Appendix B. Model results examining trends in measures of skull width, body length, mass, and condition of polar bears in the southern Beaufort Sea between 1983 and 2006.

Model results examining trends in measures of skull width, body length, mass, and condition of polar bears in the southern Beaufort Sea between 1983 and 2006

Appendix A. Model results examining relationships between the availability of sea ice habitat and measures of skull width, body length, mass, and condition of polar bears in the southern Beaufort Sea.

Model results examining relationships between the availability of sea ice habitat and measures of skull width, body length, mass, and condition of polar bears in the southern Beaufort Sea

Chukchi Sea ice data

Sea-ice data are provided in two text files: "Chukchi Sea ice data.txt" and "Southern Beaufort Sea ice data.txt". The data and methods to process them are described in the main text of Regehr et al. (2017) and the Supporting Information Appendix S3. Please see "Sea ice METADATA.txt" for further details

Southern Beaufort Sea ice data

Sea-ice data are provided in two text files: "Chukchi Sea ice data.txt" and "Southern Beaufort Sea ice data.txt". The data and methods to process them are described in the main text of Regehr et al. (2017) and the Supporting Information Appendix S3. Please see "Sea ice METADATA.txt" for further details

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'

Appendix A. Projection matrices.

Projection matrices

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 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

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