https://phys.org/news/2018-07-highly-endangered-amur-leopards-china.html

Although numbers are small, previous estimates in Russia were even less, ranging from 25 to 50 individuals. However, those surveys, based on tracks left in the snow, were extremely difficult to interpret due to the unclear relationship between numbers of tracks and number of individuals. With camera traps, each individual can be identified by its unique spot pattern, providing a much more precise estimate.

Combining data from both countries increased precision of the estimate, and provided greater accuracy. Surprisingly, about one-third of the leopards were photographed on both sides of the Sino-Russian border.