Temporal range: Holocene 
|Size compared to an average human|
The vaquita (Phocoena sinus), literally "little cow", is a species of porpoise endemic to the northern end of the Gulf of California (Sea of Cortez, Vermilion Sea). Averaging 150 cm (for females) or 140 cm (for males) in length, it is the smallest of all living cetaceans. Today, the species is on the brink of extinction. Recent research estimates the population at fewer than 10 individuals. The steep decline in abundance is primarily due to bycatch in gillnets from the illegal totoaba fishery.
The vaquita was first described as a species by two zoologists, Kenneth S. Norris and William N. McFarland, in 1958 after studying the morphology of skull specimens found on the beach. It was not until nearly thirty years later, in 1985, that fresh specimens allowed scientists to describe their external appearance fully.
The genus Phocoena comprises four species of porpoise, most of which inhabit coastal waters (the spectacled porpoise is more oceanic). The vaquita is most closely related to Burmeister's porpoise (Phocoena spinipinnis) and less so to the spectacled porpoise (Phocoena dioptrica), two species limited to the Southern Hemisphere. Their ancestors are thought to have moved north across the equator more than 2.5 million years ago during a period of cooling in the Pleistocene.Genome sequencing from an individual captured in 2017 indicates that the ancestral vaquitas had already gone through a major population bottleneck in the past, which may explain why the few remaining individuals are still healthy despite the very low population size.
The smallest living species of cetacean, the vaquita can be easily distinguished from any other species in its range. It has a small body with an unusually tall, triangular dorsal fin, a rounded head, and no distinguished beak. The coloration is mostly grey with a darker back and a white ventral field. Prominent black patches surround its lips and eyes.Sexual dimorphism is apparent in body size, with mature females being longer than males and having larger heads and wider flippers. Females reach a maximum size of about 150 cm (4' 11"), while males reach about 140 cm (4' 7"). Dorsal fin height is greater in males than in females.
Vaquita habitat is restricted to a small portion of the upper Gulf of California (also called the Sea of Cortez), making this the smallest range of any marine mammal species. They live in shallow, turbid waters of less than 50 m depth (150 ft).
Vaquitas are generally seen singly or in pairs, often with a calf, but have been observed in small groups of up to 10 individuals.
Little is known about the life history of this species. Life expectancy is estimated at about 20 years and age of sexual maturity is somewhere between 3 and 6 years of age. While an initial analysis of stranded vaquitas estimated a two-year calving interval, recent sightings data suggest that vaquitas can reproduce annually. It is thought that vaquitas have a polygynous mating system in which males compete for females. This competition is evidenced by the presence of sexual dimorphism (females are larger than males), small group sizes, and large testes (accounting for nearly 3% of body mass).
Because the vaquita was only fully described in the late 1980s, historical abundance is unknown. The first comprehensive vaquita survey throughout their range took place in 1997 and estimated a population of 567 individuals. By 2007 abundance was estimated to have dropped to 150. Population abundance as of 2018 was estimated at less than 19 individuals. Given the continued rate of bycatch and low reproductive output from a small population, it is possible that there are as few as 10 vaquitas alive today.
The drastic decline in vaquita abundance is the result of fisheries bycatch in commercial and illegal gillnets, including fisheries targeting the now-endangered totoaba, shrimp, and other available fish species. In spite of government regulations, including a partial gillnet ban in 2015 and establishment of a permanent gillnet exclusion zone in 2017, illegal fishing remains prevalent in vaquita habitat, and as a result the population has continued to decline.
Given their proximity to the coast, vaquitas are exposed to habitat alteration and pollution from runoff. There is no evidence, however, that these threats have made any significant contribution to their decline. Bycatch is the single biggest threat to the survival of the few remaining vaquita.
Predation on vaquita by sharks has also been reported from fishermen, who have seen whole or parts of individuals in the stomachs of caught sharks however no quantitative analysis is readily available. However, the biggest threat still towards vaquita are fisheries. Northern fishing fleets have had an indirect positive impact mainly on marine mammals, because fishing on predators like sharks reduces its predatory negative impact on those groups. Although, the predation of sharks towards vaquita do result in a decline in population and is seen as an alternate threat, northern fishing fleets also negatively impact this small marine mammal because the negative influence of incidental catch is greater than the positive influence of predation reduction by shark fisheries.
The species is also protected under the US Endangered Species Act, the Mexican Official Standard NOM-059 (Norma Oficial Mexicana) , and Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
The Mexican government, international committees, scientists, and conservation groups have recommended and implemented plans to help reduce the rate of bycatch, enforce gillnet bans, and promote population recovery.
Mexico launched a program in 2008 called PACE-VAQUITA in an effort to enforce the gillnet ban in the Biosphere Reserve, allow fishermen to swap their gillnets for vaquita-safe fishing gear, and provide economic support to fishermen for surrendering fishing permits and pursuing alternative livelihoods. Despite the progress made with legal fishermen, hundreds of poachers continued to fish in the exclusion zone.
With continued illegal totoaba fishing and uncontrolled bycatch of vaquitas, the International Committee for the Recovery of the Vaquita (CIRVA) recommended that some vaquitas be removed from the high-density fishing area and be relocated to protected sea pens. This effort, called VaquitaCPR, captured two vaquitas in 2017: one was later released and the other died shortly after capture after both suffered from shock.
Local and international conservation groups, including Museo de Ballena and Sea Shepherd Conservation Society, are working with the Mexican Navy to detect fishing in the Refuge Area and remove illegal gillnets. In March 2020, the U.S. National Marine Fisheries Service (NMFS) announced a ban on imported Mexican shrimp and other seafood caught in vaquita habitat in the northern Gulf of California.
To date, efforts have been unsuccessful in solving the complex socioeconomic and environmental issues that affect vaquita conservation and the greater Gulf of California ecosystem. Necessary action includes habitat protection, resource management, education, fisheries enforcement, alternative livelihoods for fishermen, and raising awareness of the vaquita and associated issues.
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