Polar bears (Ursus maritimus) are an iconic Arctic species, uniquely adapted to the marine environment. These large carnivores evolved from grizzly bear ancestors to thrive in extreme cold and on sea ice. Their thick fur and fat provide insulation, while large, flat paws aid in traction on ice and propulsion in water. These adaptations allow them to navigate and hunt in the Arctic Ocean, where they are apex predators.
Declining Sea Ice
The Arctic sea ice is a platform polar bears rely on for hunting, travel, mating, and raising cubs. Sea ice has been declining by 13% each decade since 1979 due to global warming, with the Arctic warming roughly four times faster than the rest of the world. This reduction means seasonal sea ice forms later in fall and breaks up earlier in spring, shortening the time polar bears have access to stable ice for hunting their primary prey, seals.
The shrinking and fragmented sea ice directly impacts their ability to find food, leading to malnutrition and lower energy levels. Polar bears primarily hunt blubber-rich seals from the ice, an efficient foraging method. Without stable ice, hunting becomes difficult, forcing bears to expend more energy to find prey or to swim longer distances between shrinking ice floes, sometimes leading to exhaustion and even drowning.
Prolonged ice-free periods force polar bears to spend more time on land, where food options are less nutritious and abundant. Studies show polar bears burn more calories than they consume, leading to reduced body size, struggling cubs, and weaker adults. For example, in the Baffin Bay subpopulation, bears now spend an additional 30 days on land compared to the 1990s, totaling 90 days annually, a change directly linked to sea ice breakup and formation. This increased time on land means longer fasting periods, negatively affecting their body condition, survival, and reproductive success.
The loss of sea ice also disrupts polar bear reproduction, as stable ice is necessary for successful mating and cub rearing. Pregnant females sometimes dig maternity dens in sea ice, but with less stable ice, this becomes challenging. Research indicates mother bears produce smaller litters, and cub survival rates are declining. The inability of mothers to produce sufficient milk due to fasting on land further jeopardizes cub survival, as milk energy content can drop significantly after prolonged fasting on land.
Pollution and Contaminants
Polar bears face threats from various forms of pollution, including persistent organic pollutants (POPs) and heavy metals. POPs, such as polychlorinated biphenyls (PCBs) and DDT, resist breakdown and accumulate in animal fat, biomagnifying up the food chain to polar bears. These chemicals, transported to the Arctic, have been linked to adverse health effects in polar bears, including reduced bone density, altered thyroid hormones, and disrupted lipid metabolism.
Heavy metals, particularly mercury, also pose a threat to polar bear health. As apex predators, polar bears accumulate high concentrations of mercury from their diet of seals. High levels of mercury have been associated with altered gut microbiota and potential neurotoxicological concerns. Chronic exposure to these chemicals can damage internal organs, including the liver, kidneys, and brain, and weaken their immune systems, increasing disease susceptibility.
Oil spills present immediate and long-term dangers to polar bears and their environment. Increased shipping and resource extraction in the Arctic raise the risk of such incidents. If a polar bear’s fur comes into contact with oil, it loses its insulating properties, leading to hypothermia. Bears may also ingest oil by grooming themselves or by consuming contaminated prey, which can result in kidney failure, digestive system disorders, and brain damage.
Human-Wildlife Interactions
As sea ice diminishes, polar bears spend more time on land, increasing their proximity to human populations and leading to more frequent human-bear conflicts. Bears, in search of food, may scavenge in garbage dumps or approach human settlements, creating dangerous situations. Such encounters can result in property damage, human injuries, and lethal removal of bears for public safety.
Increased human activities in the Arctic, including shipping traffic, oil and gas exploration, and tourism, cause disturbance and habitat disruption for polar bears. Noise from ice-breaking vessels, drilling operations, and other industrial activities can be unsettling to polar bears, potentially disrupting behaviors such as hunting and cub care. While polar bears are considered less vulnerable to shipping noise than some other marine mammals, the overall increase in vessel traffic still contributes to an altered acoustic environment.
Oil and Gas Exploration
Oil and gas exploration activities, beyond the risk of spills, can lead to physical destruction of sea ice habitat and bear displacement. Seismic surveys and drilling operations create noise and infrastructure that can disturb polar bears, particularly at sensitive maternity den sites. Current methods for detecting hidden dens often miss sites, raising concerns for denning mothers and cubs in development areas.
Tourism
Tourism, while offering educational opportunities, contributes to greenhouse gas emissions, exacerbating climate change. Tourist activities can also cause stress and alter polar bear behavior, with potential habituation to humans leading to greater conflict.