North Pacific right whales, like right whales in the North Atlantic Ocean, were severely depleted by commercial whaling and are now among the world's most endangered mammals. Two populations are thought to survive, one in the western North Pacific off Russia and the other in the eastern North Pacific off Alaska. The status of both populations is poorly known. The western population is thought to number in the low hundreds although reliable information to support that estimate has not been published. The eastern population appears to number a few tens of animals, making it the most endangered marine mammal population in U.S. waters.
Early in the 1960s the eastern population apparently numbered in the low hundreds and presumably was recovering slowly. However, between 1962 and 1967 Soviet whalers killed more than 350 animals in the southeastern Bering Sea and Gulf of Alaska, despite an international ban on the hunting of all right whales. It appears that this illegal whaling virtually eliminated the population. Between the late 1960s and the mid-1990s sightings of right whales in the eastern North Pacific were rare, widely scattered, and almost always involved solitary animals. Then, in the summer of 1996, a group of four animals was reported in the southeastern Bering Sea. Each year since then, the National Marine Fisheries Service has undertaken aerial, shipboard, and/or acoustic surveys of the area during the summer.