Variability of Lipids and Fatty Acids in Pacific Walrus Blubber

Chadwick V Jay,Anthony S Fischbach,Sara J Iverson

doi:10.3389/fmars.2021.603065

Chadwick V Jay, Anthony S Fischbach + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2021.603065

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Abstract

The variability of lipid content and fatty acid (FA) composition across blubber depth and body sites are important considerations for condition and diet studies of marine mammals. We investigated lipid and FA variability among inner and outer blubber layers, three body sites, four study years, and lactation status of adult female Pacific walruses (Odobenus rosmarus divergens) using blubber samples collected from subsistence-harvested walruses in spring 2007–2010. Percent lipid content did not differ between the inner and outer blubber layers at the rump, flank, or sternum of walruses. Although FA composition differed between the inner and outer blubber layers, the difference was consistent across body sites, and differences between layers within individual FAs were small (&lt;2%). Lipid content at the sternum of lactating females was 6% higher than non-lactating females, consistent with known variation in body condition among these reproductive classes. Across study years, lipid content varied 18% and individual FAs varied 6%, likely reflecting population-level interannual variability in energy budgets and small differences in diet among years. Consistency in blubber lipid content across blubber depth and body sites and detectable variation in blubber lipid content among reproductive classes and years suggests the potential for lipid content to be a useful indicator of walrus body condition. In addition to information on condition, FA composition of blubber samples could potentially provide insights into changes in walrus diet that may be expected to occur from changes in their access to prey resources resulting from continued sea ice loss.

Highlights

Changes in sea ice habitat and increased human activities in the Arctic are affecting the distribution of ice-associated marine mammals (Laidre et al, 2015)
Sample means and deviations at the rump and sternum were similar to blubber depth measured in the field at these same body sites from adult female Pacific walruses harvested during a similar time of year in another study (Quakenbush et al, 1999; rump: x = 3.9 cm, SD = 0.7, range 2.7–5.4; sternum: x = 4.0 cm, SD = 1.0, range 2.5–6.8)
We tested for differences in the between-layer difference of lipid content among body sites (Figure 2) using ANOVA where between-layer difference at each body site was treated as repeated measures within walrus (Zar, 1999)

Summary

Introduction

Changes in sea ice habitat and increased human activities in the Arctic are affecting the distribution of ice-associated marine mammals (Laidre et al, 2015). Conceptual models to forecast and predict the response of marine mammal populations to changing environments and human-induced stressors share a common pathway—stressors influence activity budgets or physiological status and an animal’s energy stores, which affect outcomes of reproduction and survival of young (National Research Council, 2005; New et al, 2014; King et al, 2015; Udevitz et al, 2017; Farmer et al, 2018). Changes in the timing and extent of seasonal sea ice cover in the Chukchi Sea (Wang et al, 2018) has consequences to the production of walrus prey (Grebmeier et al, 2015), and has led walruses to haul out on land more frequently and spend more time in water and less time resting, with probable declines in net energy gain (Jay et al, 2012, 2017; Udevitz et al, 2017)

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