Vaquita

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 (4.9 ft) (females) or 140 cm (4.6 ft) (males) in length, it is the smallest of all living cetaceans. Today, the species is on the brink of extinction. 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 (4.9 ft), while males reach about 140 cm (4.6 ft). 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 150 m (490 ft) depth.

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.