Physical mark-recapture involves the chemical immobilization, handling, and marking of individual bears. The mark consists of a permanent tattoo and ear tags. On later occasions (i.e. in subsequent capture sessions or once harvested), some of the same individuals are encountered and their identities verified. Based on the ratio of marked animals in relation to unmarked animals, among all animals captured or harvested, the total number of animals in the subpopulation can be estimated.
In addition to data being collected to estimate abundance during each capture event, physical measurements can be made (e.g. length and girth for estimation on growth and physical condition), and biological samples taken for age estimation, contaminants, disease, etc. These allow for long-term studies on polar bear health and condition, and also for the estimation of age-specific survival and reproductive rates.
The immobilization and handling of polar bears for research purposes has faced criticism from Inuit who are concerned with consuming contaminated meat and the overall impact of handling on the bears. Unfortunately, the capture and handling of polar bears for population studies is still an important and useful method which enables the most fulsome data collection. The Government of Nunavut has begun to explore the development of alternative methods that do not require capture of bears but that still provides information that is essential for effective management of the species.