Drivers and consequences of apex predator diet composition in the Canadian Beaufort Sea

Abstract

Polar bears (Ursus maritimus) rely on annual sea ice as their primary habitat for hunting marine mammal prey. Given their long lifespan, wide geographic distribution, and position at the top of the Arctic marine food web, the diet composition of polar bears can provide insights into temporal and spatial ecosystem dynamics related to climate-mediated sea ice loss. Polar bears with the greatest ecological constraints on diet composition may be most vulnerable to climaterelated changes in ice conditions and prey availability. We used quantitative fatty acid signature analysis (QFASA) to estimate the diets of polar bears (n = 419) in two western Canadian Arctic subpopulations (Northern Beaufort Sea and Southern Beaufort Sea) from 1999 to 2015. Polar bear diets were dominated by ringed seal (Pusa hispida), with interannual, seasonal, age-and sex-specific variation. Foraging area and sea ice conditions also affected polar bear diet composition. Most variation in bear diet was explained by longitude, reflecting spatial variation in prey availability. Sea ice conditions (extent, thickness, and seasonal duration) declined throughout the study period, and date of sea ice break-up in the preceding spring was positively correlated with female body condition and consumption of beluga whale (Delphinapterus leucas), suggesting that bears foraged on beluga whales during entrapment events. Female body condition was positively correlated with ringed seal consumption, and negatively correlated with bearded seal consumption. This study provides insights into the complex relationships between declining sea ice habitat and the diet composition and foraging success of a wide-ranging apex predator.

Seal body condition and atmospheric circulation patterns influence polar bear body condition, recruitment, and feeding ecology in the Chukchi Sea

“…We used a redundancy analysis to examine relationships between the percent each prey species contributed to individual polar bear diets and combinations of ice metrics, seal body condition, AO, and year variables (model set 7, Table 2) similar to the approach described by Florko et al (2020). A Hellinger transformation (square root of each dietary proportion; Florko et al, 2020) was used to reduce skewness in the data associated with variability in the prominence of some prey versus others. A forward stepwise procedure was used to identify the suite of variables that influenced prey proportions using the “vegan” package (Oksanen et al, 2019) of R (R Core Team, 2020, version 4.0.3).…”

Dietary ecology of Alaskan polar bears (Ursus maritimus) through time and in response to Arctic climate change

“…Their cranial morphology, which has evolved to accommodate their role as aquatic predators (e.g., elongated to hunt seals and fish via small holes in ice), is biomechanically weak compared to their omnivorous sister species and is poorly suited to mechanically challenging foods common in many omnivorous or herbivorous diets (Christiansen & Adolfssen, 2005;Slater et al, 2010). Sea ice decline in the 21st century has been shown to have complex effects on dietary composition and foraging success among Alaskan polar bears (Florko et al, 2020). Specialist limitations notwithstanding, polar bears which ordinarily hunt on ice and exploit marine resources of ringed and bearded (Erignathus barbatus) seals may be increasing labile land resource use at the subpopulation level with Arctic warming.…”

Characterising menotactic behaviours in movement data using hidden Markov models

“…In the spring, polar bears' primary prey, ringed seals (Pusa hispida) occupy subnivean lairs for protection from predators and the environment (Chambellant et al 2012;Florko et al 2020;Smith & Stirling 1975).…”