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

Abstract

Polar bears (Ursus maritimus) are experiencing loss of sea ice habitats used to access their marine mammal prey. Simultaneously, ocean warming is changing ecosystems that support marine mammal populations. The interactive effects of sea ice and prey are not well understood yet may explain spatial-temporal variation in the response of polar bears to sea ice loss. Here, we examined the potential combined effects of sea ice, seal body condition, and atmospheric circulation patterns on the body condition, recruitment, diet, and feeding probability of 469 polar bears captured in the Chukchi Sea, 2008-2017. The body condition of ringed seals (Pusa hispida), the primary prey of females and subadults, was related to dietary proportions of ringed seal, feeding probability, and the body condition of females and cubs. In contrast, adult males consumed more bearded seals (Erignathus barbatus) and exhibited better condition when bearded seal body condition was higher. The litter size, number of yearlings per adult female, and the condition of dependent young were higher following winters characterized by low Arctic Oscillation conditions, consistent with a growing number of studies. Body condition, recruitment, and feeding probability were either not associated or negatively associated with sea ice conditions, suggesting that, unlike some subpopulations, Chukchi Sea bears are not currently limited by sea ice availability. However, spring sea ice cover declined 2% per year during our study reaching levels not previously observed in the satellite record and resulting in the loss of polar bear hunting and seal pupping habitat. Our study suggests that the status of ice seal populations is likely an important factor that can either compound or mitigate the response of polar bears to sea ice loss over the short term. In the long term, neither polar bears nor their prey are likely robust to limitless loss of their sea ice habitat.

Energetic and health effects of protein overconsumption constrain dietary adaptation in an apex predator

“…The Chukchi Sea subpopulation ranges on sea ice over productive shallow continental shelf waters between the northwest coast of Alaska and the northeast coast of Russia. Recent studies indicate that this population is not currently prey-limited and has maintained body condition and survival rates that support a stable population 20 – 22 , 56 . Similarly, populations of the two primary prey species, bearded ( Erignathus barbatus ) and ringed seals, appear to be stable 57 .…”

“…If true, increased consumption of high protein diets would have important consequences for polar bear energetics and further support the implications of upper limits on protein consumption in carnivores. To address this hypothesis, we (a) estimated the dietary protein and fat content of diets consumed by wild polar bears in the Chukchi Sea subpopulation where prey is not currently limiting 21 , 22 , (b) measured the protein to fat dietary content selected by zoo polar bears that have never had access to high-fat marine prey to determine if protein:fat selection is genetically and physiologically based, and (c) evaluated the potential health consequences (e.g., energetic costs, diseases and lifespan) of consuming high protein diets that might affect wild polar bears when prey availability is reduced and be important in diet formulation for polar bears in managed care.…”

Ringed seal (Pusa hispida) breeding habitat on the landfast ice in northwest Alaska during spring 1983 and 1984

“…However, ringed seals have been considered to be the least sensitive to climate change of the eleven Arctic and sub-Arctic marine mammal species [ 65 ] as well as somewhat resilient based on their generalist diet, large numbers, and wide geographic range [ 66 ]. Across their range, ringed seals, as well as their primary predator [ 67 , 68 ], may have different responses to environmental changes. Ringed seals sampled in northern Alaska during 2003–2011 had thicker blubber, grew faster, matured earlier and had a higher proportion of pups in the harvest than those sampled during 1975–1984 [ 7 ].…”

Model selection isn't causal inference

“…Chinn et al 2021 What is the influence of intrinsic and extrinsic attributes on neonate survival in wild pigs? Montano-Centellas et al 2021 What are the ecological drivers of avian community assembly along a tropical elevation gr Rode et al 2021 What are the combined effects of sea ice, seal body condition and atmospheric circulation Sinnott-Armstrong et al 2021. What are the biotic and abiotic drivers of fruit colour syndrome?…”