10 January 2010

Manatees must choose between bad and less bad

Researchers observed that the Amazonian manatee Trichechus inunguis, an elusive and pacific marine herbivore who lives in the Amazonian River, mysteriously performs periodical movements from shallow to deep water areas. The reason was unknown, but a recent study found out that this migration is meant to avoid predator attacks during the low-water season.

These manatees live in quiet lakes formed within Amazonian river flood plains during the high-water season (May-June) then, during the low-water season (October-November), they start to migrate as the water level drops. The main reason could be that it’s too dangerous to remain in shallow water: animals can strand and be attacked by predators such as caimans, jaguars, and also humans.

This migration it’s not safe. During the journey, manatees have to pass through narrow channels where they are exposed to illegal hunters (their meat is appreciated). "Amazonian manatees migrate to a habitat that doesn't offer easy living conditions in order to flee from a habitat that becomes inhospitable" - commented Eduardo Moraes Arraut, first author of the study - "When you have two options that are not good, you choose the one that is less bad”.

Researchers warn that these gentle animals are in a greater danger than previously thought: they are vulnerable to hunters but also to climate change, as the flooding regime of Amazonian rivers is strongly related to large-scale climatic phenomena.

Silvia Bonizzoni

Photo credit: SeaPics.com

To read the article:
Arraut E.M., Marmontel M., Mantovani J.E., Novo E.M.L.M., Macdonald D.W., Kenward R.E. 2009. The lesser of two evils: seasonal migrations of Amazonian manatees in the Western Amazon. Journal of Zoology: doi:10.1111/j.1469-7998.2009.00655.x

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