La Plata Dolphin – A Threatened Aquatic Mammalian Species in South America

La Plata Dolphin

La Plata Dolphin

A Threatened Aquatic Mammalian Species in South America 

-Dr. Arvind Singh

La Plata dolphin which is also known as Franciscana dolphin is a rare species of mammal found in coastal Atlantic waters of southeastern South America. It is one of the smallest dolphin and has extremely long and narrow beak and a bulky head. The scientific name of La Plata dolphin is Pontoporia blainvillei and it belongs to the Pontoporiidae family of order Cetacea. It is the only member of the river dolphin group that lives in Ocean and Saltwater estuaries instead of freshwater habitat.

The common names of La Plata dolphin in South America (Brazil, Argentina, and Uruguay) are toninha and cachimbo. Like other members of the river dolphin group, La Plata dolphin also belongs to threatened category of fauna. It is listed as ‘Vulnerable’ in the Red List of Threatened Species of International Union for Conservation of Nature and Natural Resources (IUCN). Vulnerable species are those which are likely to move into the endangered category in the mid-term future if the causal factors continue to operate.

Distribution Range:
The La Plata dolphin is found in coastal Atlantic water of southeastern South America including the Rio de la plata estuary. Its distribution ranges from the Tropic of Capricorn near Ubatuba, Brazil, south to the Valdes Peninsula in Argentina. It is the only member of the river dolphin group that actually inhabits the saltwater (ocean and estuaries) rather than freshwater. Although some members of the species do spend portions of their lives outside of river systems, many individuals have their entire lives within rivers.

Physical Characteristics:
La Plata dolphin has a plumb body. Its head is rounded, narrowing to a poorly defined neck. The body is greyish brown in colour with a lighter underside. Older animals become so light in colour that fisherman of La Plata estuary call them as “white ghosts” This is the only member of freshwater dolphin group which has a true dorsal fin situated at the centre of the back. The dorsal fin has a large base and rounded tip.

La Plata dolphin is characterized by the long slender beak which is the longest beak relative to body size of any dolphin. Its beak contains 50-60 small, sharp teeth in each half of the upper and lowers jaws for a total of 200 to 240 teeth. The flippers are also very large in comparison with body size and are very broad but narrow on joining the body. The small eyes have well-developed eyesight. Males and females grow to 1.6 m and 1.8 m respectively. Thus females are bigger in size than males. The La Plata dolphin weighs up to 50 kg and the life span is up to 20 years.

Habitat and Ecology:
La Plata dolphin prefers relatively shallow, turbid waters, a coastal marine ecosystem characterized by continental runoffs with a high discharge of high-nutrient river flows.
The behaviour of the La Plata dolphin is influenced by tide and depth. The animals usually enter the channels during the high tide.

The herd size of La Plata dolphin is small ranging between 2-15 individuals. It moves very smoothly and slowly. Its blow is hardly detectable and it does not roll or jump out of the water.

La Plata dolphins are bottom feeders and the inspections of the gut have revealed that they eat at least 24 different species of fishes depending on which species are most common. The may also feed octopus, squid, and shrimp. They are hunted by killer whales and several species of sharks.

Sexual maturity is attained at 2 to 3 years of age when males are 1.3 m and females are 1.4 m long. The gestation period is around 10-11 months. Calves are about 70 cm at birth and weigh 7-9 kg. They are nursed for months. Most birth occurs between October and January.
Threats to the Survival:
Habitat degradation, pollution, and incidental catch are the main threats to the survival of La Plata dolphin.

Pollution due to increased industrialization and heavy coastal traffic represent potential threats for the habitat of La Plata dolphin. Widespread deforestation and agricultural cultivation occur in many of the basins draining into the Rio de La Plata system especially in southeastern Brazil thus adversely affecting that habitat of La Plata dolphins.

Fish species of commercial importance generally constitute the diet of La Plata dolphins, hence an increase in fishing activity could reduce available food for the dolphins. The coastal regions frequently used for boat traffic, tourism and artisanal and industrial fishing operations are the causes of habitat deterioration of La Plata dolphins.

Pesticides used to control pests enter the coastal marine ecosystem in southern Brazil and Uruguay affecting the population of La Plata dolphins. Higher concentrations of organochlorine residues have been reported from the blubber of the La Plata dolphin along Brazilian coastal waters. The concentrations of DDT and PCB were highest compared to other pesticides.

Incidental capture in fishing gear is the other main threat to the survival of La Plata dolphins. Several hundred La Plata dolphins are accidentally caught in shark net each year with past estimates as high as 1,500. Catches have been high in Uruguay, Brazil, and Argentina. Scientists from these three countries have raised their concern and asked for international assistance in highlighting the plight of the La Plata dolphins.

Scientists in South America recently carried out the first aerial surveys of the La Plata dolphins and estimate their population to be around 40,000 within the coastal waters of Brazil and Uruguay.

The La Plata dolphin is listed on Appendix I and Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). The species is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). The World Wide Fund for Nature (WWF) considers La Plata dolphin as one of the most endangered small cetaceans worldwide.

Participants in the CMS meeting held in 2000 considered it essential to prepare an integrated conservation plan which included work with the pertinent authorities, fishing communities, public awareness, environmental education, and legislation review. It was suggested that Argentina, Brazil, and Uruguay consider the possibility of developing a Memorandum of Understanding for La Plata dolphin conservation within the framework of CMS. Participants agreed to consider La Plata dolphin as the most endangered small cetacean in the South-Western Atlantic. The endemism of the La Plata dolphin and its restricted distributional area are important conditions for species besides the high impact of human activities.

The following actions are needed for the conservation of the La Plata dolphin in South America.

1. To put a complete ban on fishing in high-density areas of La Plata dolphins. 

2. To protect the southeastern coastal regions of South America from pollution. 

3. To minimize boat traffic, tourism and artisanal and industrial fishing operations in coastal regions inhabited by La Plata dolphins. 

4. To provide legal protection to Lal Plata dolphins in Brazil, Argentina, and Uruguay.

It can be concluded that La Plata Dolphin is a threatened aquatic species of mammal in South America mainly due to habitat degradation, pollution, and incidental catch. Therefore, it is of utmost need to conserve this only saltwater inhabiting species of dolphins for the maintenance of the biological diversity of the earth.

Dr. Arvind Singh is M. Sc. and Ph.D. in Botany with an area of specialization in Ecology. He is a dedicated Researcher having more than four dozen published Research Papers in the Journals of National and International repute. His main area of Research is Restoration of Mined Lands. However, he has also conducted Research on the Vascular Flora of Banaras Hindu University-Main Campus, India.

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