Polar bear Ursus maritimus conservation in Canada: an ecological basis for identifying designatable units Gregory W. Thiemann ,A ndrew E. Derocherand IanStirling

Polar bears Ursus maritimus have a circumpolar distribution that is directly tied to the Arctic sea ice. Al- though they are wide-ranging, polar bears do not belong to a single population but rather are comprised of 19 largely discrete subpopulations, 13 of which are fully or partly under Canadian jurisdiction. These subpopulations are used to manage the sustainable harvest of polar bears in Canada but for conservation purposes the species is currently con- sidered a single biological unit. Long-term climate warming has reduced the availability of sea ice that polar bears re- quire for feeding, movement and reproduction, and con- tinued declines in ice extent and duration are forecast to have significant negative effects on polar bears in some areas. Under the Canadian Species at Risk Act separate legal protection may be given to intraspecific groups (so called designatable units, DUs) that are genetically, geo- graphically and/or biogeographically distinct. We examined the conservation status of polar bears across their Canadian range and compared large-scale ecosystem properties across subpopulations. We found that threats to the conservation of polar bears are not spatially uniform and we identified five DUs that captured broad patterns of polar bear bio- diversity. We conclude that the use of DUs provides a biologically-sound framework for the conservation of polar bears.