North Sea cetaceans include various porpoise, dolphin and whale species. Porpoises range in size from the and Vaquita to the and Dall's porpoise. It is not to be confused with the Chinese white dolphin or the finless porpoise. The freshwater finless porpoise, a Class II protected species, is rarer than the giant panda. The Indo-Pacific finless porpoise ('), or finless porpoise, is one of seven porpoise species. The finless porpoise is known to also follow seasonal migrations. In 2010, the Yangtze population of finless porpoise was 1000 individuals. The reserve is now a breeding ground for the finless porpoise. The freshwater porpoise faces the same threat as the baiji. Pitted Ware sites contain bones from elk, deer, beaver, seal, porpoise, and pig. The vaquita porpoise, discovered in 1958, has become the most endangered marine species. Nothing is known about the diet of the spectacled porpoise. Only a single Burmeister's porpoise and a single spectacled porpoise have been kept in captivity. King penguins also "porpoise", a swimming technique used to breathe while maintaining speed. There are seven extant species of porpoise.