Franciscana dolphins are also known as La Plata dolphins or Toninha. There are two distinct genetic stocks, one north and one south, and it has been suggested that these populations should be further taxonomically subdivided. This genetic split is due to ecological forces rather than a geographic barrier separating gene flow.
Franciscana dolphins have the ability to detoxify their blood and store heavy metals in non-toxic forms. The mechanism that allows these dolphins to hold high amounts of mercury involve the demethlyization of mercury in the liver which turns it into mercuric selenide (non toxic and inert). They also have mechanisms that allow them to use selenium (heavy metal) and metallothioneins to detoxify the other heavy metals, such as arsenic and cadmium.
Franciscana dolphins have reduced vision, a small melon, and a small epicranial complex. They echolocate in a similar manner as harbor porpoises (Phocoena phocoena). Franciscana dolphins produce high-frequency clicks at 130 kHz that are narrow banded at 20 kHz. These ultrasonic signals are generated through the upper nasal passages and are received by the lower jaw, tympanic bone and the ear ossicles. It is unknown if echolocation is involved in communication of this species; however, it is plausible, as closely related species do so.
Perception Channels: visual ; tactile ; echolocation ; chemical
Though it is difficult to accurately estimate the population size of P. blainvillei, it is thought to be the most threatened small cetacean in the southwest Atlantic Ocean and is listed by the IUCN as vulnerable. Population growth is 2% per year, which is not enough to compensate for the upwards of 500 to 800 individuals lost annually. Mortality is primarily due to humans. Although this species is not directly exploited in Latin America, franciscana dolphins are caught in gill-nets as by-catch where they may drown or be eaten by sharks. Gill nets have more of an impact when placed closer to both the coast and the surface of the water, and catches are biased towards young franciscana dolphins and individuals with a particular haplotype. Additionally, franciscana dolphins may ingest plastics and discarded fishing gear, or accumulate high amounts of heavy metals and PCBs. Because of their high trophic level, this species is particularly susceptible to pollution.
Four different franicscana dolphin management areas (FMA) have been proposed to protect the greatest amount of genetic diversity. FMA I is Rio de Janeiro and Espirito Santo states, Brazil, FMA II is Sao Paula to Santa Catarina states, Brazil, FMA III is Rio Grande do Sul Brazil and Uruguay, and FMA IV is Argentina.
A variety of strategies to limit gill net by-catch have been suggested and/or implemented, including limiting net length, number of boats, and replacing fishing gear with dolphin friendly equipment. It is unknown why franciscana dolphins are caught in nets; they may be unable to detect the net or the net may not be perceived as a possible threat. To help dolphins detect the nets, alarms (pingers) were attached, which decreased dolphin mortality rate. However, the alarms also increased predation of captured fish by sea lions. Another problem with long term use of this system is the possibility that the dolphins may become habituated to the alarms.
US Federal List: no special status
CITES: appendix i
IUCN Red List of Threatened Species: vulnerable
Although other species of dolphins negatively impact fisheries, Franciscana dolphins rarely cause damage and generally do not eat species of fish preferred by fishermen. Thus there do not appear to be negative impacts of this species on humans.
There are no known positive economic benefits of this species on humans.
In the northern region parasites of franciscana dolphins are rare, but there have been reports of some parasites in southern populations including acanthocephalans (Polymorphus), and trematodes (Hadwenius pontoporiae). Barnacles, like Xenobalanus globicipitis, occasionally attach to these dolphins.
Commensal/Parasitic Species:
Franciscana dolphins are carnivores that specialize on fish and marine invertebrates. These mammals eat fish about 10 cm long but their most important food source is squid. Because the oral apparatus and digestive tract of Franciscana dolphins are small, they are limited in the size of the prey they can ingest. Squids, which contain a high water content, are easier to digest than many other marine species. Franciscana dolphins also exploit other pelagic and demersal species, including teleosts (Stellifer spp., Anchoa filifers, Pellona harroweri and Isoisthus parvipinnis), cephalopods (Loligo sanpaulensis and Loligo plei) and sometimes crustaceans (Artemesia longinaris and Xyphopenaeus kroyeri). Franciscana dolphins have also been known to eat Cynoscion guatucupa, Trichiurus lepturus, Macrodon ancylodon, Umbrina canosai, Micropogonias furnieri, and Urophycis brasiliensis. There is large variation in diet among coastal populations of this species. Calves primarily feed on Neomysis americana, a species of shrimp not commonly exploited by adults.
Animal Foods: fish; mollusks; aquatic crustaceans
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Eats other marine invertebrates)
Franciscana dolphins, Pontoporia blainvillei, are endemic to the west coast of Brazil, Uruguay and Argentina. They range from Itaunas, Espirito Santo, Brazil to Golfo Nuevi, Peninsula Valdes, Argentina. They are also found in estuaries, such as the La Plata River and Babitonga Bay. There are distinct gaps in their distribution between Ubatub and Macae and also between Barra de Itabapoana and Regencia. Franciscana dolphins may have a seasonal distribution in Babitonga Bay, where dolphins are found farther from the coast in winter. There are north and south genetic stocks of dolphins with a geographical boundary at Mostardas.
Biogeographic Regions: neotropical (Native )
Franciscana dolphins occupy both marine and estuarine coastal waters, which are usually warm and turbid with counter-currents. Along the coast of Argentina, they occupy waters closer to the shore in spring and summer and farther from shore during winter. In other areas, populations do not move seasonally from the coast, most likely because water temperature remains fairly constant. Preferred habitat is influenced by the tides. Franciscana dolphins favor water depths from 6 to 35 m at distances up to 55 km from the coast.
Range depth: 6 to 35 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: pelagic ; coastal
Other Habitat Features: estuarine
Franciscana dolphins typically live 13 to 20 years. The maximum known age of males is 17 years, while the female maximum is a few years longer at 21 years. Because of incidental mortality caused by by-catch in gill-nets, only a small percent of the population lives more than 12 years.
Range lifespan
Status: wild: 13 to 21 years.
Average lifespan
Status: wild: 12 years.
Average lifespan
Status: wild: 16.0 years.
Franciscana dolphins have a long, narrow beak and are smaller in size than other toothed whales. They have a small melon and epicranial complex with a very symmetrical facial skull. Females are 80 to 171 cm in length and average 32 kg while males are smaller, ranging from 76 to 147 cm in length and averaging 26 kg. Growth rates of franciscana dolphins are some of the largest in the order Cetacea, with females growing faster than males. The dorsal side can be brown to gray in color and the ventral is lighter in color. This coloration is thought to be cryptic, as the countershading could be an antipredator strategy.
The anterior teeth of franciscana are longer than posterior teeth. Some individuals have teeth that are twisted at the crown, though the function of these teeth is unknown. Franciscana dolphins have approximately 50 to 63 teeth per hemi-arch, and tooth length ranges from 6.2 to 9.1 mm.
Average mass: males 26 kg; females 32 kg.
Range length: 76 to 171 cm.
Sexual Dimorphism: female larger
Other Physical Features: endothermic ; bilateral symmetry
Average mass: 40500 g.
Killer whales have been observed attacking Franciscana dolphins, and portions of P. blainvillei have been found in their stomachs. Many speices of sharks also prey on Franciscana dolphins, including tiger sharks (Galeocerdo cuvier, Carcharias taurus), sevengill sharks (Notorynchus cepedianus), hammerheads (Sphyrna) and requiem sharks (Carcharinus).
Sharks likely attack from beneath the dolphin, where they cannot be visual spotted or sensed by echolocation. No antipredator behaviours have been reported, but it is thought that countershading helps this species elude predators.
Known Predators:
Anti-predator Adaptations: cryptic
Little is known regarding the mating systems of Franciscana dolphins. The small testis weight relative to body size suggests that sperm competition is unlikely in this species. Strong male-male competition for females is also unlikely based on the reversed sexual dimorphism (females are larger than males), and males are rarely scarred by conspecifics. It has been suggested that Franciscana are monogamous.
The northern stock of Franciscana dolphins has a sex ratio of 2:1 males to females, while the southern stock has a ratio of 1:1. Mating occurs from May to August, though the population in Rio de Janeiro mates year round. Most females calve all year. In some populations, however, the birth period ranges from November to March. Female franciscana dolphins have one calf per year with approximately 1.5 years between calf births. They have 4 to 8 offspring in their lifetime. Gestation lasts 10.5 to 11.2 months.
Calves are weaned at 8 to 9 months of age (about 105 cm in length) and reach sexual maturity fairly rapidly compared to other small Cetaceans. Males reach maturity at about 2 to 3.5 years (115 to 128 cm and 26 kg), while females mature at 2 to 5 years (130 to 138 cm and 32 kg). Size and age of maturity varies by region, particularly between northern and southern populations.
Breeding interval: Franciscana dolphins breed once yearly.
Breeding season: Most Franciscana dolphins mate between May and August.
Range number of offspring: 4 to 8.
Range gestation period: 10.5 to 11.2 months.
Range weaning age: 8 to 9 months.
Range age at sexual or reproductive maturity (female): 2 to 5 years.
Range age at sexual or reproductive maturity (male): 2 to 3.5 years.
Key Reproductive Features: seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Average birth mass: 7900 g.
Average number of offspring: 1.
Parental investment is primarily provided by female franciscana dolphins, although it is possible that father-offspring interactions occur. Females feed their offspring milk produced from lipids stored in their blubber. The milk changes composition depending on season; in winter, milk contains more fat then in the summer. Calves are weaned at 8 to 9 months of age.
Caves go through three stages with their mother. In the first stage, calves suckle and ingest only milk. At this stage, calves are 56.8 to 76.5 cm long and weigh 2.9 to 8.7 kg. In the second or transition stage, calves still nurse but begin to eat solid food, usually shrimp. Calves at this stage are 78 to 94 cm long and weigh 8.3 to 11.5 kg. In the weaning stage, calves transitions to only solid food and average 105 cm in length. Although calves differ in size, weight and diet in the transition and weaning stages, there are no physiological differences.
There have been two reports of epimeletic (nurturant) behavior in franciscana dolphins. Teeth marks from adult dolphins were found on dead calves that had been caught in fishing nets. This could be a form of nurturant behavior in which the mother attempts to save her calf from drowning in the net.
Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)
