December 25, 2009
Scientists Solve Manatee Migration Mystery
Only in recent years have scientists figured out that the secretive Amazonian manatee migrates from shallow to deeper waters. The manatees make this dangerous journey to avoid exposure to predatory attack during the low-water season.
Scientists speculate that these peaceful creatures may be at an even greater danger than thought, as migration and low-water levels make them easily accessible to hunters.Caimans, jaguars, and humans are all threats to the manatee. Even though hunting manatees is illegal they are prized by local people for their meat and the status a kill bestows on the hunter.
Dr Eduardo Moraes Arraut of the National Institute for Space Research in Sao Paulo, Brazil undertook this latest study on the manatees.
He was surprised with the difficulty of the conditions the manatee thrives in during low-water seasons.
It also was surprising to realize that many manatees are being killed annually during their migration.
"Manatees are in greater danger than previously thought because every year they are probably migrating through narrow channels where they are exposed to hunters," says Dr Arraut.
He hopes to track manatees in other regions of the Amazon to find out if this is occurring elsewhere.
The Amazon manatee is only found in the Amazon River basin from the river mouth to the upper reaches of tributaries of Brazil, Colombia, Ecuador, Guyana, and Peru. The manatees that were studied live within the Mamiraua and Amana Sustainable Development Reserves in the north west of Brazil.
The research consisted of scientists asking local people about the animals' movements, studying shapes and depths of local rivers and lakes, and using radio tracking tags to follow movements of 10 individual manatees.
Scientists found that manatees move to tranquil lakes that form within river flood plains during the high-water season usually between May and the end of June. Here they consume up to 8% of their body weight in aquatic plants each day. Then during the low-water season, the animals start to migrate as the water level drops. This occurs normally between October and November.
The manatees' journey to deeper water within long narrow lakes, which are submerged river valleys. They do this because the shallow waters are far too dangerous for them. If they do not migrate, they become stranded and exposed to hunters that stalk the water margins. The migration has another downside however; it forces them to fast for several months due to lack of marine plant life.
"Amazonian manatees migrate to a habitat that doesn't offer easy living conditions in order to flee from a habitat that becomes inhospitable," says Dr Arraut. "When you have two options that are not good, you choose the one that is less bad," he adds.
The international team of researchers from Brazil and the UK published their findings in the Journal of Zoology.
On the Net: