La Plata dolphin

The La Plata dolphin, also called the franciscana or toninha (Pontoporia blainvillei), is a special kind of river dolphin that lives in the coastal Atlantic waters of southeastern South America. Unlike other river dolphins, the La Plata dolphin is the only one in its group that lives in the ocean and salty estuaries, instead of only in freshwater rivers.

This small dolphin is quite unique because most of its relatives stay in rivers, but it enjoys the salty waters near the coast. It belongs to the Inioidea group, which includes several other freshwater dolphins found in different parts of the world.

However, the La Plata dolphin faces some challenges. Places where people grow crops and industries release waste into the water. This pollution can harm the dolphin’s home and even poison the food they eat, making it harder for them to survive.

Taxonomy

The La Plata dolphin is the only species in its genus, Pontoporia, and is often placed in its own family, Pontoporiidae. It was first described by Paul Gervais and Alcide d'Orbigny in 1844. The La Plata dolphin is also widely known as the Franciscana (the Argentine and Uruguayan name), and is called toninha in Brazil.

Description

The La Plata dolphin has a long beak, making up to 15% of its body size. Males grow to about 1.6 meters (5.2 feet), while females can reach 1.8 meters (5.9 feet). Their bodies are greyish brown with a lighter belly, and they have large, broad flippers that are almost triangular. The dolphin's dorsal fin has a long base and a rounded tip.

These dolphins can weigh up to 50 kilograms (110 pounds) and live for around 20 years. They reach maturity between two and three years old. Females have a two-year cycle for having babies. Calves are about 70 to 75 centimeters long when born after a pregnancy of 10 to 11 months. Calves are weaned when they are one year old, and females might start having babies by the age of five.

Reproduction

The La Plata dolphin grows up and can have babies when it is about two to three years old, though sometimes it may take up to five years. Scientists studied a group of these dolphins near Brazil and found that most babies are born between September and February, during the spring and summer there. It takes about 11 months for a baby dolphin to develop inside its mother before it is born.

These dolphins have smaller reproductive organs, which suggests they usually stay with one partner during the time they have babies. While this doesn’t mean they only ever have one partner, it shows they might pair up for a part of the breeding season. Scientists think these dolphins might have a cycle where they have babies every two years, but they need to study this more to be sure.

Behavior and feeding

The La Plata dolphin moves very smoothly and slowly, making it hard to spot unless the water is very calm. It often swims alone or in small groups, though groups of up to 15 have been seen. These dolphins eat by searching the bottom of the water and have been found to eat at least 24 different kinds of fish, plus octopus, squid, and shrimp. They need to watch out for killer whales and several types of sharks, including tiger sharks, sand tiger sharks, broadnose sevengill sharks, hammerhead sharks (Sphyrna), and requiem sharks Carcharhinus.

Range and habitat

The La Plata dolphin lives in the coastal Atlantic waters of southeastern South America, including the Río de la Plata estuary. You can find them from the Tropic of Capricorn near Ubatuba, Brazil, all the way south to Península Valdés, Argentina. This dolphin is special because it is the only river dolphin that lives in the ocean and salty estuaries, instead of only in freshwater rivers.

These dolphins have been seen in places like Miramar in Buenos Aires Province, Rio Negro Province, and Bahia Rosas. Along the Brazilian coast, they are usually found in waters that are 8 to 30 meters deep, sometimes even deeper for accidental catches. There are a few reports of them being found farther away from the shore.

Threats

The La Plata dolphin faces many challenges that can harm its health and population. One big problem is habitat destruction and water pollution. Scientists have found plastic and other synthetic materials in the stomachs of these dolphins, but more study is needed to see how much this hurts them. Sadly, about 90% of the dolphin population in Guanabara Bay disappeared over just three decades. Dolphins also get caught in fishing nets and other fishing gear while looking for food.

Areas with lots of farming or factories can also be harmful. Waste and pollution from these places make the dolphins' homes worse and put toxic chemicals into the fish they eat. Even though La Plata dolphins are small, they must be careful because sharks and killer whales sometimes hunt them. Because of these dangers, these dolphins tend to stay quiet and live in shallow coastal waters.

Conservation

The La Plata dolphin is considered "Vulnerable" on the IUCN Red List of Threatened Species. This dolphin is especially worrying because it lives in a small area and can get caught in fishing nets by accident. Many dolphins have been caught this way, especially in places like Uruguay, Brazil, and Argentina.

This dolphin is also protected under international agreements to help save it from disappearing. Countries work together to protect these dolphins and their homes, and to make sure they can keep moving safely.