Reintroduction of captive-raised Amazonian manatees in Brazil

Summary

The Amazonian manatee, the only exclusively freshwater sirenian, has been reduced across the Amazon basin by centuries of hunting for oil, hide and meat, and orphaned calves rescued from illegal hunting and fishing-net entanglement have been rehabilitated at Brazil's National Institute of Amazonian Research since 1974. A first release phase in 2008 and 2009 put four sub-adult manatees directly from captivity into the Cuieiras River, but two died within about 130 days, a third lost its tracking belt after losing weight, and the fourth was recaptured 120 days later having lost 30 percent of its body mass, leading researchers to conclude captive-raised manatees have little instinct for the Amazon's seasonal flood cycle. The program was redesigned around an intermediate step: since 2011, candidates for release spend at least a year in a 13-hectare semi-natural lake to adapt gradually, and from 2016 to 2017, nine manatees were released this way into the Piagacu-Purus reserve, a new site chosen partly for its floodplain and lake habitat. All 12 released animals were tracked by VHF radio belt, moving an average of 3 km a day and up to 100 km from the release point, mostly alone, consistent with the species' solitary habits, though contact with wild manatees was recorded. Post-release survival reached 100 percent under the revised protocol. The project rates itself a failure overall, given the losses from the first phase, but credits the semi-natural adaptation stage, local community involvement including former hunters, and protected release sites with turning the program around.