Chukchi Sea Polar Bear Locations (2008-2013)

These data are the locations (latitude and longitude) of polar bears in the Chukchi Sea that were used in the analysis by Rode et al. The data include the date and time of the location, the unique identifier of the bear the locations are from, and the accuracy classification of the location. Location accuracy is based on Argos error classes (3,2,1,0,A,B). If a location was obtained from GPS, its accuracy is labeled as 'GPS'

Increased Land Use by Chukchi Sea Polar Bears in Relation to Changing Sea Ice Conditions

<div><p>Recent observations suggest that polar bears (<i>Ursus maritimus</i>) are increasingly using land habitats in some parts of their range, where they have minimal access to their preferred prey, likely in response to loss of their sea ice habitat associated with climatic warming. We used location data from female polar bears fit with satellite radio collars to compare land use patterns in the Chukchi Sea between two periods (1986–1995 and 2008–2013) when substantial summer sea-ice loss occurred. In both time periods, polar bears predominantly occupied sea-ice, although land was used during the summer sea-ice retreat and during the winter for maternal denning. However, the proportion of bears on land for > 7 days between August and October increased between the two periods from 20.0% to 38.9%, and the average duration on land increased by 30 days. The majority of bears that used land in the summer and for denning came to Wrangel and Herald Islands (Russia), highlighting the importance of these northernmost land habitats to Chukchi Sea polar bears. Where bears summered and denned, and how long they spent there, was related to the timing and duration of sea ice retreat. Our results are consistent with other studies supporting increased land use as a common response of polar bears to sea-ice loss. Implications of increased land use for Chukchi Sea polar bears are unclear, because a recent study observed no change in body condition or reproductive indices between the two periods considered here. This result suggests that the ecology of this region may provide a degree of resilience to sea ice loss. However, projections of continued sea ice loss suggest that polar bears in the Chukchi Sea and other parts of the Arctic may increasingly use land habitats in the future, which has the potential to increase nutritional stress and human-polar bear interactions.</p></div

Differences in the ice retreat date along the Chukchi Sea coastline in Alaska and Russia between current (2008–2013) and historic (1986–1995) periods.

<p>Negative values indicate earlier ice retreat dates currently than during historic conditions. Units are in days.</p

Relationship between the mean daily percent of the continental shelf covered by sea ice (≥15% concentration) between the months of August and October and mean (± 1 stdev) number of days denning and non-denning female polar bears were on land during those months for each of 10 years in which data were available for at least two individuals (1987, 1988, 1990–1993; 2009–2011, 2013).

<p>Only bears that spent more than 7 days on land were included. Sample sizes are provided in parentheses above data points.</p

Locations of female polar bear winter dens 1986–1995, 1995–2007 and 2008–2013.

<p>The majority of den locations were determined from satellite telemetry locations of collared bears. Six den locations on land were determined from observation. Dens are assumed to be maternity denning attempts although some bears may have exited early without cubs.</p

Description of sea ice variables used in the analysis of factors influencing the timing of arrival on shore, length of stay, and timing of departure back to sea ice by polar bears from the Southern Beaufort Sea subpopulation.

<p>Description of sea ice variables used in the analysis of factors influencing the timing of arrival on shore, length of stay, and timing of departure back to sea ice by polar bears from the Southern Beaufort Sea subpopulation.</p

Locations where adult female polar bears were captured and fitted with satellite radio collars in 1986–1995 and 2008–2013.

<p>The area used for ice analysis is outlined in black.</p

Rapid Environmental Change Drives Increased Land Use by an Arctic Marine Predator

<div><p>In the Arctic Ocean’s southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased substantially since the late 1990s. Historically, polar bears (<i>Ursus maritimus</i>) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska’s north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (<i>Balaena mysticetus</i>) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities.</p></div

Percent of Chukchi Sea female polar bears denning on or within 5 km of land in different geographic areas during two time periods based on observed locations from collared bears (n = 56) and directly observed dens (n = 6).

<p>Denning location could not be determined for all bears identified to have denned based on collar temperature data. North (N) Alaska included land in Alaska north of Point Hope and south (S) Alaska included land in Alaska south of Point Hope.</p

Relationship between the probability (± SE represented by the gray polygon) of a section of terrestrial, coastal habitat being used during the summer (i.e., for > 7 days between August and October) by female polar bears in 1986–1995 and 2008–2013 (A) or for denning in 1986–1999 and 2000–2013 (B) in the Chukchi Sea and ice retreat date (i.e., the first ordinal date in which ice of ≥15% concentration exceeded 50 km from the coastal location).

<p>Summering data were only available during the time periods included in (A) whereas some dens were identified between 1996–2007 (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0142213#pone.0142213.g003" target="_blank">Fig 3</a>). Coastal habitats included locations in Alaska, Chukotka, and on Wrangel and Herald Islands.</p