I. Diagnostic Characters and Comments on Taxonomy
The franciscana (Pontoporia blainvillei) is also known as the La Plata River dolphin. In Uruguay and Argentina * it is called franciscana whereas in Brazil it is called ton-inha or cachimbo. While both this species and the Yangtze river dolphin, Lipotes vexillifer, were until recently regarded as of the family Pontoporiidae, the franciscana is now the sole member of this family. The franciscana is the only one of the four river dolphin species living in the marine environment. It is one of the smallest dolphins and has an extremely long and narrow beak and a bulky head. The franciscana is brownish to dark gray above turning lighter on the flanks and belly (Fig. 1). The number of teeth in the upper and lower jaws ranges from 53 to 58 and from 51 to 56, respectively.
II. Distribution/Range Map
The species is endemic in southwestern Atlantic waters. Based on the distribution of sightings and catches, the franciscana lives in a narrow strip of coastal waters beyond the surf to the 30 m isobath (Fig. 2). The complete range known for the franciscana extends from Itaunas (18°25′S, 39°42′W) in Espi-rito Santo, Brazil, to the northern coast of Golfo San Matias (41°10′S) in northern Patagonia, Argentina.
III. Geographic Variation
Skull morphology, genetic markers, and parasites have been used to identify stocks. The existence of two potential populations was tested by means of the differences in skull morphology. A northern (smaller) form was proposed between Rio de Janeiro and Santa Catarina, and a southern (larger) form for Rio Grande do Sul, Uruguay, and Argentina. The existence of differences between populations was confirmed some years later using mitochondrial DNA from samples collected at Rio de Janeiro and Rio Grande do Sul. It was found that six exclusive haplotypes were present in the northern population and 5 in the southern one, indicating some degree of segregation between the stocks. Gastrointestinal parasites were also used as bioindi-cators in order to study the existence of stocks in franciscana. The parasites seem to indicate segregation into two functional or ecological stocks between southern Brazil-Uruguay and Argentina. Three species of parasites were recommended as biological tags [Hadwenins pontoporiae, Polymorphns (P) cetacetun and Anisakis typica]. On the basis of this information, at least three stocks or populations could exist.
IV. Ecology
Little is known about the northern stock or population, between Espirito Santo and Santa Catarina, a region that is under the influence of the Brazil tropical current. Between southern Brazil and Golfo San Matias, the franciscana lives in a transition zone in which the surface circulation of the southwestern Atlantic is dominated by the opposing flows of subtropical and sub-Antarctic water masses. The coastal marine ecosystem is characterized by continental runoffs with a high discharge of high-nutrient river flows (e.g.. Lagoa dos Patos, Rio de la Plata). Juvenile sciaenids, the most important prey of the franciscana, are typically associated with those continental runoffs and the influence of subtropical shelf waters. The franciscana feeds mostly near the bottom on fishes of several families, such as sciaenids, engraulids, batrachoidid. gadids, carangids, and atherinids. However, sciaenids account for most of the fish species. The diet also includes squids, octopus, and shrimps. The franciscana feeds on the most abundant species in the region and seems to change its diet according to seasonal prey fluctuations. A comparison of results between two studies carried out 15 years apart in Rio Grande do Sul showed shifts in prey composition in which important prey of the former period were depleted in artisanal fisheries. Among predators, remains of franciscanas were found in stomach contents of killer whales and several species of sharks.
V. Behavior
Very little is known about the behavior of free-ranging franciscanas, in part because they are difficult to observe in the wild and in part as a consequence of low sighting effort. The franciscana is thought to be solitary or not gregarious. Herd size may range from 2 to 15 individuals. In aerial surveys carried out in southern Brazil with the objective of estimating abundance, 37 sightings gave a mean herd size of 1.19 (SD: 0.47, range; 1-3). A study of wild behavior at Baliia Anegada in southern Buenos Aires Province showed a seasonal pattern with cooperative feeding, with traveling activities increasing during winter and high tide. The mean swimming speed was estimated in 1.3 m/see (±0.09) with a maximum of 1.8 m/sec, and mean dive duration was estimated in 21.7 sec (±19.2) (range from 3 to 82 sec).
Figure 1 Lateral view of a 137.5-cm adult female franciseana.
VI. Notable Anatomy, Physiology, Life History
Females are larger than males. Adult females range between 137 and 177 cm in total length whereas males range between 121 and 158 cm. The weight of mature females ranges between 34 and 53 kg and that of males ranges between 29 and 43 kg. Neonates in Uruguay range in size between 75 and 80 cm, whereas in southern Brazil they range between 59 and 77 cm (some of the smaller neonates could be near-term fetuses). Neonates weigh around 7.3 to 8.5 kg. Age at sexual maturity was estimated to be 2.7 years, and the gestation period is between 10.5 and 11.1 months. Females gave birth around November and lactation lasts for 9 months. However, calves take solid food around the third month, weighing between 77 and 83 cm. Mating seems to occur in January and February. The calving interval is around 2 vears; nevertheless, few females were found lactating and pregnant at the same time. Reproductive capacities and life span are low for the species, which is a problem for the population to sustain the mortality rates caused by fisheries. Longevity has been estimated close to 15 years for males and 21 for females, fairly low when compared to most of the small cetaceans. Few individuals attain ages over 10 years. Three types of acoustic signals have been recorded, including low, high, and ultra high frequency clicks.
Figure 2 Distribution range of the franciscana dolphin in the southwestern Atlantic Ocean. The shaded area represents the area inside the approximate 30-m isobath.
VII. Fossil Record
Three records have been related to the franciscana and assigned to the family Pontoporiidae: Brachidelphis mazeasi, a middle miocene fossil from the Pisco Formation (Peru); Pontistes rec-tifrons, a late miocene fossil found in the Parana Formation (Argentina); and Pliopontos littoralis, a pliocene fossil closely related to the living species described for the Pisco Formation (Peru).
VIII. Interactions with Humans
Incidental catches in gill nets, mostly of juvenile individuals, became a serious problem for the species throughout its distribution range probably since the end of World War II. At that time, many artisanal fisheries for sharks developed in the region for vitamin A production, which was exported to Europe. During the 1970s, gill net mortality in Uniguay was estimated at above 400 individuals/year and fell to around 100 individuals/year in the last few years for economic reasons. Nevertheless, minimum mortality rates were always estimated at several thousands of individuals throughout the distribution range. At present, higher mortality rates are shown by the fisheries at Rio Grande do Sul and Buenos Aires Province, where no less than 700 and 500 are, respectively, incidentally taken. The estimated mortality for the whole distribution range could be no less than 1500 individual per year. It is not known if these mortality rates are sustainable. There has been only one attempt to estimate abundance, carried out at Rio Grande do Sul, where around 42,000 individuals were estimated to be in 64,000 km2 between the coast and the 30-m isobath. The upper limit of the abundance estimation cannot sustain the lowest estimates of mortality. Therefore, more precise estimates are needed along with conservation measures in order to preserve the species. Other threats to the franciscana include habitat degradation. A large proportion of the distribution range is subject to pollution from several sources, especially the agricultural use of land and heavy industries between Sao Paulo in Brazil and Bahfa Blanca in Argentina. The coastal zone is also intensely used for boat traffic, tourism, and artisanal and industrial fishing operations.
