Rarest cetacean

The world's rarest species of cetacean is the vaquita or Gulf of California porpoise (Phocoena sinus). Confined entirely to the northern portion of the Gulf of California in north-eastern Mexico, in November 2016 this very small species' total number of individuals was estimated to be around 30. Due to accidental trapping in fish nets and also nowadays to inbreeding, resulting in a decrease in individual survival fitness, the vaquita's population is estimated to be falling by as much as 49% a year and the species is therefore in grave danger of extinction in the near future. It is categorized as Critically Endangered by the IUCN.

The previous holder of this record was the Chinese river dolphin or baiji (Lipotes vexillifer). Formerly native to China's Yangtze River, it was officially declared extinct in December 2006, since when no confirmed sightings have been documented. In 2007, a video was filmed of what may have been a living baiji, but the creature's identity was not confirmed. In any case, if only a single individual remains alive the species is deemed to be functionally extinct, because it cannot reproduce.