The vaquita (Phocoena sinus) is a rare species of porpoise. It is endemic to the northern part of the Gulf of California. Estimates of the number of individuals alive range from 100 to 300. The word "vaquita" is Spanish for little cow. Since the baiji (Lipotes vexillifer) is believed to have gone extinct in 2006, the vaquita has taken on the title of the most endangered cetacean in the world.
Vaquita have never been hunted directly, but it is known that the vaquita population is declining. Estimates placed the vaquita population at 567 in 1997. With their population dropping as low as 150 individuals in 2007 and possibly even lower today, inbreeding depression has begun to affect the fitness of the species,further accelerating the population’s decline. The decline in the vaquita population is believed to be due to animals becoming trapped in gillnets intended for capturing the totoaba, another species endemic to the Gulf.
The vaquita is one of few marine mammal species and is considered the most endangered. The vaquita has been classified as one of the top 100 Evolutionary Distinct and Globally Endangered (EDGE) mammals in the world. The vaquita is an evolutionarily distinct animal and has no close relatives. These animals represent more, proportionally, of the tree of life than other species, meaning they are top priority for conservation campaigns. The EDGE of Existence Programme is a conservation effort that attempts to help conserve endangered animals that represent large portions of their evolutionary trees. The U.S. government has listed the vaquita as endangered under the Endangered Species Act (ESA). The vaquita is also listed by the International Union for the Conservation of Nature (IUCN) and the Convention on International Trade in the Endangered Species of Wild Fauna and Flora (CITES) in the most critical category at risk of extinction.