The long-beaked La Plata River dolphin, a small species living in in South America's Atlantic coastal waters, is increasingly threatened with extinction from big-net fishing, Brazilian researchers warn.

At last 1,000 of these dolphins die every year near the coast of (Brazil's) Rio Grande do Sul," scientist Emanuel Carvalho Ferreira told AFP Friday.

Ferreira led a study funded by cosmetic giant Boticario's Foundation for Nature Protection on the mortality of these marine mammals which "showed that fishnets have become increasingly bigger over the past few years and now can be 30 kilometers (19 miles) long."

"This is a virtually insurmountable barrier for these small dolphins," said Ferreira, who works with Rio Grande do Sul's marine mammals laboratory and with the KAOSA non-governmental organization campaigning for the protection of the La Plata River dolphin.

There are currently an estimated 40,000 to 50,000 of these river dolphins, which grow to be between four and six feet long (1.20 to 1.80 meter) and weigh up to 50 kilograms (110 pounds).

It is the only species of river dolphins that can be found in salt water.

Although their sightings are scarce, they can be found in Brazil's Doce River, the Valdes Peninsula in Argentina and in the coastal waters of Uruguay.

But they are most threatened in Brazilian waters because fishing in Uruguay and Argentina is conducted in a less intensive manner.

"In Brazil, the boats are bigger with 20 fishermen (against four or five in Uruguay and Argentina) who stay at sea for up to 20 days, which leads to the accidental capture of many cetaceans," said Ferreira.

To remedy the situation, he said his team recommends reducing the size of fishnets and banning fishing up to a depth of 20 meters (66 feet).

"We did a simulation by excluding fishing up to a depth of 20 meters and the accidental capture and dolphin mortality rates fell by 72 percent," he added.

Ferreira said new rules had been set to reduce the size of fishnets to 15 kilometers.

"We will then gradually reduce them further. We also launched a campaign of awareness among the fishermen," he added.