Elephants Without Borders made the discovery as part of an ongoing aerial survey, including parts of the Okavango Delta, the BBC reports.
Dr Mike Chase, founder and director of the conservation group, said the find was further evidence of the scale of poaching activity in Africa.
He said the group had seen elephant poaching double in Botswana since 2015 when it carried out its Great Elephant Survey.
That survey, said Dr Chase, estimated around a third of the world’s elephants had been killed over the past decade.
He added the rise coincided with the disarmament of Botswana’s anti-poaching unit.
