Polar bears, large carnivores native to the Arctic, are apex predators uniquely adapted to their icy habitat. Despite their formidable nature, they face various threats that can lead to their demise.
Predation and Intraspecific Aggression
While polar bears are at the top of the Arctic food chain, they are not entirely free from predation risks. Orcas, or killer whales, rarely interact with polar bears due to habitat differences. No documented cases of orcas hunting polar bears exist, though scientists acknowledge the possibility if a bear is vulnerable. Orcas are primarily open-water hunters, and their large dorsal fins hinder movement in ice-filled waters.
A more common biological threat comes from within their own species. Adult male polar bears engage in infanticide, killing cubs to eliminate potential mating competition. Territorial disputes and resource competition among adults also lead to aggressive encounters, sometimes resulting in injury or death. Adult walruses, with their formidable tusks, can also inflict serious injury or death upon polar bears, especially in aquatic confrontations.
Environmental Stressors
The most significant threat to polar bear survival stems from environmental stressors, primarily rapid changes in the Arctic due to climate warming. Polar bears depend heavily on sea ice for essential activities like hunting seals, mating, and resting. Arctic temperatures are rising, leading to earlier spring melts and later fall freeze-ups of sea ice. This reduction in sea ice duration directly impacts hunting success, as bears rely on ice platforms to ambush seals.
Diminished access to prey leads directly to starvation, a major cause of mortality. When forced onto land for extended periods, polar bears struggle to find sufficient high-fat food sources, as terrestrial foods do not provide the necessary energy. Longer distances between ice floes and unexpected ice break-ups also increase the risk of drowning, particularly for cubs who are more susceptible to hypothermia during long swims.
Human Activities and Interactions
Human activities contribute directly and indirectly to polar bear mortality. Regulated subsistence hunting by Indigenous communities is permitted in certain areas and is generally considered sustainable. These hunts are typically managed with quotas and specific regulations to ensure the use of the animal and prevent waste. Illegal poaching also occurs.
Oil spills and pollution pose severe threats to polar bears. Oil contamination can destroy the insulating properties of a bear’s fur, leading to hypothermia. Polar bears may ingest toxic oil while grooming themselves or consuming contaminated prey, which can result in kidney failure, liver damage, and neurological issues. There is currently no proven method to effectively clean up oil spills in icy Arctic waters. Persistent organic pollutants (POPs) also accumulate in the Arctic food chain, leading to health problems.
Human-polar bear conflict is increasing as melting sea ice forces bears to spend more time on land and closer to human settlements in search of food. This proximity elevates the risk of encounters, which can result in defense kills by humans when their lives or property are threatened. Such interactions are dangerous for both bears and people, often leading to the bear’s death.
Health Issues
Polar bears, like other large mammals, are susceptible to various health issues, including diseases and parasites. While historically not a primary driver of mortality, environmental changes are increasing their vulnerability. Pathogens such as morbilliviruses, including canine distemper, have been detected in polar bear populations. Though rare, cases of rabies have also been confirmed.
Parasitic infections are also present, with larvae of Trichinella found throughout their range and antibodies to Toxoplasma gondii detected in some populations. Recent research indicates an increased exposure to certain parasites like Neospora caninum and Toxoplasma gondii in polar bears, particularly in regions experiencing significant sea ice loss. This heightened exposure may be linked to bears spending more time on land, where they encounter novel pathogens, or through shifts in their diet. A weakened health status can make polar bears more susceptible to other threats, including starvation or physical injury.