Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Area of Science:

• Ecological and Evolutionary Biology
• Marine Mammal Science
• Stable Isotope Ecology

Background:

• Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in animal tissues offer insights into diet, physiology, and movement patterns.
• Accurate interpretation of isotope values is complicated by factors like lipid content, tissue-specific discrimination, and turnover rates, which vary by species and tissue.

Purpose of the Study:

• To develop lipid normalization models for δ¹³C in Pacific walrus tissues.
• To assess the impact of chemical lipid extraction on δ¹³C and δ¹⁵N values in walrus muscle, liver, and skin.
• To evaluate tissue-specific isotope discrimination in Pacific walrus muscle, liver, skin, and bone collagen.

Main Methods:

• Generated lipid normalization models for δ¹³C analysis.
• Performed chemical lipid extractions on Pacific walrus muscle, liver, and skin samples.
• Measured δ¹³C and δ¹⁵N values in multiple tissue types (muscle, liver, skin, bone collagen).

Main Results:

• Lipid-free δ¹³C values in skin and bone collagen were similar; δ¹⁵N values in muscle and liver were also similar.
• Significant differences in δ¹³C and δ¹⁵N were observed among other tested tissues.
• Observed tissue-specific isotope differences largely aligned with established marine mammal discrimination factors, with the exception of skin.

Conclusions:

• This study provides essential data for refining stable isotope analyses in Pacific walrus.
• Findings enhance the understanding of walrus diet and Arctic food web dynamics.
• Results facilitate direct comparisons between contemporary, historical, and paleoecological isotope studies of walrus.