Comments: Loss of the polar bear's primary habitat (sea ice) is the primary threat. Sea ice is rapidly diminishing throughout the Arctic, and the best available evidence is that Arctic sea ice will continue to be affected by climate change for the foreseeable future (see USFWS 2008 for extensive discussion).
USFWS (2008) determined that harvest is likely exacerbating the effects of habitat loss in several populations. In addition, polar bear mortality from harvest and negative bear-human interactions may in the future approach unsustainable levels for several populations, especially those experiencing nutritional stress or declining population numbers as a consequence of habitat change. Continued efforts are necessary to ensure that harvest or other forms of removal do not exceed sustainable levels. However, USFWS (2008) concluded that overutilization does not currently threaten the polar bear throughout all or a significant portion of its range.
USFWS (2008) evaluated the best available scientific information on disease and predation and determined that disease and predation (including intraspecific predation) do not threaten the species throughout all or any significant portion of its range. Potential for disease outbreaks, an increased possibility of pathogen exposure from changed diet or the occurrence of new pathogens that have moved northward with a warming environment, and increased mortality from cannibalism all warrant continued monitoring and may become more significant threat factors in the future for polar bear populations experiencing nutritional stress or declining population numbers.
Industrial development may hinder natural movement, feeding and breeding patterns, and could expose bears to chemical contaminants. Persistent organic pollutants, such as PCBs, may be adversely affected bear immune systems, thyroid function, and reproduction (Siegel and Cummings 2005: Appendix D). However, USFWS (2008) determined that contaminants, ecotourism, and shipping do not threaten the polar bear throughout all or any significant portion of its range. Some of these, particularly contaminants and shipping, may become more significant threats in the future for polar bear populations experiencing declines related to nutritional stress brought on by sea ice and environmental changes.
Low reproductive rate makes this species slow to recover from declines (Stirling 1991).