Their population in the Ruaha and Rungwa game reserves in central Tanzania dropped to 8,500 from 20,000 in 2013, ecologists told Der Spiegel.
They said this was largely due to ivory trade. Tanzania has one of the world's largest elephant populations, and is a safari mecca for hunters, in addition to ivory poachers.
The Tanzanian government has been receiving millions in aid from environmental protectionists on the pledge to restore its population of African elephants, considered one of the most desired hunting trophies. To keep the right for financial help, the authorities have been concealing the real elephant population trends.
The European Union has allowed to bring in up to 200 elephant tusks as trophies this year. Conservationists say this quota is based on the outdated estimates.