Franciscana Dolphins (Pontoporiidae)
Franciscana Dolphins (Pontoporiidae)
Small gray or brown dolphin with very long and slender beak and prominent forehead; the flippers are broad with a squared trailing edge and the dorsal fin is triangular with a rounded tip
Females 4.4–5.7 ft (1.34–1.74 m), males 4.1–5.2 ft (1.25–1.58 m); mature females weigh 75–117 lb (34–53 kg), males 64–94.8 lb (29–43 kg)
Number of genera, species
1 genus; 1 species
Temperate coastal waters and estuaries
Central Atlantic waters of South America from Espírito Santo, Brazil (18°25′S) to Peninsula Valdés (42°35′S), Argentina
Evolution and systematics
Two fossils (Pliopontes and Brachydelphis), dating from early Pliocene and middle Miocene, were recovered from Peru. Uncertainty continues to surround the fossil Parapontoporia; some workers argue that it is similar to Lipotes (baiji) and include it in superfamily Lipotoidae.
Phylogenetic relationships continue to be debated. A consensus suggests a close association between the franciscana (Pontoporia blainvillei) and boto, or the Amazon River dolphin (Inia geoffrensis), forming a sister group of Delphinoidea (porpoises, monodontids, and marine dolphins). Thus, P. blainvillei is seen as distant from other river dolphins such as the Ganges and Indus river dolphin, Platanista gangetica.
Pontoporia blainvillei is the single member of the family Pontoporiidae. Together with I. geoffrensis, it forms the superfamily Inioidea. Classification of this species is still controversial. By some, it has been grouped with Lipotes in the family Pontoporidae, while other researchers combined the three species under the family Iniidae.
The taxonomy for this species is Pontoporia blainvillei (Gervais and d'Orbigny, 1844), mouth of the Rio de La Plata near Montevideo, Uruguay. Other common names include: English: La Plata river dolphin; French: Dauphin de la Plata; Spanish: Delfín de la Plata, tonina.
Franciscana is one of the smallest cetaceans, not exceeding 5.2 ft (1.58 m) in males and 5.7 ft (1.74 m) in females. The most distinct feature is the long and slender beak, which in adults reaches 15% of the total length. The mouth line is straight, curving slightly upward at the ends. The forehead is prominent, particularly in juveniles. The dorsal fin is triangular with a rounded tip. The flippers are broad and truncated, while the flukes are crescent-shaped with a medial notch. Like other river dolphins, all the cervical vertebrae are separated, providing great flexibility. Coloration is dark gray or brown, lighter ventrally and on the lower flanks.
The brain is the smallest among cetaceans (0.45–0.55 lb [205–250 g]).
Franciscana occurs in the coastal central Atlantic waters of South America. Currently, it ranges from Espirito Santo in southeastern Brazil to Golfo Nuevo, Peninsula Valdés in Argentina. Although related to other river dolphin species, it is primarily a marine species. Franciscana is the only representative of the four river dolphins to inhabit marine waters. It is also known as La Plata River dolphin because the first described specimen was from the mouth of La Plata River in Uruguay.
Morphometrical and genetic differences between dolphins occurring south and north of Santa Catarina, Brazil, suggest the existence of at least two populations.
The range of franciscana overlaps, at least partially, with other small odontocete species such as the bottlenosed dolphin (Tursiops truncatus), dusky dolphin (Lagenorhynchus obscurus), tucuxi (Sotalia fluviatilis), and Burmeister's porpoise (Phocoena spinipinnis).
Franciscana is found in coastal waters and estuaries, mainly in shallow waters less than 100 ft (30 m) deep and within 30 nautical miles (56 km) of shore. Occasionally, it is found further offshore in waters up to 200 ft (60 m) deep. In much of its range, the water is very turbid. Franciscanas are often found in areas of high turbulence such as countercurrents and eddies.
Unlike the case in Brazilian waters, seasonal movements of franciscanas have been reported in Argentine waters, in which dolphins move offshore during the winter. Seasonality in Argentina has been attributed to the marked variation in water temperature (42.8–69.8°F [6–21°C]), in contrast to the more constant temperature in Brazilian waters (68–75.2°F [20–24°C]).
Franciscana are found in small groups of one to 15 dolphins, typically fewer than six animals. Their social organization remains unknown, partly because these dolphins are difficult to detect and observe. They seem to avoid boats and spend very little time (4%) at the surface. Moreover, their coloration closely matches that of the murky waters they inhabit, and their surfacing behavior is very inconspicuous. Typically, the beak emerges first, followed by the head, then the body arches forward, exposing little more than the dorsal fin.
Franciscanas produce low- to high-frequency clicks that are associated with echolocation used for navigation and foraging.
Sevengill (Notorlynchus cepedianus) and hammerhead sharks (Sphyrna spp.), and possibly killer whales (Orcinus orca), are believed to be their only predators. However, direct attacks by these species have not been documented.
In parts of its range, feeding and breeding is more prevalent near shore. Tides may influence activity patterns. For example, feeding increases during high tide.
Feeding ecology and diet
Franciscanas have a diversified diet, consisting of at least 24 species of fish, cephalopods (e.g., squid, octopus), and, less importantly, crustaceans such as shrimp. The target fish species vary across their range, but mostly consist of demersal (bottom-dwelling) species. Common prey fish species belong to the families Sciaenidae (croakers, drums), Engraulidae (anchovies), and Batrachoididea (toadfishes). Prey is mostly juvenile fish, less than 3.9 in (10 cm) long.
Franciscana may engage in cooperative feeding by swimming in a circle in a coordinated manner, thus concentrating the fish in the center.
Sexual maturity is reached between two to five years in females and two to three years in males. Researchers have reported differences across its range of about one year in the age of sexual maturity of females: Uruguay (2.8 years), Brazil (3.7 years), and Argentina (4.5 years). However, more current data are needed for Uruguay to allow reliable comparisons,
since estimates there are based on data collected more than 25 years ago.
After 11 months of gestation, females give birth to one calf, whose length may range 2–2.6 ft (0.6–0.8 m). Lactation may last nine months, but calves may start feeding on prey as early as three months of age. Females may give birth every year or every other year. Calving is seasonal in some areas, occurring from September to December. In northern Brazil, calving occurs throughout the year.
Compared to most odontocetes, franciscana has a lower age of sexual maturity, shorter calving intervals, and a very short life span (estimated at 15 years for females and 18–20 years for males). Their mating system is unknown.
Franciscana is endemic to the southwest Atlantic. Sadly, it is the most rare, and among the most poorly understood, of the South American dolphins. Its distribution makes it particularly vulnerable to entanglements in gillnets used in coastal fisheries. It is one of the most threatened small cetaceans in the southwest Atlantic due to substantial incidental takes in fisheries. Entanglements occur both in surface and bottom gillnets. Gillnet fisheries target sharks, anchovies, and sciaenids, depending on the region. Incidental catches occur throughout its range but are of particular concern on the coasts of southern Brazil (Rio Grande do Sul) and Uruguay. In these areas, density of franciscana is estimated to be 1.8 dolphins per mi2(0.7 dolphins per km2), and annual catches reach 550–1,500 dolphins. These takes correspond to an annual removal rate of 1–3.5% of the stock. It is estimated that a 2% rate of removal may not be sustainable for this population.
Despite the growing pressure resulting from the rapid expansion of the coastal fisheries, franciscana is classified as Data Deficient in the IUCN Red List. This is because estimates of abundance and incidental mortality are unavailable for its entire range. A recent study using population viability analysis (PVA) to model the impact of incidental catches in southern Brazil found that this population is decreasing. The same model predicted that if the current incidental catch level persists, this population could plummet to as little as 10% of its current abundance within 25 years.
National regulations in all three countries of its range prohibit hunting.
Significance to humans
Blubber of dolphins caught incidentally is occasionally used as bait in the longline shark fishery. However, franciscanas are not targeted for this purpose. In Uruguay, the blubber oil has been used in the tanning industry, and carcasses are discarded or used as fish flour.
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United Nations Environmental Programme (UNEP). PO Box 30552, United Nations Avenue, Gigiri, Nairobi, Kenya. Phone: 254 (2) 621234. Fax: 254 (2) 624489. E-mail: [email protected] Web site: <http://www.unep.org>
The Whale and Dolphin Conservation Society (WDCS). 38 St Paul Street, Chippenham, Wiltshire, SN15 1LY United Kingdom. Phone: 44 (0) 1249-449500. Fax: 44 (0) 1249-449501. E-mail: [email protected] Web site: <http://www.wdcs.org>
Paula Moreno, MS