As human activities lead to rising greenhouse gas concentrations in Earth’s atmosphere, less incoming solar energy is released back into space, causing a net energy gain that increases global temperatures. Climate change will be an important driver of biodiversity loss into the foreseeable future. Habitat degradation, phenological shifts and ecosystem change are expected to result in an increasing number of species of conservation concern.
The Arctic is warming at a rate three times greater than the global average and Arctic sea-ice extent is declining rapidly. The Arctic Ocean is expected to be seasonally ice-free by as early as the 2030’s. Arctic marine mammals depend on sea ice for many aspects of their life history and some are particularly vulnerable due to specialized feeding or habitat requirements. Sea-ice declines represent losses of shelter from inclement weather, protection from open-water predators and many forms of human disturbance, foraging habitats, platforms for birthing, nursing, resting and molting in the case of ice-associated seals and in a loss of hunting habitat and transport platforms for polar bears.
Projected sea-ice loss in the 21st century is expected to negatively affect polar bears throughout much of their range, because the species depends fundamentally on sea-ice for access to its primary prey. Polar bears are dependent on a sea-ice platform for hunting seals that are hauled out on sea ice or still-hunting at breathing holes. Sea-ice melting reduces the opportunities for polar bears to capture seals, leaving them at risk of expending more energy in the pursuit of food than they can obtain. Animal energy use is typically described by two terms. The resting metabolic rate (RMR) includes the energy cost of basic organismal functions, such as blood circulation and breathing. The field metabolic rate (FMR) includes RMR as well as the energy cost of additional activities, such as movement and foraging. Because energy balance influences whether an animal survives and reproduces, RMR and FMR are critical variables in ecology and conservation. Spring is a critical hunting period for polar bears; after the long dark winter when many female bears have been in the den rearing young and fasting, finding food quickly to replenish depleted energy stores is important.
Polar bears in most Arctic regions primarily hunt ringed seals and their pups. Do to broken glacier ice, polar bears must do aquatic approaches, sneaking in on seals and then bursting onto the ice to capture their prey. This hunting technique has been suggested to be a ‘specialty’ hunting strategy, only used by some bears. Longer periods of ice melt are lengthening the time during which polar bears much endure food deprivation. Polar bears move longer distances per day in the summer months, but have smaller home ranges in August, suggesting that polar bears are searching more for food but are restricted in the area that they search, potentially due to reductions in sea ice. Declines of sea ice in coastal areas has decreased the ability of polar bear to hunt traditionally, ice-associated prey during summer and autumn, leading to increased usage of alternate prey resources to meet energy demands. Increases in the number of human-bear conflicts also suggest that more bears are on shore or that changes in their movement patterns are bringing them into contact with people more frequently.
Consequently, near-term management actions will likely focus on secondary factors or threats with the intent of protecting populations until global action leads to a stabilized climate system. Polar bear subsistence harvest is important because it has cultural, nutritional, and economic value to native people in the Arctic. Fifteen polar bear subpopulations currently support a legal subsistence harvest, although this is not considered a threat to polar bears at a species level, there are concerns about harvest for individual subpopulations. Habitat loss could increase vulnerability to overutilization if populations become smaller or less resilient and removal levels are not adjusted accordingly. The best possible outcomes for polar bears include control hunting and other factors in an effect to make populations with the lower numbers sustainable. However, a ban on hunting would be a serious cultural loss for the Arctic’s aboriginal people. The future remains uncertain, but it is now more clearly in the hands of policy-makers. There is cause for optimism, but that requires optimism about our ability to change.