Polar bears never hesitate to swim as a matter of fact they love spending hours in water. There is a reason why they are also called marine mammals. They will cover kilometers 62 miles in a single journey with ease. One of bears holds the highest record in which it covered as much as mi km in a single venture. She swam in the icy cold water of the Bering Sea. After taking rest for few hours she resumed her journey and covered another 1, miles 1, km.
This shows that polar bears are no less than other marine mammals in their swimming traits. Scientists also observed swimming records of several female polar bears in the southern Beaufort Sea. Coastal space use was overrepresented in this study: two-thirds of the polar bears were considered to belong to the local ecotype, while this group as a whole constitutes maybe only a tenth of the subpopulation 17 , While the analysis indicated broadly similar patterns in the amount and timing of swimming performed by local polar bears and offshore polar bears, differences may have been masked by the large individual variation in aquatic behaviour and relatively small sample for polar bears using the offshore strategy.
This is the first report of the diving capabilities of polar bears based on data from biologging instruments. However, they are clearly physically and behaviourally capable of diving to greater depths. One individual in the study stood out in this regard, by diving more regularly to greater depths. This individual might be a specialist in aquatic stalking, as she also dove when she was offshore in the drifting sea ice. Alongside swimming below ice floes during aquatic stalking, accessing coastal underwater resources such as cadavers or seaweed are likely reasons for the dives made by polar bears in this study.
It is well documented that macroalgae is part of the polar bear diet 1 , 6 , The maximum dive depth reported in this study was Within this depth range, breath-hold abilities are not likely to limit the depth of dives. The Barents Sea subpopulation of polar bears has experienced the largest reduction in sea ice of all the subpopulations of polar bears throughout the circumpolar Arctic in recent decades The extended ice-free season has already had clear effects on strategic choices by polar bears such as their choice of denning areas, with traditional core denning habitats on some islands now rarely being accessible for use due to late arrival of winter sea ice or poor sea ice conditions 32 , While polar bears in Svalbard do swim between the islands within the archipelago, and between these islands and the MIZ, they do not seem to swim south to reach their traditional denning islands in autumn.
Offshore bears have the option of denning in Franz Josef Land, the Russian archipelago east and north of Svalbard, and an observed reduction in the number of dens in the eastern parts of Svalbard is thought to reflect an ongoing shift in preferred denning areas Offshore females with COYs that have denned in Svalbard may at some point have to choose between staying locally in Svalbard the first summer after denning, or risking losing their offspring on a long swim, as the pack ice continues to move farther away from Svalbard earlier in the summer.
Local polar bears staying in Svalbard will face somewhat different challenges when dealing with shorter seasons with sea ice: reduced extent and duration of traditionally good seal hunting habitat, altered prey availability and access. Individuals that master aquatic stalking or other specialized, alternative hunting strategies may have an advantage in the coming decades.
When and how polar bears undertake swimming and diving is an integral part of their overall ecological strategy, which includes hunting strategies or, more broadly, diet , energetics, reproductive strategies and risk management. Any extra energetic costs incurred via swimming, diving, or walking long distances, might be compensated for by enhanced access to better hunting areas or other types of food resources, higher hunting success, or higher quality denning or mating areas.
This study quantified the amount of swimming done by female polar bears in the Barents Sea subpopulation, with the results indicating that it may be a more important behaviour than previously thought, especially for some individuals.
This study did not attempt to discern or disentangle impacts on fitness of the various strategies used by the polar bears. Some strategies employed by Svalbard bears involve more swimming and diving, or increased likelihood of long distance swimming, than others. As the sea ice in the Arctic and in the Barents Sea in particular, continues to change and decline, the energetics costs, feasibility or risks associated with each strategy may be shifting.
This study indicates that in the face of these changes, polar bears have the possibility to include extensive swimming in their strategy. It may become an important skill that will allow them to persist in an altered habitat - but only if the overall strategy is and remains profitable. This study was based on data from 57 adult female polar bears that were captured in Svalbard and equipped with various biologging devices with saltwater switches and pressure sensors that detect marine immersions and diving depths Table 1 ; additional details in Appendix 1.
These devices included two polar bear collar types with integrated sensors. The TDRs are archival tags that need to be retrieved to access the data, a sample size of 29 resulted from deployments. In all these various designs the saltwater switch was located low on the collar so that it was submerged when a polar bear was swimming normally. Captures of polar bears for collar deployments and retrievals followed standard protocols Stirling et al. Some individuals were instrumented in more than one year with different combinations of the equipment described above consecutively or simultaneously.
All animal handling protocols were approved by the Norwegian Animal Research Authority. The work was carried out in accordance with the relevant guidelines and regulations and under the permit of the Governor of Svalbard. Time spent in water and the probability of swimming were explored in relation to season, reproductive status whether females are accompanied by cubs, and the age of the cubs , and offshore or local space use strategies.
The descriptive summaries presented are based on different subsets of the data, provided by the different tag types described above.
Hence, the sample sizes vary for the different analyses. Mean values of time spend in water were calculated monthly for each polar bear, but never based on fewer than five days of data. Three polar bears were not included in any of the analyses based on monthly means because their short or intermittent data records did not meet this criterion for any months. Dive depths are only shown from the six polar bears with SMRU collars that were recaptured and whose complete diving record could be downloaded.
A recorded swim with a maximum depth indicating the polar bear had been fully submerged e. Daily maximum depths were used in the summary of dive depths, as these gave a standardized measure against time.
Polar bear reproductive status, i. Females captured in April that had been in a maternity den that winter had COYs, which are about 4 months old during the spring tagging campaigns. Alternatively, females could be alone or accompanied by yearling cubs about 16 months old.
Females accompanied by two-year-olds about 28 months old were classified in this study as being alone, because mothers and cubs separate around this time. Some females with COYs and yearlings undoubtedly lost their cubs at some time during the year, but the timing of such a potential cub-loss was not known. Any instrumented females that were recaptured post-tag-deployment with yearling s or two-year-old s , were known to have been accompanied by COY s or yearling s during the previous year.
Time in water was compared across polar bears of different reproductive status by month, and statistical inference was based on a simple linear model with cub s age as the single predictor using data from each month. An initial comparison of polar bears with yearlings and polar bears with no cubs was made, to explore whether they could be pooled in a comparison against females with COYs.
The comparison was limited to spring and summer months as sample size was small for the autumn months. Monthly time in water was compared for the two main behavioural strategies that exist in the subpopulation 16 , Whether polar bears stay coastal or go offshore was classified by visual inspection of the tracking data. Five polar bears could not be classified because their tracks did not span an entire summer.
Example tracks with location and time in water for three polar bears N, N, and N were chosen to illustrate individual strategies that involve swimming to different degrees.
These three polar bears also showed three different types of swimming: coastal swimming at glacier fronts, likely associated with hunting, coastal swimming that was directional, and swimming during transits between land and the MIZ. Long-distance swims are described with distances and swimming durations. Because GPS locations were not acquired when a polar bear was in water antenna submerged , locations during directional movements transit trips and coastal trips were interpolated between two known GPS positions, and these were considered the start and end of each trip.
How swimming behaviour varied with sea ice concentration when polar bears were not close to shore was modelled using generalized additive mixed effect models GAMMs. The models were fitted to a subset of the data for which both GPS-tracks and time-in-water data were available. Swimming data were allocated to geographical areas according to GPS positions from the collars. This interval was chosen to avoid long periods of interpolation, while allowing for moderate gaps in the data record during long swims, as these often coincided with extended time spent in the water.
Sea ice concentration was extracted from daily The dataset was limited to the period 1 March — 13 August, as there was little swimming data from other times of the year fulfilling the screening criteria.
Altogether, 11, locations 1, of these interpolated from 18 different polar bears were used in the offshore swimming models. GAMMs were chosen to model possible nonlinearities in how swimming depended on season or sea ice concentration.
These response variables were modelled with the same model structure, a spline for sea ice concentration as the main predictor variable, and a spline for Julian day to control for seasonality.
The error structure included polar bear identity as a random effect on the intercept, and an autoregressive correlation with a lag of 1 corAR1 to remove autocorrelation from the residual errors. Residual errors were assumed to follow a binomial distribution.
Predictions regarding how swimming varied with sea ice concentration were made for the beginning, middle and end of the modelled time period Julian days 61, , i. Stirling, I. Midsummer observations on the behavior of wild polar bears Ursus maritimus.
Article Google Scholar. Pagano, A. Long-distance swimming by polar bears Ursus maritimus of the southern Beaufort Sea during years of extensive open water. Russell, R.
The food habits of polar bears of James Bay and southwest Hudson Bay in summer and autumn. Arctic , — Dyck, M. Observations of a wild polar bear Ursus maritimus successfully fishing Arctic charr Salvelinus alpinus and Fourhorn sculpin Myoxocephalus quadricornis. Polar Biol. Smith, T. Predation of belugas and narwhals by polar bears in nearshore areas of the Canadian High Arctic. Arctic 43 , 99— The polar bear Ursus maritimus Phipps in the Svalbard area.
Norsk Polarinstitutt Skrifter Comparative hunting abilities of polar bear cubs of different ages. Amstrup, S. Polar bear, — Johns Hopkins University Press, Pilfold, N. Migratory response of polar bears to sea ice loss: To swim or not to swim. Ecography 40 , — Durner, G. Consequences of long-distance swimming and travel over deep-water pack ice for a female polar bear during a year of extreme sea ice retreat.
Monnett, C. Observations of mortality associated with extended open-water swimming by polar bears in the Alaskan Beaufort Sea. Mauritzen, M. Functional responses in polar bear habitat selection.
Oikos , — Freitas, C. Importance of fast ice and glacier fronts for female polar bears and their cubs during spring in Svalbard, Norway. Aars, J. If you want to know more about polar bears, and maybe even watch them swimming, you can visit them at one of the facilities with polar bear exhibits or maybe even try to see one in the wild in its natural habitat.
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