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.
The country is understood to be home to the world’s largest elephant population.
The discovery comes less than a month after World Elephant Day, a cause that has in recent years received the backing of certain sectors of the travel industry.
Intrepid Travel is said to have been the first global travel company to stop offering elephant rides and excursions on its trips in 2014, with more than 150 other operators having followed suit including the likes of G Adventures.
Earlier this year, Intrepid launched its #bekind video campaign highlighting the cruelty and violence elephants often suffer while being trained for riding.