However, CWI points out that tusks from African, but not Asian elephants, can be brought into the U.S. as hunting trophies.
Another law, the U.S. African Elephant Conservation Act, prohibits any raw ivory exports from the U.S. and any imports of raw ivory from nations that don't have wild elephant populations.
But the CWI study mentions that the law allows U.S. residents to import ivory items that are antiques—older than a hundred years.
"There are two loopholes here," said Martin, who worked on the report with Daniel Stiles, an anthropologist and wildlife trade investigator.
"One is that tusks come in from Africa as trophies and are sometimes sold within the U.S., which is illegal. The second problem is that people often declare worked ivory items to be antiques when in fact they were made after 1989," Martin added.
"Nearly one-third of the items we found, about 7,400 pieces, likely had been smuggled in into the U.S. since the 1990 ivory trade ban."
There have, however, also been more recent ivory seizures in the U.S. than in any other country, the report points out.
Today's study comes amid worrisome signs that elephants are being slaughtered in record numbers.
Conservationists recently reported, for instance, that seventeen elephants were killed in the past few weeks for their ivory in the Democratic Republic of the Congo's Virunga National Park.
"The illegal ivory trade has undergone a major escalation since 2005, and the increasing demand from high-paying industrialized nations is one important cause," said Samuel K. Wasser, director of the Center for Conservation Biology at the University of Washington, Seattle.
"China is typically cited as the country that is most driving this demand," added Wasser, who was not involved with the study.
"But this report by Martin and Stiles identifies the U.S. as the second-largest ivory market, with most of this ivory being illegally imported from China. Thus U.S. demand for ivory appears to be indirectly adding to China's demand."
In a study published last year in the Proceedings of the National Academy of Sciences, Wasser reported that in 2006 illegal trade in elephant ivory reached record levels and that elephant poaching rates were higher than at any point since the enactment of the CITES ivory ban.
Some 23,000 elephants were killed for their tusks in 2006, according to that study.
Ivory on the Internet
Today's CWI report also notes that there are more ivory crafters in the U.S. than in Europe; that they acquire ivory through the Internet, auctions, and estate sales; and they are largely unregulated by U.S. officials.
"The most common types of ivory items manufactured by U.S. ivory craftsmen are scrimshawed knife handles and tusk tips or plaques, pistol grips, billiard cue inlays, jewelry, parts for musical instruments, and Nantucket baskets, or baskets decorated with ivory," the report says.
What's more, the report notes that the Web has become a major means for moving ivory across borders.
In late April, Nantucket, Massachusetts, scrimshander Charles Manghis was arrested on charges including smuggling, conspiracy, and making false statements to federal agents in connection to illegally imported sperm-whale teeth and elephant ivory.
According to an indictment filed in Massachusetts Federal Court last week, Manghis used email to arrange deliveries of the illegal animal products via California through a Ukrainian man, Andriy Mikhalyov, who is still at large.
The investigation involved federal officers from the U.S. Fish and Wildlife as well as the Massachusetts Environmental Police.
John J. Regan, Manghis's attorney, had no comment when reached by telephone on Friday.
Meanwhile, Sandra Cleva, spokesperson for U.S. Fish and Wildlife Service Law Enforcement, defended the agency's work and said the CWI report contains "disturbing allegations."
"From 1994 to 2005, FWS seizures of illegal ivory accounted for about 30 percent of all reported seizures in the world," she said via email.
Cleva said the FWS "routinely investigates" public complaints of possible illegal ivory sales both domestically and through the Internet.
"We believe that it would have been more productive if [CWI] had brought their information and concerns to the FWS so that we could have evaluated their findings to determine the scope of the alleged illegal activity in relation to U.S. laws," she said.
Cleva also took aim at the report's conclusion.
"The vast majority of U.S. seizures ... involve small non-commercial quantities, a fact that refutes the claim that large-scale illegal ivory trade exists in the United States," she said.
Nantucket Environmental Police Sergeant Dean Belanger, who assisted in the arrest of Manghis, said in a telephone interview that his agency does focus on ivory investigations but is hampered by budgetary problems.
"We simply don't get the funds we need," he said.
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