See the little orange things on the end of this gray whale fluke? Those are sea lice. Those parasitic little crustaceans can actually tell us a lot about the lives of whales. .
Sea lice are spread by body contact. So if whales have the same kind of lice, then you know they've been close to each other.
From this, researchers at the Federal University of Rio de Janeiro have followed the 7 different populations of humpback whales who summer in Antarctica. These populations disperse to different breeding grounds in the winter. Populations who had less contact with each other had lice which were more genetically distinct.
From this, researchers could tell that the whales wintering in the west south Atlantic seemed to prefer whales from the south Pacific over their close neighbors in the east south Atlantic.
What other secrets could whale lice tell us?