The two most common methods to estimate polar bear population abundance are capture-mark-recapture (involving the physical or genetic marking of animals) and aerial survey methods. The two methods have different strengths and weaknesses and rely on different assumptions. Physical and genetic capture-recapture studies are usually part of a program where samples are collected from individuals over multiple years and thus provide a lot of additional data besides estimates of population size, such as information on survival and reproduction, along with condition and age of individual animals (see separate page on capture-mark-recapture). However, in some areas, the assumptions required for estimating population size with these methods can be difficult to meet and in other areas, access to physically mark polar bears has been logistically challenging. Further, these approaches can be stressful to animals, requiring pursuit by helicopter, and chemical immobilization in the case of physical capture-recapture. However, it is important to realize that aerial surveys provide an estimate of the number of bears in a specific region at a specific time, whereas capture-recapture analyses produce estimates of a superpopulation, defined as all animals with a non-negligible probability of using the sampling area over the course of the study. Because there are likely some temporary emigrations from a subpopulation (i.e. not all animals with fidelity to an area are available for sampling each year), it is expected that estimates of a superpopulation size are larger than estimates from an aerial survey (Laidre et al. 2023).
Wiig and Derocher (1999) advocated for an aerial survey approach, using distance sampling, for the Barents Sea subpopulation to estimate population size, due to the large extent and the lack of bases needed for capture-recapture based estimates. This led to the first polar bear aerial survey on a subpopulation-level scale, performed in August 2004 (Aars et al. 2009). A new aerial survey was conducted in Foxe Basin in 2009 (Stapleton et al. 2014) and in recent years, several polar bear aerial surveys, using a variety of methods, have been conducted in Canada, e.g. in the Foxe Basin, Western Hudson Bay and Southern Hudson Bay subpopulations (Stapleton et al. 2016; Obbard et al. 2015, 2018), in the Barents Sea in 2015 (Aars et al. 2017), and in the Kane Basin subpopulation (Wiig et al. 2022). The literature on aerial surveys to estimate animal abundance is extensive and has benefitted from decades of development by wildlife biologists and statisticians.