Elephant numbers have dramatically fallen in the Central African Republic and Gabon because they are being killed for their ivory, the study says.
Ivory trade
One tusk sells for $22
Many local people earn 75 cents a day
1997: Ivory cost $3/kg
2001: Ivory cost $12/kg
The body which regulates the trade in endangered species, Cites, is due to discuss the ivory trade next month in Chile.
Five Southern African nations with large elephant populations want the ivory trade ban to be lifted to allow a limited sell-off.
But animal rights campaigners and countries such as Kenya oppose them, arguing that allowing even a limited trade in ivory will lead to an increase in poaching.
Big business
The French news agency, AFP, reports that the ivory from one elephant tusk can fetch 15,000 CFA francs ($22) - more than many local people earn in a month.
Ivory prices have risen in recent years, the EU study said, from 2,000 CFA per kilo in 1997 to 8,000 CFA last year.
Ivory is smuggled from Central African capitals, such as Brazzaville, Kinshasa, Bangui and Libreville, to West Africa and Asia, where ivory ornaments are highly prized.
Poaching has almost cut Congo's elephant population in half, from 50,000 in the 1990s to less than 30,000, according to Dominique Nsoso from the environment ministry.
While in Gabon, poachers kill between 500 and 1,000 elephants a year out of a population of 20,000, the EU study said.
'Paying their way'
"We have taken steps on a regional level to fight poaching in border areas, but the poachers still remain very active," Mr Nsoso said.
The ivory trade was outlawed in 1989 after poachers had decimated elephant populations, especially in East Africa.
In 1999, Botswana, Namibia and Zimbabwe were allowed to hold a one-off sale of 60 tonnes of ivory to Japan.
Now, South Africa and Zambia have joined their three neighbours in seeking to sell 80 tonnes of ivory from their stockpiles.
There are some 242,000 elephants in southern Africa and they say they should not be punished for their sound elephant-protection policies.
They argue that allowing elephants to "pay their way" by selling ivory is actually the best way of ensuring their survival in the long term.