To identify individual blue whales we take photographs of the pigmentation patterns on both flanks. Because of their length, two pictures of each flank are needed. The first picture covers the blowhole to mid body and the second from mid body to dorsal fin. Pigmentation patterns vary from light gray on a predominantly dark gray background pigment to the inverse where a dark gray pattern stands. We take both sides, because the pigmentation pattern is symmetric but not identical on both sides.
Minke whales are much more difficult in comparison. Although they do have some pigmentation on their sides, it is very subtle and mostly visible after the final breath as they round out to dive exposing more of their sides. Because taking such ID images is difficult, we predominantly take pictures of the dorsal fin. Limited in this manner, we cannot identify all individuals as easily as with the other species, and have to estimate the proportion of animals carrying recognizable marks.