Mystery of Amazon manatee migration solved

On the run, the gentle manatee migrates away from harm

The mystery of why Amazonian manatees migrate has been solved.

Only in recent years did scientists find that the secretive aquatic mammal migrates from shallow to deep water.

Now researchers can reveal that the manatees make this perilous journey to avoid being exposed to attack by predators during the low-water season.

That means the species may be at greater risk than thought, say scientists, as migration and low water levels make them vulnerable to hunters.

The international team of researchers from Brazil and the UK publish their findings in the Journal of Zoology.

Great escape

The elusive Amazonian manatee (Trichechus inunguis) is a large plant-eating mammal that lives in freshwater.

Due to its peculiar shape it has been described as a cross between a seal and a hippo.

The species 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 researchers studied manatees that live within the Mamiraua and Amana Sustainable Development Reserves in the north west of Brazil.

To obtain their results, the researchers asked local inhabitants about the animals' movements, studied the shapes and depths of the local rivers and lakes and then used radio tracking tags to follow the movements of 10 manatees.

During the high-water season, between mid May and the end of June, manatees live in quiet lakes called varzeas that form within river flood plains, the scientists found.

Here the manatees consume 8% of their body weight in aquatic plants each day.

Then during the low-water season, between October and November, the animals start to migrate as the water level drops.

They journey to deeper water within long narrow lakes called rias, which are submerged river valleys.

They do this because it becomes too dangerous to remain in shallow water, the scientists say.

If the manatees do not move, they become stranded and exposed to hunters such as caimans, jaguars and humans who stalk the water margins.