La Plata Dolphin

## Background Information

### Alternate Name(s)

Franciscana, Toninha, Cachimbo, Argentine river dolphin, Uruguayan river dolphin, White ghost, Silver dolphin

## Classification

### Species

P. blainvillei

The La Plata dolphin ***(Pontoporia blainvillei)*** also commonly known as the franciscana, is a species of Marine dolphin that inhabits the coastal waters and estuaries of southeast South America. The La Plata dolphin has olive-brownish skin which differs in comparison to the appearance of other South American dolphin species however, in general body and beak shape the La Plata dolphin remains quite similar to other South American dolphins. Unlike other dolphin species in South America, La Plata dolphins are not classed as iniids and are instead placed in their own family, pontoporiidae. The La Plata dolphin has remained the only living species in the family since its discovery in 1844, when it was placed taxonomically in its own genus. Though the La Plata dolphin belongs to Pontoporiidae, it is still classified in the Iniioid super family along with other South American dolphin species. In physical appearance the dolphin uniquely has the longest beak to body ratio of any Cetacean, in fact, some adult's beaks make up an astounding 15% of their total body length. The fins of the dolphins are also disproportionately large in comparison to other dolphins, being quite broad at their largest. The dorsal fin of the La Plata dolphin appears more muted and is generally more stout comparatively to other marine dolphins. The teeth of the La Plata dolphin are quite long, and decrease in size towards the back of the mouth. Interestingly, the dentition of some individuals appears warped, with some having twisted crowns on their teeth. The purpose of this genetic variation is unknown. Female La Plata dolphins are generally larger than males measuring up to a length of 1.8m (5.9ft) and males measuring to a length of 1.6m (5.2ft). Both sexes however, weigh 50kg (110lbs). Interestingly, some estimations conclude that dolphins can grow only to a length of 80cm and 76cm (31in and 29.9in) for females and males respectively. All in all these measurements make La Plata dolphins the smallest river dolphins.

## Diet

Though they often eat a wide variety of estuarine fish species, La Plata dolphins specialise in the consumption of squids. Squids are an extremely convenient source of food for La Plata dolphin, as the dolphin's narrow digestive tract discourages dolphins from consuming large prey. Squids and other Cephalopods do not inhibit the dolphin's feeding and do not only digest easier, but they also contain a high amount of water which is essential for nutritional stability. Other than squids, the dolphins also prey upon many species of crustaceans, with calves feeding primarily on the opossum shrimp ***(Neomysis americana)***, which is abundant in the region. Due to the wide range of the species, desired prey items may differ between sub-populations in accordance to the species native to the region.

## Conservation Status

Currently, La Plata dolphins are classed as vulnerable by the IUCN and are threatened by a variety of both human and natural factors. Gillnets and accidental fishing equipment entanglement remaining the largest threats to the dolphins, as such pollution can lead to the accidental casualties of ensnared individuals. Bycatch is a common factor that causes unexpected death in populations, and though direct exploitation of the La Plata dolphin does not occur, many individuals still die through the cause of bycatch. In Uruguay, an estimated 1,500-2,000 individuals were ensnared by bycatch in two fishing villages alone. However, a change in target species by fishing industries had lead to a noticeable decrease in bycatch casualties during the 1980's. During the early 2000's, studies conducted concluded that upwards of 2,900 individuals had become ensnared in bycatch in all management stocks combined. However, due to multiple factors such as the tally not counting non monitored types of practices, such as gillnet fishing and trawling, dolphins jumping or falling from nets upon retrieval or under reporting of bycatch instances from fishermen. These factors may conclude that the final tally is an underestimation of a much larger number of ensnarement cases. In following years from 2002-2005, many reports have estimated a range of data surrounding the number of La Plata dolphins that have been ensnared in bycatch. From estimates as low as 500-800 individuals to 1,300 individuals, these estimations make it apparent that bycatch remains unsustainable, and a major threat to the survivability of the La Plata dolphin. Pollution has also remained a large threat to the dolphin population and many dolphin specimens have been found to be carrying various plastics and synthetic packaging materials, such as cellophane, in their stomachs. These specimens were extracted from Rio Grande Do Sul (a Brazilian province) and also appear to have ingested nylon net, which is a form of fishing equipment. This hazardous pollution was found in 17% of the total 36 Rio Grande individuals. Pollutants are also a major problem in the dolphin's Northern Argentine range, where similar materials were found to be apparent in 16%, 32% and 45% of the stomachs of examined specimens. Unfortunately, the effects on the eternal structure of individual dolphins that pollution causes, has not been studied and implications relating to sub-populations of the species are also uncertain. Accidental ingestion of these debris has been a relatively new threat to the species, at least in Uruguay, where it had not been reported throughout the 1970's. A multitude of less significant threats may also be apparent, such as habitat degradation in the form of overfishing and bycatching of prey items however, the damage these threats have caused to the general La Plata dolphin population is unknown.

## Range and Population

La Plata river dolphins occur in the freshwater environments of coastal South America, being prominent in Argentina, Brazil and Uruguay. despite being a member of the Iniioid superfamily, (a group containing all freshwater South American dolphins) the La Plata river is found most frequently in brackish estuary environments. The La Plata dolphin was described first in the La Plata river in Uruguay, which is the river that the species is named after. Despite being named after the river, La Plata dolphins are much more commonly found in saltwater habitats when compared to estuaries. Though the species is most often found in coastal regions, they are not exclusive to these environments and can less commonly be found in the open ocean surrounding Islands. La Plata dolphins prefer more shallow waters, being found in depths from 6-35m (19-114ft) and will also favour areas further from the coast, occurring around 55km (34mi) offshore.

## Behaviour

La Plata dolphins are shy natured, rarely breaching, typically only raising their head from the water to breathe. They travel in large pods of up to 20 individuals however some estimate that pods may rarely consist of up to 40 individuals. It is suspected that these pods may also be matriarchal, with the oldest female being the dominant member of the pod, similarly to killer whales ***(Orcinus orca)***. La Plata dolphin pods are known as familiar or kin groups, meaning the members of the pod are all blood related or at least mates. These larger pods will typically form in the breeding season (May-August) or more frequently in Winter months when food is less abundant and hunting requires cooperation. According to Encyclopedia.Com, La Plata dolphins will hunt cooperatively by closing a tight circle around their prey by swim in circles around them. Individuals in Argentina and Babitonga bay, Brazil will typically swim further offshore in these Winter months however, further migration is not suspected. Little is known about the reproductive and breeding nature of La Plata dolphins It is thought that males do not compete for females due to reverse sexual dimorphism that is represented in the species and also that the species is monogamous, not seeking out another mate until death. Regional differences between mating behaviour makes it difficult to study the species as a whole. For example, The Northern population of dolphins have a 2:1 male to female ratio, meaning that there are an approximate two males for every one female, whether as the Southern population has a ratio of 1:1. Another regional difference between the North and South populations is the age of sexual maturity between individuals, though typically males will become sexually mature at age two and females at age three.The most unique population in Rio de Janeiro is different to other populations in that they will mate year round, as opposed to the typical May-August breeding season. One factor that remains constant in subpopulations is the rearing of calves. A calf will be born usually between the months of November and May, after the mother's 10-11 month gestation period and will typically be breastfed until the age of 8-9 months when it begins weaning. Females will usually have an average of 4-8 calves in an entire lifetime. La Plata dolphins navigate using echolocation, having reduced but still strong eyes. Despite their typical dependence on echolocation, the dolphins have a rather small melon when compared to other species.

### Relationship with humans

La Plata dolphins are extremely shy Cetaceans, preferring to avoid human interaction however it is not uncommon to spot them in areas of abundance. In their pursuit of avoiding humans and motorised vessels, La Plata dolphins do not hunt near fisheries, and will also avoiding taking fish from catches. This is different to other dolphin species which are known to be detrimental for fisheries. Because of their history and proximity to humans, the dolphins have multiple names depending on the region they are found. The most common name for the dolphin (outside of its English name) is the franciscana. This name is used to refer to the animal almost as frequently as its English name. The exact origin of the name franciscana is debated, the American Cetacean Society proposes that the name is of Spanish origin and was first used to refer to the dolphins by European settlers in Uruguay. Brazilian populations of the dolphin have an alternative name too, being most commonly referred to as toninhas. Throughout its range the La Plata dolphin is commonly called the white ghost by South American fishermen, as the species is known to become lighter in colour with age.

## In Captivity

Due to the rarity of the La Plata dolphin, there are no individuals in captivity. The changing attitudes towards Cetacean welfare in captivity has also made an impact on housing La Plata dolphins.

## Sources

* IUCN Red List of Threatened Species - https://www.iucnredlist.org/species/17978/123792204
* La Plata River Dolphin | DOLPHINS-WORLD - https://www.dolphins-world.com/la-plata-river-dolphin/
* Franciscana Dolphin | Encyclopedia.Com - https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/franciscana-dolphin-pontoporiidae
* Franciscana | Animal Diversity Web University of Michigan, Museum of Zoology - https://animaldiversity.org/accounts/Pontoporia\_blainvillei/
* La Plata Dolphin | MarineBio - https://www.marinebio.org/species/la-plata-dolphins/pontoporia-blainvillei/
* Franciscana | American Cetacean Society - https://www.acsonline.org/franciscana?
* Knowing me, knowing you: the fate of the toninha, a small dolphin endemic to the Western South Atlantic | Geospatial Ecology of Marine Megafauna Laboratory - https://blogs.oregonstate.edu/gemmlab/2019/04/16/knowing-me-knowing-you-the-fate-of-the-toninha-a-small-dolphin-endemic-to-the-western-south-atlantic/