The range of Phocoena sinus is extremely restricted. This species of porpoise is found only in the northern end of the Gulf of California. Phocoena sinus (commonly known as the vaquita) are found only in shallow water, close to shore.
An interesting feature of the vaquita is that it is the only species of porpoise that is found in such warm waters. Most phocoenids are restricted to water cooler than 20 degrees Celsius, vaquitas are unique in their ability to tolerate large annual fluctuations in temperature (Hohn, et al, 1996). The Gulf of California may experience temperature ranges from 14 degrees C in January to 36 degrees C in August. This may have an effect on the reproductive seasonality of this species.
Adult vaquitas are typically 1.2 to 1.5m in length with females being slightly larger than males. At birth their average length is 0.6-0.7m. Juveniles also have white spots on their dorsal fins.
Phocoena sinus has between 34-40 teeth which are unicuspid, or "acorn like" (Silber, 1990) and a blunted rostral profile. P. sinus are physically similar to the Harbor Porpoise (/Phocoena phocoena/) in many ways with an exception being that the vaquita is more slender. This has been explained in terms of their warmer habitat--the slender body increases surface area/volume ratio thus increasing heat dissipation in a warm environment. This explanation has also been used to explain the occurrence of larger appendages within this species (Hohn et al., 1996).
Vaquitas are usually solitary. This would indicate a social system in which sperm competition is extremely important (Hohn et al., 1996). Within such systems, males attempt to maximize their fitness not by monopolizing access to females, but rather by mating with as many females as possible. As would be expected in multi-male breeding systems, male vaquitas have relatively large testes size in comparison to their body size.
Sexual maturity is believed to be reached between the ages of three and six years. Body mass may help to distinguish mature from immature specimens for both males and females (Hohn et al., 1996). Vaquitas have highly seasonal reproduction. During the spring there is a complete lack of larger calves. The mating period is from mid-April to May, with a gestation period of roughly 10.6 months. Births occur at the beginning of the following March. P. sinus have non-annual ovulation, thus they do not produce calves each year (Hohn et al., 1996). Females have one calf per pregnancy and lactate for less than one year.
Vaquitas have been observed singly or in small groups, indicating that they are primarily solitary individuals. Like many other phocoenids, P. sinus uses sonar as a means of communicating and navigating through its habitat.
Vaquitas feed on teleost fishes and squid, which are found near the surface of the water. In several individuals the remains of Guld croakers were found.
This species is not used directly by humans. It is interesting in the sense that it is a unique phocoenid morphologically and behaviorally. The fact that it is limited in its range and is extremely endangered should encourage study of the vaquita.
P. sinus may interfere with human activity is in that it may inadvertantly become entangled in fishing nets set for shrimp, sharks, and totoabo causing a nuisance and possibly reducing catch during one net hauling.
Vaquita are listed as critically endangered. They are perhaps the most endangered of the cetaceans with only a few hundred remaining. Phocoena sinus are often caught in fishing nets which are set to catch other marine animals, most often shrimp. This species becomes entangled either in the shrimp nets or within gillnet fisheries for sharks. It is estimated that 25-30 individuals drown each year as a result. To further complicate the situation, relatively few individuals reach maturity because of the high mortality of young individuals (they are highly susceptible to being netted), and the remaining older individuals are approaching the upper limit of their lifespan so as to be contributing little to future reproduction (Hohn et al, 1996).
An interesting side note concerning the survival of this species is that it is often directly tied to the survival of the endangered totoabo, a fish resembling the seabass. Totoabo have been widely fished as they are considered a delicacy. Unfortunately totoabo are similar in size and shape to vaquitas and they are often mistaken. In this manner, the more sought after totoabo are, the more bleak the chances of survival for vaquitas. Fishing for totoabo has become illegal but continues to occur on a wide scale. Conservation of these species must occur in tandem.
Devon Landes (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats fish
having more than one female as a mate at one time
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
"The Porpoise Page" (On-line). Accessed November 18, 1999 at http://www.geocities.com/CapeCanaveral/Lab/9336/vaquita.html.
"Vaquita, phocoena sinus" (On-line). Accessed November 18, 1999 at http://phocoena.org/factsheets/vaquita.html.
Hohn, A., A. Read, S. Fernandez, O. Vidal, L. Findley. 1996. Life History of the Vaquita, Phocoena sinus. Journal of Zoology, 239: 235-251.
Silber, G. 1990. Occurrence and Distribution of the Vaquita Phocoena sinus in the Northern Gulf of California. Fishery Bulletin, 88, no #2: 339-346.