The country is home to over half of Africa's forest elephants who are highly valued because of the quality of their tusks.
Campaigners say the situation in what was believed to be a safe haven for these elephants is "out of control."
They blame the ongoing high demand for jewellery and other ivory products in Asia.
Gabon holds about 13% of the forests of Central Africa but it is home to around 40,000 forest elephants, a smaller species that are attractive to poachers because their ivory is tinged with pink and is very hard.
The new research has been carried out by the Gabonese national parks agency (ANPN) alongside WWF and the Wildlife Conservation Society (WCS).Cross border poachers
Dr Fiona Maisels of the WCS explained that they had analysed the population of elephants in the Minkebe national park and compared it with their data gathered in the same area 9 years ago.
"Between 44-77% of the elephants have been killed," she said. "In other words 11,100 elephants have been lost since 2004."