, plus a relatively small but unknown fraction of the population residing further north around Prince Patrick Island. In 1992 to 1994, a capture effort focused in the area around Prince Patrick Island confirmed significant mixing between northern and southern segments of the population, that some bears residing in the extreme northern portions of the population may not have been equally available for capture during other sampling periods, and that the number of polar bears around Prince Patrick Island was not large relative to the rest of the population. Thus, we consider our estimates of total abundance during the other three sampling periods to be slightly low. Currently the NB polar bear population appears to be stable, probably because ice conditions remain suitable for feeding through much of the summer and fall in most years and the Inuvialuit harvest has not exceeded sustainable levels.”[14]
“Polar bears are distributed throughout the ice-covered waters of the circumpolar Arctic in 19 relatively discrete populations. Their preferred habitat is the annual ice over the relatively shallower waters of the continental shelf and inter-island channels of various archipelagos, which are more biologically productive and where seals are more abundant than in the deep polar basin. Although polar bears may occasionally capture a seal in open water, they are fundamentally dependent upon sea ice as a platform from which to hunt seals in both winter and summer. Thus, changes in the distribution, total amount, and types of sea ice, and the patterns of freeze-up and breakup, have the potential to influence significantly the survival and reproductive success of polar bears. For example, progressively earlier breakup of the sea ice in Western (WH) and Southern (SH) Hudson Bay, because of climate warming, has shortened the critical polar bear feeding period in late spring and early summer. The shortened feeding period causes bears to be in poorer condition when they come ashore to fast through the open-water season until freeze-up later in the fall. In WH, the deterioration of physical condition has further resulted in lowered reproductive and survival rates, and a decline in the total population size. Stirling and Parkinson also predict that if climate warming in the Arctic continues as projected by the Intergovernmental Panel on Climate Change, then the trend toward progressively earlier breakup and a longer ice-free period in Hudson Bay would continue, and the SH polar bear population would decline, as well as would adjacent populations, where bears also fast on their stored fat reserves through an extended open-water period in summer and fall.”[15]
“In polar bear populations such as the Southern Beaufort Sea (SB) and NB that are distributed around the southern edge of the polar basin, where the annual ice along the coast melts in early summer, the bears move north to remain on ice along the southern edges of the polar pack, where they can continue to hunt seals until the ice re-freezes again in fall.”[16]
“Since 1979, when it first became possible to monitor patterns of break- and freeze-up of sea ice over the entire Arctic Ocean using satellite images, the total amount of ice remaining at the annual minimum in late summer has declined at a rate of 9.8% per decade. In recent years, there have been several record sea ice minima in the Arctic. One consequence has been a shift of the southern edge of the pack ice over much of the Beaufort and Chukchi seas, from remaining over the continental shelf in summer and fall, to being positioned further north, away from the shelf and over the deep polar basin where biological productivity is much lower. Correlated with the trend toward a longer open-water season and sea ice being further offshore, there have been several indications that the polar bear population in the SB is being nutritionally stressed, and it now appears to be in decline due to decreased recruitment.
In contrast, through most of the open-water period in the NB, at least some sea ice remains over the continental shelf along the west coast of Banks and Prince Patrick islands, M’Clure Strait, and often into western Amundsen Gulf, south of Sachs Harbor. Thus, in most years, the bears still have access to ice over the continental shelf, where seals are more available than they are over the deep polar basin. Possibly because of that difference, polar bears in the NB have been in better overall condition than those in the SB, through 2003-2006 at least.”[17]
“Since 1968, the NB polar bear population has also been harvested by Inuvialuit hunters under a quota system. Between 1968 and the present, the annual quota has increased from 36 to 65, partly because scientific studies have suggested that a higher annual harvest level could be sustained and partly as a result of arbitrary (non-biological) re-assignment of portions of adjacent quotas by management agencies (unpublished data). Using estimates from the previous study of population abundance as a basis, a population size of 1200 was agreed upon for management purposes and a sustainable annual harvest of 54 was recommended, based on calculations in Taylor et al.”[18]
“Overall, estimates of abundance were remarkably similar through the 1970s, 1980s, and 2000s (Figure 6; Table 9). The average numbers of bears estimated to be in this segment of the population during each decade were as follows: 1972 to 1975 = 745 (± 246, 95% CI), 1985 to 1987 = 867 (± 141, 95% CI), 1992 to 1994 = 289 (± 62, 95% CI), and during 2004 to 2006 = 980 (± 155, 95% CI). Estimates during the 1990s were lower but, as previously stated, capture effort was also focused on the area between the north-western corner of Bank Island to the west coast of Prince Patrick Island during that period. These results are not included when considering long term trends in NB. Note that the confidence interval on the size estimate in 2006 (i.e., 617 bears ± 220 95CI) did not overlap the confidence interval for the size estimate in 2005, indicating a significant decline in 2006 relative to 2005, in statistical terms at least.”[19]
"Previous to this study only one other study directly estimated the size of the NB polar bear population. Stirling et al. used a capture-recapture analysis following DeMaster et al. and the Fisher-Ford method to estimate population size from 1985-1987. The point estimates from the latter method were very similar to those of our estimates while the confidence intervals from analysis indicated the estimates were not significantly different from the estimates derived by DeMaster et al.
We produced population size estimates for years of intensive capture effort. However, for estimation of average population size during the major capture-recapture periods, we considered only estimates made in years when the annual capture sample exceeded 50The only intensive capture years with fewer than 50 captures were 1972, 1989, and 1992 –1994. Excluding these years, the three averaged decadal estimates for the mid-1970s, mid-1980s, and 2000s were 745 ± 246 (95% CI867 ± 141 (95% CI), and 980 ± 155 (95% CI). For reasons stated below, we believe these estimates include nearly all bears in NB, but should be considered slightly low. Unfortunately, we cannot objectively show much too low these estimates might be.”[20]
“Although there is a trend in the point estimates toward a slow increase in population size over these time periods, the averaged estimates are not significantly different from each other statistically. However, Stirling reported that in the 1970s, polar bears in the Canadian sector of the Beaufort Sea were recovering from a period of overharvest that ceased only when quotas were established in 1968. In the decade or more that followed, the average age of both males and females increased from about 4 to about 8, after they fluctuated over a narrower range, apparently in relation to fluctuations in conditions and ringed seal productivity. Similarly, in the early 1970s when the population was still in the early stages of recovery from being overharvested, there few bears older than 10 years of age. For example, in harvest samples collected between 1970 – 1971 and 1972 – 1973, the oldest animal recorded was only 11 years old, and the next oldest bears were both 8 years old. By the late 1970s, the proportion of bears 10 years of age or older had increased to 20 – 30% for males and slightly more for females, after which there were decadal-scale fluctuations similar to those of the average age. Taken together, these data suggest that, even though the estimates for the three periods were not statistically different, it is likely the population increased in size from the early 1970s into the 1980s, after which it remained relatively stable.”[21]
“The reduced estimate of population size in 2006 should be viewed with caution because the last capture probability and the last survival parameter are confounded in standard CJS models, and it is unclear what extent of confounding may exist between these parameters in our model because we included individual covariates... In other words, used the relationship between covariates and capture probability to estimate size in 2006, even though capture probability that year was not separately estimable. Also, partly because of the poor weather during the 2006 capture season, we obtained a smaller capture sample than in previous years despite flying a similar number of kilometres in search of polar bears. However the recapture rate (19%) was double that of the previous two years (8% and 9%) which would also have the effect of reducing the estimate of population size. The estimates of 1100-1200 in 2004 and 2005 may more accurately reflect the current number of polar bears in NB. The averaged population estimate for the 1990s was 289 ± 62 (95% CI), which is significantly lower than for the other three sampling periods. Despite our efforts to model reduced capture probability of southern bears in the 1990s using period and other effects, we may not have succeeded fully, and it is difficult to determine mathematically whether the decline in the 1990s is real or an artifact of sampling. However, estimates for the 1990s are not directly comparable to those of the other three study periods because much of the area sampled during the three main years (1992-1994) was north of the northern limit of most of the areas surveyed in the other main periods and very little was done near Sachs Harbor.” [22]
“Additionally, the averaged population estimate of only 289 ± 62 (95% CI) appears to confirm that polar bears are not as abundant in the most northerly areas in spring as they were further south along the western and southern coasts of Banks Island and in Amundsen Gulf. All this leads us to believe that the segment of the NB population in the north that was uncatchable (probability of capture = 0) during the primary study periods, if it existed at all, was small and inconsequential. Unfortunately, we cannot objectively estimate the fraction of the overall population that was sampled during the primary periods. We conclude that our abundance estimates during primary sampling periods are for a large but unknown fraction of the overall NB population, and should be considered slightly low.”[23]
Polar Bear Population Status in the Southern Beaufort Sea
“Polar bears depend entirely on sea ice for survival. In recent years, a warming climate has caused major changes in the Arctic sea ice environment, leading to concerns regarding the status of polar bear populations. Here we present findings from long-term studies of polar bears in the southern Beaufort Sea (SBS) region of the U.S. and Canada, which are relevant to these concerns. We applied open population capture-recapture models to data collected from 2001 to 2006, and estimated there were 1,526 (95% CI = 1,211; 1,841) polar bears in the SBS region in 2006. The number of polar bears in this region was previously estimated to be approximately 1,800. Because precision of earlier estimates was low, our current estimate of population size and the earlier ones cannot be statistically differentiated. For the 2001–06 period, the best fitting capture-recapture model provided estimates of total apparent survival of 0.43 for cubs of the year (COYs), and 0.92 for all polar bears older than COYs. Because the survival rates for older polar bears included multiple sex and age strata, they could not be compared to previous estimates.”[24]
“In western Hudson Bay, Canada, a significant decline in population size was preceded by observed declines in cub survival and physical stature. The evidence of declining recruitment and body size reported here, therefore, suggests vigilance regarding the future of polar bears in the SBS region.”[25]
“Polar bears residing in the southern Beaufort Sea (SBS) region of the U.S. and Canada have been studied since 1967. Results of these studies provide insights into how changes in the environment may affect the status of polar bears in this region.”[26]
“To determine sustainable harvest levels, early polar bear research in the SBS region was focused on estimating population size and developing indices of recruitment and survival which could be used to evaluate trends in population status. The size of the SBS polar bear population was first estimated to be approximately 1,800 animals in 1986.”[27]
“Throughout the 1980s and early 1990s, empirical observations such as the frequency of encounters of polar bears during research flights over the sea ice, increased sightings of polar bears near onshore human settlements, and increasing numbers of maternal dens observed on land, suggested that the population of the SBS region was increasing.”[28]
“That analysis was limited to female polar bears because research objectives resulted in the under-sampling of males in some years. The estimate of 1,180 females (95% CI = 635; 1,725) for the late 1980s was consistent with the previous estimate of at least 1,800 total polar bears (i.e., females and males) in the SBS region at that time. For the late 1990s, the estimated number of females developed by Amstrup and others suggested that the total population may have increased to as many as 2,500 polar bears.”[29]
“We initiated a new study in 2001, to re-assess the status of the SBS polar bear population and to address the potential effects, on polar bear status, of changing sea ice conditions in the Arctic basin. Here we present estimates of survival and population size derived from capture-recapture data collected from 2001 to 2006, and compare these estimates to those developed earlier. We also document changes in the productivity and physical stature of polar bears using data collected from the late 1960s through the present.”[30]
“In our analysis of the 2001–06 data, we did not find clear evidence for a relationship between sea ice coverage in the SBS region (i.e., the covariate ice) and survival. However, this should be interpreted in light of the short duration of the study and the limitations of the data. Polar bears are long-lived mammals that are well adapted to periods of resource shortage. Our study may not have been long enough, and may not have included enough interannual variation in sea ice, to detect a significant relationship between changing sea ice and survival.”[31]
“Because polar bears are entirely dependent on sea ice for foraging, reduced access to sea ice translates directly into reduced feeding opportunity. In other parts of the polar bear range, reductions in the spatiotemporal availability of sea ice have been shown to negatively impact polar bear stature, productivity, and survival of juvenile, subadult and senescent animals.”[32]
“Our best estimate of the population size for the SBS region was 1,526 polar bears (95% CI = 1,211; 1,841). We believe that this estimate—the mean for the period 2004–06—is relatively unbiased for several reasons.”[33]
“Amstrup and others estimated that there were 1,180 (95% CI = 635; 1,725) female polar bears in the SBS region in the late 1980s. Sample sizes during this period were similar to those in the 2001–06 study, which allows for a reasonable comparison of estimated population sizes. If the sex ratio of the population in the late 1980s was similar to what (54 percent female) we estimated for the 2001–06 period, the Amstrup and others female-only estimate corresponded to a total population size in the late 1980s of approximately 2,185 polar bears. Because the estimate and confidence interval were calculated for females only, however, we do not know the statistical variance associated with this estimate of the total population size. We do know, however, that the variance associated with the estimate of the total population was necessarily greater than the variance for the female-only estimate (SE = 278). Therefore, the confidence interval around the total population size estimate of 2,185 must have exhibited considerable overlap with the confidence interval around the current estimate of 1,526 (95% CI = 1,211; 1,841). This overlap, in conjunction with the similarity between the current estimate and the original Amstrup and others estimate of 1,800 (95% CI not available), precludes a statistical determination that the total number of polar bears in the SBS region has changed in recent years.”[34]
“Estimating the size of wildlife populations is inherently difficult. This is especially true for animals that occur at low densities in remote regions, because of the potential for bias introduced by heterogeneity in recapture probability (e.g., due to differences in distribution, behaviour, sightability). We believe that the estimated population sizes for 2004–06 are accurate.”[35]
“In our analysis of cub production data, we controlled for the first source of bias by excluding capture data from March. For the 1967–89 period, however, spring samples still included a higher proportion of yearlings than of COYs. This suggests that the under-representation of COYs in the spring sample for the early period was due to bears that denned far offshore. Indeed, new analyses of the distribution of denning in the U.S. portion of the SBS region confirm that more bears denned in far offshore regions in early years of polar bears studies than in the recent decade. We attribute this shift in denning distribution to sea ice conditions that have become less suitable as a substrate for denning.”[36]
“The suspected shift over time towards more onshore denning cannot account for the profound decline in the number of COYs per adult female captured in the autumn (0.61 versus 0.25). During the freeze-up period of our autumn sampling, polar bears in the SBS region are concentrated in the nearshore areas where they are highly vulnerable to capture by shore-based research crews. Therefore, the observed decline in the number of COYs per adult female captured in the autumn must reflect an actual decline in the survival of cubs between den emergence and the autumn sampling period, and not a sampling artifact. This decline in turn appears to be the principal cause of the increase in COYs and decrease in yearlings that we observed in the spring capture data after 1989.”[37]
“Observed changes in the physical stature of polar bears in the SBS region appear to parallel declines in recruitment. Declines in skull size for both COYs and adult males were significant. The decline in body weight for adult males was significant. Such changes in physical stature may suggest different impacts of reduced summer sea ice on adult male and female polar bears. In the spring, adult males often forgo foraging opportunities and focus their efforts on locating females for mating. Therefore, adult males enter the summer period in relatively poorer nutritional condition. They may then be more vulnerable to summer sea ice retreats, which can separate polar bears from foraging habitats thought to be the most productive. Conversely, reduced foraging opportunity for adult females usually is first reflected in poorer survival of young. Although the average body weight of COYs did not decline significantly between the two periods, their weights were slightly lower in the latter period. Evidence from other portions of the polar bear’s range suggest lower weights, combined with significantly smaller skull sizes, may be related to the poorer survival we observed for COYs in recent years.”[38]
“In western Hudson Bay, Canada, which is near the southern extreme of the species range, declines in cub survival and physical stature were recorded for years before a statistically significant decline in population size was confirmed. In western Hudson Bay, we associated the decline in population size with reduced survival of juvenile polar bears and adults that were beyond prime ages. Poorer survival of animals in those age classes was directly related to the reduced availability of sea ice. The situation in western Hudson Bay offers insight into the future status of polar bears in more northern regions such as the SBS, because recently observed declines in the area and extent of sea ice are predicted to continue throughout the polar basin.”[39]
“Evidence of declining physical stature and poorer survival of COYs in the SBS region is consistent with other observations, which suggest that changes in the sea ice may be adversely affecting polar bears. Previously, human harvest accounted for most documented polar bear mortalities in the SBS region. In contrast, several recently observed mortalities were directly related to sea ice retreat, or appeared related to changes in food availability that may be associated with sea ice retreat. In autumn of 2004, four polar bears were observed to have drowned while attempting to swim between shore and the distant pack ice. Despite offshore surveys extending back to 1987, similar observations had not previously been recorded. During winter and early spring of 2004, three observations were recorded of polar bears hunting, killing, and consuming other polar bears in the Beaufort Sea. Similar observations had not been recorded in that region despite studies extending back for decades. In spring of 2006, three adult female polar bears and one yearling were found dead. Two of these females and the yearling had depleted their lipid stores and apparently starved to death. Although the third adult female was too heavily scavenged to determine a cause of death, her death appeared unusual because prime age females have had very high survival rates in the past. Similarly, the yearling that was found starved was the offspring of another radio-collared prime age female that had recently disappeared from the airwaves. Annual survival of yearlings, given survival of their mother, was previously estimated to be 0.86. Therefore, the probability that this yearling died while its mother was still alive was only approximately 14 percent. These anecdotal observations, in combination with both the changes in survival of young and in physical stature reported here, suggest mechanisms by which a changing sea ice environment can affect polar bear demographics and the status of populations.”[40]
“Information on changes in survival and physical stature, reported here, indicate that the status of polar bears in the SBS region is changing. Annual survival rates of COYs estimated from the 2001 to 2006 capture-recapture study were lower than survival rates estimated in previous studies. The increased loss of cubs during the first 6 months of life may be associated with the smaller physical stature of COYs observed in recent years. The smaller physical stature of COYs was paralleled by a smaller physical stature of adult males, even though the average age of adult males has increased. Despite these indicators of a declining status for the SBS polar bear population, our best estimate of the current size of the population does not show a statistically significant decline. This may mean there has been no change in numbers in recent years, or it could reflect insufficient precision in current and past estimates to resolve such a change. Although our 2001–06 capture-recapture study did not provide evidence for a change in the size of the SBS polar bear population, significant changes in cub survival and physical stature must ultimately have population level effects. Lowered body weight has been implicated in declining survival of polar bear cubs in western Hudson Bay, Canada. There, reduced cub survival, associated with declines in physical stature caused by reduced foraging opportunity, was recorded long before a statistically significant decline in population size was confirmed. The relationship between decreased availability of sea ice and declining population size in western Hudson Bay, which is near the southern extreme of polar bear range, is cause for concern regarding the future status of polar bears in more northern regions such as the SBS. Because more profound declines in sea ice area and extent are predicted for these northern regions, continued monitoring and conservative management of the SBS polar bear population is warranted.”[41]
Polar Bears in the Southern Beaufort Sea I: Survival and Breeding in Relation to Sea Ice Conditions, 2001-2006
References
--Nichole Hoskin 17:57, 20 August 2008 (EST)
1. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 5.
2. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 5.
3. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 6.
4. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 6.
5. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 6.
6. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 6.
7. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 6.
8. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 7.
9. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 7.
10. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 7.
11. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, p 15.
12. Martyn E. Obbard, Trent L. McDonald, Eric J. Howe, Eric V. Regehr and Evan S. Richardson, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in Southern Hudson Bay, Canada, pp 16-17
13. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 1.
14. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 1.
15. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 2.
16. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 2.
17. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, pp 2-3.
18. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 3.
19. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, pp 10-11.
20. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, pp 12-13.
21. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 13.
22. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 13.
23. Ian Stirling, Trent L. McDonald, Evan S. Richardson and Eric V. Regehr, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bear Population Status in the Northern Beaufort Sea, p 14.
24. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 1.
25. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 1.
26. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 1.
27. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 1.
28. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 2.
29. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 2.
30. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 2.
31. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 12.
32. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 12.
33. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 12.
34. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 12.
35. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 12.
36. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 13.
37. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 13.
38. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 13.
39. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 13.
40. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, pp 13-14.
41. Eric V. Regehr, Steven C. Amstrup and Ian Stirling, USGS, Polar Bear Population Status in the Southern Beaufort Sea, p 14.
42. Eric V. Regehr, Christine M. Hunter, Hal Caswell, Steven C. Amstrup, and Ian Stirling, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bears in the Southern Beaufort Sea I: Survival and Breeding in Relation to Sea Ice Condition, 2001-2006, p 7.
43. Eric V. Regehr, Christine M. Hunter, Hal Caswell, Steven C. Amstrup, and Ian Stirling, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bears in the Southern Beaufort Sea I: Survival and Breeding in Relation to Sea Ice Condition, 2001-2006, p 7.
44. Eric V. Regehr, Christine M. Hunter, Hal Caswell, Steven C. Amstrup, and Ian Stirling, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bears in the Southern Beaufort Sea I: Survival and Breeding in Relation to Sea Ice Condition, 2001-2006, p 7.
45. Eric V. Regehr, Christine M. Hunter, Hal Caswell, Steven C. Amstrup, and Ian Stirling, USGS Science Strategy to Support U.S. Fish and Wildlife Service Polar Bear Listing Decision: Polar Bears in the Southern Beaufort Sea I: Survival and Breeding in Relation to Sea Ice Condition, 2001-2006, p 7.
