Most ivory confiscated in Africa since 2002 came from elephants that had died within three years, with very little “old” ivory making its way into large shipments.
Thure Cerling from the University of Utah and colleagues from the US, UK and Kenya took 231 samples of ivory taken from 14 seizures (of a half-tonne or more) between 2002 and 2014 and, using radiocarbon dating, calculated the lag time between the animals’ death and the date of confiscation. They found more than 90% of samples were taken from animals that died less than three years before the confiscation.
The work was published in the Proceedings of the National Academy of Sciences.
African elephant populations are in the midst of a poaching crisis – the worst wave of killings since the 1970s and 80s. It’s big business, too – since 2010, more than 70% of all ivory seizures have been bundles of more than half a tonne, and brings an enormous US$597 million per year into Africa.
But no one knew if the tusks on offer were “old” (more than a decade old and sourced from long-term government stockpiles) or freshly poached.
So Cerling and his colleagues used “bomb carbon-14” dating to find out if the ivory was new or old. Carbon-14 is a naturally occurring isotope of carbon and produced by cosmic rays interacting with our atmosphere.
But above-ground nuclear weapons testing in the early 1960s pumped an influx of carbon-14 into the atmosphere which mostly existed in carbon dioxide.
As plants photosynthesised carbon dioxide-14 and were eaten by animals – such as elephants – the carbon-14 made its way into the food web. And as elephants ate and grew, laying layers of toothy material called dentine onto their tusks, so was the carbon-14 locked away.
When an elephant died, carbon-14 was no longer sequestered in its tusks. Measuring carbon-14 levels in an ivory sample and comparing it to carbon-14 levels over time could tell researchers when the animal passed away.
Cerling and his crew found only three specimens from 231 samples with a lag time between death and ivory confiscation of more than five years. A further one was very old – it had a lag time of more than 19 years.
If the ivory came from government stockpiles, they researchers write, they would expect times for 27 years or more. This means poached ivory is the main driver of the illegal trade.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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