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Pontoporia blainvilleifranciscana

By stacey collerone

Geographic Range

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. (Bassoi, et al., 2009; Bastida, et al., 2002a; Bordino, et al., 2008; Cremer and Simoes-Lopes, 2008; Danilewicz, et al., 2003a; Di Beneditto and Ramos, 2001; Hamilton, et al., 2004)

Habitat

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. (Abud, et al., 2009; Bassoi, et al., 2009; Bastida, et al., 2002a; Bordino, et al., 1999)

  • Range depth
    6 to 35 m
    19.69 to 114.83 ft

Physical Description

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. (Botta, et al., 2010; Cremer and Simoes-Lopes, 2008; Danilewicz, et al., 2003b; Di Beneditto, et al., 2000; Hamilton, et al., 2004; Higa, et al., 2002; Hohn and Pinedo, 2000; Huggenberger, et al., 2010; Praderi and Trimble, 2006)

  • Sexual Dimorphism
  • female larger
  • Average mass
    males 26 kg; females 32 kg
    lb
  • Average mass
    40500 g
    1427.31 oz
    AnAge
  • Range length
    76 to 171 cm
    29.92 to 67.32 in

Reproduction

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. (Bordino, et al., 1999; Carrera, et al., 2004; Danilewicz, 2003)

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. (Abud, et al., 2009; Bastida, et al., 2002a; Bordino, et al., 1999; Caon, et al., 2007; Danilewicz, 2003; Danilewicz, et al., 2003b; Di Beneditto and Ramos, 2001; Valsecchi and Zanelatto, 2003)

  • Breeding interval
    Franciscana dolphins breed once yearly.
  • Breeding season
    Most Franciscana dolphins mate between May and August.
  • Range number of offspring
    4 to 8
  • Average number of offspring
    1
    AnAge
  • 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

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. (Bordino, et al., 1999; Caon, et al., 2008; Caon, et al., 2007; Cremer, et al., 2006; Danilewicz, 2003; Di Beneditto and Ramos, 2001; Di Beneditto, et al., 2007; Pilleri, 1971)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Lifespan/Longevity

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. (Abud, et al., 2009; Botta, et al., 2010; Danilewicz, et al., 2003b; Di Beneditto and Ramos, 2001)

Behavior

Franciscana dolphins are diurnal and have been observed in groups of 10 to 20 individuals. The social structure may be matriarchal, and these dolphins may travel in kin groups. They likely form groups during the mating season and/or during the winter when decreases in food abundance may lead to cooperative foraging. Kin grouping could be a form of male mate guarding, which is beneficial to small populations when successful parents remain together. It is not known if this behavior truly occurs, although males and females have been observed traveling together.

Franciscana dolphins spend more time foraging during high tide and traveling during low tide. They exhibit a type of cooperative feeding in which a group of dolphins moves in a circle around a school of fish.

Franciscana dolphins average a swimming speed of 0.09 m/sec with a maximum speed of 1.8 m/sec. Ventilation rate decreases with swimming and diving speed. Franciscana dolphin move in a variety of ways, including milling, diving, swimming in a set direction, and erratic patterns with abrupt changes in direction or speed. (Bordino, et al., 2008; Bordino, et al., 1999; Cremer and Simoes-Lopes, 2008; Crespo and Di Cidre, 2005; Valsecchi and Zanelatto, 2003)

Home Range

The home range of Franciscana dolphins is likely influenced by the distribution of the fish they consume. They may regularly visit areas within their home range where they have successfully found fish in the past. (Cremer and Simoes-Lopes, 2005)

Communication and Perception

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. (Adams, et al., 2000; Bordino, et al., 2008; Hamilton, et al., 2004; Huggenberger, et al., 2010)

Food Habits

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. (Bastida, et al., 2002b; Bittar and Di Beneditto, 2009; Bordino, et al., 1999; Di Beneditto and Ramos, 2001; Di Beneditto, et al., 2007; Di Beneditto, et al., 2009)

  • Primary Diet
  • carnivore
    • piscivore
    • eats non-insect arthropods
    • eats other marine invertebrates
  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

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. (Bastida, et al., 2002b; Botta, et al., 2010; Danilewicz and Ott, 1998; Di Beneditto, 2004; Netto and Santos, 2005)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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. (Andrade, et al., 2002; Di Beneditto and Ramos, 2001; Di Beneditto, et al., 2007)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known positive economic benefits of this species on humans.

Economic Importance for Humans: Negative

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. (Albarbeda, et al., 2002; Di Beneditto, et al., 2007)

Conservation Status

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. (Albarbeda, et al., 2002; Bordino, et al., 2008; Botta, et al., 2010; Colborn, et al., 1993; Cremer and Simoes-Lopes, 2008; Crespo, et al., 2010; Danilewicz, et al., 2003b; Di Beneditto and Ramos, 2001; Di Beneditto, et al., 2007; Fillmann, et al., 2010; Gaddy, et al., 1975; Hamilton, et al., 2004)

Other Comments

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. (Bordino, et al., 1999; Botta, et al., 2010; Di Beneditto, et al., 2007; Hamilton, et al., 2004)

Contributors

stacey collerone (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Gail McCormick (editor), Animal Diversity Web Staff.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

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.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

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Adams, J., F. Schulmeyer, H. Oelschlager. 2000. Specialized sound reception in dolphins—a hint for the function of the dorsal cochlear nucleus in mammals. Historical biology, 14(1): 53-56.

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Carrera, A., J. Claver, D. Danilewicz, E. Secchi, N. Fontoura. 2004. Reproductive biology of male franciscanas (Pontoporia blainvillei) (Mammailia: Cetacea) from Rio Grande do Sul, southern Brazil. Fishery Bulletin, 102(4): 581-592.

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