Vaquita

The vaquita ( və-KEE-tə; Phocoena sinus) is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Reaching a maximum body length of 150 cm (4.9 ft) (females) or 140 cm (4.6 ft) (males), it is the smallest of all living cetaceans. The species is currently on the brink of extinction, and is listed as Critically Endangered by the IUCN Red List; the steep decline in abundance is primarily due to bycatch in gillnets from the illegal totoaba fishery.

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 cetacean species. They live in shallow, turbid waters of less than 150 m (490 ft) depth.

Mexico

Vaquitas are generalists, foraging on a variety of demersal fish species, crustaceans, and squids, though benthic fish such as grunts and croakers make up most of the diet.

Vaquitas are generally seen alone 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 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).

Vaquitas reach sexual maturity from three to six years old. Vaquitas have synchronous reproduction, suggesting that calving span is greater than a year. Their pregnancies last from 10 to 11 months, and vaquita calves are nursed by their mothers for 6–8 months until becoming independent. Vaquitas give birth about every other year to a single calf, usually between the months of February and April. Because of their low reproduction rates, long gestation periods and larger species size, vaquitas are considered a K-selected species. K-selected species are more vulnerable to extinction as they cannot repopulate at the rate of r-selected species. Vaquitas are on the brink of extinction because their numbers are few and they cannot replenish their population fast enough to exceed the number of vaquitas dying off.

The vaquita was defined 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. "Vaquita" is Spanish for "little cow". 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 (4.9 ft), while males reach about 140 cm (4.6 ft). Dorsal fin height is greater in males than in females. They are also known to weigh around 27 kg (60 lb) to 68 kg (150 lb). This makes them one of the smallest species in the porpoise family.

Given their proximity to the coast, vaquitas are exposed to habitat alteration and pollution from runoff. Pesticides present in the water as a result of runoff from agriculture are a threat as they can be ingested by the vaquitas, causing harm and even death. Exposure to toxic compounds has also had a deleterious effect on vaquitas. Bycatch, which is the incidental catch of non-target species in fishing gear, is not only the largest threat to the survival of the vaquita, but to all marine mammals around the world. A series of simulations in a 2022 study indicate that the species has a chance to survive and recover if all bycatch is halted, despite the presence of other threats. 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. Populations that experience a sudden decline in numbers are often more vulnerable to other threats in the future due to a bottleneck of genetic diversity within the reduced population. The reduced gene pool lowers the rate of adaptation and increases the rate of inbreeding, potentially leading to inbreeding depression. This phenomenon is attributed to the anthropogenic Allee effect, specifically on the end where small population size leads to low species fitness because of a lack of genetic diversity and the potential for inbreeding. Because of their small population size, vaquitas are experiencing a negative Allee effect, attributing to even smaller population growth rates, driving them further into extinction. However, a 2022 study on the genetic diversity of the vaquita suggests that the marine mammal's historically small population ensures it is unlikely to greatly suffer from inbreeding depression. Attempts to start a population in captivity have proved to be more threatening to the population than helpful. A November 2017 effort ended up traumatizing and killing one female vaquita, as well as subjecting a juvenile to unnecessary stress. Still, creating a captive population could be used as a last resort to save the species and to further educate on vaquitas.

The vaquita is listed as critically endangered on the IUCN Red List, which is only one level above being completely extinct in the wild. It is considered the most endangered marine mammal in the world. The vaquita has been listed as critically endangered by the IUCN Red List of Threatened Species since 1996. The vaquita is at risk of extinction due to its small population size. In 2019, the UNESCO World Heritage Site where the last vaquita are located was classified as a World Heritage Site in Danger. The vaquita is also protected under the Endangered Species Act of 1973, the Mexican Official Standard NOM-059 (Norma Oficial Mexicana), and Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). For a small population such as the vaquita to recover after a severe decline in population size is very difficult. This conservation status is strongly influenced in part of the species reproductive biology. The large number of unknowns surrounding the key reproductive parameters of the vaquita makes understanding its potential for recovery even harder.

The vaquita was defined 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. "Vaquita" is Spanish for "little cow".