Kevin Schafer / Minden Pictures / Getty Images Scientists say that if the population decline observed in one conservation area is occurring in the wider unprotected region, two species of freshwater dolphin found in the Amazon—the boto (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis)—could be at serious risk of extinction. A survey conducted from 1994 to 2017 at the Mamirauá Sustainable Development Reserve, 500 km west of Manaus, suggests that the populations of these two species are halving every 10 years, despite them being protected by law. The number of sightings of the boto dolphin, which can reach up to 2.5 meters (m) in length, fell from 2000 onward, with increasing reports of accidental capture by net fishing and the use of its meat as bait for piracatinga (Calophysus macropterus), a type of catfish commonly eaten in Colombia. The tucuxi population, which measures about 1.5 m and is more likely to die when trapped in fishing nets, constantly declined over the analyzed period (PLOS ONE, May 2). The study was coordinated by biologist Vera Maria Ferreira da Silva, from the Brazilian National Institute of Amazonian Research (INPA), and attributes the population decline to illegal capture outside the reserve; such activities are prohibited in Mamirauá, and other aquatic predators there continue to thrive. The researchers do not know if their findings in the reserve are representative of the entire Amazon region and no such surveys have been conducted in other areas, but they claim that use of these animals as bait is widespread. Today, the level of threat to both species is unknown. If the decline observed in Mamirauá is characteristic of the Amazon in general, they would be critically endangered according to the criteria established by the International Union for Conservation of Nature (IUCN).
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