In this Jan. 15, 2010 file photo, a sea otter is seen in Morro Bay, Calif. From sea otters to blue whales, marine mammals are under stress from climate change, ocean acidification, hunting and other threats. Researchers have identified 20 important sites around the world where they say conservation efforts should concentrate. (AP Photo/Reed Saxon, File)

(AP) -- From sea otters to blue whales, marine mammals are under stress from climate change, ocean acidification, hunting and other threats. Researchers have identified 20 important sites around the world where they say conservation efforts should concentrate.

Marine mammals are widely distributed in the oceans and some freshwater locations, but 11 of the conservation sites are home to creatures found nowhere else, according to the study led by Sandra Pompa of the National Autonomous University of Mexico.

Researchers dubbed those sites "irreplaceable" and added that the nine others selected include representatives of 84 percent of all marine mammals.

Currently the most endangered marine mammal is the vaquita, a porpoise that lives in the northern section of the Gulf of California, Pompa said.

The 11 sites deemed irreplaceable were the Hawaiian Islands, Galapagos Islands, Amazon River, San Felix and Juan Fernandez Islands off the coast of Chile, Mediterranean Sea, Caspian Sea, Lake Baikal in Russia, Yangtze River, Indus River, Ganges River and the Kerguelen Islands in the southern Indian Ocean.

In addition, the nine sites picked for their species richness were along the coasts of Baja California, much of the eastern coast of the Americas (the Atlantic coast of the U.S. and including coastal areas of Cuba, Hispaniola, Colombia and Venezuela), Peru, Argentina, Northwestern Africa, South Africa, Japan, Australia and New Zealand.

The findings in the study, published in the Proceedings of the National Academy of Sciences, will be valuable as a conservation tool for organizations and governments that want to focus on endangered species, Pompa said.

At least three species - the Caribbean monk seal, Atlantic gray whale and Steller's sea cow - became extinct because of hunting for their fur, blubber and meat during the 19th and 20th centuries, the researchers noted. The most recent extinction, declared in 2008, was the baiji, a type of porpoise, from the Yangtze River in China.

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http://www.pnas.org

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