Fig 1.
The Pacific walrus geographical range and sample harvest locations.
Pacific walrus liver tissues were collected by subsistence hunters from several communities in the Bering Strait and from the North Slope of Alaska. The range of the Pacific walrus spans the northern Bering and Chukchi Seas, with sex-segregated distributions throughout the year (green/yellow shading). The Distributed Biological Observatory regions 1 and 4 (boundaries denoted by the black boxes; Grebmeier et al. [4]) encompass prominent Pacific walrus breeding and foraging grounds, which were used for extracting satellite-derived sea ice measurements and nitrogen stable isotope data for primary consumers from previous studies for the relative trophic position analysis. Pacific walrus range data was modified from Garlich-Miller et al. [22] and Smith [23]. Open-source coastline data was retrieved from Natural Earth (https://www.naturalearthdata.com/).
Table 1.
Summary of Pacific walrus samples.
The region and year of subsistence harvested Pacific walrus liver tissues with annual sample sizes (n) by sex. Annual sea ice persistence (days/year) associated with the year of collection and the sea ice organic carbon content (mean ± SE %) and stable nitrogen isotope composition δ15N (mean ± SD ‰) by sex. Mean sea ice organic carbon values were adjusted to account for a significant interaction between region and sex.
Fig 2.
Sea ice persistence in the Pacific Arctic.
a) Sea ice persistence (days/year) by year for the northern Bering Sea and Chukchi Sea, b) Sea ice persistence anomalies for 2012 (15 September 2011–14 September 2012), c) Sea ice persistence anomalies for 2014 (15 September 2013–14 September 2014). Made with Natural Earth coastline data. Sea ice persistence anomalies initiate in September for the preceding calendar year to include sea ice formation and retreat in one sea ice season and were compared to a 1980/1981-2009/2010 base period.
Fig 3.
Sea ice indexes and sea ice organic carbon.
(a) Monthly mean sea ice concentration (%) and mean sea ice organic carbon. Individual points represent the mean sea ice organic carbon with standard deviation. (b) Sea ice persistence (days/year) and sea ice organic carbon.
Fig 4.
Regional analysis of sea ice organic carbon.
a) Ordination plots based on the individual highly branched isoprenoids (HBIs), including IP25, HBI II and HBI III, used to calculate sea ice organic carbon (iPOC) content. Data points are colored by region and the considered environmental vectors as blue arrows. b) Boxplots for iPOC (%) by year and region. Boxes depict the interquartile range from the first to third quartiles, including the median (horizontal line), minimum/maximum (vertical lines) and outliers (individual points).
Fig 5.
Sea ice organic carbon by region and sex for 2012, 2014 and 2016 (NBS only).
The boxplot indicates the interquartile range from the first to third quartiles, with the median shown as the horizontal line within each box for females and males for each region. All individual data points are shown. The red-dashed line indicates 50% sea ice organic carbon utilization, with values above this level suggesting elevated sea ice organic carbon.
Fig 6.
Sea ice organic carbon (iPOC%) by age class in the Chukchi Sea.
Box plots represent the interquartile range of values for adults (n = 9) and calves (n = 7) in the Chukchi Sea. The red-dashed line indicates the 50% sea ice organic carbon threshold, with values above this level suggesting elevated sea ice organic carbon contributions to the Pacific walrus diet.
Table 2.
Trophic position (TP) estimates for Pacific walruses by region and sex.
TP estimates are shown as the median with 95% confidence levels (CL). Regions included the northern Bering Sea (NBS) and Chukchi Sea. The values shown in bold and italicized were significantly different (p<0.05).