The Pacific walrus (Odobenus rosmarus divergens) feeds on benthic invertebrates on the continental shelf of the Chukchi and Bering seas and rests on sea ice between foraging trips. With climate warming, ice-free periods in the Chukchi Sea have increased and are projected to increase in frequency and duration. We radio-tracked walruses to estimate areas of walrus foraging and occupancy in the Chukchi Sea during June–November of 2008–2011, years when sea ice was sparse over the continental shelf. The earlier and more extensive sea ice retreat in June–September and delayed freeze-up of sea ice in October and November, allowed walruses to arrive earlier, occupy slightly more northern areas, and stay later in the Chukchi Sea than in the past. The lack of sea ice over the continental shelf in September-October caused walruses to forage in nearshore areas in contrast to offshore areas in the past. Walruses rarely moved into deep waters of the Arctic Basin when sea ice retreated off the shelf. Walruses foraged in most areas they occupied, and areas of concentrated foraging generally corresponded to regions of high benthic biomass, such as in the northeastern (Hanna Shoal) and southwestern Chukchi Sea. A notable exception was the occurrence of concentrated foraging in a nearshore area of northwestern Alaska that is apparently depauperate in walrus prey. With increasing sea ice loss, it is likely that walruses will increase their use of coastal haul-outs and nearshore foraging areas, with consequences to the population that are yet to be understood.
Data is structured by month, which ranges from June (6) through November (11). Within each month we estimated walrus utilization distributions using two methods: ("Foraing") by weighting the kernel density distribution by the amount of time spent foraging during each recorded track segment. We present contour intervals ranging from 10th to 95th percentile. Portable Network Graphic files for each month are provided along with a Portable Network Graphic file for the legend. Areas outside of the 95th percentile contour are indicated as transparent.
Jay, C. V., Fischbach, A.S., Kochnev, A.A., 2012. Walrus areas of use in the Chukchi Sea during sparse sea ice cover, journal article, Marine Ecology Progress Series, 466, doi: 10.3354/meps10057.
This zip file contains files that may be used in a geographic information system to portray the walrus distributions depicted in figure 4 of the USGS / Chukotka TINRO publication Jay et al. (2012).
FILES:
Listed below are the file names, formats, their contents, and projection system.
File Format Content Projection
USGS_Walrus_UD_Forage_aed170_70_06.png Geo PNG Walrus foraging utilization distribution in June Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_aed170_70_07.png Geo PNG Walrus foraging utilization distribution in July Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_aed170_70_08.png Geo PNG Walrus foraging utilization distribution in August Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_aed170_70_09.png Geo PNG Walrus foraging utilization distribution in September Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_aed170_70_10.png Geo PNG Walrus foraging utilization distribution in October Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_aed170_70_11.png Geo PNG Walrus foraging utilization distribution in November Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Forage_Jun_Nov_BrowseImage.png PNG Browse image for GIS layers provided in this zip file (Fig. 4 in Jay et al 2012)
USGS_Walrus_UD_Forage_Legend.png PNG Legend graphic for foraging utilization distributions
USGS_Walrus_UD_Occupancy_06.kmz KMZ Walrus occupancy utilization distribution in June Geographic (WGS84)
USGS_Walrus_UD_Occupancy_07.kmz KMZ Walrus occupancy utilization distribution in July Geographic (WGS84)
USGS_Walrus_UD_Occupancy_08.kmz KMZ Walrus occupancy utilization distribution in August Geographic (WGS84)
USGS_Walrus_UD_Occupancy_09.kmz KMZ Walrus occupancy utilization distribution in September Geographic (WGS84)
USGS_Walrus_UD_Occupancy_10.kmz KMZ Walrus occupancy utilization distribution in October Geographic (WGS84)
USGS_Walrus_UD_Occupancy_11.kmz KMZ Walrus occupancy utilization distribution in November Geographic (WGS84)
USGS_Walrus_UD_Occupancy_aed170_70.shp ESRI Shape File Walrus occupancy utilization 50th and 95th percentile contours for each month Azimuthal equaldistant centered on 170W 70N
USGS_Walrus_UD_Occupancy_geo.shp ESRI Shape File Walrus occupancy utilization 50th and 95th percentile contours for each month Geographic (WGS84)
In this collection, a zip file titled "Walrus_Forage_Jun_Nov_KMZs.zip" contains KMZ files showing monthly forage utilization distribution during June through November. All KMZs have transparent backgrounds, which were created in Global Mapper and may be displayed in Google Earth.
