The international wildlife trade monitoring group Traffic, based in Cambridge, England, said 23 tons of illegally shipped ivory were seized, representing at least 2,500 dead animals, the BBC reported Thursday.
Traffic's elephant expert Tom Milliken said 2011 "has been a horrible year for elephants."
"In 23 years of compiling ivory seizure data ... this is the worst year ever for large ivory seizures," he said.
Trading in ivory was banned in 1989 to save elephants from extinction but has continued illegally because of huge demand in Asia, where ivory fashioned into decorative objects.
"The escalating large ivory quantities involved in 2011 reflect both a rising demand in Asia and the increasing sophistication of the criminal gangs behind the trafficking," Traffic said in a statement. "Most illegal shipments of African elephant ivory end up in either China or Thailand."
Intercepting illegally shipped ivory is difficult, the group said.
"The only common denominator in the trafficking is that the ivory departs Africa and arrives in Asia, but the routes are constantly changing, presumably reflecting where the smugglers gamble on being their best chance of eluding detection," Traffic said.
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