Summer/fall diet and macronutrient assimilation in an Arctic predator

Area of Science:

• Marine ecology
• Wildlife nutrition
• Isotope ecology

Background:

• Estimating free-ranging predator diets is challenging due to logistical constraints.
• Existing molecular tracers often fail to capture complete macronutrient contributions (protein and lipid).
• Polar bears (Ursus maritimus) preferentially consume blubber, but diet studies have used incomplete isotopic data.

Purpose of the Study:

• To develop an improved method for estimating polar bear diet composition and macronutrient assimilation.
• To simultaneously account for both protein and lipid intake using stable isotope analysis.
• To infer summer/fall diet and macronutrient proportions in Chukchi Sea polar bears.

Main Methods:

• Analysis of carbon and nitrogen isotope compositions in polar bear guard hair (n=229) from 2008-2017.
• Inclusion of lipid-containing prey muscle and blubber in isotopic analysis.
• Application of isotope mixing models to determine prey contributions and macronutrient proportions.

Main Results:

• Ice-associated seals, particularly pups, were the primary summer/fall prey.
• Pacific walruses and whales contributed less to the diet.
• Blubber consumption was confirmed as preferential, showing the highest documented lipid assimilation for any animal.

Conclusions:

• This study provides a more comprehensive understanding of polar bear summer/fall prey and macronutrient utilization.
• High lipid assimilation highlights the importance of blubber for polar bear nutrition.
• Findings are relevant to understanding polar bear adaptation to nutritional bottlenecks near sea ice minimums.