"Freshwater dolphins living in the Amazon river basin are being attacked and killed by local fishermen.
Conservationists have found a number of boto and tucuxi dolphins that have been struck with machetes and harpoons and left to die.
The fishermen attack the dolphins fearing they are stealing their fish and ruining their fishing gear.
Some of the killings may also be driven by strong cultural taboos that suggest the animals bring bad luck.
The discovery of the dolphins came during a survey designed to monitor the mortality rate of both Amazonian dolphins and manatees conducted by researchers at the Mamirauá Institute for Sustainable Development in Tefe, Brazil.
During the survey, the research team led by Miriam Marmontel and Carolina Loch recovered 18 dead dolphins, six of which were botos (Inia geoffrensis), also known as the Amazon river dolphin or pink river dolphin, and 12 were tucuxi (Sotalia fluviatilis), another species that lives in the Amazon basin that is more closely related to oceanic dolphins.
Three of the dolphins had unusual injuries.
"These lesions were recognisable as marks made by stabbing with machetes and harpoon wounds," says Loch.
The dolphins were found in two adjacent areas.
Both tucuxi carcasses were found floating in Amana Lake within the Amana Sustainable Development Reserve, a protected area, while the dead boto was found floating in the unprotected Tefe Lake.
Both locations are in the northwestern Brazilian state of Amazonas.
Crucially, no parts of the dolphins' bodies had been harvested, the researchers report in the journal Biodiversity and Conservation.
In some areas in the Amazonian basin, particularly in Colombia and Brazil, dolphins are killed for their body parts which are sold.
"The genital organs and eyes of tucuxis and botos are sometimes sold as amulets in popular markets of some Amazonian cities," says Loch.
She also explains that there is a growing trend toward using boto meat and blubber as bait to catch a scavenging catfish called the 'piracatinga' or Calophysus macropterus.
"This practice is possibly widespread in the Brazilian Amazon and may severely threaten [the boto's] conservation," Loch says.
But the three carcasses were unmolested apart from the initial fatal wounds.
That means that fishermen are killing the dolphins simply to eliminate rather than exploit them.
"Aquatic mammals such as whales, dolphins and sea lions are frequently seen as unwanted competitors for fisheries resources," says Loch. "This sense is also widespread in the Amazonian region, especially among fishermen."
Loch's team think the fishermen suspect the dolphins of taking too many fish, both from the river and from their nets, and damaging their fishing gear in the process.
Cultural beliefs, myths and superstitions may also be driving some of the killings.
For example, in some parts of the Amazonian, the boto is traditionally viewed as a mischievous and tempestuous being, both feared and respected.
In extreme cases, it is thought the dolphins transform themselves into handsome men who come ashore and seduce young women, which explains why their reproductive organs are sold as charms.
But while such beliefs sometimes protect the boto and other dolphins from harm, they can also lead people to kill them out of fear or to prevent unexpected teenage pregnancies.
The researchers say the three carcasses suggest that many more Amazonian dolphins are being intentionally killed, and the practice may pose a significant threat to their conservation.
An extensive education program must be started to mitigate the problem, Loch says.
"Environmental education activities with school children are fundamental to avoid these conflicts in the future," she says.
"Amazonian dolphins play an important role in the local culture of Amazonian region, and positive aspects of this influence should be reinforced and encouraged."
"Negative myths and legends linked to undesired pregnancy of women and enchantment of people should be respected as part of their culture, but should be clarified and negative attitudes towards animals should be discouraged."
Please click the following link to see photos of the beloved dolphins.