The number of elephants in two wildlife sanctuaries in Tanzania has fallen by nearly 42 percent in just three years, a census showed on Tuesday, as poachers increasingly killed the animals for their tusks, Reuters reported. The census at the Selous Game Reserve and Mikumi National Park revealed elephant numbers had plunged to 43,552 in 2009 from 74,900 in 2006. It was carried out by the east African country's wildlife authority, Tanzania Wildlife Research Institute, as part of a government plan to conserve wildlife. The rapid fall prompted President Jakaya Kikwete to order an investigation, his office said on Tuesday. Conservationists estimate Tanzania has a total elephant population of between 110,000 and 140,000, making it one of the largest sanctuaries in Africa. But in recent years, Tanzania and neighbouring Kenya have suffered a steep rise in poaching as criminals killed elephants and rhinos for their tusks and horns for sale in Asia. TRAFFIC, a conservation group that tracks trends in wildlife trading, said in a statement last week that 2011 had been a record year for ivory seizure. It pointed to a surge in elephant poaching in Africa to meet Asian demand for tusks for use in jewelry and ornaments. Elephants, the world's largest land mammals, are also under pressure in many parts of the continent from loss of habitat to humans, pollution and climate change. Their number has fallen to 470,000-685,000 from millions just decades ago, conservationists say. Kikwete also ordered the Tanzania Wildlife Research Institute to investigate the disappearance of the rare Roosevelt's sable antelope from national parks, and to look for ways of re-introducing the animal in at least in one of the parks, the statement said. The last Convention on International Trade in Endangered Species (CITES) in 2007 agreed to a nine-year moratorium on any further trade in ivory, after some 105 tonnes of elephant ivory had been sold from Botswana, Namibia, South Africa and Zimbabwe to China and Japan.