Right whales were a preferred target for whalers because of their docile nature, their slow surface-skimming feeding behaviors, their tendency to stay close to the coast, and their high blubber content (which makes them float when they are killed, and which produced high yields of whale oil). Today, the North Atlantic and North Pacific right whales are among the most endangered whales in the world, and both species are protected in the United States by the Endangered Species Act. The North Atlantic right whale has a single surviving breeding population in the western North Atlantic, and is classed as critically endangered, with a total population best estimate of 411 individuals remaining alive as of 2017. The North Pacific right whale population is classed overall as endangered and has two surviving populations, eastern and western, with the western Pacific population much larger at an estimated 1147 individuals in 2016. The eastern North Pacific population has fewer than 50 individuals remaining, and this population is considered critically endangered.