The Vaquita 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.
The Vaquita has a classic porpoise shape (stocky and curved into a star shape when viewed from the side). It is the smallest of the porpoises, a group of marine mammals that differ from dolphins in their stockier, robust body, lack of an elongated beak, and their distinctively shaped teeth. Individuals may reach a mature size of 1.2-1.5 m (4-5 ft) and may weigh 40-55 kg (90-120 lb). They have large black eye rings and lip patches. The upper side of the body is medium to dark grey. The underside is off-white to light grey but the demarcation between the sides is indistinct. The flippers are proportionately larger than in other porpoises and the fin is taller and more falcate. The skull is smaller and the rostrum is shorter and broader than in other members of the genus.
The habitat of the vaquita is thought to be restricted to the northern area of the Gulf of California. The Vaquita lives in shallow, murky lagoons along the shoreline and is rarely seen in water much deeper than 30 meters; indeed, it can survive in lagoons so shallow that its back protrudes above the surface. The Vaquita is most often sighted in water 11 to 50 meters deep, 11 to 25 kilometers from the coast, over silt and clay bottoms. Its habitat is characterized by turbid water with a high nutrient content. Other characteristics of its habitat are strong tidal mixing, convection processes and high primary and secondary productivity.
There are very few records of the Vaquita in the wild. It appears to swim and feed in a leisurely manner, but is elusive and will avoid boats of any kind. It rises to breathe with a slow, forward-rolling movement that barely disturbs the surface of the water, and then disappears quickly, often for a long time. It has an indistinct blow, but makes a loud, sharp, puffing sound reminiscent of the Harbor Porpoise.
All of the 17 fish species found in vaquita stomachs can be classified as demersal and or benthic species inhabiting relatively shallow water in the upper Gulf of California, and it appears that the vaquita is a rather non-selective feeder on small fishes and squids in this zone. Like other cetaceans, the vaquita produces high-frequency clicks which are used in echolocation. This may be used to locate their prey, but several of the fish species it feeds on are known to produce sound and so it is possible that the vaquita locates them by following their sound, rather than by echolocating.