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.
Other names include cochito, Gulf of California harbor porpoise, Gulf of California porpoise, and gulf porpoise.
Physical description 
The vaquita are the smallest species of porpoise and are found only in the northern end of the Gulf of California. The vaquita has a classic porpoise shape. They are stocky and curve into a star shape when viewed from the side. The species is distinguishable by the dark rings surrounding their eyes, patches on their lips, and a line that extends from their dorsal fins to their mouth. Their back is a dark grey that fades to a white underside. As vaquitas mature, the shades of grey lighten . Individuals only reach a size of 1.2-1.5 m (4–5 ft) and a weight of 40–55 kg (90-120 lb) when fully mature. The flippers are proportionately larger than other porpoise's 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 females are discernible from the males due to their larger size.
The habitat of the vaquita is restricted to the northern area of the Gulf of California, or Sea of Cortez. Vaquitas live in shallow, murky lagoons along the shoreline. They rarely swim deeper than 30 meters and are known to survive in lagoons so shallow that their back protrudes above the surface. The vaquita is most often sighted in water 11 to 50 metres deep, 11 to 25 kilometres from the coast, over silt and clay bottoms. Vaquitas tend to choose habitats with turbid waters, due to the fact that they have high nutrient content. The high nutrient content is important because it attracts the small fish, squid, and crustaceans that Vaquitas feed on. They are able to withstand the significant temperature fluctuations characteristic of shallow, turbid waters and lagoons.
There are very few records of the vaquita in the wild. They appear to swim and feed in a leisurely manner, but they are elusive and will avoid boats of any kind. Vaquitas rise to breathe with a slow, forward-rolling movement that barely disturbs the surface of the water, and then disappear quickly, often for a long time. In order to explore their environment and communicate with each other, vaquitas use sonar and produce high-frequency clicks that are used in echolocation.
Like other Phocoena, the vaquita are usually seen by themselves. If they are seen together, it is usually in small groups, ranging from 1 - 3 individuals in size. Less often groups of around 8 to 10 have been observed, with the most ever seen at once being 40 individuals.
Vaquitas tend to forage near lagoons. 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. It appears that the vaquitas are rather non-selective feeders on small fishes and squids in this area. Like other cetaceans, vaquitas may use echolocation to locate prey. It also is possible that vaquitas locate their prey by following the sounds given off by prey movement.
Vaquitas sexually mature at 1.3 meters, between 3 and 6 years old. They have seasonal reproduction, and usually have one calf in March. Their gestation period is between 10 and 11 months. The interbirth period, or elapsed time between offspring birth, is between 1 and 2 years. The maximum observed life span is 21 years.
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.
Because vaquitas are indigenous to the Gulf of California, Mexico is predominantly leading conservation efforts with the creation of the International Committee for the Recovery of the Vaquita (CIRVA), which has attempted to help prevent the accidental deaths of vaquita by outlawing the use of fishing nets within the vaquita’s habitat. CIRVA has worked together with the CITES, the ESA, and the Marine Mammal Protection Act (MMPA) to make a plan to nurse the vaquita population back to a point at which they can sustain themselves. CIRVA concluded in 2000 that between 39 and 84 individuals are killed each year by such gillnets. In order to try to prevent extinction, the Mexican government has created a nature reserve covering the upper part of the Gulf of California and the Colorado River delta. CIRVA recommends that this reserve be extended southwards to cover the full known area of the vaquita's range and that trawlers be completely banned from the reserve area.
On October 28, 2008, Canada, Mexico, and the United States launched the North American Conservation Action Plan (NACAP) for the vaquita., under the jurisdiction of the Commission for Environmental Cooperation (CEC), a NAFTA environmental organization. The NACAP is a strategy to support Mexico’s efforts to recover the vaquita.
Possible Threats 
- Other lesser-discussed culprits of human-based threats on the vaquita population include pollutants and habitat alterations. The habitat of the vaquita is small and the food supply in marine environments is largely dependent on water levels. The damming of the upper Colorado river has potentially decreased the food supply by decreasing water levels, indirectly effecting the vaquita population and ability to reproduce. In addition to reduced flow of freshwater from the Colorado River due to damming, the use of chlorinated pesticides and depression due to inbreeding may also have a detrimental effect. Despite the potential detrimental effects, it is important to note that most of the recovered bodies of the vaquitas show no signs of emaciation or environmental stressors, implying that the decline in the vaquita population is accredited almost solely to by-catch. However these additional hazards may pose a threat in the long-term. Even with a gillnet ban through The Refuge Area for the Protection of the Vaquita which contains 50% of the vaquita’s habitat, the population is still in decline which suggests a complete ban of gillnet use may be the only solution to saving the vaquita population.
Primary Impact 
- Removal of the vaquita will have a significant ecological impact on the Northern Gulf of California. The Gulf of California is considered a Large marine ecosystem (LME), due to its high species diversity and large habitat size. With such biodiversity in the region, it is important to consider the potentially harmful effects of slight drops in the vaquita population on seemingly unrelated species due to apparent competition.
- Sharks have been determined to be the only predators of vaquitas. Due to its limited number of predator species, the vaquita population is sensitive to small changes in predation from sharks. Although the vaquita accounts for only a small percentage of the diets of sharks in the region, extinction of the vaquita could potentially cause negative effects on shark population sizes. Extinction of the vaquita may also impact the vaquita prey populations in the Northern Gulf ecosystem. The disappearance of the vaquita could lead to potential over-population of their prey species such as benthic fishes, squid, and crustaceans.
- Conservation efforts for the vaquita are mainly focused on fishing restrictions to prevent vaquita bycatch. These fishing restrictions could prove beneficial for the fish in the upper gulf as well as the vaquita. As a result of increased restrictions on gillnet use, the populations of the targeted fish and shrimp species will receive protection from overfishing. Historically, numerous commercially fished species have experienced devastating impacts due to overfishing, and the vaquita conservation program may lessen the severity of such devastation in the future. Another solution to prevent vaquita bycatch might be to redesigning fishing nets. A redesigned net could be used to effectively catch fish but leave the vaquita untouched.
Secondary Impact of Declining Numbers 
- Though the major cause of vaquita porpoise mortality is bycatch in gillnets, numbers continue to dwindle and new factors will arise that will cause the population to further decline. One future problem that will arise with the current rate of population decline is reduced breeding rates. With less vaquita porpoise individuals in the habitat, there will eventually be significantly less contact between the different sexes and consequently less reproduction. With an even lower reproductive rate, the rate of population decline will increase. With lower contact levels between sexes, there may likely be reduced fitness due to inbreeding and less genetic variability in the gene pool, following the bottleneck effect.
- When inbreeding depression occurs, the population experiences reduced fitness because deleterious recessive genes can manifest the population. In small populations where genetic variability is low, individuals are more genetically similar. When the genomes of mating pairs are more similar, recessive traits appear more often in offspring. The more related two individuals are in the breeding pair, the more deleterious homozygous genes the offspring will likely have which can greatly lower fitness in the offspring  It is important to note that these secondary impacts of dwindling vaquita numbers are not necessarily a threat yet, but they will become problematic if the vaquita population continues to decline.
See also 
This article incorporates text from the ARKive fact-file "Vaquita" under the Creative Commons Attribution-ShareAlike 3.0 Unported License and the GFDL.
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- Examining the risk of inbreeding depression in a naturally rare cetacean, the Vaquita, Taylor and Rojas-Bracho, Marine Mammal Science Vol 15. Pages 1004-1028.
- "Vaquita (Phocoena sinus)". The Zoological Society of London. Retrieved 22 April 2013.
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- Gerrodette, T., B. L. Taylor, R. Swift, S. Rankin, A. M. Jaramillo-Legorreta, and L. Rojas-Bracho. A combined visual and acoustic estimate of 2008 abundance, and change in abundance since 1997, for the vaquita, Phocoena sinus., Marine Mammal Science, 2011
- Diaz-Uribe, J. Gabriel; Francisco Arreguín-Sánchezb, Diego Lercari-Bernierc, Víctor H. Cruz-Escalonab, Manuel J. Zetina-Rejónb, Pablo del-Monte-Lunab, Susana Martínez-Aguilara (10). "An integrated ecosystem trophic model for the North and Central Gulf of California: An alternative view for endemic species conservation". Ecological Modeling 230: 73–91. Retrieved 21 April 2013.
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- General references
- Preventing the extinction of a small population: Vaquita fishery mortality and mitigation strategies D'Agrosa, Lennert and Vidal. Conservational Biology vol 14. pages 1110-1119
- National Audubon Society: Guide to Marine Mammals of the World, Reeves et al. 2002, ISBN 0-375-41141-0
- Convention on Migratory Species