Although North Atlantic right whales, humpback whales and bowhead whales–all species of baleen whales–are some of the largest animals on Earth, they are also among the most critically endangered. These whales were hunted nearly to extinction over the last 300 years for their blubber, which was used to produce oil. Fortunately, these species are repopulating, but because they reproduce slowly, their numbers are more vulnerable to dangers such as collisions with ships and entanglement in fishing lines.