(CNN) The number of orangutans on the island of Borneo has more than halved in 16 years, as hunting of the critically endangered species continues and rampant deforestation destroys its habitat, scientists say.

An article published in Current Biology found the population had declined by more than 148,000 between 1999 and 2015, leaving an estimated 70,000 to 100,000 on the Southeast Asian island.

The study projected a further drop of 45,000 from deforestation alone by 2050 if nothing changes, in a grim forecast for the great ape's future.

Orangutans exist on only two islands -- Sumatra in Indonesia and Borneo, which is shared by Indonesia, Malaysia and Brunei.

Indonesia and Malaysia have for decades struggled to curb deforestation and illegal logging, losing swaths of tropical forest to palm oil and paper plantations, as well as mining, destroying crucial orangutan habitat.

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