The graph below shows population estimates for the Porcupine Caribou herd between 1953 and 2001. Since 1972, population estimates have been based on Aerial-Photo-Direct-Count-Extrapolation, or photocensus. Prior to 1972, other methods were used to obtain population estimates but have been considered somewhat less reliable.

A photocensus is done every 3 years at the time when caribou get into large groups, known as post-calving aggregations. Barren ground caribou aggregate for a short period of time when mosquitoes and other flies are at their worst. The harassment of these insects forces the caribou into large groups. The groups of caribou are located by plane and when they form very tight groups of animals, another plane with a large format camera mounted on the belly flies over and takes photographs. Having satellite and radio collars on caribou is extremely helpful for finding these groups of caribou. Radio collars were first used in 1982, and the first satellite collars in 1985.