Franciscana

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Published: April 1, 2011, 12:00 am
Updated: August 29, 2011, 2:03 pm
Author: Encyclopedia of Life
Contributing Author: Peter Saundry
Topic Editor: C Michael Hogan
Topics:
Content Cover Image

Female Franciscana incidentally caught by gillnet at São Sebastião, Brazil. Source: Projeto SOS Mamíferos Marinhos

The Franciscana or the La Plata dolphin (scientific name: Pontoporia blainvillei) is one of three species of River Dolphins in the family Inia. The other two are the Amazon River dolphin and the Chinese River dolphin (which may be extinct.)

La Plata dolphins are exclusively marine however they "earned" the title of river-dolphin because they inhabit the salt-water estuary of the La Plata River. They inhabit shallow caost waters of the Atlantic Ocean off of South America from the Doce River, north of Rio de Janeiro, Brazil (19o 37' S) to the Valdes Peninsula, Argentina (43o 30' S). There appear to be two main subpopulations: "a smaller form in the northern part of the species' range (north of 27°S) (those in the far north are of intermediate size) and a larger form in the coastal waters of southern Brazil, Uruguay and Argentina (south of 27°S)" (IUCN).

A sighting of a La Plata is very special because these dolphins reside in isolated areas and are rarely seen by humans. They are known to fishermen as "the white ghost" because their bodies are light in color and because they flit away when they see humans.

Franciscana01.jpg Franciscana. Source: Whale and Dolphin Conservation Society
500px-la plata dolphin size.png Size comparison of an average human against the Franciscana. Source: Chris Huh

Conservation Status:
IUCN Conservation Status - Vulnerable.png.jpeg

Scientific Classification

Kingdom: Animalia
Phylum:--- Chordata
Class:------ Mammalia
Order:-------- Cetacea
Family:-------- Iniidae
Genus:--------- Pontoporia
Species:-------- Pontoporia blainvillei (Gervais and d'Orbigny, 1844)

Common Names:
La Plata Dolphin
Franciscana

They are extremely shy and evasive by nature. Human knowledge of them is surrounded by superstition as there are so few facts known about them. The La Plata dolphin and other river-dolphins are, in general, smaller and less well-known than most other dolphins.They have the longest beak-to-body ratio of any dolphin.

La Plata dolphins are limited in their distribution to temperate and coastal waters of eastern South America.

River-dolphins are considered rather primitive by comparison to other cetaceans with their long beaks, interlocking conical teeth, and their poor eyesight

Physical Description

La Plata dolphins are considered extremely primitive marine mammals. They have disproportionately small heads, pronounced melons, short bodies, and long slender beaks that curve down slightly. They are light colored, either mostly white or pale brown on top converging into lighter brown on their bellies. The number of teeth has been counted at 210-42.

Length 1.25 - 1.75 meters. Weight: 20 - 61 kg. Females are slightly larger than males.

La Plata dolphins have very poor vision. Not much is known about their hearing. La Plata dolphins also have very sensitive echolocation which allows them to navigate in turbulent and murky river waters.

Reproduction

La Plata dolphins are capable of reproducing when males are 4.5 feet (1.37 meters) long and females are 4.6 feet (1.4 meters) long.La Plata dolphin calves are born about 2.7 feet (0.8 meters) long after a 12.5 month gestation period, usually from October to January. Calves of the species nurse for nine months and tend to give birth every two years.

Lifespan/Longevity

La Plata dolphins are thought to live for about 20 years. Members of the species were often killed accidentally in nearshore shark gillnets through the late 1960s. This mortality decreased markedly as the shark fishery moved progressively offshore.

Distribution & Movements

The species is chiefly found along the Atlantic Coast of South America. Franciscana distribution.png.jpeg They inhabit shallow coastal waters of the Atlantic Ocean off of South America from the Doce River, north of Rio de Janeiro, Brazil (19o 37' S) to the Valdes Peninsula, Argentina (43o 30' S).

Habitat

This dolphin chiefly uses coastal and estuarine habitats.

The IUCN Red List provides the following details:

Franciscanas inhabit shallow coastal waters (and they sporadically enter the estuary of the La Plata River) of tropical and temperate regions of the western South Atlantic Ocean (Crespo 2002). They are found only along the east coast of South America (Brazil, Uruguay, and Argentina), from the northern Golfo San Matias, central Argentina (ca. 42°10'S), to Espirito Santo, southeastern Brazil (18°25'S) (Siciliano 1994; Crespo et al. 1998). The species is not distributed continuously throughout its range. Surveys (including beach surveys, museum specimens, and interviews with local people) indicate that franciscanas are extremely rare or absent in two areas of the northern parts of their range between Macaé (southern Rio de Janeiro State) and Ubatuba (northern São Paulo State) and in Espírito Santo State (Azevedo et al. 2002; Siciliano et al. 2002; Secchi et al. 2003). The reasons for these gaps are unclear, but because the species prefers shallow, turbid waters (Brownell 1989; Pinedo et al. 1989), water transparency and depth may be among the factors responsible (Siciliano et al. 2002).

Although sometimes described as a ‘river dolphin’, the franciscana is not a freshwater species. Franciscanas apparently do not migrate, although seasonal inshore/offshore movements have been documented in some areas (Bordino et al. 1999, Bordino 2002). Predation by both large sharks and killer whales has been documented (Praderi 1985; Ott and Danilewicz 1996; Santos and Netto 2005).

Franciscanas are generally found in turbid waters < 30 m deep (Pinedo et al. 1989, Secchi and Ott 2000). Although they are found mainly in marine waters and only occasionally in estuaries, they are relatively common in the Uruguayan part of the La Plata River estuary (Praderi 1986). Franciscanas are primarily coastal, ranging no farther offshore than the 30 m isobath. Some sightings have been made in waters seaward of the 50 m isobath and 55 km offshore, but the density offshore is very low.

Food & Feeding Habits

La Plata dolphins are primarily bottom feeders and consume a wide variety of fish, as well as shrimp, squid, and octopus.

Predation

The IUCN Red List reports:

The main problem facing the species is incidental mortality in gillnet fisheries (there is no indication of direct exploitation of franciscanas), which has been observed since at least the early 1940s (Van Erp 1969). In the 1960s, the bycatch in Uruguay alone was as high as 1,500-2,000 animals (Brownell and Ness 1969; Pilleri 1971). Current estimates total at least 2,900 animals per year in all four management stocks, combined (e.g., Ott et al. 2002; Secchi et al. 2003b), but the numbers used to get that total are thought to be underestimated to an unknown extent, primarily due to: (1) captures in other non-monitored types of fisheries (e.g., active gillneting, Secchi et al. 1997; shrimp trawling, Cappozzo et al. 2000); (2) under-reporting of bycatch by fishermen; and (3) dolphins captured sometimes falling from the net before or during haul-out (Secchi et al. 2003b). Bycatch is higher in FMA III with estimates being above 1,300 animals incidentally caught annually (Ott et al. 2002; Secchi et al. 2003b, 2004), followed by FMA IV: approximately 800 individuals (Bordino and Albareda 2005), FMA II: > 700 dolphins (Rosas et al. 2002; IWC 2004), and FMA I: > 110 franciscanas (Di Beneditto 2003).

Stomach contents of franciscanas from Rio Grande do Sul have included many kinds of debris: discarded fishing gear such as pieces of nylon net (17% of 36 stomachs), cellophane, and plastic fragments (6%) (Bassoi 1997). This problem has also been reported in northern Argentina, where cellophane, fishing debris, and plastic were found in 45%, 32% and 16% of the stomachs (Bastida et al. 2000; Danilewicz et al. 2002). The effects of such debris ingestion on health status of individual franciscanas have not been determined, and the subpopulation-level implications are uncertain. However, debris could have a negative effect in at least some areas.

Other potential threats include various forms of habitat degradation (e.g. overfishing; destruction of benthic community and bycatch of small sciaenid fish – main franciscana prey – by trawling) (e.g. Bassoi and Secchi 2000; Danilewicz et al. 2002; Rodríguez et al. 2002).

Threats & Conservation Status

The IUCN Red List reports:

There is no current abundance estimate for the species as a whole, but there is an estimate for the management stock inhabiting FMA III (hereafter referred as the RS/URU management unit). During aerial surveys of coastal waters of Rio Grande do Sul State in 1996 (Secchi et al. 2001), this stock’s abundance was estimated at 42,078 (95% CI 33,047-53,542). This extrapolated result must be used very cautiously, however, because it is based on a density estimate for only a small fraction of the coastline, representing approximately 0.7% of the possible range of the subpopulation (ca. 64,045 sq. km), and there is limited information on the distribution pattern of franciscanas within their total range. This and other estimates of franciscana density and abundance need to be interpreted cautiously as they could be either positively or negatively biased. The IWC Scientific Committee concluded, after reviewing the methods and limitations of franciscana surveys through 2003-2004, that it was not appropriate to consider them as providing minimum estimates of abundance (IWC 2005a).

While the overall abundance of the species would seem relatively high, in most areas the gillnet mortality alone is not thought to be sustainable. Secchi (2006) projected the four management units 25 years into the future based on a stage-structured matrix model using a variety of scenarios of fishing effort. Because there were estimates of franciscana density and abundance only for FMA III and IV (Secchi et al. 2001; Crespo et al. 2004), Secchi (2006) used the density estimated for FMA III ( ) and applied a correction factor based on the ratio of capture per unit of effort (CPUE) between the other areas and FMA III. This was assumed to represent a valid index of abundance because the unit of fishing effort is the same and the fishing gears are similar among management units. The corrected densities were multiplied by the entire area of both FMA I and II to obtain the estimate of total abundance. Uncertainty in the parameter estimates was incorporated through appropriate probability distributions. The scenarios considered most realistic (i.e. those that aimed to compensate for underestimation of the bycatch and that modelled environmental stochasticity) resulted in relatively high probabilities that each management unit would decline by at least 30% below its initial size with the exception of FMA I. However, it should be noted that estimates of bycatch in FMA I come from only one fishing village and it is known that bycatch occurs in other parts of this FMA (e.g. Freitas-Neto and Barbosa 2003).

The modelling exercise described above is considered to underestimate the risk of decline of franciscanas. The most recent data on bycatch (e.g. Rosas et al. 2002; Bordino and Albareda 2005; A. Zerbini as summarized in IWC 2005b) indicate that the numbers caught annually in FMAs II and IV are roughly twice as high as the values used by Secchi (2006) in his projections.

References

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Citation

Encyclopedia of Life (2011). Franciscana. ed. C. Michael Hogan. Encyclopedia of Earth. National Council for Science and Environment. Washington DC.  Retrieved from http://editors.eol.org/eoearth/wiki/Franciscana
Retrieved from "https://editors.eol.org/eoearth/index.php?title=Franciscana&oldid=143397"