JOHANNESBURG (Reuters) - Seized illicit shipments of elephant ivory are almost entirely made up of tusks from recently poached animals rather than siphoned from government stockpiles, scientists using a forensic technique reported on Monday.

A Kenya Wildlife Service (KWS) ranger stacks elephant tusks, part of an estimated 105 tonnes of confiscated ivory to be set ablaze, on a pyre at Nairobi National Park near Nairobi, Kenya April 20, 2016. REUTERS/Thomas Mukoya/File Photo

There has been speculation that some ivory making its way illicitly between Africa and Asia has been illegally diverted from state stockpiles, which are collected from domestic seizures and animals that have died naturally in the wild.

But the study, published in the Proceedings of the National Academy of Sciences of the United States of America, found that 90 percent of the ivory in 14 large seizures between 2002 and 2014 came from animals that had died less than three years before the tusks were confiscated.

The findings show that high-profile environmental campaigns, international treaties and millions of dollars of aid and NGO funds over decades have failed to solve a poaching crisis in Africa, where tusks from slain animals are quickly finding their way to market.

“We find no evidence that long-term government or other stockpiles have been contributing significant amounts of ivory to the illegal ivory trade, emphasizing that poached ivory is being rapidly moved into the illegal trade,” the authors of the study wrote.

The lag time between killing and confiscation was generally between six and 35 months, with ivory from east Africa making it into shipments faster, the study said.

The authors, using a radiocarbon dating technique known as Carbon-14, found that, of 231 ivory specimens examined, only one came from an animal that had expired longer than six years beforehand.

“We had assumed older ivory from stockpiles was leaking into trade, particularly from more corrupt countries. This study shows that’s not the case. The source is from freshly poached elephant,” said Liz Bennett, vice president of species conservation at the U.S.-based Wildlife Conservation Society.

The lack of old or stored ivory among the contraband may show that governments are securing stockpiles better. It may also stem from the fact that a number of countries including Gabon and Kenya have destroyed stockpiles.

The authors said their technique for revealing lag times between date of death and seizure could also be applied to illegal trade in other animal parts, providing useful information to police, governments and conservationists.

Africa’s elephant population fell around 20 percent between 2006 and 2015 because of a surge in ivory poaching, the International Union for Conservation of Nature (IUCN) said in a report in September.

Elephant poaching has risen to meet demand among fast-growing consumer markets in Asian economies such as China’s, where ivory is a coveted commodity used in carving and ornamental accessories.