The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Within this order, there are two suborders, the Mysticeti, or baleen whales, and the Odontoceti, or toothed whales. However, these terms can also be used as a way to distinguish size among species, with cetaceans longer than about 9 feet considered whales, and those less than 9 feet considered dolphins and porpoises.
The four major differences between dolphins and porpoises:
1. Dolphins have cone-shaped teeth while porpoises have flat or spade-shaped teeth.
2. Dolphins usually have a pronounced “beak,” while porpoises do not have a beak.
3. Dolphins have a very curved or hooked dorsal fin, while porpoises have a triangular dorsal fin.
4. Porpoises are generally smaller than dolphins.
To get even more specific, the term porpoise should also refer only to the six species that are in the family Phocoenidae (harbor porpoise, vaquita, spectacled porpoise, Burmeister’s porpoise, finless porpoise and Dall’s porpoise.)
Vaquita
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, Gulf Porpoise, Hafenschweinswal, and Marsouin du Golfe de Californie.
Physical Description
The vaquita is the smallest of all cetaceans. The current known maximum length is 1.5 m, and the weight about 45 - 50kg. Females are larger than males, as is the case with most species of the porpoise family. The flippers are proportionately larger and the dorsal fin is taller and more falcate. Although it shares the typical stocky body shape of all porpoises with a girth up to 68% of its body length and a blunt beakless head, the vaquita’s appearance is quite distinct from the other five porpoise species. The vaquita has an even, dark gray tone on the back that morphs into a lighter gray on the sides ending in a whitish belly. However, by far its most distinguishing feature is its face. The vaquita sports a black ring around each eye, a stripe from chin to flipper and a definitive black lipped-smile.
Habitat and Range
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.
Status
Classified as Critically Endangered (CR) on the IUCN Red List.
Population
Estimates of the number of individuals alive range from 100 to 300 and is still falling by 40 animals every year.
Biology
The vaquita is an elusive marine mammal, which surfaces slowly, barely disturbing the water’s surface when it breathes and then quickly disappearing for long periods. Its cryptic behavior and rarity may be the reasons why little is known about the biology of the vaquita, except that most vaquita births occur around March, gestation is believed to last around 10 to 11 months and one individual was estimated to have lived for 21 years.
Little is also known about the social organization of this enigmatic species. While the vaquita is most often seen in schools of one to three individuals, groups as large as eight or ten have been seen, and these small schools may form large, loose aggregations for short periods.
The vaquita has a varied diet, comprising fish that live on or near the ocean bottom, squid and crustaceans. 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 echolocation. In the murky waters of its habitat, echolocation may also be used to communicate with other vaquitas.
Threat
It was estimated in 2007 that only around 150 vaquita remained in the world; a number that is declining rapidly as the species is impacted by significant threats. The upper Gulf of California is not only home to this Critically Endangered species; it is also the site of intensive commercial and artisanal fishing. Vaquitas become entangled in the gill nets and trawl nets that are used in these activities, claiming the lives of an estimated 39 to 84 vaquitas each year. This is considered the principal threat to the vaquita’s survival.
The habitat of the vaquita has undoubtedly been changed by the damming of the Colorado River in the United States and the resulting loss of its flow into the Gulf of California; however, the Gulf remains incredibly productive and loss of river input is not believed to be an immediate threat to the vaquita.
Conservation
Time is quickly running out for the vaquita, with a group of scientists in 2007 stating that they believed there were only two years remaining in which to find a solution to saving this species. Some measures have already been implemented; the Mexican government created the Upper Gulf of California and Colorado River Delta Biosphere Reserve in 1993 to protect the vaquita and other endangered species. In 2005, the Government also created a vaquita reserve, the area of which partially overlaps with the Biosphere Reserve. A ban on gillnet fishing is currently being enforced within the vaquita reserve, but gillnetting and shrimp trawling continues in the Biosphere Reserve and elsewhere within the range of vaquita. Whilst these are incredibly important steps in the battle to save the vaquita, if conservation efforts are not increased substantially the vaquita will become extinct.
The Mexican government created the International Committee for the Recovery of the Vaquita (CIRVA): a group of scientists from the UK, Canada, US and Mexico. CIRVA recommends that the most critical measure for the conservation of the vaquita is to reduce by-catch to zero as soon as possible. This will need to be achieved by banning the use of all entangling fishing nets within the vaquitas range. Unfortunately, this is not an easy law to implement, as this will have a serious impact on the people whose livelihoods depend on fishing in the Gulf of California. Funds are urgently needed to buy out these net fisheries and to develop economic alternatives for those people affected. One can only hope that lessons are learnt from the tragic tale of the baiji and that necessary measures are implemented before the vaquita too is driven to extinction.
References
http://en.wikipedia.org/wiki/Vaquita
http://www.defenders.org/vaquita/basic-facts
http://wwf.panda.org/what_we_do/endangered_species/cetaceans/about/vaquita/
http://vaquita.tv/about-vaquita/